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: SDO captures images of two mid-level flares

add to favorites email to friend print save as pdf

Related Stories

Cosmic impacts might help synthesize organic compounds

Dec 12, 2014

Bullets of ice shot at high speeds can deposit organic compounds on surfaces they strike. The new findings suggest that comets might, indeed, have helped deliver key ingredients of life to Earth and perhaps ...

How was the Earth formed?

Dec 10, 2014

Just how did the Earth—our home and the place where life as we know it evolved—come to be created in the first place? In some fiery furnace atop a great mountain? On some divine forge with the hammer ...

Researchers look at Oort cloud asteroids

Dec 09, 2014

Sky & Telescope reports on "A fresh look at a nagging problem—asteroids moving in comet-like orbits" where the research "concludes that asteroids must make up about 4 percent of the vast, distant Oort C ...

Frost-covered chaos on Mars

Nov 27, 2014

Thanks to a break in the dusty 'weather' over the giant Hellas Basin at the beginning of this year, ESA's Mars Express was able to look down into the seven kilometre-deep basin and onto the frosty surface ...

Recommended for you

SDO captures images of two mid-level flares

Dec 19, 2014

The sun emitted a mid-level flare on Dec. 18, 2014, at 4:58 p.m. EST. NASA's Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts ...

Why is Venus so horrible?

Dec 19, 2014

Venus sucks. Seriously, it's the worst. The global temperature is as hot as an oven, the atmospheric pressure is 90 times Earth, and it rains sulfuric acid. Every part of the surface of Venus would kill you ...

Image: Christmas wrapping the Sentinel-3A antenna

Dec 19, 2014

The moment a team of technicians, gowned like hospital surgeons, wraps the Sentinel-3A radar altimeter in multilayer insulation to protect it from the temperature extremes found in Earth orbit.

Video: Flying over Becquerel

Dec 19, 2014

This latest release from the camera on ESA's Mars Express is a simulated flight over the Becquerel crater, showing large-scale deposits of sedimentary material.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.