Astronomers Solve Mystery of Vanishing Electrons in Earth's Outer Radiation Belt

UCLA researchers have explained the puzzling disappearing act of energetic electrons in Earth's outer radiation belt, using data collected from a fleet of orbiting spacecraft. (Credit: NASA Goddard Space Flight Center / Image by Reto Stöckli /Enhancements by Robert Simmon)

UCLA researchers have explained the puzzling disappearing act of energetic electrons in Earth's outer radiation belt, using data collected from a fleet of orbiting spacecraft.

In a paper published Jan. 29 in the advance online edition of the journalNature Physics, the team shows that the missing electrons are swept away from the planet by a tide of solar wind particles during periods of heightened solar activity.

"This is an important milestone in understanding Earth's space environment," said lead study author Drew Turner, an assistant researcher in the UCLA Department of Earth and Space Sciences and a member of UCLA's Institute for Geophysics and Planetary Physics (IGPP). "We are one step closer towards understanding and predicting space weather phenomena."

During powerful solar events such as coronal mass ejections, parts of the magnetized outer layers of sun's atmosphere crash onto Earth's magnetic field, triggering geomagnetic storms capable of damaging the electronics of orbiting spacecraft. These cosmic squalls have a peculiar effect on Earth's outer radiation belt, a doughnut-shaped region of space filled with electrons so energetic that they move at nearly the speed of light.

"During the onset of a geomagnetic storm, nearly all the electrons trapped within the radiation belt vanish, only to come back with a vengeance a few hours later," said Vassilis Angelopoulos, a UCLA professor of Earth and space sciences and IGPP researcher.

The missing electrons surprised scientists when the trend was first measured in the 1960s by instruments onboard the earliest spacecraft sent into orbit, said study co-author Yuri Shprits, a research geophysicist with the IGPP and the departments of Earth and space sciences, and atmospheric and oceanic sciences.

"It's a puzzling effect," he said. "Oceans on Earth do not suddenly lose most of their water, yet radiation belts filled with electrons can be rapidly depopulated."

Even stranger, the electrons go missing during the peak of a geomagnetic storm, a time when one might expect the radiation belt to be filled with energetic particles because of the extreme bombardment by the solar wind.

Where do the electrons go? This question has remained unresolved since the early 1960s. Some believed the electrons were lost to Earth's atmosphere, while others hypothesized that the electrons were not permanently lost at all but merely temporarily drained of energy so that they appeared absent.

"Our study in 2006 suggested that electrons may be, in fact, lost to the interplanetary medium and decelerated by moving outwards," Shprits said. "However, until recently, there was no definitive proof for this theory."

To resolve the mystery, Turner and his team used data from three networks of orbiting spacecraft positioned at different distances from Earth to catch the escaping electrons in the act. The data show that while a small amount of the missing energetic electrons did fall into the atmosphere, the vast majority were pushed away from the planet, stripped away from the radiation belt by the onslaught of solar wind particles during the heightened solar activity that generated the magnetic storm itself.

A greater understanding of Earth's radiation belts is vital for protecting the satellites we rely on for global positioning, communications and weather monitoring, Turner said. Earth's outer radiation belt is a harsh radiation environment for spacecraft and astronauts; the high-energy electrons can penetrate a spacecraft's shielding and wreak havoc on its delicate electronics. Geomagnetic storms triggered when the oncoming particles smash into Earth's magnetosphere can cause partial or total spacecraft failure.

"While most satellites are designed with some level of radiation protection in mind, spacecraft engineers must rely on approximations and statistics because they lack the data needed to model and predict the behavior of high-energy electrons in the outer radiation belt," Turner said.

During the 2003 "Halloween Storm," more than 30 satellites reported malfunctions, and one was a total loss, said Angelopoulos, a co-author of the current research. As the solar maximum approaches in 2013, marking the sun's peak activity over a roughly 11-year cycle, geomagnetic storms may occur as often as several times per month.

"High-energy electrons can cut down the lifetime of a spacecraft significantly," Turner said. "Satellites that spend a prolonged period within the active radiation belt might stop functioning years early."

While a mechanized spacecraft might include multiple redundant circuits to reduce the risk of total failure during a solar event, human explorers in orbit do not have the same luxury. High-energy electrons can punch through astronauts' spacesuits and pose serious health risks, Turner said.

"As a society, we've become incredibly dependent on space-based technology," he said. "Understanding this population of energetic electrons and their extreme variations will help create more accurate models to predict the effect of geomagnetic storms on the radiation belts."

Key observational data used in this study was collected by a network of NASA spacecraft known as THEMIS (Time History of Events and Macroscale Interactions during Substorms); Angelopoulos is the principal investigator of the THEMIS mission. Additional information was obtained from two groups of weather satellites called POES (Polar Operational Environmental Satellite) and GOES (Geostationary Operational Environmental Satellite).

A new collaboration between UCLA and Russia's Moscow State University promises to paint an even clearer picture of these vanishing electrons. Slated for launch in the spring of 2012, the Lomonosov spacecraft will fly in low Earth orbit to measure highly energetic particles with unprecedented accuracy, said Shprits, the principal investigator of the project. Several key instruments for the mission are being developed and assembled at UCLA.

Earth's radiation belts were discovered in 1958 by Explorer I, the first U.S. satellite that traveled to space.

"What we are studying was the first discovery of the space age," Shprits said. "People realized that launches of spacecraft didn't only make the news, they could also make scientific discoveries that were completely unexpected."

This project received federal funding from NASA and the National Science Foundation. Other co-authors include Michael Hartinger, a UCLA graduate student in Earth and space sciences.

Story Source:

The above story is reprinted from materials provided by University of California - Los Angeles. The original article was written by Kim DeRose.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

---

Journal Reference:

1. Drew L. Turner, Yuri Shprits, Michael Hartinger, Vassilis Angelopoulos. Explaining sudden losses of outer radiation belt electrons during geomagnetic storms.Nature Physics, 2012; DOI: 10.1038/nphys2185

Video: China's Shenzou Spacecraft Successfully Docks With Orbiting Module

China's space station ambitions hit another benchmark
Shenzou 8 Docks With Tiangong-1 CCTV

The journey toward a Chinese space station has taken a huge step forward. Yesterday China’s Shenzou 8 spacecraft, which launched earlier this week, successfully docked with the country’s Tiangong-1 space module, which was placed in orbit by an earlier launch. The successful docking maneuver demonstrated a leap forward for China’s manned space program, and the first in a series of missions designed to test technologies that China hopes to cultivate into a manned space station by decade’s end.

Both spacecraft were unmanned for the mission. The Shenzou craft was the active participant in the docking, firing its thrusters to nudge its way closer to the (relatively) stationary Tiangong-1. Guided by optical and radar sensors, the two glided to a secure lock between their docking rings, at which time twelve hooks locked the two spacecraft together. A dozen pins then made electrical connections between the two. The maneuver took place at roughly 211 miles altitude directly above China and required just ten minutes to complete.

The docked pair will orbit for 12 days before separating and then docking a second time. They will then orbit for two more days before Shenzou 8 heads back to Earth with its science payload about two weeks from now.

