Mars Odyssey, 2001

William Boynton

The mission I’m associated with mostly now, the Mars Odyssey mission, was one where we finally got to send the gamma ray spectrometer back to Mars that didn’t make it because the first one [Mars Observer] blew up. In this case, they actually said that if I thought I could build a better instrument than Martin-Marietta—which was now called Lockheed-Martin—then I could go ahead and build my own design. In fact we came up with what turned out to be a much better design, and we built it ourselves, right here across the hall in this lab in Tucson.

It was a pretty elaborate project but we got a darn good instrument out of it, and made some interesting discoveries. We discovered vast quantities of ice buried just beneath the surface that nobody knew was there. Some people suspected there might be a small amount of ice just filling the pore space between the sand grains, but what we found was that it was mostly ice with just a little bit of dirt mixed in with it, rather than the other way around. That really changed people’s thinking about Mars.

We also found some interesting things going on with the atmosphere. One of the people working with me, Ann Sprague, was looking at the argon data. Argon is a rare gas that’s in the atmosphere but it doesn’t condense out at low temperatures, whereas the carbon dioxide that’s in the atmosphere does condense out at low temperatures, and that’s what makes the seasonal frost that happens in the wintertime there. 

What she found is that the argon was being enriched over the poles in the wintertime, because a significant fraction of the atmosphere would move toward the winter pole, and the CO2 would condense out, and more atmosphere would come to replace it, and every time more atmosphere comes to replace it, it brings with it more argon. But the argon doesn’t condense out so we were just building up a concentration of that argon.

I looked into the data to see that, indeed, it looked like that was happening, but Ann, who’s got more background in studying atmospheres, looked at the data and she’s been processing it and found out that it’s really telling us interesting things about the motion of the atmosphere on Mars.

Originally when the instrument was proposed, it was thought it was going to be mostly a geochemical instrument mapping the elements over most of the planet. But it turned out I think probably the discovery of the ice and looking at what goes on with the argon in the atmosphere—it’s been surprising that the instruments turned out to be probably as valuable or maybe even more so in ways that we didn’t even contemplate or proposed. I think the fact that we discovered ice in the polar regions probably helped NASA decide that we really need to go with the Phoenix mission, which is going to go to this polar area.