NTB: Has NASA set a launch date and chosen a point of impact yet?
Dr. Colaprete: Right now the baseline launch date is October 28, 29 and 30th. That’s our first 3-date window. Then there are approximately 3-date windows every two weeks going through 2008.
Since we are a secondary payload to LRO, we have to be ready to go whenever they go, so we have picked an impact site for each launch date depending on the geometry of the Earth, Sun and Moon. The geometry of a particular impact site can differ from launch date to launch date. For our first October 28 launch date, the impact site is a large crater named Faustini. It’s approximately 30 to 32 kilometers across and it’s probably about 3 to 3.5 billion years old. We will impact an area approximately a kilometer across inside that crater.
For October 29 it remains the same; our impact site is still Faustini, but on October 30 we move to a different crater — Shoemaker, the one where Prospector impacted. We do this shift primarily due to illumination changes. As the Sun, Earth and Moon geometries change, we maximize, or optimize, the illumination of the ejecta cloud and our ability to observe it from Earth. So for every different launch date we look at several different craters and we pick the one that’s best.
NTB: You are also heavily involved in studying Martian climate and the formation of clouds around that planet. What have you learned from those studies?
Dr. Colaprete: I am currently doing both numerical and laboratory measurements with a colleague here at NASA Ames on the formation of water ice clouds under Martian conditions. Actually, I got into the LCROSS project – or I put in the proposal – a couple of years ago based on work with the NASA Ames General Circulation Model where I was simulating the climate effects of an impact on the Martian climate. So I learned a lot about impacts and what they would do, and I extended that to the Moon, and that’s how LCROSS came to be.
What we’re studying now is how clouds form under these very, very cold, rarified air conditions on Mars. We’ve discovered some very interesting things that are not only relevant to Mars, but very relevant to Earth. It turns out that at these cold temperatures – and by cold I mean about 100 to 110 degrees below zero Centigrade – it becomes much, much more difficult to form a cloud. While these temperatures seem ridiculously cold on Mars, they’re typical, and on Earth, quite often, in the stratosphere and even more likely in the mesosphere, you see these kinds of temperatures regularly. But we still see clouds in these regions.
On Mars we see clouds very frequently. So what we’ve been working on is trying to really understand what it takes to form these clouds, and then turning those laboratory measurements into constraints for general circulation and climate models on Mars. What we found is the clouds probably have a very difficult time forming. Much of the water vapor will not go into clouds on Mars and overall cloud particles will probably be larger and, therefore, make the atmosphere drier because they can fall out of the atmosphere more quickly. So what we’re predicting is a drier atmosphere than previous models predicted, based on these laboratory measurements, and as it turns out a lot of the new observations of water vapor and water clouds, from the missions that are currently orbiting Mars, seem to suggest that previous observations were overestimating the total water amount. The Martian atmosphere may actually be drier than we first thought, and for water-based clouds, the formation process may be a little more complicated and less understood than we once thought.
But that’s science – for every question you answer, two more pop up.