Two more missions, Shenzou 9 and Shenzou 10, are planned for next year. Both are expected to dock with Tiangong-1 and, if Shenzou 8 proves successful over the next two weeks, those missions will likely be manned (it’s rumored that one of them could include China’s first female astronaut).

Big picture, this docking is similar to the strides made by the American space program during Gemini in the middle 1960s. But the pace of China’s sprint toward becoming a space power is frenetic. China is only the third country to put a manned space travel program into action--its first manned flight was in 2003--and the rate at which they are ticking off milestones is impressive. It’s also somewhat troubling to Washington, where some are worried about China’s military ambitions in space (note the PLA officers seated in mission control in the video below, and the fact that a military officer addressed the room after the successful docking).

China hopes to have its very own 66-ton space station in orbit--or at least underway--by 2020. That’s about the same time the International Space Station is scheduled to be decommissioned (unless its lease is extended again). Draw from that whatever you will.

[BBC]

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Kepler spacecraft discovers new multi-planet solar system

ScienceDaily (Oct. 5, 2011) — A team of researchers led by Bill Cochran of The University of Texas at Austin has used NASA's Kepler spacecraft to discover an unusual multiple-planet system containing a super-Earth and two Neptune-sized planets orbiting in resonance with each other.

They are announcing the find in Nantes, France at a joint meeting of the European Planetary Science Conference and the American Astronomical Society's Division of Planetary Science. The research will be published in a special Kepler issue of The Astrophysical Journal Supplement Series in November.

Cochran's team is announcing three planets orbiting Kepler-18, a star similar to the Sun. Kepler 18 is just 10 percent larger than the Sun and contains 97 percent of the Sun's mass. It may host more planets than the three just announced.

The planets are designated b, c, and d. All three planets orbit much closer to Kepler-18 than Mercury does to the Sun. Orbiting closest to Kepler-18 with a 3.5-day period, planet b weighs in at about 6.9 times the mass of Earth, and twice Earth's size. Planet b is considered a "super-Earth." Planet c has a mass of about 17 Earths, is about 5.5 times Earth's size, and orbits Kepler-18 in 7.6 days. Planet d weighs in at 16 Earths, at 7 times Earth's size, and has a 14.9-day orbit. The masses and sizes of c and d qualify them as low-density 2Neptune-class" planets.

Planet c orbits the star twice for every one orbit d makes. But the times that each of these planets transit the face of Kepler-18 "are not staying exactly on that orbital period," Cochran says. "One is slightly early when the other one is slightly late, [then] both are on time at the same time, and then vice-versa."

Scientifically speaking, c and d are orbiting in a 2:1 resonance. "It means they're interacting with each other," Cochran explains. "When they are close to each other ... they exchange energy, pull and tug on each other."

Kepler uses the "transit method" to look for planets. It monitors a star's brightness over time, looking for periodic dips that could indicate a planet passing in front of the star. A large part of the Kepler science team's work is proving that potential planets they find aren't something else that mimics the transit signature (such as a perfectly aligned background star, specifically either an eclipsing binary star or a single star orbited by a giant planet).

That follow-up work to Kepler is done by scores of scientists using ground-based telescopes the world over (including several at The University of Texas at Austin's McDonald Observatory) as well as Spitzer Space Telescope.

Kepler-18's planets c and d did astronomers a favour by proving their planet credentials up front via their orbital resonance; they had to be in the same planetary system as each other for the resonance to occur.

Confirming the planetary bona fides of planet b, the super-Earth, was much more complicated, Cochran says. His team used a technique called "validation," instead of verification. They set out to figure out the probability that it could be something other than a planet.

First, they used the Palomar 5-meter (200-inch) Hale Telescope with adaptive optics to take an extremely high-resolution look at the space around Kepler-18. They wanted to see if anything close to the star could be positively identified as a background object that would cause the transit signal they had attributed to a super-Earth.

"We successively went through every possible type of object that could be there," Cochran says. "There are limits on the sort of objects that can be there at different distances from the star." Astronomers know how many of different types of objects (various kinds of stars, background galaxies, and more) are seen on average in the sky. They didn't find anything in the Palomar image.

"There's a small possibility that [planet b] is due to a background object, but we're very confident that it's probably a planet," Cochran says. His team calculated that the likelihood the object is a planet is 700 times more likely than the likelihood that it's a background object.

The process is called "planet validation," rather than the usual "planet verification." Cochran says it's important to understand the difference -- not just for this system, but for future discoveries from Kepler and other missions.

"We're trying to prepare the astronomical community and the public for the concept of validation," he says. "The goal of Kepler is to find an Earth-sized planet in the habitable zone [where life could arise], with a one-year orbit. Proving that such an object really is a planet is very difficult [with current technology]. When we find what looks to be a habitable Earth, we'll have to use a validation process, rather than a confirmation process. We're going to have to make statistical arguments."

Kepler was selected as the tenth NASA Discovery mission. NASA Ames Research Center, Moffett Field, Calif., is the home organization of the science principal investigator, and is responsible for the ground system development, mission operations and science data analysis. Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission development. Ball Aerospace & Technologies Corp. of Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. The Space Telescope Science Institute in Baltimore archives, hosts, and distributes the Kepler science data. For more information about the Kepler mission, visit: http://www.nasa.gov/kepler.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by McDonald Observatory, University of Texas at Austin.

Note: If no author is given, the source is cited instead.

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Kepler spacecraft discovers new multi-planet solar system

ScienceDaily (Oct. 5, 2011) — A team of researchers led by Bill Cochran of The University of Texas at Austin has used NASA's Kepler spacecraft to discover an unusual multiple-planet system containing a super-Earth and two Neptune-sized planets orbiting in resonance with each other.

They are announcing the find in Nantes, France at a joint meeting of the European Planetary Science Conference and the American Astronomical Society's Division of Planetary Science. The research will be published in a special Kepler issue of The Astrophysical Journal Supplement Series in November.

Cochran's team is announcing three planets orbiting Kepler-18, a star similar to the Sun. Kepler 18 is just 10 percent larger than the Sun and contains 97 percent of the Sun's mass. It may host more planets than the three just announced.

The planets are designated b, c, and d. All three planets orbit much closer to Kepler-18 than Mercury does to the Sun. Orbiting closest to Kepler-18 with a 3.5-day period, planet b weighs in at about 6.9 times the mass of Earth, and twice Earth's size. Planet b is considered a "super-Earth." Planet c has a mass of about 17 Earths, is about 5.5 times Earth's size, and orbits Kepler-18 in 7.6 days. Planet d weighs in at 16 Earths, at 7 times Earth's size, and has a 14.9-day orbit. The masses and sizes of c and d qualify them as low-density 2Neptune-class" planets.

Planet c orbits the star twice for every one orbit d makes. But the times that each of these planets transit the face of Kepler-18 "are not staying exactly on that orbital period," Cochran says. "One is slightly early when the other one is slightly late, [then] both are on time at the same time, and then vice-versa."

Scientifically speaking, c and d are orbiting in a 2:1 resonance. "It means they're interacting with each other," Cochran explains. "When they are close to each other ... they exchange energy, pull and tug on each other."

Kepler uses the "transit method" to look for planets. It monitors a star's brightness over time, looking for periodic dips that could indicate a planet passing in front of the star. A large part of the Kepler science team's work is proving that potential planets they find aren't something else that mimics the transit signature (such as a perfectly aligned background star, specifically either an eclipsing binary star or a single star orbited by a giant planet).

