Lab Mimics Jupiter's Trojan Asteroids Inside a Single Atom

Rice University graduate student Shuzhen Ye used an ultraviolet laser to create a Rydberg atom in order to study the orbital mechanics of electrons. (Credit: Jeff Fitlow/Rice University)

ScienceDaily  — Rice University physicists have gone to extremes to prove that Isaac Newton's classical laws of motion can apply in the atomic world: They've built an accurate model of part of the solar system inside a single atom of potassium.

In a new paper published this week in Physical Review Letters, Rice's team and collaborators at the Oak Ridge National Laboratory and the Vienna University of Technology showed they could cause an electron in an atom to orbit the nucleus in precisely the same way that Jupiter's Trojan asteroids orbit the sun.

The findings uphold a prediction made in 1920 by famed Danish physicist Niels Bohr about the relationship between the then-new science of quantum mechanics and Newton's tried-and-true laws of motion.

"Bohr predicted that quantum mechanical descriptions of the physical world would, for systems of sufficient size, match the classical descriptions provided by Newtonian mechanics," said lead researcher Barry Dunning, Rice's Sam and Helen Worden Professor of Physics and chair of the Department of Physics and Astronomy. "Bohr also described the conditions under which this correspondence could be observed. In particular, he said it should be seen in atoms with very high principal quantum numbers, which are exactly what we study in our laboratory."

Bohr was a pioneer of quantum physics. His 1913 atomic model, which is still widely invoked today, postulated a small nucleus surrounded by electrons moving in well-defined orbits and shells. The word "quantum" in quantum mechanics derives from the fact that these orbits can have only certain well-defined energies. Jumps between these orbits lead to absorption or emission of specific amounts of energy termed quanta. As an electron gains energy, its quantum number increases, and it jumps to higher orbits that circle ever farther from the nucleus.

In the new experiments, Rice graduate students Brendan Wyker and Shuzhen Ye began by using an ultraviolet laser to create a Rydberg atom. Rydberg atoms contain a highly excited electron with a very large quantum number. In the Rice experiments, potassium atoms with quantum numbers between 300 and 600 were studied.

"In such excited states, the potassium atoms become hundreds of thousands of times larger than normal and approach the size of a period at the end of a sentence," Dunning said. "Thus, they are good candidates to test Bohr's prediction."

He said comparing the classical and quantum descriptions of the electron orbits is complicated, in part because electrons exist as both particles and waves. To "locate" an electron, physicists calculate the likelihood of finding the electron at different locations at a given time. These predictions are combined to create a "wave function" that describes all the places where the electron might be found. Normally, an electron's wave function looks like a diffuse cloud that surrounds the atomic nucleus, because the electron might be found on any side of the nucleus at a given time.

Dunning and co-workers previously used a tailored sequence of electric field pulses to collapse the wave function of an electron in a Rydberg atom; this limited where it might be found to a localized, comma-shaped area called a "wave packet." This localized wave packet orbited the nucleus of the atom much like a planet orbits the sun. But the effect lasted only for a brief period.

"We wanted to see if we could develop a way to use radio frequency waves to capture this localized electron and make it orbit the nucleus indefinitely without spreading out," Ye said.

They succeeded by applying a radio frequency field that rotated around the nucleus itself. This field ensnared the localized electron and forced it to rotate in lockstep around the nucleus.

A further electric field pulse was used to measure the final result by taking a snapshot of the wave packet and destroying the delicate Rydberg atom in the process. After the experiment had been run tens of thousands of times, all the snapshots were combined to show that Bohr's prediction was correct: The classical and quantum descriptions of the orbiting electron wave packets matched. In fact, the classical description of the wave packet trapped by the rotating field parallels the classical physics that explains the behavior of Jupiter's Trojan asteroids.

Jupiter's 4,000-plus Trojan asteroids -- so called because each is named for a hero of the Trojan wars -- have the same orbit as Jupiter and are contained in comma-shaped clouds that look remarkably similar to the localized wave packets created in the Rice experiments. And just as the wave packet in the atom is trapped by the combined electric field from the nucleus and the rotating wave, the Trojans are trapped by the combined gravitational field of the sun and orbiting Jupiter.

The researchers are now working on their next experiment: They're attempting to localize two electrons and have them orbit the nucleus like two planets in different orbits.

