On July 16, Discovery successfully launched on a mission to the International Space Station, the first shuttle launch since the 2003 Columbia disaster. Courtesy of NASA.
Geotimes: What do you think the top planetary science stories
are this year?
DJS: I would say its been a big year, and a very important year, and three things come to mind. One of them is a continuing story and that is, of course, the Mars rovers.
The Mars rovers have continued to find interesting things, and theres been a consolidation during the past calendar year. The evidence from both rovers strongly suggests the role of running water on the surface of Mars in the distant past, and this role is expressed in the rocks that are seen. Of course that was a big discovery 18, 20 months ago, so in that sense its not really a new story, but the story has been strengthened, and I think thats very significant.
Now, the two new stories: first is the discovery of a body in the Kuiper Belt thats bigger than Pluto.
Geotimes: What is the broader impact of finding that object?
DJS: Actually the broader story is that were developing a picture of the Kuiper Belt, the family of bodies [located beyond Neptune], one of which is Pluto, and now we have a whole bunch of others.
[Its important] not to focus on the fact that a bigger one has been found, but that were seeing a diversity of bodies out there.
The exciting information that Im aware of is not yet published. The discoveries are done by Mike Brown [of Caltech], two doors down from me, so I know whats going on. Its evident already that these objects are not all the same; in other words, theyre not just Pluto-like. They have different surfaces; they have different material properties. Because there are spectra for some of these objects, its not just that they have been discovered: People have collected spectra, theyve looked at whats on the surface of these objects, [and] theyre not all the same.
Geotimes: And that has implications for the way the solar system
DJS: Yes, although exactly how to interpret that, I think, is quite mysterious at the moment. Its a discovery story rather than a synthesis story. We dont quite really know what it all means yet, but this is exciting science its at a stage where people are finding things; they arent sure what it all means yet.
I also think that although its important to focus on the question of why it all matters, the fact remains that [astronomers have found] the biggest object in the solar system that orbits the sun since the discovery of Neptune, which was in 1846 isnt that a good story?
Geotimes: So, what was the third thing?
DJS: The third thing would be Titan. Cassini, together with the Huygens probe, which dropped into the atmosphere of Titan [Saturns largest moon] last January, has opened up a view of a remarkable body. We now see on the surface of Titan channels that look like rivers, plains that look as though they might have been created through deposition of material that was carried by liquid, and structures on the surface of Titan that some people want to attribute to volcanism. This is an extraordinary thing, and it is a combination of the data collected by the Huygens probe and the information collected from the spacecraft that orbits Saturn and occasionally passes Titan every couple of months. And from that, there are radar pictures and also pictures in the near-infrared that allow you to see down to the surface.
So, here is a body that from the point of view of process is a planet yes, it orbits Saturn, but it has planetary processes: dense atmosphere and rainfall (the rain is methane of course). As a consequence, it has the climatic cycle and the geologic cycle. The materials are very different, of course, but the processes on Titan right now have greater similarity to the processes on Earth right now than any other planet in the solar system, including Mars, and thats remarkable.
Geotimes: Those are the three big things. Anything else that
you would mention?
DJS: The extrasolar planet game continues to be an enormously productive business. The number of extrasolar planets is up to 150 [and] keeps going up. Were getting an increasingly better picture of what these objects are, what their masses are, the extent to which there are multiple planet systems, what it is that dictates whether a star will have a planet. Theres some indication that when you have an abundance of heavy elements, you are likely to have planets. Thats an ongoing story in the same sense that Mars is an ongoing story.