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Meet Dr. Michael A'Hearn, SD-NExT Co-Investigator

  Dr. Mike A'Hearn

What does it mean to you to return to comet Tempel 1?
Returning to Tempel 1 is exciting on two fronts. Most obviously, the fact that the material we excavated from Tempel 1 with Deep Impact was broken into such fine particles that we never say through to the crater. Stardust-NExT will give us the first look at the crater and this will tell us a lot about the physical properties of the outer layers. Secondly, we will have a chance, for the first time for any comet, to see how the natural activity over an entire orbital period has changed the surface. We should expect to see noticeable changes.

You are also the Principal Investigator for the EPOXI mission can you briefly tell us about what that mission is doing?
The EPOXI mission has finished its observations of transiting Exo-Planets and has one more scheduled sequence of observations of Earth. Meanwhile, we are undertaking various calibration activities and preparing for our encounter with comet Hartley 2 in November 2010.

Have you only worked on comets during your science career?

My first published paper, as a graduate student, was about comets and was based on a problem assigned by my advisor at the time. After that I worked on the Venusian clouds and then on interstellar dust.  Since the 1970s, however, I have been studying both comets and asteroids as my primary research.

What will exploring all these comets do for our understanding of them?
We have now sent spacecraft to four comets. While we are beginning to see similarities, we also see huge differences from one to another that we don't understand. Progress in the science comes from finding patterns that suggest how things came about, and ultimately how the solar system came to be. We don't need to go to all the comets in order to understand the scientific questions. We do need to go to enough of them to understand the large variations among them.  That clearly takes more than 4, since we don't see the patterns yet, but it certainly does not take 100 and probably not even dozens. We need to choose the comets by the properties we can measure from Earth in order to characterize the range of variability.

Why is exploring comets so important for space exploration in general?

The comets are particularly important because they, or rather others more or less like them, may have originally provided most of the water and organic chemicals to Earth 4 billion years ago.They provide a key record of what conditions were like 4 to 4.5 billion years ago. Comets also occasionally hit Earth in modern times. Fortunately, not very often and specifically none in our lifetimes, although a few people still think that the airblast above Tunguska in 1908 might have been a comet.

What advice do you have for someone just starting their career in this field?
Working in planetary science requires a wide range of technical background. As a student, having studied a lot of physics is what has helped me the most. Above all, a sense of wonder and of curiosity is crucial.

Has there been any surprises so far in your career that you would like to share?
Many times I have been surprised by the results of an observation. This happens whenever you do something entirely new. The crucial thing is to be ready to act on surprises and understand what they mean for planetary (or cometary) science.

Do you work for NASA?
I work for NASA in the sense that NASA ultimately pays for most of my research, but I find it better to be officially employed by a university. This provides an environment in which I can thrive, it provides a lot of contact with students, which I find important, and it gives me the freedom to change what I am working on as I see fit.

Are there any surprises so far from the Deep Impact findings that you can tell us about?
The surprises from Deep Impact include; a) surprisingly little difference in the gases released from Deep Inside by the impact compared to the gases released naturally from near the surface. Theoreticians had predicted significant differences; b) different gases apparently being released from very different parts of the nucleus; c) the grains excavated from the crater were much smaller than we expected - no hint of large, solid rocks at all; d) huge, very smooth regions that look like flows but with no physical explanation for what produced them; e) lots of round holes that in every way are consistent with impact craters but with no explanation of why so many should be present if the surface is eroding away as rapidly as it must.

Science In-Depth

Exploring Comets

Meet The Science Team

Meet The Science Team


“When we see comets up in the sky they're really spectacular. But unless you get close to a comet, you can't really figure out what's going on.”

-Joe Veverka