Astronomers find comet full of fizz

Friday, 17 June 2011 Stuart Gary

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The researchers believe material ablating from the ends of the comet resurface its smooth saddle region (Science/AAAS/NASA)

 

Active iceball Close-up images of a peanut-shaped comet, taken by a recycled spacecraft, have found its surface is be unusually active, spraying vast amounts of ice and water into space.

The comet, 103P/Hartley 2 is smaller but far more active than any of the four other comets studied up close so far, providing a new insight into these primordial celestial bodies left over from the formation of the solar system 4.6 billion years ago.
Scientists including Professor Michael A'Hearn from the University of Maryland in the United States used NASA's EPOXI mission spacecraft to study the comet.
Originally named Deep Impact, the spacecraft fired a projectile into comet Tempel-1 on 4 July 2005, before being renamed EPOXI - Extrasolar Planet Observation and Deep Impact Extended Investigation.
It flew to within 694 kilometres of the comet's icy surface on 4 November 2010, just a week after perihelion, the closest point to the Sun in Hartley 2's six year orbit through the solar system.

Weird and strange

Reporting in the journal Science, A'Hearn and colleagues say Hartley 2 is producing more water than should be possible from such a small surface area. They say it seems to be occurring as carbon dioxide and other volatile gases evaporate, dragging chunks of ice out of the nucleus.
That's different from other comets studied close up which release water when ice on their surfaces turn to gas as the travel nearer the Sun from the frozen outer reaches of the solar system.
Hartley 2's peanut looking nucleus has a smooth saddle-shaped waist between the two lobes.
A'Hearn and colleagues say most of the comet's degassing water seems to be coming from this saddle region, while volatile materials such as carbon dioxide and other organic compounds erupt from the older, rougher-looking lobes.
They speculate this volatile material is carrying chunks of water ice that hasn't fully ablated and is falling back onto the saddle region, resurfacing it. Eventually this water melts and evaporates from the saddle making the area look unusually smooth.

Comet may be new

Astronomer, Dr Jonty Horner from the University of New South Wales in Sydney says the data indicates Hartley 2 may be a relatively new comet.
"Based on their orbits, scientists can't tell if they're a new comet to the inner solar system, having spent their time in the cold outer reaches and only recently come in, or whether they've been on their current orbit for much longer and are actually old, depleted, and not the pristine things we hope to see," Horner says.
"I think the results show Hartley 2 was captured by Jupiter and turned into a short period comet recently, after being held in cold storage since the solar system formed. The evidence is all the volatile material", says Horner.
According to Horner short duration comets should be more carbon-dioxide depleted than Hartley 2 appears to be.
"We know water-ice boils in comets when they reach the warmer inner solar system near the orbit of Mars. But carbon-dioxide starts to evaporate at much colder temperatures further out near Jupiter's orbit."
"The fact that it's so active and has so much carbon-dioxide suggests that it's not been around very long."