Michael F. A'Hearn
Interview with Dr. Michael A'Hearn - Principal Investigator
Deep Impact Mission
Interviewer: Flavio J. Martinez
University of Maryland, College Park Scholars
Flavio Martinez: Thank you for taking the time today to come speak with me. Lets begin the interview by asking
you a series of questions and then gear things toward the Deep impact mission. To start off, I'd like to know what persuaded
you to pursue space exploration. What was the initial thrust, or spark?
Mike A'Hearn: Well, I didn't start out in space exploration I started out doing astronomy - classical, ground-based
astronomy among a variety of things. And in fact, the early part of exploration of the solar system, I had absolutely no
connection with at all. I've only gotten into space exploration relatively recently as it's become possible to do a mission to the
kinds of objects that I'm interested in studying, namely comets and asteroids. So I was involved in the attempt to have a mission
called "Craft," which was later canceled before it was ever built. It was to be a joint program with the Cassini mission that is now
going to Saturn.
I got involved with space exploration to some extent with Halley, though not direct involvement with a mission, but running
a part of the international Halley launch, which ultimately did archive all of the data from the space missions to comet Halley.
And since then, I've become more involved in a couple of roles with the Rosetta mission, which is a European Space Agency
mission. I have my own Deep Impact mission, but it's really driven by being able to go to the objects that I want to study, and
I'm still interested in studying them from the earth as well.
FM: So it's these objects that actually initiate or that gives that spark to you to continue space exploration?
FM: Have you ever had any missions change as far as space exploration is concerned and did these goals change?
MA: Well, it's only in recent years that there has been a major change between doing the missions that are safe
where you take lots of detailed measurements and doing the other kinds of missions where you can't predict what's going to
happen. In that sense it's much more an exploratory mission. Some of the early missions to the planets were that way. They
were purely exploratory. We had no idea what we'd find. We evolved from that into missions that just refine the details. Then
when we went to new classes of bodies, like comets and asteroids there was a tendency to do that same thing - measure lots of
details about these bodies where you know you can safely take the measurements and use sophisticated interpretation, but it
doesn't answer the most interesting questions. And that thinking has changed in the whole community within the last ten years.
MA: Well, I think it's just the realization that you need to be thinking of new ways to look, to run space missions in
order to find out new kinds of things instead of just refining what you already know.
FM: You belong to the International Astronomical Union? I did some research on this and I believe that most of the
scientists and astronomers are from different parts of the world, is that correct?
MA: Officially, most of the international science organizations real members are national academies of science and
such like that, so the United States in that sense has one member. The International Astronomical Union is unusual among these
groups in having also individual members, individual scientists as members. The real goal of the IAU is to number one, promote
astronomical research and number two, do the kinds of coordination that need to be done to make it easy for everyone to work
together. This means, for example, defining standard terms. There's a corresponding group for physics that works on standard
units for weights and measures. Astronomers do the same thing for defining standard coordinate systems to just make it easy for
everyone to talk a common language. So there's a fair bit of that. The focus of the interest has now mostly become just
promoting science, running scientific meetings, but the underlying need for coordinating some activities is still the driver for
having such international organization.
FM: And also, naming specific bodies?
MA: Yes, just so we have a fixed set of names for everything - planets, asteroids, stars; well-defined systems for
FM: If I wanted a comet or some kind of object in space to be named after my name, would that be possible?
Could I call upon the IAU and request that, could I offer some kind of payment for that?
MA: Well, you could do that, however if you offered payment, you'd be turned down immediately.
FM: It seemed as though people expect, or automatically think that these names of certain bodies in space are
named after people but usually they have numbers, it's not really names or anything like that.
MA: In general they all have catalogue numbers of one sort or another. Certain classes of bodies also have names.
The only class of objects I can think of that don't have catalogue numbers are geographical features and geological features on
the planets and the satellites. In which case, they are just identified by the thing that corresponds to a catalogue number - the
coordinates, the latitude and longitude of the feature on the planet. So they don't get numbers, they only get named other things
that get named like the satellites themselves. Or asteroids and comets, they all have catalogue numbers as well as names.
Names are easier to remember.
FM: Is there a way that you pick the names?
MA: Well, over time, guidelines have developed as to what kinds of names you use for different kinds of bodies.
We no longer name stars, although they used to be named. There are still some stars that are referenced by names. There's a
star called Barnard's Star which was studied by Barnard and is very close to the Earth. And tends to be remembered by that
name instead of it's catalogue number. In some cases the guidelines say, for example, Europa, which is a satellite of Jupiter -
craters will be named for Celtic mythological figures and deities. Craters on the moon are named for well-known people,
scientists, and explorers.
FM: I believe you worked on the NEAR mission. Is that correct?
MA: Not directly, on the mission. But we're in charge of archiving the mission as a part of NASA's planetary data
system. We've worked with them very closely; we're not officially on the mission.
FM: What were your responsibilities?
