Interview with Hermann Boehnhardt
What has been your involvement during the Deep Impact observation campaign?
I am principal investigator (PI) of one of two successful proposals to observe the Deep Impact event from ESO. The scientific goals of this proposal focuses on the dust and nucleus of the comet. There is another proposal led by Heike Rauer who will observe the gas phase phenomena of the event. Heike and I plus the principal investigators (PIs) of two more proposals who observed the comet before the event are closely collaborating. The team of colleagues who will help us to perform the observations and data analysis of Deep Impact at ESO comprises more than 15 people from Chile and several European countries.
Why is the ESO campaign so particular among the observations made from Earth both before and after the impact?
In Paranal and La Silla, two of the best astronomical sites in the world, we will observe the Deep Impact event simultaneously with all seven ESO telescopes, among them the four VLT 8.2m telescopes that, when used together as we do, form the largest telescope in the world. The usage of the ESO telescopes with all together 10 instruments during our campaign has an enormous power and potential, since we can measure the comet at different wavelengths in the visible and infrared by imaging, spectroscopy and polarimetry. Such multiplexing capabilities of the instrumentation does not exist at any other observatory in the world.
Could you describe the way you will be working at La Silla Observatory on the 4th of July and following days?
We will have one team of observers and data analysists each at Paranal and at La Silla. Each telescope will be equipped with one observer and one data analysist such that we can hope for smooth operations and almost simultaneous data evaluation despite a possibly demanding workload for the people. On each site the team is coordinated by one of the PIs of the two proposals: Heike Rauer will take care of this task at Paranal and I will do so at La Silla. I assume that we will "work around the clock", i.e. there will be always someone from the teams awake working for the campaign for most of the day. However, the daily work of the team will start in the early afternoon with a on-site team meeting followed by a video conference between the VLT and LSO teams. These meetings will be used to summarize the recent results - not only from the two ESO sites, but also from other groups worldwide - and to define the plans for the upcoming observations. The PIs will also have a videocon in the afternoon with the DI mission coordinator of the Earth-based observations, Karen Meech in Hawaii. Before the start of the observations each day a short debriefing of the site teams will be performed. During the observing runs, the observers and data analysts will be in the control rooms of the VLT and at La Silla, respectively, i.e. the on-site teams will have direct access to follow the observations at all 4 telescopes in Paranal and the 3 telescopes in La Silla. Contact between sites is possible by email, telephone and videolink if needed and data can be transfered almost in real time between the teams. After the end of the Di observations, typically around 01:00 (Chilean Time) in the night, the two teams will meet again by video to perform a first synoptic assessment of the observations and the results achieved. Here, further tasks for data processing or preparation of the observations for the following day will be defined and the work of the several team members will continue during the rest of the night while others may go to sleep to resume work again early in the morning.
How soon will your team at La Silla be able to get and process images from Tempel 1 after the impact?
We hope to get the first images of the comet after impact on 4 July around 14-15 Chilean time. These images will come from the mid-IR instrument TIMMI2 at the La Silla 3.6m telescope where we expect to be able to observe the comet during daytime. All 7 La Silla and Paranal telescopes will point the comet around 45min after sunset and around 19:00 Chilean time images and spectra in various wavelength regions will become available.
What results do you expect to obtain?
Well, a prediction of the expected results is simple and difficult at the same time. The simple part is that we know what and how we can measure physical and chemical properties of the comet. For instance, with the ESO telescopes and instruments we can determine the amount and the chemistry of gas and dust in the cometary atmosphere that is produced by the nucleus and the impact crater and we will be able to detect larger fragments of the comet possibly created by DI. All this information gives us a "message in the bottle" from the past history of the planetary system, i.e. from its formation some 4.5 billion years ago. The difficult part is played by the comet and we depend on it to be cooperative for our scientific observations. The goal of Deep Impact is to produce a deep and wide crater on the nucleus that will expose to sunlight for the very first time after its creation the original unaltered material from the formation period of the solar system. And this in turn will only allow us to measure its physical and chemical properties of the primordial matter. Otherwise, we will see heavily processed and altered cometary dust and gas from an unknown evolutionary history of the object, still very interesting and challenging, however most likely not the original material the Sun, the planets, the comets and all matter in the solar system are made of.
