This has been an extraordinary week for planets (moons), exoplanets, and astrobiology. I’m hard pushed to write properly about all these things but sometimes the sheer tidal mass of discoveries tells its own story.
And tidal masses is the first one up. This week new results from the Cassini mission around Saturn were presented in Nature (and discussed in this nice piece) that suggest Titan’s surface responds to the gravitational tides of Saturn by lifting and relaxing a substantial 10 meters in altitude. This indicates that Titan’s interior is quite flexible, in fact it indicates something that has long been suspected – Titan probably has a subsurface ocean of liquid water, somewhere within 100 km of the surface. Sustained in part by radioisotope decay in Titan’s rocky core, this would be far from pure water, but water nonetheless.
Far, far away, around a distant star called Tau Bootis, astronomers have now succeeded in obtaining the first direct measurement of the spectrum of light from the atmosphere of a hot Jupiter planet. All previous measurements of the atmospheric spectrum and composition of such worlds have come from data taken during transits of the parent star (where starlight serves as a brilliant back-light through the outer layers of atmosphere). By nailing the light coming directly from the plant known as Tau Boo b, astronomers have not only pinned down the planetary mass (by learning the orbital inclination relative to our viewpoint) but have set a precedent for the future. The direct measurement of light from exoplanets is one of the holy grails of astronomy (yeah, there’s lots of these grails in science, I know).
And for another hot Jupiter, the planet HD 189733b (distinguished by transiting a star that at 63 light years away appears pleasantly bright in our skies, enabling lots of great observations to be made) has been observed to respond directly to a pummeling from a flare event on its parent star. In a stroke of luck the star underwent a large X-ray bright flare event just 8 hours before the transiting planet was observed with the Hubble Space Telescope. Unlike earlier measurements, this one showed a clear ‘plume’ or tail of atmosphere being lost by the planet – adding it to the family of evaporating worlds, albeit periodically.
And finally (although I’ve skipped all sorts of other goodies, like peculiarly close super-Earth exoplanets that come as close as 1.2 million miles every 97 days), some more food for thought in the search for life elsewhere. Some new work indicates that the martian moon Phobos is in the direct line of fire for material that’s blasted off the martian surface by asteroid impacts. As this small moon scoots around Mars every 7.5 hours it can collect a significant amount of Mars filth. Why is this interesting? Well, it’s an awful lot easier to go and land on Phobos than it is to land on Mars – so perhaps we should be thinking of sieving through the sands of Phobos in order to get a sampling of eons of Mars ejecta, and any possible microorganisms…
Just another week in science.