Dale P. Cruikshank is an astronomer and planetary scientist in the Astrophysics Branch at Ames Research Center. His research specialties are spectroscopy and radiometry of planets, asteroids, satellites, and other bodies in the solar system. In his most recent studies with the Cassini spacecraft, he and his colleagues found hydrocarbons on several of Saturn’s satellites.
NASA Tech Briefs: Your research specialties are spectroscopy and radiometry of planets and small bodies in the solar system. I’m interested in your work with NASA ESA-Cassini mission. Can you tell our readers what that mission was and what it told you about Saturn’s satellites?
Dr. Dale P. Cruikshank: The Cassini mission to the Saturn system has been a tremendously successful space mission conducted both jointly by NASA and ESA, and it’s still in progress, and, in fact, it’s expected to be in progress until the middle of 2017. The mission is a flagship-class mission in that it’s a very large spacecraft with numerous instruments aboard. The ESA component was the Huygens probe, which roughly a year after we arrived at Saturn was released from the main spacecraft bus, and then made a parachute descent through the atmosphere of Saturn’s largest moon Titan and eventually landed on the surface. And, in fact, it conducted scientific measurements for two and a half hours after it landed, even though it wasn’t technically designed to be a lander, per se. The remaining part of the mission, which essentially continues, includes an investigation of the planet Saturn itself, its atmosphere, the aurora that occur in the atmosphere, Saturn’s magnetic field, and the trapped particles that are in it, as well as Saturn’s rings, of course, and Saturn’s satellites, too. Saturn has a very large number of satellites, something like 62, I think, of which the largest ones are close into the planet, and those are the ones that we’ve been studying with several of the instruments on board the spacecraft.
NTB: You found many kinds of ice on several small planetary bodies. Where have you found the ice, and what kinds of conclusions are you able to draw from these findings?
Dr. Cruikshank: Ices are kind of a natural thing to suspect might be present in the cold reaches of the planetary system, and what we have found over the years, both from telescopic observations made from the ground, and now more recently with spacecraft observations, is that there’s a wide variety of ices, not just frozen water, but frozen carbon dioxide, which we find on Mars, in the polar caps, for example, dry ice. When we move farther out into the solar system, in addition to frozen water, we find frozen methane, natural gas, and other hydrocarbons, such as ethane and possibly still more that haven’t been fully identified. If we go even farther out into the solar system, as far as out as Neptune and Pluto, at which the temperatures are something like 35 to 40 degrees absolute, we find frozen nitrogen. And, of course, nitrogen is the same thing that’s in the Earth’s atmosphere, but at those extremely low temperatures, nitrogen freezes into a nice shiny ice on the surface of these bodies.
So, a good bit of what I’ve been interested in over the years, is the exploration of the solar system in terms of its ices – and also minerals by the way – but in particular, the ices. Together, with a couple of colleagues in 1976, which seems like a long time ago, we discovered the methane ice on the surface of Pluto, and we also found, a few years later, methane ice on Triton, which is Neptune’s largest moon, and since then, nitrogen and frozen methane have been found on a number of objects out beyond Neptune, in what’s called the trans-Neptunian object region of the solar system.