Evidence for more dust than ice in comets

Oct 13, 2005
Ejecta plume from Tempel 1, 13 seconds after impact

Observations of Comet 9P/Tempel 1 made by ESA’s Rosetta spacecraft after the Deep Impact collision suggest that comets are ‘icy dirtballs’, rather than ‘dirty snowballs’ as previously believed.

Image: Ejecta plume from Tempel 1, 13 seconds after impact

Comets spend most of their lifetime in a low-temperature environment far from the Sun. Their relatively unchanged composition carries important information about the origin of the Solar System.

On 4 July this year, the NASA Deep Impact mission sent an ‘impactor’ probe to hit the surface of Comet 9P/Tempel 1 to investigate the interior of a cometary nucleus.

The 370 kg copper impactor hit Comet Tempel 1 with a relative velocity of 10.2 kilometres per second. The collision was expected to generate a crater with a predicted diameter of about 100-125 metres and eject cometary material. It vaporised 4500 tonnes of water, but surprisingly released even more dust.

Tempel 1's icy nucleus, roughly the size of central Paris, is dynamic and volatile. Possibly the impact would also trigger an outburst of dust and gas, and produce a new active area on the comet’s surface.

Just before impact, the Hubble Space Telescope spotted a new jet of dust streaming from the icy comet. No one knows for sure what causes these outbursts.

Rosetta, with its set of very sensitive instruments for cometary investigations, used its capabilities to observe Tempel 1 before, during and after the impact.

At a distance of about 80 million kilometres from the comet, Rosetta was in the most privileged position to observe the event.

European scientists using Rosetta's OSIRIS imaging system observed the comet’s nucleus before and after the impact. OSIRIS comprises a narrow-angle camera (NAC) and a wide-angle camera (WAC). Both cameras imaged the extended dust coma from the impact in different filters.

OSIRIS measured the water vapour content and the cross-section of the dust created by the impact. The scientists could then work out the corresponding dust/ice mass ratio, which is larger than one, suggesting that comets are composed more of dust held together by ice, rather than made of ice comtaminated with dust. Hence, they are now ‘icy dirtballs’ rather than ‘dirty snowballs’ as previously believed.

The scientists did not find evidence of enhanced outburst activity of Comet 9P/Tempel 1 in the days after the impact, suggesting that, in general, impacts of meteoroids are not the cause of cometary outbursts. Scientists also hope to make a 3D reconstruction of the dust cloud around the comet by combining the OSIRIS images with those taken from ground observatories.

Source: ESA

Explore further: Mysteries of space dust revealed

add to favorites email to friend print save as pdf

Related Stories

Dinosaurs doing well before asteroid impact

Jul 29, 2014

A new analysis of fossils from the last years of the dinosaurs concludes that extra-terrestrial impact was likely the sole cause of extinction in most cases.

NASA Mars spacecraft prepare for close comet flyby

Jul 26, 2014

NASA is taking steps to protect its Mars orbiters, while preserving opportunities to gather valuable scientific data, as Comet C/2013 A1 Siding Spring heads toward a close flyby of Mars on Oct. 19.

Looking back at the Jupiter crash 20 years later

Jul 16, 2014

(Phys.org) —Twenty years ago, human and robotic eyes observed the first recorded impact between cosmic bodies in the solar system, as fragments of comet Shoemaker-Levy 9 slammed into the atmosphere of Jupiter.

Recommended for you

Mysteries of space dust revealed

21 hours ago

The first analysis of space dust collected by a special collector onboard NASA's Stardust mission and sent back to Earth for study in 2006 suggests the tiny specks open a door to studying the origins of the ...

A guide to the 2014 Neptune opposition season

Aug 29, 2014

Never seen Neptune? Now is a good time to try, as the outermost ice giant world reaches opposition this weekend at 14:00 Universal Time (UT) or 10:00 AM EDT on Friday, August 29th. This means that the distant ...

How can we find tiny particles in exoplanet atmospheres?

Aug 29, 2014

It may seem like magic, but astronomers have worked out a scheme that will allow them to detect and measure particles ten times smaller than the width of a human hair, even at many light-years distance.  ...

Spitzer telescope witnesses asteroid smashup

Aug 28, 2014

(Phys.org) —NASA's Spitzer Space Telescope has spotted an eruption of dust around a young star, possibly the result of a smashup between large asteroids. This type of collision can eventually lead to the ...

User comments : 0