"The level of control that we're able to achieve in these atoms would have been unthinkable just a few years ago and has potential applications in, for example, quantum computing and in controlling chemical reactions using ultrafast lasers," Dunning said.

The research was funded by the National Science Foundation, the Robert A. Welch Foundation, the Austrian Science Fund and the Department of Energy. Paper co-authors include S. Yoshida of the Vienna University of Technology; C.O. Reinhold of Oak Ridge National Laboratory and the University of Tennessee; and J. Burgdörfer of Vienna University of Technology and the University of Tennessee.

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The above story is reprinted from materials provided by Rice University.

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---

Journal Reference:

1. B. Wyker, S. Ye, F. Dunning, S. Yoshida, C. Reinhold, J. Burgdörfer. Creating and Transporting Trojan Wave Packets. Physical Review Letters, 2012; 108 (4) DOI:10.1103/PhysRevLett.108.043001

Scientist searches for moons around asteroids

ScienceDaily (Oct. 7, 2011) — Most people know that some planets have moons but would be surprised to know that some asteroids do, too. According to Joshua Emery, assistant professor of earth and planetary sciences at the University of Tennessee, Knoxville, about 20 percent of them do.

Emery is part of an international team of planetary astronomers, led by Franck Marchis of the Carl Sagan Center of the SETI Institute in Mountain View, Calif., searching for moons around asteroids. The discovery of moons around asteroids is important because it can provide clues to the asteroid's formation.

Emery and his team's research has focused on the triple asteroid Minerva, the fourth asteroid located in the main-belt -- which houses most of the solar system's asteroids -- known to possess two moons.

"Minerva was thought to be a pretty typical, unremarkable asteroid until we discovered its two moons," said Emery. "Now, interest in this system has grown, and through a lot of new observations from both ground-based and space-based telescopes, we have developed a much more detailed understanding of Minerva and its moons."

The team studied the asteroid in detail using the large W.M. Keck telescope in Hawaii and a small robotic telescope at Kitt Peak in Arizona. By piecing together old and new observations, the astronomers were able to make precise determinations of the moons' orbits. With shape, size, and mass in hand, the scientists then derived the asteroid's density -- determining that Minerva is different than the other large asteroids in the main-belt.

"All other large main-belt asteroids with one or more moons are very porous," said Emery. "Such high porosity strongly suggests that they are piles of rubble held together by gravity rather than solid rocks. Imagine an asteroid being completely blasted apart in a collision, then the pieces coalescing back together--this is how we think most of these large, multiple asteroid systems form. From these glimpses into the interior structure of asteroids, we gain insight not only into the history and formation of multiple asteroid systems, but also the structure and origin of asteroids in general."

The results of the group's findings were released at the EPSC-DPS meeting in Nantes, France. Other members of the international team of planetary astronomers are J.E. Enriquez, of Carl Sagan Center at the SETI Institute, Calif.; P. Descamps, J. Berthier, and F. Vachier of the Institut de Mecanique Celeste et de Calcul des Ephemerides, France; J. Durech of Charles University, Prague, Czech republic; P. Dalba, UC Berkeley, Calif.; A.W. Harris of DLR, Berlin, Germany; J. Melbourne of Caltech, Pasadena, Calif.; A.N. Stockton and T.J. Dupuy of the University of Hawaii, Honolulu; and C.D. Fassnacht of the University of California at Davis, Calif.

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Scientist searches for moons around asteroids

ScienceDaily (Oct. 7, 2011) — Most people know that some planets have moons but would be surprised to know that some asteroids do, too. According to Joshua Emery, assistant professor of earth and planetary sciences at the University of Tennessee, Knoxville, about 20 percent of them do.

Emery is part of an international team of planetary astronomers, led by Franck Marchis of the Carl Sagan Center of the SETI Institute in Mountain View, Calif., searching for moons around asteroids. The discovery of moons around asteroids is important because it can provide clues to the asteroid's formation.

Emery and his team's research has focused on the triple asteroid Minerva, the fourth asteroid located in the main-belt -- which houses most of the solar system's asteroids -- known to possess two moons.

"Minerva was thought to be a pretty typical, unremarkable asteroid until we discovered its two moons," said Emery. "Now, interest in this system has grown, and through a lot of new observations from both ground-based and space-based telescopes, we have developed a much more detailed understanding of Minerva and its moons."