How is it possible for astronomers to know from Earth the make-up of an object located farther than 100 million km from Earth?
The telescopes and instruments on Earth and in space measure the comet in various wavelength regions from X-rays, UV, visible to infrared and radio, basically over the whole electromagnetic spectrum the object is emitting light in. These measurements tell us much about the cometary constitution, chemistry and its physical appearance. However, they cannot answer to all questions a scientist would like to get an answer for. For instance, with Earth-based telescopes we cannot obtain clear and well-resolved images of the cometary nucleus nor can we really analyse the emitted gas and dust by experiments like in terrestrial laboratories. Here, spacecraft missions help and bring cameras and lab experiments in the immediate neighbourhood of the comet. The latter is a tremendous effort, time consuming and very expensive, and can thus only be done for a few well selected samples as a kind of highlight of cometary science. The Earth-based observations can be done on many more objects and provide the overall framework for our astronomical subject, the comets.
From your personal point of view, how challenging is it to take part in a project like Deep Impact observation?
The Deep Impact project is a unique event for cometary science maybe comparable to the impact of comet Shoemaker-Levy 9 on Jupiter in 1994. It is the first experiment of its kind and only a few colleagues worldwide will have the opportunity to take part in it at the telescopes, so to say in one of the best seats of the Earth-based theaters that can watch the event. DI is a real "premiere" for cometary science that has the potential to produce a tremendous progress in our understanding of these primordial bodies that were important ingredients in the formation of our planetary system. And this "premiere" will happen without rehearsals and exercises before and without repetitions afterwards. This mixture of unique science to be collected in a short period of time around the impact day comprises the challenge and the thrill for me as a scientist.
Short Bio of Hermann Boehnhardt
Hermann Boehnhardt, 50 years, is a cometary scientist at the Max-Planck-Institute for Solar System Research (MPS) in Katlenburg-Lindau/Germany. After studies of physics and astronomy at the University of Erlangen, and a diploma on orbital dynamics of earth satellites in 1981, he obtained his PhD thesis on cometary dust in 1985. Thereafter, he spent five years of post-doctoral research on comets at Dr. Remeis Observatory in Bamberg/Germany. In 1990-1992, he is dynamics analyst at the European Space Operations Center (ESOC) of the European Space Agency in Darmstadt/Germany. As of 1992, he is project manager and senior scientist of the FORS instrument project for the ESO VLT with duty station at the University Observatory in Munich/Germany. Close to the completion of the first FORS instrument in 1997, he moved to the La Silla Observatory as ESO staff astronomer, and from 1999 to 2002 he was staff astronomer at VLT at Paranal. He then returned to Germany, first to the Max-Planck-Institute for Astronomy in Heidelberg/Germany, managing the LINC-NIRVANA interferometry project for the Large Binocular Telescope at Mt. Graham/USA. Finally, in 2004, he returns to his scientific roots when accepting a senior staff position at the MPS. He became responsible for the small bodies group and for coordinating the MPS science teams of the experiments onboard ESA's cometary mission ROSETTA, as well as lead scientist of the ROSETTA Lander PHILAE. His main scientific interest are comets, the Kuiper Belt, asteroids, moons of the outer planets and a bit of exoplanets as well as the building of instruments for doing the necessary observations from the ground and in space.
During free time, he likes gardening at home, travelling to exotic places (when affordable), reading books and listening music (from classic to heavy metal) - and enjoying to live with his family and animals in a nice home in a 100-people village in a beautiful landscape close the Harz mountain range in the middle of Germany.