That follow-up work to Kepler is done by scores of scientists using ground-based telescopes the world over (including several at The University of Texas at Austin's McDonald Observatory) as well as Spitzer Space Telescope.

Kepler-18's planets c and d did astronomers a favour by proving their planet credentials up front via their orbital resonance; they had to be in the same planetary system as each other for the resonance to occur.

Confirming the planetary bona fides of planet b, the super-Earth, was much more complicated, Cochran says. His team used a technique called "validation," instead of verification. They set out to figure out the probability that it could be something other than a planet.

First, they used the Palomar 5-meter (200-inch) Hale Telescope with adaptive optics to take an extremely high-resolution look at the space around Kepler-18. They wanted to see if anything close to the star could be positively identified as a background object that would cause the transit signal they had attributed to a super-Earth.

"We successively went through every possible type of object that could be there," Cochran says. "There are limits on the sort of objects that can be there at different distances from the star." Astronomers know how many of different types of objects (various kinds of stars, background galaxies, and more) are seen on average in the sky. They didn't find anything in the Palomar image.

"There's a small possibility that [planet b] is due to a background object, but we're very confident that it's probably a planet," Cochran says. His team calculated that the likelihood the object is a planet is 700 times more likely than the likelihood that it's a background object.

The process is called "planet validation," rather than the usual "planet verification." Cochran says it's important to understand the difference -- not just for this system, but for future discoveries from Kepler and other missions.

"We're trying to prepare the astronomical community and the public for the concept of validation," he says. "The goal of Kepler is to find an Earth-sized planet in the habitable zone [where life could arise], with a one-year orbit. Proving that such an object really is a planet is very difficult [with current technology]. When we find what looks to be a habitable Earth, we'll have to use a validation process, rather than a confirmation process. We're going to have to make statistical arguments."

Kepler was selected as the tenth NASA Discovery mission. NASA Ames Research Center, Moffett Field, Calif., is the home organization of the science principal investigator, and is responsible for the ground system development, mission operations and science data analysis. Jet Propulsion Laboratory, Pasadena, Calif., managed the Kepler mission development. Ball Aerospace & Technologies Corp. of Boulder, Colo., developed the Kepler flight system and supports mission operations with the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. The Space Telescope Science Institute in Baltimore archives, hosts, and distributes the Kepler science data. For more information about the Kepler mission, visit: http://www.nasa.gov/kepler.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by McDonald Observatory, University of Texas at Austin.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Krypton Hall effect thruster for spacecraft propulsion

ScienceDaily (Oct. 6, 2011) — Electric propulsion (EP) is the future of astronautics. It can already compete successfully with chemical thrusters, especially for attitude control, orbit transfer and/or orbital station-keeping as well as for the main propulsion system for deep space missions. However, xenon, the propellant of choice in most EP devices, has a substantial drawback: its cost is very high. On the basis of the experience with plasma jet accelerators, a team of scientists and engineers from the Institute of Plasma Physics and Laser Microfusion in Warsaw has designed the Hall effect thruster optimised to work with krypton, a much more affordable noble gas.

Chemical propulsion is invaluable for the launch of payloads into space. The thrust, generated exclusively from the energy released by combustion of the propellants, is very large, but limited to durations of the order of seconds or minutes. In space, however, where atmospheric drag is negligible, technologies delivering much lower thrust over significantly longer durations (months or even years) have proven much more efficient. The leading low-thrust technology is plasma propulsion, where xenon is the preferred working gas. In the Institute of Plasma Physics and Laser Microfusion (IPPLM) in Warsaw, a Hall effect thruster has been designed to work with krypton, a noble gas ten times cheaper than xenon.

The Hall effect thruster is one of several existing electric propulsion technologies. In use since the 1970s in unmanned space flights, it has made it possible to manoeuvre precisely and correct satellite orbits. Lately, devices of this type have increasingly been used as the main propulsion system for deep space missions.

Hall effect thrusters convert the propellant into a plasma and produce thrust using an external electrical power source, most typically solar panels. Plasma particles (ions and electrons) are electrically charged and can thus be accelerated by an electric field to high velocities, of the order of 15-30 km/s as is the case with Hall thrusters (in contrast, expelled gases do not reach more than 4 km/s with chemical propulsion). Plasma propulsion produces a low thrust (from a few to 1000 mN depending on available power) but can operate over long durations and ultimately increase the velocity of the spacecraft by several kilometres per second.

"Plasma jet accelerators have been studied for many years in IPPLM. Building on this experience, our team has started, in May 2008, the development of a plasma Hall effect thruster using krypton as a propellant," said Dr Jacek Kurzyna, the person responsible for the project.

The propellant used in the vast majority of Hall effect thrusters is xenon, a very rare and therefore expensive noble gas. Krypton, another noble gas, is up to ten times less expensive. Although a slightly higher energy is necessary to produce krypton ions, they are lighter than xenon ions and accordingly require lower acceleration voltages to achieve the same velocity. "From the very beginning, our thruster has been developed and optimised to operate with krypton. We had to design properly the magnetic field configuration and the appropriate magnetic circuit. Some elements had to be constructed in such a way that they can withstand increased heat loads," explains Dariusz Danilko, a PhD student from IPPLM.

The new thruster is medium-power, continuous-thrust propulsion device. Weighing less than 5 kg, it operates at a power of about half a kilowatt. "The SMART-1 lunar space probe sent by the European Space Agency (ESA) had a xenon thruster with power below 2 kW. It accelerated the vehicle by 3,6 km/s. Our thruster could therefore prove suitable as a main propulsion system in small spacecrafts," says Dr Serge Barral from IPPLM.

The newly built Hall effect thruster is a prototype device ready to be tested in vacuum conditions. "If the outcome of the tests is positive, optimization of the device and a round of assessment tests will follow. The project, submitted to the second PECS call (Plan for European Cooperating State, an agreement concluded between Poland and ESA), has been recommended for funding. If funding is confirmed, this project will mark the beginning of the qualification process," explains Dr Kurzyna.

The research on krypton Hall effect thrusters is expected to find applications beyond the field of astronautics. Plasma accelerators are routinely used in many technological processes, inter alia, for surface cleaning by plasma sputtering or etching, surface modification and thin film (e.g. diamond-like carbon) deposition. The team of scientists from IPPLM has suggested, in particular, a deposition process of thin oxide layers for photovoltaic solar panels based on the Hall thruster technology.

The design and construction of the Hall effect thruster have been entirely funded by IPPLM.

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Hyperactive Hartley 2 has a split history, comet-exploring spacecraft finds

ScienceDaily (Oct. 5, 2011) — The latest analysis of data from NASA's Deep Impact spacecraft shows that comet 103P/Hartley 2 is hyperactive in terms of the material it spews out, compared to the other comets observed up close to date. The comet also shows surprising diversity -- ice on the comet's sunlit surface is found in patches that are isolated from areas of dust. In addition, one lobe of the dog-bone shaped comet may have lost much more of the primordial material from the formation of the comet than the other, suggesting that Hartley 2 was originally two comets that came together in a gentle collision.