The team studied the asteroid in detail using the large W.M. Keck telescope in Hawaii and a small robotic telescope at Kitt Peak in Arizona. By piecing together old and new observations, the astronomers were able to make precise determinations of the moons' orbits. With shape, size, and mass in hand, the scientists then derived the asteroid's density -- determining that Minerva is different than the other large asteroids in the main-belt.

"All other large main-belt asteroids with one or more moons are very porous," said Emery. "Such high porosity strongly suggests that they are piles of rubble held together by gravity rather than solid rocks. Imagine an asteroid being completely blasted apart in a collision, then the pieces coalescing back together--this is how we think most of these large, multiple asteroid systems form. From these glimpses into the interior structure of asteroids, we gain insight not only into the history and formation of multiple asteroid systems, but also the structure and origin of asteroids in general."

The results of the group's findings were released at the EPSC-DPS meeting in Nantes, France. Other members of the international team of planetary astronomers are J.E. Enriquez, of Carl Sagan Center at the SETI Institute, Calif.; P. Descamps, J. Berthier, and F. Vachier of the Institut de Mecanique Celeste et de Calcul des Ephemerides, France; J. Durech of Charles University, Prague, Czech republic; P. Dalba, UC Berkeley, Calif.; A.W. Harris of DLR, Berlin, Germany; J. Melbourne of Caltech, Pasadena, Calif.; A.N. Stockton and T.J. Dupuy of the University of Hawaii, Honolulu; and C.D. Fassnacht of the University of California at Davis, Calif.

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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.

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NASA space telescope finds fewer asteroids near Earth

ScienceDaily (Sep. 29, 2011) — New observations by NASA's Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.

Astronomers now estimate there are roughly 19,500 -- not 35,000 -- mid-size near-Earth asteroids. Scientists say this improved understanding of the population may indicate the hazard to Earth could be somewhat less than previously thought. However, the majority of these mid-size asteroids remain to be discovered. More research also is needed to determine if fewer mid-size objects (between 330 and 3,300-feet wide) also mean fewer potentially hazardous asteroids, those that come closest to Earth.

The results come from the most accurate census to date of near-Earth asteroids, the space rocks that orbit within 120 million miles (195 million kilometers) of the sun into Earth's orbital vicinity. WISE observed infrared light from those in the middle to large-size category. The survey project, called NEOWISE, is the asteroid-hunting portion of the WISE mission. Study results appear in the Astrophysical Journal.

"NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population," said Amy Mainzer, lead author of the new study and principal investigator for the NEOWISE project at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's like a population census, where you poll a small group of people to draw conclusions about the entire country."

WISE scanned the entire celestial sky twice in infrared light between January 2010 and February 2011, continuously snapping pictures of everything from distant galaxies to near-Earth asteroids and comets. NEOWISE observed more than 100 thousand asteroids in the main belt between Mars and Jupiter, in addition to at least 585 near Earth.

WISE captured a more accurate sample of the asteroid population than previous visible-light surveys because its infrared detectors could see both dark and light objects. It is difficult for visible-light telescopes to see the dim amounts of visible-light reflected by dark asteroids. Infrared-sensing telescopes detect an object's heat, which is dependent on size and not reflective properties.

Though the WISE data reveal only a small decline in the estimated numbers for the largest near-Earth asteroids, which are 3,300 feet (1 kilometer) and larger, they show 93 percent of the estimated population have been found. This fulfills the initial "Spaceguard" goal agreed to with Congress. These large asteroids are about the size of a small mountain and would have global consequences if they were to strike Earth. The new data revise their total numbers from about 1,000 down to 981, of which 911 already have been found. None of them represents a threat to Earth in the next few centuries. It is believed that all near-Earth asteroids approximately 6 miles (10 kilometers) across, as big as the one thought to have wiped out the dinosaurs, have been found.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass.

The situation is different for the mid-size asteroids, which could destroy a metropolitan area if they were to impact in the wrong place. The NEOWISE results find a larger decline in the estimated population for these bodies than what was observed for the largest asteroids. So far, the Spaceguard effort has found and is tracking more than 5,200 near-Earth asteroids 330 feet or larger, leaving more than an estimated 15,000 still to discover. In addition, scientists estimate there are more than a million unknown smaller near-Earth asteroids that could cause damage if they were to impact Earth.

"NEOWISE was just the latest asset NASA has used to find Earth's nearest neighbors," said Lindley Johnson, program executive for the Near Earth Object Observation Program at NASA Headquarters in Washington. "The results complement ground-based observer efforts over the past 12 years. These observers continue to track these objects and find even more."

