1) Is there an atmosphere on the martian moons? If not, why not?
No, there is not. Phobos and Deimos are both too small to hold on to an
atmosphere. Their gravity is so low that if you put air around them, it
would just drift off into space.
2) Is the atmosphere changing on Mars?
It is not changing in ways we know about, at least if you look at the
big picture. Seasonally, the atmosphere gets bigger and smaller, and
the temperature and the amount of dust in the atmosphere changes. Like
places on Earth, places on Mars also have cloudy times of year as well
as less cloudy times. The big changes, like when Mars went from a
thicker and wetter atmosphere to its current state, all happened
billions of years ago.
3) What is ozone? Could Mars form an ozone layer?
Ozone is a molecule made of oxygen atoms. There are 3 atoms in ozone,
unlike the oxygen molecule, which has 2 oxygen atoms. It forms in a lot of ways.
One way is when ultraviolet sunlight breaks up oxygen atoms and they
combine into ozone. That is what happens in Earth's stratosphere, where our ozone
layer is. That happens on Mars too, and Mars has ozone. There is much less
oxygen to start with, so there is not very much ozone on Mars. It doesn't form a layer
there, it reaches all the way to the surface. And there is little
enough ozone that far more ultraviolet light reaches the surface of Mars than the
surface of Earth -- you could get a bad sunburn very fast there.
4) What college classes did you take to prepare you for your current job with the Athena Mission?
As an undergraduate, taking regular college classes, I didn't
specialize in planetary science at all. I majored in physics, and that requires
taking a lot of math classes, too. I took a few astronomy and geology classes, but
many of my "elective" classes were in things like philosophy and
communication. Many other people in the mission started with a geology or chemistry
major instead of physics. Graduate school is where I got really speciallized
-- I was in a planetary science department, and I took some (Earth)
geophysics classes, too
5) What are some of the specific questions that you hope the MER
missions will address? What are you "looking" for as evidence of past
life?
The overall goal of the mission is not so much to look for past life. We
are trying to get a better understanding of Mars' past habitability. We
can learn a lot without finding life. For instance, life requires water,
a source of energy, and organic molecules. We know Mars is inhospitable
to life now, but in the past the water on Mars may have been liquid. In
fact, we are sure the water has been liquid, but we do not know how long
the liquid water lasted. If we find a place where water lasted for
millions of years or more—instead of days—then we would know where to
start looking for past life. If we find the water associated with
organic molecules and energy sources—food—then we have another good
sign. So, what we are looking for would be any sign of the past presence
of water.
We will look at the minerals, especially iron compounds. Some minerals
form in the presence of water; without water, we would see a different
mix of minerals. We will look at the landscape. From orbit,
Gusev Crater looks
like it must have been a lake for some time. If we see a landscape that
looks like a dried up lakebed, we can confirm those suspicions.
Meridiani Planum has a mineral (coarse hematite) that forms in liquid
water over long periods of time. The trouble is, it can form in other
ways, too. So again, we will look at the landscape and the minerals to
find evidence that can help solve the puzzle. In this case, close up
investigation of the hematite itself will be a major priority.
I will spend most of my time looking at something else. Much of Mars is
covered by dust. That dust blows around in the wind and covers
everything. It gets in the way of many of our measurements—on the rovers
we have a Rock Abrasion Tool
that is capable of
brushing the dust off as well as scraping down into rocks. With a few of
the other scientists, I will be using the cameras to study the dust
cycle. We hope to watch the dust being thrown into the sky by dust
devils, we will certainly see the airborne dust and measure its
properties, and we will use targets on the lander to measure the rate
the dust falls out of the sky. With the rovers we will see only a small
part of a very big picture: as the dust moves around Mars over long time
periods, whole craters can be buried and then exhumed again.
6) What is the goal that you hope to achieve on Mars?