Mike A'Hearn and Lori Feaga are presenting their findings at the EPSC-DPS Joint Meeting 2011 in Nantes, France.

Deep Impact made its closest encounter of Hartley 2 on Nov. 4, 2010. Over the past year, the science team has been pouring over the data to gain a more detailed understanding of the processes that drive the comet's activity.

"Hartley 2 works differently from Tempel 1, which was encountered by Deep Impact in 2005 and from Wild 2, which was observed by the Stardust mission. It ejects a huge amount of material for its size. Halley, which was observed by the Giotto mission lies somewhere in the middle of the spectrum of activity. Since the encounter, we have been able to dig deeper into the data and have provided more evidence of how ice and dust is released from the nucleus," said A'Hearn, the Principal Investigator of Deep Impact's mission extension, EPOXI.

Carbon dioxide gas, or dry ice, sublimates beneath the comet's surface when it feels heat from the Sun and this fuels extensive jet activity on the comet. Much more carbon dioxide is escaping Hartley 2 than the other comets observed, including Tempel 1. The Deep Impact cameras and spectrometer have observed fragile chunks of water ice and dust being dragged from the nucleus with the escaping carbon dioxide into the comet's atmosphere, or coma. The latest results are giving the team a better understanding of the nucleus and how the micrometre-sized grains of pure ice and centimetre sized dust particles are released from Hartley 2 into the coma. They have found that, despite the hyperactive release of material, both the ice and the volatiles within the dust are actually moving and subliming very slowly.

The team has found a large region of bright, rough terrain on the surface that is covered in water ice particles, a few hundredths of a millimetre in size. Through a combination of surface temperature analysis and the fact that the ice exists on the sunlit surface, they have deduced that these ice particles must be physically separate from the warm, dark dust and not intimately mixed.

Although inferred by the wealth of approach and departure data and preliminary mapping of the coma at closest approach, the team has also definitively reported that the larger lobe of Hartley 2's nucleus currently has less carbon dioxide being released from it than the smaller lobe. This means that the volatile ices, primordial material from the formation of the comet located tens of centimetres deep into the nucleus, may be depleted in the larger lobe.

Lori Feaga, from the University of Maryland, says, "The heterogeneity between lobes is most likely due to compositional differences in the originally accreted material."

"We are speculating that this means that the two lobes of the comet formed in different places in the Solar System. They came together in a gradual collision and the central part of the dog-bone was in-filled with dust and ice from the debris," adds A'Hearn

From observations made from telescopes here on Earth, Deep Impact collaborators Matthew Knight and David Schleicher have shown that the grains are gradually shedding water and all the material is slowly moving away from the sun. This result complements the findings from the spacecraft team.

A'Hearn concludes, "All of these detailed findings put together, those from the spacecraft and supporting ground-based telescopes, may require us to rethink cometary origins."

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Hyperactive Hartley 2 has a split history, comet-exploring spacecraft finds

ScienceDaily (Oct. 5, 2011) — The latest analysis of data from NASA's Deep Impact spacecraft shows that comet 103P/Hartley 2 is hyperactive in terms of the material it spews out, compared to the other comets observed up close to date. The comet also shows surprising diversity -- ice on the comet's sunlit surface is found in patches that are isolated from areas of dust. In addition, one lobe of the dog-bone shaped comet may have lost much more of the primordial material from the formation of the comet than the other, suggesting that Hartley 2 was originally two comets that came together in a gentle collision.

Mike A'Hearn and Lori Feaga are presenting their findings at the EPSC-DPS Joint Meeting 2011 in Nantes, France.

Deep Impact made its closest encounter of Hartley 2 on Nov. 4, 2010. Over the past year, the science team has been pouring over the data to gain a more detailed understanding of the processes that drive the comet's activity.

"Hartley 2 works differently from Tempel 1, which was encountered by Deep Impact in 2005 and from Wild 2, which was observed by the Stardust mission. It ejects a huge amount of material for its size. Halley, which was observed by the Giotto mission lies somewhere in the middle of the spectrum of activity. Since the encounter, we have been able to dig deeper into the data and have provided more evidence of how ice and dust is released from the nucleus," said A'Hearn, the Principal Investigator of Deep Impact's mission extension, EPOXI.

Carbon dioxide gas, or dry ice, sublimates beneath the comet's surface when it feels heat from the Sun and this fuels extensive jet activity on the comet. Much more carbon dioxide is escaping Hartley 2 than the other comets observed, including Tempel 1. The Deep Impact cameras and spectrometer have observed fragile chunks of water ice and dust being dragged from the nucleus with the escaping carbon dioxide into the comet's atmosphere, or coma. The latest results are giving the team a better understanding of the nucleus and how the micrometre-sized grains of pure ice and centimetre sized dust particles are released from Hartley 2 into the coma. They have found that, despite the hyperactive release of material, both the ice and the volatiles within the dust are actually moving and subliming very slowly.

The team has found a large region of bright, rough terrain on the surface that is covered in water ice particles, a few hundredths of a millimetre in size. Through a combination of surface temperature analysis and the fact that the ice exists on the sunlit surface, they have deduced that these ice particles must be physically separate from the warm, dark dust and not intimately mixed.

Although inferred by the wealth of approach and departure data and preliminary mapping of the coma at closest approach, the team has also definitively reported that the larger lobe of Hartley 2's nucleus currently has less carbon dioxide being released from it than the smaller lobe. This means that the volatile ices, primordial material from the formation of the comet located tens of centimetres deep into the nucleus, may be depleted in the larger lobe.

Lori Feaga, from the University of Maryland, says, "The heterogeneity between lobes is most likely due to compositional differences in the originally accreted material."

"We are speculating that this means that the two lobes of the comet formed in different places in the Solar System. They came together in a gradual collision and the central part of the dog-bone was in-filled with dust and ice from the debris," adds A'Hearn

From observations made from telescopes here on Earth, Deep Impact collaborators Matthew Knight and David Schleicher have shown that the grains are gradually shedding water and all the material is slowly moving away from the sun. This result complements the findings from the spacecraft team.

A'Hearn concludes, "All of these detailed findings put together, those from the spacecraft and supporting ground-based telescopes, may require us to rethink cometary origins."

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Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Spacecraft Earth to perform asteroid 'flyby' this fall

