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Hubble sees outburst from Deep Impact comet 
In a dress rehearsal for the rendezvous between NASA's Deep Impact spacecraft and Comet 9P/Tempel 1, the NASA/ESA Hubble Space Telescope captured dramatic images of a new jet of dust streaming from the icy comet. The images are a reminder that Tempel 1's icy nucleus, roughly the size of central Paris, is dynamic and volatile. Astronomers hope the eruption of dust seen in these observations is a preview of the fireworks that may come on 4 July, when a probe from the Deep Impact spacecraft hits the comet and may cause a similar plume of material.
The Earth-orbiting observatory was 120 million kilometres away from the comet when these images were taken by the high-resolution Advanced Camera for Surveys (ACS). The telescope’s views complement close-up images being taken by cameras aboard Deep Impact, which is speeding toward the comet.
The nucleus, a potato-shaped object, is 14 kilometres long and four kilometres wide. Viewing it is difficult and could be compared with standing in Madrid and trying to see a potato in Stockholm!
The photo at right, snapped at 16:15 (CEST), reveals the jet (the bright fan-shaped area). The jet is pointing in the direction of the Sun. Comets frequently show outbursts in activity, but astronomers still do not know exactly why they occur.
Or, perhaps a portion of the crust itself was lifted off the nucleus by the pressure of heated gases beneath the surface. This porous crust might then crumble into small dust particles shortly after leaving the nucleus, producing a fan-shaped coma on the sunward side. Whatever the cause, the new feature may not last for long.
Astronomers hope that the 4 July collision will unleash more primordial material trapped inside the comet, which formed thousands of millions of years ago. Comets are thought to be ‘dirty snowballs’, porous agglomerates of ice and rock that dwell in the frigid outer boundaries of our Solar System. Periodically, they make their journey into the inner solar system as they loop around the Sun.
The Hubble Space Telescope is a project of international co-operation between ESA and NASA. The contrast in these images has been enhanced to highlight the brightness of the new jet. For more information: Lars Lindberg Christensen Hubble ESA Information Centre, Garching, Germany Tel: +49 89 3200 6306 Mobile: +49 173 3872 621 E-mail: lars @ eso.org
P. Feldman
H. Weaver
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