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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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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Pacific volcanoes share split personality

Dual chemistry of island chains reflects variations in their deep source Web edition : Monday, September 19th, 2011 Kilauea powFireworks can ensue when lava meets ocean, seen here at Hawaii's Kilauea Volcano. Geochemical studies suggest that the molten rock forming Hawaii and other Pacific island chains may pull from two distinct sources.Michael Poland/USGS

Hawaii’s scenic volcanoes come in two chemical flavors, and now scientists think the igneous peaks on several other Pacific island chains do, too.

Two parallel lines of volcanoes stretch from the Big Island of Hawaii in the southeast to Molokai in the northwest.  Volcanoes on the Samoan and Marquesas islands are similarly paired. A new study finds that, as in Hawaii, one row is richer than the other in versions of elements such as lead and neodymium.

“This might be a common feature for all the Pacific hotspots,” says Shichun Huang, a geochemist at Harvard University and lead author of a paper appearing online September 18 in Nature Geoscience.

If so, these island chains may tap the same source deep in Earth’s mantle. Molten rock rises toward the surface in two chemically distinct streams, one stream feeding each row of volcanoes.

Geologists think Hawaii, Samoa, and the Marquesas each formed as a plate of Earth’s crust moved across a “hotspot,” the top of a plume carrying molten material from the planet’s deep interior. Like a welding torch passing across a piece of metal, the hotspot punched out island after island as the plate moved over it.

Recent studies have shown that the hotspots are more complex than once thought, says isotope geochemist Dominique Weis of the University of British Columbia. The mantle plume rising below Hawaii, for instance, feeds individual streams of chemically distinct magmas into Mauna Loa and Mauna Kea, both on the Big Island. Mauna Loa has a higher ratio of the most abundant form of lead on Earth, lead-208, compared with lead-206, which has two fewer neutrons in its nucleus.

By analyzing published data on lava samples, Huang and his colleagues have now shown that this chemical difference also exists in Samoa and the Marquesas.

The plumes feeding these island chains (as well as Hawaii’s) apparently tap a single massive reservoir that underlies much of the central and southern Pacific. This reservoir contains chemical signatures of ancient surface rock that plowed into the interior eons ago through plate tectonics. As a plume rises, it carries part of this material with it.

The new work shows how surface volcanoes can be linked to deep sources of magma, says geochemist Albrecht Hofmann of the Max Planck Institute for Chemistry in Mainz, Germany. A few other scientists have questioned the existence of mantle plumes, but the new work “strongly suggests that at least these particular hotspots are actually mantle plumes that ascend from the lowermost mantle,” Hofmann says.

Huang’s group is now checking other Pacific island chains to see if they too show this same two-faced nature.

Found in: Earth and Earth Science

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Water's surface not all wet: Some water molecules split the difference between gas and liquid

ScienceDaily (June 9, 2011) — Air and water meet over most of Earth's surface, but exactly where one ends and the other begins turns out to be a surprisingly subtle question.

A new study in Nature narrows the boundary to just one quarter of water molecules in the uppermost layer -- those that happen to have one hydrogen atom in water and the other vibrating freely above.

Such molecules straddle gas and liquid phases, according to senior author Alexander Benderskii of the University of Southern California: The free hydrogen behaves like an atom in gas phase, while its twin below acts much like the other atoms that make up "bulk" water.

The finding matters for theoretical reasons and for practical studies of reactions at the water's surface, including the processes that maintain a vital supply of nitrogen, oxygen and carbon dioxide in the atmosphere.

"The air-water interface is about 70 percent of the Earth's surface," Benderskii said. "A lot of chemical reactions that are responsible for our atmospheric balance, as well as many processes important in environmental chemistry, happen at the air-water interface."

He added that the study provided a new way for chemists and biologists to study other interfaces, such as the boundary between water and biomembranes that marks the edge of every living cell.

"Water interfaces in general are important," Benderskii said, calling the study "an open door that now we can walk through and broaden the range of our investigations to other, perhaps more complex, acqueous interfaces."

In their study, Benderskii and his colleagues used techniques they invented to test the strength of hydrogen bonds linking water molecules (from the hydrogen of one molecule to the oxygen of another). These are the bonds that keep water a liquid at room temperature.

Specifically, the researchers inferred the bond strength by measuring the hydrogen-oxygen vibration frequency. The bond gets stronger as the frequency decreases, similar to the pull one feels when slowing down a child on a swing.

In the case of straddling molecules with one hydrogen in water, when compared to bonds below the surface, "the hydrogen bond is surprisingly only slightly weaker," according to Benderskii.

Likewise, the bond for the hydrogen atom sticking out of the water is similar in strength to bonds in the gas phase.

The researchers concluded that the change between air and water happens in the space of a single water molecule.

"You recover the bulk phase of water extremely quickly," Benderskii said.

While the transition happens in the uppermost layer of water molecules, the molecules involved change constantly. Even when they rise to the top layer, molecules for the most part are wholly submerged, spending only a quarter of their time straddling air and water.

The study raises the question of how exactly to define the air-water boundary.

If the straddling molecules constitute the boundary, it would be analogous to a wood fence where three of every four boards are missing -- except that since water molecules always are moving between submerged and straddling positions, the location of the fourth board would change millions of times per second.

If the boundary were the entire top layer of water molecules, the analogy would be a fence where one in four boards is sticking out at any one time.

A physical chemist, Benderskii began the study at Wayne State University in Detroit before joining the USC Dornsife College of Letters, Arts and Sciences in 2009 as an associate professor.

Benderskii's collaborators were lead author Igor Stiopkin, formerly at Wayne State and now at the University of Wisconsin-Madison; Champika Weeraman, also previously at Wayne State and now at Canada's National Research Council in Ottawa; Piotr Pieniazek and James Skinner of the University of Wisconsin-Madison; and Fadel Shalhout, formerly at Wayne State and now at USC Dornsife College.

The National Science Foundation and the U.S. Department of Energy funded the study.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Southern California. The original article was written by Carl Marziali.

Journal Reference:

Igor V. Stiopkin, Champika Weeraman, Piotr A. Pieniazek, Fadel Y. Shalhout, James L. Skinner, Alexander V. Benderskii. Hydrogen bonding at the water surface revealed by isotopic dilution spectroscopy. Nature, 2011; 474 (7350): 192 DOI: 10.1038/nature10173

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