ScienceDaily (May 4, 2011) — Since the dawn of the space age, humanity has sent 16 robotic emissaries to fly by some of the solar system's most intriguing and nomadic occupants -- comets and asteroids. The data and imagery collected on these deep-space missions of exploration have helped redefine our understanding of how Earth and our part of the galaxy came to be. But this fall, Mother Nature is giving scientists around the world a close-up view of one of her good-sized space rocks -- no rocket required.
"On November 8, asteroid 2005 YU55 will fly past Earth and at its closest approach point will be about 325,000 kilometers [201,700 miles] away," said Don Yeomans, manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif. "This asteroid is about 400 meters [1,300 feet] wide -- the largest space rock we have identified that will come this close until 2028."
Despite the relative proximity and size, Yeomans said, "YU55 poses no threat of an Earth collision over, at the very least, the next 100 years. During its closest approach, its gravitational effect on Earth will be so miniscule as to be immeasurable. It will not affect the tides or anything else."
Then why all the hubbub for a space rock a little bit wider than an aircraft carrier? After all, scientists estimate that asteroids the size of YU55 come this close about every 25 years.
"While near-Earth objects of this size have flown within a lunar distance in the past, we did not have the foreknowledge and technology to take advantage of the opportunity," said Barbara Wilson, a scientist at JPL. "When it flies past, it should be a great opportunity for science instruments on the ground to get a good look."
2005 YU55 was discovered in December 2005 by Robert McMillan, head of the NASA-funded Spacewatch Program at the University of Arizona, Tucson. The space rock has been in astronomers' crosshairs before. In April 2010, Mike Nolan and colleagues at the Arecibo Observatory in Puerto Rico generated some ghostly images of 2005 YU55 when the asteroid was about 2.3 million kilometers (1.5 million miles) from Earth.
"The best resolution of the radar images was 7.5 meters [25 feet] per pixel," said JPL radar astronomer Lance Benner. "When 2005 YU55 returns this fall, we intend to image it at 4-meter resolution with our recently upgraded equipment at the Deep Space Network at Goldstone, California. Plus, the asteroid will be seven times closer. We're expecting some very detailed radar images."
Radar astronomy employs the world's most massive dish-shaped antennas. The antennas beam directed microwave signals at their celestial targets -- which can be as close as our moon and as far away as the moons of Saturn. These signals bounce off the target, and the resulting "echo" is collected and precisely collated to create radar images, which can be used to reconstruct detailed three-dimensional models of the object. This defines its rotation precisely and gives scientists a good idea of the object's surface roughness. They can even make out surface features.
"Using the Goldstone radar operating with the software and hardware upgrades, the resulting images of YU55 could come in with resolution as fine as 4 meters per pixel," said Benner. "We're talking about getting down to the kind of surface detail you dream of when you have a spacecraft fly by one of these targets."
At that resolution, JPL astronomers can see boulders and craters on the surfaces of some asteroids, and establish if an asteroid has a moon or two of its own. (Note: the 2010 Arecibo imaging of YU55 did not show any moons). But beyond the visually intriguing surface, the data collected from Goldstone, Arecibo, and ground-based optical and infrared telescopes are expected to detail the mineral composition of the asteroid.
"This is a C-type asteroid, and those are thought to be representative of the primordial materials from which our solar system was formed," said Wilson. "This flyby will be an excellent opportunity to test how we study, document and quantify which asteroids would be most appropriate for a future human mission."
Yeomans reiterated Wilson's view that the upcoming pass of asteroid 2005 YU55 will be a positive event, which he describes as an "opportunity for scientific discovery." Yeomans adds, "So stay tuned. This is going to be fun."
The 70-meter (230-foot) Goldstone antenna in California's Mojave Desert, part of NASA's Deep Space Network, is one of only two facilities capable of imaging asteroids with radar. The other is the National Science Foundation's 1,000-foot-diameter (305 meters) Arecibo Observatory in Puerto Rico. The capabilities of the two instruments are complementary. The Arecibo radar is about 20 times more sensitive and can detect asteroids about twice as far away, but because the main dish is stationary it can only see about one-third of the sky. Goldstone is fully steerable and can see about 80 percent of the accessible sky, so it can track objects several times longer per day and can image asteroids at finer spatial resolution. To date, Goldstone and Arecibo have observed 272 near-Earth asteroids and 14 comets with radar. JPL manages the Goldstone Solar System Radar and the Deep Space Network for NASA.
NASA detects, tracks and characterizes asteroids and comets passing close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called "Spaceguard," discovers these objects, characterizes a subset of them, and plots their orbits to determine if any could be potentially hazardous to our planet.
JPL manages the Near-Earth Object Program Office for NASA's Science Mission Directorate in Washington. JPL is a division of the California Institute of Technology in Pasadena.
More information about asteroids and near-Earth objects is at: http://www.jpl.nasa.gov/asteroidwatch .
More information about asteroid radar research is at: http://echo.jpl.nasa.gov/ .
More information about the Deep Space Network is at: http://deepspace.jpl.nasa.gov/dsn .
Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Jet Propulsion Laboratory.

Note: If no author is given, the source is cited instead.
Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

NASA's Dawn spacecraft approaches protoplanet Vesta

ScienceDaily (June 10, 2011) — NASA's Dawn mission to the doughnut-shaped asteroid belt between Mars and Jupiter, which launched in September 2007, is now approaching Vesta, a protoplanet that is currently some 143 million miles from Earth. Many surprises are likely awaiting the spacecraft.

"We often refer to Vesta as the smallest terrestrial planet," said Christopher T. Russell, a UCLA professor of geophysics and space physics and the mission's principal investigator. "It has planetary features and basically the same structure as Mercury, Venus, Earth and Mars. But because it is so small, it does not have enough gravity to retain an atmosphere, or at least not to retain an atmosphere for very long.

"There are many mysteries about Vesta," Russell said. "One of them is why Vesta is so bright. Earth reflects a lot of sunlight -- about 40 percent -- because it has clouds and snow on the surface, while the moon reflects only about 10 percent of the light from the sun back. Vesta is more like Earth. Why? What on its surface is causing all that sunlight to be reflected? We'll find out."

Dawn will map Vesta's surface, which Russell says may be similar to the moon's. He says he expects that the body's interior is layered, with a crust, a mantle and an iron core. He is eager to learn about this interior and how large the iron core is.

Named for the ancient Roman goddess of the hearth, Vesta has been bombarded by meteorites for 4.5 billion years.

"We expect to see a lot of craters," Russell said. "We know there is an enormous crater at the south pole that we can see with the Hubble Space Telescope. That crater, some 280 miles across, has released material into the asteroid belt. Small bits of Vesta are floating around and make their way all the way to the orbit of Earth and fall in our atmosphere. About one in every 20 meteorites that falls on the surface of Earth comes from Vesta. That has enabled us to learn a lot about Vesta before we even get there."

Dawn will arrive at Vesta in July. Beginning in September, the spacecraft will orbit Vesta some 400 miles from its surface. It will then move closer, to about 125 miles from the surface, starting in November. By January of 2012, Russell expects high-resolution images and other data about surface composition. Dawn is arriving ahead of schedule and is expected to orbit Vesta for a year.

"It's been a long trip," said Russell, who started planning the journey back in 1992. "Finally, the moment of truth is about to arrive."

Vesta, which orbits the sun every 3.6 terrestrial years, has an oval, pumpkin-like shape and an average diameter of approximately 330 miles. Studies of meteorites found on Earth that are believed to have come from Vesta suggest that Vesta formed from galactic dust during the solar system's first 3 million to 10 million years.

Dawn's cameras should be able to see individual lava flows and craters tens of feet across on Vesta's surface.

"We will scurry around when the data come in, trying to make maps of the surface and learning its exact shape and size," Russell said.

Dawn has a high-quality camera, along with a back-up; a visible and near-infrared spectrometer that will identify minerals on the surface; and a gamma ray and neutron spectrometer that will reveal the abundance of elements such as iron and hydrogen, possibly from water, in the soil. Dawn will also probe Vesta's gravity with radio signals.

