Post-Impact Interview with Olivier Hainaut

Following the impact on July 4, 2005, and a week-long observing campaign with all ESO telescopes, we talked again with Olivier Hainaut, the head of Paranal Science Operations and specialist of minor bodies in the solar system. You can also read his pre-impact interview.

What did you feel on July 4, at the time of the impact?
The images from the space probe were awesome. I was really thrilled to follow this in real time, and proud to be part of that great adventure.

What was the effect of the impactor on the comet?
A major release of thin dust. The effect was rather short lived, as it seems that the dust slowly dispersed. This dust cloud was superimposed to the "usual" pre-impact coma. Once dispersed, the coma went back to its normal state. It seems therefore that the impact did not induce any long-term changes on the comet.

Did a crater form?
From a physical point of view, a crater must have been formed, 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.

Did pristine material from beneath the surface get ejected?
We really don't know yet. At this point, the analysis of the plume of dust and gas does not seem to reveal any major differences, but the detailed analysis might show a difference between the material usually released by the comet and that released at the time of the impact. It is really too early to say: as this requires the most accurate data processing and analysis, this will take more time.

What quantity of matter was ejected?
We do not know yet.

Are you disappointed by the lack of post-impact activity?
Which lack of post-impact activity? I can assure you that at the ESO La Silla Paranal Observatory, and at the ESO Offices in Santiago, there has been -and still is- a LOT of activity! Concerning the comet itself, the fact that the comet does not seem to show long-term effects is a result, and a very interesting one. It will be easier to analyze once we have more details about the crater, but in the meantime, it is really interesting to see that the comet is recovering that fast.

Are the scientific goals of the Deep Impact mission fulfilled or will they be?
From our point of view, it is the first time ever that such a fantastic collection of data covering all the possible techniques have been acquired simultaneously on a comet. So, even without Deep Impact, I am sure that we will learn a lot about this comet, and therefore about comets in general. The fact that the impact did happen adds a very specific event in the picture, that we can analyze and study in unprecedented details.

You observed with many telescopes for several days. What was the strategy? Did it prove right?
We used all the telescopes of ESO, and almost all the instruments. This gave us an incredible (and unique) flexibility to adapt to changes on the comet, but also to weather affecting one observatory and not the other. Thanks to the permanent communication between the two ESO sites, this was very efficient.

Did you encounter problems in the observations?
We had only a small fraction of time lost due to the weather, mostly on La Silla, and really only very minor technical problems.

What did you learn about the comet?
It is really too early to reply to this.

Did you detect any new molecules?
No, not yet - but the analysis of the spectra is still on going.

This observing campaign is part of a worldwide collaboration. Can you describe it?
The "DI-Collab" system (private web site, email exploder and videoconferencing system) was extremely powerful to instantly exchange information with all the other observatories. Everybody collaborated saying what (s)he had seen -or not seen- which was very useful for all the others, in order to optimize their observations.

You are all together now in Santiago to analyse the data. For how long? When do you expect the results?
We are here for the whole week. The main purpose of this is to get the bulk of the data reduction done while we still have all the information fresh in our mind, and also to have all the colleagues at hand, so that we can exchange information and data. As we are some 15 comet specialists here, it also means that the total cumulated experience in comet and comet data processing is huge. This is very efficient. The next step will be to analyze these results to understand what they mean! That is going to take place during the next weeks. Stay tuned!