WISE is managed and operated by JPL for NASA's Science Mission Directorate in Washington. The principal investigator, Edward Wright, is at the University of California, Los Angeles. The WISE science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft was built by Ball Aerospace and Technologies Corp. in Boulder, Colo. Science operations and data processing occur at the Infrared Processing and Analysis Center at the California Institute of Technology.

For more information about the mission, visit: http://www.nasa.gov/wise .

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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 space telescope finds fewer asteroids near Earth

ScienceDaily (Sep. 29, 2011) — New observations by NASA's Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.

Astronomers now estimate there are roughly 19,500 -- not 35,000 -- mid-size near-Earth asteroids. Scientists say this improved understanding of the population may indicate the hazard to Earth could be somewhat less than previously thought. However, the majority of these mid-size asteroids remain to be discovered. More research also is needed to determine if fewer mid-size objects (between 330 and 3,300-feet wide) also mean fewer potentially hazardous asteroids, those that come closest to Earth.

The results come from the most accurate census to date of near-Earth asteroids, the space rocks that orbit within 120 million miles (195 million kilometers) of the sun into Earth's orbital vicinity. WISE observed infrared light from those in the middle to large-size category. The survey project, called NEOWISE, is the asteroid-hunting portion of the WISE mission. Study results appear in the Astrophysical Journal.

"NEOWISE allowed us to take a look at a more representative slice of the near-Earth asteroid numbers and make better estimates about the whole population," said Amy Mainzer, lead author of the new study and principal investigator for the NEOWISE project at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "It's like a population census, where you poll a small group of people to draw conclusions about the entire country."

WISE scanned the entire celestial sky twice in infrared light between January 2010 and February 2011, continuously snapping pictures of everything from distant galaxies to near-Earth asteroids and comets. NEOWISE observed more than 100 thousand asteroids in the main belt between Mars and Jupiter, in addition to at least 585 near Earth.

WISE captured a more accurate sample of the asteroid population than previous visible-light surveys because its infrared detectors could see both dark and light objects. It is difficult for visible-light telescopes to see the dim amounts of visible-light reflected by dark asteroids. Infrared-sensing telescopes detect an object's heat, which is dependent on size and not reflective properties.

Though the WISE data reveal only a small decline in the estimated numbers for the largest near-Earth asteroids, which are 3,300 feet (1 kilometer) and larger, they show 93 percent of the estimated population have been found. This fulfills the initial "Spaceguard" goal agreed to with Congress. These large asteroids are about the size of a small mountain and would have global consequences if they were to strike Earth. The new data revise their total numbers from about 1,000 down to 981, of which 911 already have been found. None of them represents a threat to Earth in the next few centuries. It is believed that all near-Earth asteroids approximately 6 miles (10 kilometers) across, as big as the one thought to have wiped out the dinosaurs, have been found.

"The risk of a really large asteroid impacting the Earth before we could find and warn of it has been substantially reduced," said Tim Spahr, the director of the Minor Planet Center at the Harvard Smithsonian Center for Astrophysics in Cambridge, Mass.

The situation is different for the mid-size asteroids, which could destroy a metropolitan area if they were to impact in the wrong place. The NEOWISE results find a larger decline in the estimated population for these bodies than what was observed for the largest asteroids. So far, the Spaceguard effort has found and is tracking more than 5,200 near-Earth asteroids 330 feet or larger, leaving more than an estimated 15,000 still to discover. In addition, scientists estimate there are more than a million unknown smaller near-Earth asteroids that could cause damage if they were to impact Earth.

"NEOWISE was just the latest asset NASA has used to find Earth's nearest neighbors," said Lindley Johnson, program executive for the Near Earth Object Observation Program at NASA Headquarters in Washington. "The results complement ground-based observer efforts over the past 12 years. These observers continue to track these objects and find even more."

WISE is managed and operated by JPL for NASA's Science Mission Directorate in Washington. The principal investigator, Edward Wright, is at the University of California, Los Angeles. The WISE science instrument was built by the Space Dynamics Laboratory in Logan, Utah, and the spacecraft was built by Ball Aerospace and Technologies Corp. in Boulder, Colo. Science operations and data processing occur at the Infrared Processing and Analysis Center at the California Institute of Technology.

For more information about the mission, visit: http://www.nasa.gov/wise .

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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