The study of Vesta, however, is only half of Dawn's mission. The spacecraft will also conduct a detailed study of the structure and composition of the "dwarf planet" Ceres. Vesta and Ceres are the most massive objects in the main asteroid belt between Mars and Jupiter. Dawn's goals include determining the shape, size, composition, internal structure, and the tectonic and thermal evolution of both objects, and the mission is expected to reveal the conditions under which each of them formed.

Dawn, only the second scientific mission to be powered by an advanced NASA technology known as ion propulsion, is also the first NASA mission to orbit two major objects.

"Twice the bang for the buck on this mission," said Russell, who added that without ion propulsion, Dawn would have cost three times as much.

Unlike chemical rocket engines, ion engines accelerate their fuel nearly continuously, giving each ion a tremendous burst of speed. The fuel used by an ion engine is xenon, a gas that is also used in photo-flash units and which is more than four times heavier than air. Xenon ions shoot out the back of the engine at a speed of 90,000 miles per hour.

UCLA graduate and postdoctoral students work with Russell on the mission. Now is an excellent opportunity for graduate students to join the project and help analyze the data, said Russell, who teaches planetary science to UCLA undergraduates and solar and space physics to undergraduates and graduate students.

After orbiting Vesta, Dawn will leave for its three-year journey to Ceres, which could harbor substantial water or ice beneath its rock crust -- and possibly life. On the way to Ceres, Dawn may visit another object. The spacecraft will rendezvous with Ceres and begin orbiting in 2015, conducting studies and observations for at least five months.

Russell believes that Ceres and Vesta, formed almost 4.6 billion years ago, have preserved their early record, which was frozen into their ancient surfaces.

"We're going back in time to the early solar system," he said.

The Dawn mission is managed by the Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, Calif., for NASA's Science Mission Directorate. Team members include scientists from JPL, the NASA Goddard Space Flight Center, the Planetary Science Institute, the Massachusetts Institute of Technology and other institutions.

Scientific partners include the Max Planck Institute for Solar System Research in Katlenburg, Germany; the DLR Institute for Planetary Research in Berlin; the Freie Universitaet in Berlin; the Italian National Institute for Astrophysics in Rome; and the Italian Space Agency.

Orbital Sciences Corp. of Dulles, Va., designed and built the Dawn spacecraft.

UCLA is in charge of Dawn's science and public outreach. Russell leads the science team; he and his colleagues make science decisions through the science center at UCLA's Institute of Geophysics and Planetary Physics. His science team has the lead role in analyzing and interpreting the data from Dawn.

Dawn is part of NASA's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala., in which scientists find innovative ways to unlock the mysteries of our solar system by answering some of humanity's oldest questions.

For more information, visit www.nasa.gov/dawn and http://dawn.jpl.nasa.gov.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Los Angeles. The original article was written by Stuart Wolpert.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

NASA's Dawn spacecraft approaches protoplanet Vesta

ScienceDaily (June 10, 2011) — NASA's Dawn mission to the doughnut-shaped asteroid belt between Mars and Jupiter, which launched in September 2007, is now approaching Vesta, a protoplanet that is currently some 143 million miles from Earth. Many surprises are likely awaiting the spacecraft.

"We often refer to Vesta as the smallest terrestrial planet," said Christopher T. Russell, a UCLA professor of geophysics and space physics and the mission's principal investigator. "It has planetary features and basically the same structure as Mercury, Venus, Earth and Mars. But because it is so small, it does not have enough gravity to retain an atmosphere, or at least not to retain an atmosphere for very long.

"There are many mysteries about Vesta," Russell said. "One of them is why Vesta is so bright. Earth reflects a lot of sunlight -- about 40 percent -- because it has clouds and snow on the surface, while the moon reflects only about 10 percent of the light from the sun back. Vesta is more like Earth. Why? What on its surface is causing all that sunlight to be reflected? We'll find out."

Dawn will map Vesta's surface, which Russell says may be similar to the moon's. He says he expects that the body's interior is layered, with a crust, a mantle and an iron core. He is eager to learn about this interior and how large the iron core is.

Named for the ancient Roman goddess of the hearth, Vesta has been bombarded by meteorites for 4.5 billion years.

"We expect to see a lot of craters," Russell said. "We know there is an enormous crater at the south pole that we can see with the Hubble Space Telescope. That crater, some 280 miles across, has released material into the asteroid belt. Small bits of Vesta are floating around and make their way all the way to the orbit of Earth and fall in our atmosphere. About one in every 20 meteorites that falls on the surface of Earth comes from Vesta. That has enabled us to learn a lot about Vesta before we even get there."

Dawn will arrive at Vesta in July. Beginning in September, the spacecraft will orbit Vesta some 400 miles from its surface. It will then move closer, to about 125 miles from the surface, starting in November. By January of 2012, Russell expects high-resolution images and other data about surface composition. Dawn is arriving ahead of schedule and is expected to orbit Vesta for a year.

"It's been a long trip," said Russell, who started planning the journey back in 1992. "Finally, the moment of truth is about to arrive."

Vesta, which orbits the sun every 3.6 terrestrial years, has an oval, pumpkin-like shape and an average diameter of approximately 330 miles. Studies of meteorites found on Earth that are believed to have come from Vesta suggest that Vesta formed from galactic dust during the solar system's first 3 million to 10 million years.

Dawn's cameras should be able to see individual lava flows and craters tens of feet across on Vesta's surface.

"We will scurry around when the data come in, trying to make maps of the surface and learning its exact shape and size," Russell said.

Dawn has a high-quality camera, along with a back-up; a visible and near-infrared spectrometer that will identify minerals on the surface; and a gamma ray and neutron spectrometer that will reveal the abundance of elements such as iron and hydrogen, possibly from water, in the soil. Dawn will also probe Vesta's gravity with radio signals.

The study of Vesta, however, is only half of Dawn's mission. The spacecraft will also conduct a detailed study of the structure and composition of the "dwarf planet" Ceres. Vesta and Ceres are the most massive objects in the main asteroid belt between Mars and Jupiter. Dawn's goals include determining the shape, size, composition, internal structure, and the tectonic and thermal evolution of both objects, and the mission is expected to reveal the conditions under which each of them formed.

Dawn, only the second scientific mission to be powered by an advanced NASA technology known as ion propulsion, is also the first NASA mission to orbit two major objects.

"Twice the bang for the buck on this mission," said Russell, who added that without ion propulsion, Dawn would have cost three times as much.

Unlike chemical rocket engines, ion engines accelerate their fuel nearly continuously, giving each ion a tremendous burst of speed. The fuel used by an ion engine is xenon, a gas that is also used in photo-flash units and which is more than four times heavier than air. Xenon ions shoot out the back of the engine at a speed of 90,000 miles per hour.

UCLA graduate and postdoctoral students work with Russell on the mission. Now is an excellent opportunity for graduate students to join the project and help analyze the data, said Russell, who teaches planetary science to UCLA undergraduates and solar and space physics to undergraduates and graduate students.

After orbiting Vesta, Dawn will leave for its three-year journey to Ceres, which could harbor substantial water or ice beneath its rock crust -- and possibly life. On the way to Ceres, Dawn may visit another object. The spacecraft will rendezvous with Ceres and begin orbiting in 2015, conducting studies and observations for at least five months.

Russell believes that Ceres and Vesta, formed almost 4.6 billion years ago, have preserved their early record, which was frozen into their ancient surfaces.

