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New Insights Into Comet Siding Spring

Nov. 10, 2014
Tucson, Ariz. -- Data from the Hubble Space Telescope gathered on Comet C/2013 A1 (Siding Spring) as it approached and closely passed Mars could offer insights on the formation of our Solar System, a Planetary Science Institute researcher said.
“The HST images reveal how the comet looked as it raced towards Mars, not only helping us understand its composition and physical properties, but also, more critically, providing a wealth of unique information to understand the dust coma of the comet that Mars and the spacecraft around it had to pass through,” said Jian-Yang Li, a research scientist at the Planetary Science Institute.
Li is lead author on a paper, “Constraining the Dust Coma Properties of Comet C/Siding Spring (2013 A1) at Large Heliocentric Distances” that will appear in Astrophysical Journal Letters.  Li gave a presentation on this research today, and will discuss his findings at a press conference Tuesday, at the 46th Annual Division for Planetary Science conference held in Tucson Nov. 9-14.  He will also present at the meeting the preliminary results from the Hubble Space Telescope observations of the comet during its close encounter with Mars that occurred on October 19.
“The color of this comet suggests the existence of water ice in its coma, when it was observed more than 3 AU from the Sun.  At this distance, the bulk of comet activity is driven by the sublimation of CO and CO2. Water ice is like rock,” Li said. “This is similar to our results for C/ISON, and may indicate a common phenomenon among dynamically new comets. Comets like C/Siding Spring visit the Sun’s vicinity only once every million of years or even once in their lifetimes.” 
“This work provides important insight into the nature of comet nuclei. It suggests that ice in the comet nucleus may be mechanically similar to its rocky components – separate chunks capable of being lofted by outgassing, instead of being welded to surrounding ice,” said PSI Director Mark Sykes, who participated in a separate study on the potential hazard of this dust to orbiting spacecraft at Mars.
Images are available at
PSI Senior Scientist Nalin H. Samarasinha is a co-author of the paper.
The research was funded by a NASA grant subcontract to PSI from the Space Telescope Science Institute.
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