MA: Every NASA space mission has to archive their data so it's available in a useful form to other scientists. Solar
system exploration missions such as NEAR do this through the planetary data system, which is funded by NASA. Within that, I
manage the part that has to do with all the missions to comets and asteroids, so NEAR is one of those missions that we have to
FM: There are some concerns that the asteroid may approach Earth's atmosphere and possibly penetrate Earth's
MA: Well Eros is an Earth crossing asteroid so in principle, at some time in the very distant future, it could hit
Earth. But the orbit is well enough known that it cannot do that in the foreseeable future.
FM: Okay, I guess that Hollywood capitalized on this as far as the Deep Impact movie is concerned?
MA: Oh, yeah. There are asteroids and comets both that do hit the Earth on a regular basis.
FM: Are we talking the Earth's atmosphere, or actually penetrate and hit the surface?
MA: Well, every meteorite crater on the Earth was from an asteroid or comet that has made it through the
atmosphere. The really big ones cause major effects. The best known one is from 65 million years ago, which landed and is
credited by most people with the extinction of the dinosaurs, among other things. That was a relatively large asteroid or comet,
not sure which. It was probably at least 10 kilometers in diameter.
FM: What is that exactly?
MA: It's the size of Washington D.C.
FM: So something that large could cause this ecological change?
MA: The objects that are generally thought to be causing globally severe effects are objects bigger than about
one kilometer in diameter, so - a factor of ten, smaller than Washington D.C.
FM: Can you explain exactly what could have happened with this collision in Mexico? Did it hit water or did it
MA: That one, I think it hit in the water, because there's more of the crater in the water than on land, and it does
extend into both. The actual impact was in the water. There are clear signs around the Caribbean of a major tidal wave,
which would suggest it hit in the water. Although you could get that if it just hit near the water and the crater expands into
FM: Obviously, call this a major flood.
MA: Yeah, the crater was discovered by the Mexican oil exploration company, MX, and the crater itself is something
like 150 to 200 km in diameter. This is typical when you have terrestrial impact craters. The crater is something like 10 times
larger than the body that caused it - sometimes even 20 times larger.
FM: What is the purpose of NASA's discovery program?
MA: NASA's discovery program is a response to the fact that missions were getting bigger, more expensive, and
therefore much less frequent. So, discovery was invented to get cheaper and more diverse missions, more opportunities to go
into space. Discovery is a program within solar system exploration. Astrophysics has similar programs for small Earth orbiting
satellites, called Earth orbiters and medium explorers. Those are the astrophysics analogs of the Discovery program.
FM: Did the government make cutbacks to NASA, and was this a result of that?
MA: The Discovery program wasn't a result directly of cuts, but it was a result of looking at where the budget was
going to go - effectively stay flat. And try to reconcile that with the fact that missions were getting more expensive and
therefore fewer and fewer scientists could play a role in space missions.
FM: I understand that you're the Principal Investigator of NASA's Deep Impact mission that is set to launch January
1st 2004 and impact July 4th 2005. What exactly are your responsibilities as principal investigator?
(Note: The Deep Impact launch period has since been changed to begin in January 2005).
MA: My responsibility is to make sure that NASA's money is well spent and gets us an impact and scientific results
from that impact.
FM: Are you excited?
MA: Sure. The mission is very different from most missions in that it is probably the only mission that's ever been
planned that will do an experiment that is on the scale of a celestial body. We do experiments from a lot of missions that
take a tiny sample and analyze with various experiments. The closest thing we have to doing planet scale experiments, the
only one I can think of, is when we dropped the lunar module back onto the moon and measured the resulting shock waves that
propagated to moon quake sensors that had been distributed by the Apollo astronauts. So that was a planet scale experiment.
FM: Is this along those lines?
MA: Yes, just a bigger scale on a smaller body.
FM: But there was a mission planned to actually land on the comet, which was not carried out, was there a reason
why it wasn't carried out?
MA: That mission was funded in a peculiar combination of technology trades and science money.
MA: Unusual. There are technology development programs within NASA, and there are science development
programs within NASA. The science programs try to design missions, which are secure and safe as you can imagine so you
get data back. With the technology demonstration missions, we are testing new technologies and what you want to find out is,
what are the limits of those technologies. And you only find that out when the mission fails, or when it succeeds beyond what you
expected. So you tend to have very different approaches between these types of missions. And that particular mission
combined money from both the technology program and the science in ways that didn't always work well together. They were
having cost problems because landing on a comet is very difficult - because we don't know how to anchor on a comet. We don't
know what a comet is.
FM: That would have helped your Deep Impact mission.
MA: Yes, that would have complimentary information that we can't provide directly. And ideally, from the science
point of view, it would have been better if they arrived at Temple 1 before we did - then we arrived and did our testing while
they were there watching. The way the missions were designed, for practical reasons, were going to be reversed. We would
do our testing, then they would arrive 6 or 8 months later. Scientifically, that wasn't optimum. That would have given us useful
information that we can't get ourselves.