New technique set to aid exploration of comets
Astronomers can now identify the active regions on a comet's surface thanks to a new method developed by scientists in Germany and Spain. The technique, described in the journal Astronomy and Astrophysics, could help researchers work out safe routes for space probes travelling to comets in the future.
Comets are complex structures, say experts, and studying them close up is fraught with danger. The Sun's heat causes volatile substances, such as water, carbon dioxide and carbon monoxide, to be emitted from so-called 'active regions' on the comet's surface. These emissions carry dust particles out into space, and these dusty fountains can damage space probes.
'Pictures taken from Earth show the comet and its jets as a two-dimensional projection,' explained Dr Hermann Böhnhardt of the Max Planck Institute for Solar System Research (MPS) in Germany. This makes it hard to identify the sources of the dust clouds and gases. Previous efforts to localise the active regions faltered because they were based on the assumption that comets are either spherical or ellipsoid in shape. In fact, many comets have rather bizarre forms.
In this study, researchers from the MPS and the Instituto de Astrofísica de Andalucía (IAA) in Spain calculated the true shape of a comet by watching it for an entire rotation period and studying changes in its luminance. This information was fed into a computer programme, along with assumptions of where active regions might be and 'educated guesses' of the size and velocity of the dust particles as they leave the comet. The computer simulation delivered an image of the comet as it would be seen from a telescope on Earth. Finally, the simulated image is refined by comparing it with an actual image taken through a telescope.
The astronomers tested their technique on the comet Tempel 1. NASA (the US-based National Aeronautics and Space Administration) paid a visit to Tempel 1 back in 2005 as part of its Deep Impact mission.
'Even though ever since this mission we know where Tempel 1's active regions are, we pretended not to,' commented Jean-Baptiste Vincent of the MPS. The team succeeded in localising and characterising six active regions on the comet, and their map of the comet confirmed data taken from the Deep Impact spacecraft.
The new computer model also delivered important information about the spin axis orientation of Tempel 1. This information is critical to the success of the Stardust-NExT (New Exploration of Tempel) mission, which will fly past Tempel 1 in 2011 to observe how the comet has changed since NASA's last visit.
Meanwhile, the MPS and IAA researchers are planning to use their new technique to identify the active regions of the comet Churyumov-Gerasimenko that will be visited by the Rosetta Lander Philae in late 2014. Operated by the European Space Agency (ESA), Rosetta has been heading out towards Mars and the asteroid belt since 2004. Information from the newly developed computer model could be used to work out a safe route for Rosetta through the cometary coma (the sheath of gas and dust that surrounds the core of the comet) and possibly find a landing site for Philae.
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Data Source Provider: Max Planck Institute for Solar System Research; Astronomy and Astrophysics
Document Reference: Vincent, J.B., et al: (2010) A numerical model of cometary dust coma structures: Application to comet 9P/Tempel 1. Astronomy and Astrophysics 512 (A60), published online 2 April. DOI: 10.1051/0004-6361/200913418.
Subject Index: Coordination, Cooperation; Scientific Research; Space & satellite research