My goal is to study the dust cycle on Mars. On Mars, like Earth, there
are many cycles. The hydrological cycle (which would be rainfall,
rivers, and evaporation on Earth) on Mars is not very active now. The
carbon cycle on Earth includes all life, as well as plate tectonics and
volcanism. On Mars, the carbon cycle is much more limited. Mars’ dust
cycle is weak compared to Earth’s cycles. There is much to study in the
dust cycle: dust devils and dust storms have been seen raising dust into
the sky. Dust falls onto the surface, and can change a dark area into a
bright area with just a thin layer—such changes have been seen from
Earth. Orbiter images have shown craters that were previously buried by
dust being exhumed again. From the rovers we cannot study all of this.
The atmospheric researchers will use the cameras and mini-TES to study
the dust in the sky (as well as studying the atmosphere itself). We hope
to learn more of the properties of the dust. Other people will study the
dust after it falls, including the
magnetic properties.
Together,
we can investigate how the dust was formed, and what the environment was
like when it was formed.
7) Why does Mars have such a thin atmosphere?
Essentially, because Mars is smaller than Earth. Its gravity is weaker,
and so it cannot hold its atmosphere as well. There is more to it than
that, though. Mars does not have a global magnetic field to protect its
atmosphere from the solar wind, like Earth does. Mars is also so cold
that its atmosphere, which is mostly carbon dioxide, can condense at the
poles during winter. This means that the amount of atmosphere Mars has
actually varies during its year, as dry ice condenses and sublimates at
the poles, especially the south pole. People have speculated that if
Mars were warmed up, the dry ice would all return to the atmosphere.
Carbon dioxide is what we call a greenhouse gas—with more of it in Mars’
atmosphere, things could warm up more. Unfortunately for those who are
interested in such changes (called terraforming), there may not be as
much dry ice as was previously thought.
8) If humans could go to Mars, what experiments would they do?
I was struck during Pathfinder operations by the pace of discovery.
Pathfinder was a very successful mission, exceeding its engineering and
science goals by a substantial margin. Yet Pathfinder accomplished in
the first two weeks what a human field geologist could have accomplished
in half an hour. The first things a person would do are simple: look
around, turn over some rocks, scrape the dust, and so on. A person would
have walked up a nearby hill to get a better view of the surrounding
terrain—within the first hour a human would certainly have traveled
farther than the Sojourner rover did in its 83 sols on Mars. The goals
would be similar to NASA’s current goals. A person would use
instruments, including ones similar to those on the rover, to examine
the rocks and dust. A person would be well equipped to go further: when
you are immersed in the field site, all of your senses give you some
information about the context; when you study with a robot, you see
narrowly only what you are looking for.
9) Have you ever been in space? Would you like to go there? Why?
No, I haven't. I wouldn’t mind a short trip, if it were ever safe for tourists.
Really, though, that would just be for fun. From a work perspective, I
like to take advantage of the fact that there are some things that
robots can do better than humans. One of those is exploring extreme
environments relatively cheaply. Someday I expect we will be able to
afford to send astronauts following the rovers to Mars, but I’m not
planning to make the trip. There are many fascinating planets in the
solar system, but Earth is my favorite.
10) What color is the sky on Mars? Why is it that color?
The sky is sort of a butterscotch/rust color. The sky on Earth is blue
because gas molecules scatter blue sunlight better than red sunlight, so
the blue light fills the sky. On Mars, there is much less of an
atmosphere—the surface pressure is less than 1% of Earth’s. So, the sky
would be a very dark blue, with stars shining, if the atmosphere were
clear. So far, though, every Mars landing has found a dusty atmosphere.
The dust may be some sort of a clay-like mineral, but the color is
because it contains small amounts of oxidized iron. And oxidized iron is
a fancy way of saying rust. We know Mars has global and regional dust
storms, but even away from the dust storms there are dust devils that
throw dust into the sky. So, away from a dust storm, there is not a lot
of dust in the sky, but there seems to be enough to keep the sky a
bright rusty color.
An interesting thing about the sky’s appearance is related to the
sunset. On Earth, sunsets are red and orange because all of the blue
light has been scattered away from the Sun into the sky. On Mars, all
colors are scattered away, but a lot of the blue light is absorbed by
the dust (making the sky yellowish-red). The blue light that is
scattered stays close to the Sun, and the result is a blue sunset in a
rusty sky, instead of Earth’s rusty sunset in a blue sky.
