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

Date:
October 5, 2011
Source:
Europlanet Media Centre
Summary:
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.

On the inbound leg of the trip past comet Hartley 2, the Deep Impact spacecraft saw water ice on the surface of the comet. The presence of water ice is suggested in an enhanced color High Resolution Instrument (HRI) image, left panel, along the morning edge of the nucleus. The blue color is indicative of ice. In the middle HRI image, bright rough terrain can be seen. In the right panel, a map of the amount and location of water ice on the large lobe of the nucleus, estimated from spectral data, is overlaid on an HRI visible image to show the collocation of water ice with the bright rough terrain. Blue indicates ice concentrations while pink indicates a warm, dusty nucleus with no ice. Spectroscopic data at this resolution of the small lobe do not exist.
Credit: J. Sunshine et al.

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."


Story Source:

The above story is based on materials provided by Europlanet Media Centre. Note: Materials may be edited for content and length.


Cite This Page:

Europlanet Media Centre. "Hyperactive Hartley 2 has a split history, comet-exploring spacecraft finds." ScienceDaily. ScienceDaily, 5 October 2011. <www.sciencedaily.com/releases/2011/10/111004132821.htm>.
Europlanet Media Centre. (2011, October 5). Hyperactive Hartley 2 has a split history, comet-exploring spacecraft finds. ScienceDaily. Retrieved August 21, 2014 from www.sciencedaily.com/releases/2011/10/111004132821.htm
Europlanet Media Centre. "Hyperactive Hartley 2 has a split history, comet-exploring spacecraft finds." ScienceDaily. www.sciencedaily.com/releases/2011/10/111004132821.htm (accessed August 21, 2014).

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