Brussels, 18 Jul 2005
Ten days after part of the NASA Deep Impact spacecraft plunged into Comet Tempel 1 with the aim of creating a crater and exposing untouched material from beneath the surface, ESO astronomers are back in their offices in Santiago, after more than a week at the ESO La Silla Paranal Observatory.
ESO, the European Southern Observatory, is an intergovernmental, pan-European organisation for astronomical research with 11 member countries. It operates at three sites in the Atacama desert region in Chile.
On 4 July 2005, a 360 kg impactor, part of the Deep Impact spacecraft was launched onto Comet 9P/Tempel 1. This experiment represented a first opportunity to study the crust and interior of a comet, revealing new information on the early phases of the Solar System. ESO actively participated in pre- and post-impact observations.
During the campaign, ESO was connected by telephone, e-mail and videoconference with colleagues in all major observatories worldwide, and data were freely exchanged between the different groups. This unique collaborative spirit provided astronomers with data taken almost around the clock for several days and this, along with the large variety of instruments, makes the Deep Impact observing campaign one of the most successful of its kind.
From current analysis, it appears most likely that the impactor did not create a large new zone of activity and may have failed to free up a large quantity of untouched material from beneath the surface. The images obtained at the VLT show that after the impact, the morphology of Comet Tempel 1 changed with the appearance of a new plume-like structure, produced by matter being ejected with a speed of about 700 to 1000 km/h.
In a recent interview published by ESO, Olivier Hainaut, head of Paranal Science Operations and specialist in minor bodies in the solar system, explained that this was likely to be caused by a major release of thin dust. This effect was, though, rather short lived, as it seems that the dust slowly dispersed, and the comet took back the appearance it had before the impact. The impact did not apparently induce any long-term changes to the comet.
'From a physical point of view, a crater must have been formed,' said Dr Hainaut, 'but we have to wait for the Deep Impact mission specialists to answer this more precisely. This should still take some time as they need to dig into a large quantity of data taken by the spacecraft, 'he added.
The data accumulated during ten nights around the impact have provided the astronomers with the best ever time series of optical spectra of a Jupiter Family comet, with a total of more than 40 hours of exposure time. This unique data set has already allowed the astronomers to characterise the normal gas activity of the comet and also to detect, to their own surprise, an active region not related to the impact.
Tempel 1 may have gone back to sleep, but work has only just started for the astronomers. Measurements of the detailed chemical composition of the materials both released by the impact and coming from that source will be performed by the astronomers in the coming months.
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