"We're going back in time to the early solar system," he said.

The Dawn mission is managed by the Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, Calif., for NASA's Science Mission Directorate. Team members include scientists from JPL, the NASA Goddard Space Flight Center, the Planetary Science Institute, the Massachusetts Institute of Technology and other institutions.

Scientific partners include the Max Planck Institute for Solar System Research in Katlenburg, Germany; the DLR Institute for Planetary Research in Berlin; the Freie Universitaet in Berlin; the Italian National Institute for Astrophysics in Rome; and the Italian Space Agency.

Orbital Sciences Corp. of Dulles, Va., designed and built the Dawn spacecraft.

UCLA is in charge of Dawn's science and public outreach. Russell leads the science team; he and his colleagues make science decisions through the science center at UCLA's Institute of Geophysics and Planetary Physics. His science team has the lead role in analyzing and interpreting the data from Dawn.

Dawn is part of NASA's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala., in which scientists find innovative ways to unlock the mysteries of our solar system by answering some of humanity's oldest questions.

For more information, visit www.nasa.gov/dawn and http://dawn.jpl.nasa.gov.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of California - Los Angeles. The original article was written by Stuart Wolpert.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Dawn spacecraft reaches milestone approaching asteroid Vesta

ScienceDaily (May 4, 2011) — NASA's Dawn spacecraft has reached its official approach phase to the asteroid Vesta and will begin using cameras for the first time to aid navigation for an expected July 16 orbital encounter. The large asteroid is known as a protoplanet -- a celestial body that almost formed into a planet.

At the start of this three-month final approach to this massive body in the asteroid belt, Dawn is 1.21 million kilometers (752,000 miles) from Vesta, or about three times the distance between Earth and the moon. During the approach phase, the spacecraft's main activity will be thrusting with a special, hyper-efficient ion engine that uses electricity to ionize and accelerate xenon. The 12-inch-wide ion thrusters provide less thrust than conventional engines, but will provide propulsion for years during the mission and provide far greater capability to change velocity.

"We feel a little like Columbus approaching the shores of the New World," said Christopher Russell, Dawn principal investigator, based at the University of California in Los Angeles (UCLA). "The Dawn team can't wait to start mapping this Terra Incognita."

Dawn previously navigated by measuring the radio signal between the spacecraft and Earth, and used other methods that did not involve Vesta. But as the spacecraft closes in on its target, navigation requires more precise measurements. By analyzing where Vesta appears relative to stars, navigators will pin down its location and enable engineers to refine the spacecraft's trajectory. Using its ion engine to match Vesta's orbit around the sun, the spacecraft will spiral gently into orbit around the asteroid. When Dawn gets approximately 16,000 kilometers (9,900 miles) from Vesta, the asteroid's gravity will capture the spacecraft in orbit.

"After more than three-and-a-half years of interplanetary travel, we are finally closing in on our first destination," said Marc Rayman, Dawn's chief engineer, at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We're not there yet, but Dawn will soon bring into focus an entire world that has been, for most of the two centuries scientists have been studying it, little more than a pinpoint of light."

Scientists will search the framing camera images for possible moons around Vesta. None of the images from ground-based and Earth-orbiting telescopes have seen any moons, but Dawn will give scientists much more detailed images to determine whether small objects have gone undiscovered.

The gamma ray and neutron detector instrument also will gather information on cosmic rays during the approach phase, providing a baseline for comparison when Dawn is much closer to Vesta. Simultaneously, Dawn's visible and infrared mapping spectrometer will take early measurements to ensure it is calibrated and ready when the spacecraft enters orbit around Vesta.

Dawn's odyssey, which will take it on a journey of 4.8-billion kilometers (3-billion miles), began on Sept. 27, 2007, with its launch from Cape Canaveral Air Force Station in Florida. It will stay in orbit around Vesta for one year. After another long cruise phase, Dawn will arrive at its second destination, an even more massive body in the asteroid belt, called Ceres, in 2015.

These two icons of the asteroid belt will help scientists unlock the secrets of our solar system's early history. The mission will compare and contrast the two giant bodies, which were shaped by different forces. Dawn's science instrument suite will measure surface composition, topography and texture. In addition, the Dawn spacecraft will measure the tug of gravity from Vesta and Ceres to learn more about their internal structures.

The Dawn mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of SMD's Discovery Program, which is managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Va., designed and built the Dawn spacecraft. The framing cameras have been developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau in Germany, with significant contributions by the German Aerospace Center (DLR) Institute of Planetary Research in Berlin, and in coordination with the Institute of Computer and Communication Network Engineering in Braunschweig. The framing camera project is funded by NASA, the Max Planck Society and DLR.

JPL is a division of the California Institute of Technology, Pasadena.

For more information about Dawn, visit: http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov

To learn more about Dawn's approach phase, read the latest Dawn Journal at http://blogs.jpl.nasa.gov/2011/05/dawn-begins-its-vesta-phase/

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Jet Propulsion Laboratory.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

NASA's Dawn spacecraft captures first image of nearing asteroid

ScienceDaily (May 11, 2011) — NASA's Dawn spacecraft has obtained its first image of the giant asteroid Vesta, which will help fine-tune navigation during its approach. Dawn is expected to achieve orbit around Vesta on July 16, when the asteroid is about 188 million kilometers (117 million miles) from Earth.

The image from Dawn's framing cameras was taken on May 3 when the spacecraft began its approach and was approximately 1.21 million kilometers (752,000 miles) from Vesta. The asteroid appears as a small, bright pearl against a background of stars. Vesta is also known as a protoplanet, because it is a large body that almost formed into a planet.

"After plying the seas of space for more than a billion miles, the Dawn team finally spotted its target," said Carol Raymond, Dawn's deputy principal investigator at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This first image hints of detailed portraits to come from Dawn's upcoming visit."

Vesta is 530 kilometers (330 miles) in diameter and the second most massive object in the asteroid belt. Ground- and space-based telescopes obtained images of the bright orb for about two centuries, but with little surface detail.

Mission managers expect Vesta's gravity to capture Dawn in orbit on July 16. To enter orbit, Dawn must match the asteroid's path around the sun, which requires very precise knowledge of the body's location and speed. By analyzing where Vesta appears relative to stars in framing camera images, navigators will pin down its location and enable engineers to refine the spacecraft's trajectory.

Dawn will start collecting science data in early August at an altitude of approximately 1,700 miles (2,700 kilometers) above the asteroid's surface. As the spacecraft gets closer, it will snap multi-angle images, allowing scientists to produce topographic maps. Dawn will later orbit at approximately 200 kilometers (120 miles) to perform other measurements and obtain closer shots of parts of the surface. Dawn will remain in orbit around Vesta for one year. After another long cruise phase, Dawn will arrive in 2015 at its second destination, Ceres, an even more massive body in the asteroid belt.

Gathering information about these two icons of the asteroid belt will help scientists unlock the secrets of our solar system's early history. The mission will compare and contrast the two giant bodies shaped by different forces. Dawn's science instruments will measure surface composition, topography and texture. Dawn will also measure the tug of gravity from Vesta and Ceres to learn more about their internal structures. The spacecraft's full odyssey will take it on a 5-billion-kilometer (3-billion-mile) journey, which began with its launch in September 2007.

Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala.

The University of California in Los Angeles is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Va., designed and built the spacecraft. The framing cameras were developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau in Germany, with significant contributions by the German Aerospace Center (DLR) Institute of Planetary Research in Berlin and in coordination with the Institute of Computer and Communication Network Engineering in Braunschweig. The framing camera project is funded by NASA, the Max Planck Society and DLR.

For more information about Dawn, visit: http://www.nasa.gov/dawn .

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Jet Propulsion Laboratory.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

Dawn spacecraft reaches milestone approaching asteroid Vesta

ScienceDaily (May 4, 2011) — NASA's Dawn spacecraft has reached its official approach phase to the asteroid Vesta and will begin using cameras for the first time to aid navigation for an expected July 16 orbital encounter. The large asteroid is known as a protoplanet -- a celestial body that almost formed into a planet.

At the start of this three-month final approach to this massive body in the asteroid belt, Dawn is 1.21 million kilometers (752,000 miles) from Vesta, or about three times the distance between Earth and the moon. During the approach phase, the spacecraft's main activity will be thrusting with a special, hyper-efficient ion engine that uses electricity to ionize and accelerate xenon. The 12-inch-wide ion thrusters provide less thrust than conventional engines, but will provide propulsion for years during the mission and provide far greater capability to change velocity.

"We feel a little like Columbus approaching the shores of the New World," said Christopher Russell, Dawn principal investigator, based at the University of California in Los Angeles (UCLA). "The Dawn team can't wait to start mapping this Terra Incognita."

Dawn previously navigated by measuring the radio signal between the spacecraft and Earth, and used other methods that did not involve Vesta. But as the spacecraft closes in on its target, navigation requires more precise measurements. By analyzing where Vesta appears relative to stars, navigators will pin down its location and enable engineers to refine the spacecraft's trajectory. Using its ion engine to match Vesta's orbit around the sun, the spacecraft will spiral gently into orbit around the asteroid. When Dawn gets approximately 16,000 kilometers (9,900 miles) from Vesta, the asteroid's gravity will capture the spacecraft in orbit.

"After more than three-and-a-half years of interplanetary travel, we are finally closing in on our first destination," said Marc Rayman, Dawn's chief engineer, at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We're not there yet, but Dawn will soon bring into focus an entire world that has been, for most of the two centuries scientists have been studying it, little more than a pinpoint of light."

Scientists will search the framing camera images for possible moons around Vesta. None of the images from ground-based and Earth-orbiting telescopes have seen any moons, but Dawn will give scientists much more detailed images to determine whether small objects have gone undiscovered.

The gamma ray and neutron detector instrument also will gather information on cosmic rays during the approach phase, providing a baseline for comparison when Dawn is much closer to Vesta. Simultaneously, Dawn's visible and infrared mapping spectrometer will take early measurements to ensure it is calibrated and ready when the spacecraft enters orbit around Vesta.

Dawn's odyssey, which will take it on a journey of 4.8-billion kilometers (3-billion miles), began on Sept. 27, 2007, with its launch from Cape Canaveral Air Force Station in Florida. It will stay in orbit around Vesta for one year. After another long cruise phase, Dawn will arrive at its second destination, an even more massive body in the asteroid belt, called Ceres, in 2015.

These two icons of the asteroid belt will help scientists unlock the secrets of our solar system's early history. The mission will compare and contrast the two giant bodies, which were shaped by different forces. Dawn's science instrument suite will measure surface composition, topography and texture. In addition, the Dawn spacecraft will measure the tug of gravity from Vesta and Ceres to learn more about their internal structures.

The Dawn mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of SMD's Discovery Program, which is managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Va., designed and built the Dawn spacecraft. The framing cameras have been developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau in Germany, with significant contributions by the German Aerospace Center (DLR) Institute of Planetary Research in Berlin, and in coordination with the Institute of Computer and Communication Network Engineering in Braunschweig. The framing camera project is funded by NASA, the Max Planck Society and DLR.

JPL is a division of the California Institute of Technology, Pasadena.

For more information about Dawn, visit: http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov

To learn more about Dawn's approach phase, read the latest Dawn Journal at http://blogs.jpl.nasa.gov/2011/05/dawn-begins-its-vesta-phase/

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by NASA/Jet Propulsion Laboratory.

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

View the original article here

NASA's Dawn spacecraft captures first image of nearing asteroid

ScienceDaily (May 11, 2011) — NASA's Dawn spacecraft has obtained its first image of the giant asteroid Vesta, which will help fine-tune navigation during its approach. Dawn is expected to achieve orbit around Vesta on July 16, when the asteroid is about 188 million kilometers (117 million miles) from Earth.

The image from Dawn's framing cameras was taken on May 3 when the spacecraft began its approach and was approximately 1.21 million kilometers (752,000 miles) from Vesta. The asteroid appears as a small, bright pearl against a background of stars. Vesta is also known as a protoplanet, because it is a large body that almost formed into a planet.

"After plying the seas of space for more than a billion miles, the Dawn team finally spotted its target," said Carol Raymond, Dawn's deputy principal investigator at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "This first image hints of detailed portraits to come from Dawn's upcoming visit."

Vesta is 530 kilometers (330 miles) in diameter and the second most massive object in the asteroid belt. Ground- and space-based telescopes obtained images of the bright orb for about two centuries, but with little surface detail.

Mission managers expect Vesta's gravity to capture Dawn in orbit on July 16. To enter orbit, Dawn must match the asteroid's path around the sun, which requires very precise knowledge of the body's location and speed. By analyzing where Vesta appears relative to stars in framing camera images, navigators will pin down its location and enable engineers to refine the spacecraft's trajectory.

Dawn will start collecting science data in early August at an altitude of approximately 1,700 miles (2,700 kilometers) above the asteroid's surface. As the spacecraft gets closer, it will snap multi-angle images, allowing scientists to produce topographic maps. Dawn will later orbit at approximately 200 kilometers (120 miles) to perform other measurements and obtain closer shots of parts of the surface. Dawn will remain in orbit around Vesta for one year. After another long cruise phase, Dawn will arrive in 2015 at its second destination, Ceres, an even more massive body in the asteroid belt.

Gathering information about these two icons of the asteroid belt will help scientists unlock the secrets of our solar system's early history. The mission will compare and contrast the two giant bodies shaped by different forces. Dawn's science instruments will measure surface composition, topography and texture. Dawn will also measure the tug of gravity from Vesta and Ceres to learn more about their internal structures. The spacecraft's full odyssey will take it on a 5-billion-kilometer (3-billion-mile) journey, which began with its launch in September 2007.

Dawn's mission to Vesta and Ceres is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala.

The University of California in Los Angeles is responsible for overall Dawn mission science. Orbital Sciences Corp. of Dulles, Va., designed and built the spacecraft. The framing cameras were developed and built under the leadership of the Max Planck Institute for Solar System Research in Katlenburg-Lindau in Germany, with significant contributions by the German Aerospace Center (DLR) Institute of Planetary Research in Berlin and in coordination with the Institute of Computer and Communication Network Engineering in Braunschweig. The framing camera project is funded by NASA, the Max Planck Society and DLR.

For more information about Dawn, visit: http://www.nasa.gov/dawn .

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