Over the weekend of February 19th and 20th, I was privileged to attend the annual meeting of the American Association for the Advancement of Science in Washington, D.C. This is always one of my favorite scientific meetings, mostly because it covers such a wide range of topics, and the topics are the sort that are of interest to the scientifically literate public. No talks about the evidence for mass fractionation in noble gas isotopic ratios in meteorites, blah, blah, ZZZZZZZ—at least not unless something like this is put in a broader context.
I was especially interested in this meeting because it had a number of symposia dealing with astronomical topics. I can type a lot faster than I can write, so I propped up my laptop and happily took notes for each of the three hour sessions. I attended another session that wasn’t astronomy-related, but I’ll spare you that one.
Kepler: Looking for Other Earths—the much-anticipated description of the first four months of data from the Kepler spacecraft (see previous post on this). Some highlights from my notes:
• All of the objects being discussed are planetary candidates; confirmation as bona fide planets awaits further work. To simplify matters, I will refer to them all as planets rather than as candidates.
• About 44% of the stars observed so far have planets.
• Early data is still biased toward large planets in orbits close to their stars. Future work will emphasize smaller planets and longer orbital periods.
• Subtle variations in the timing of planetary transits can be used to determine the densities of all planets in a multi-planet system
• Most interesting planet to me: Kepler-10b, one that apparently has clouds (of what, is a good question). The way they figured this out is fascinating, and depends on the exquisite sensitivity of the light-measuring device on board.
o A planet will decrease the total amount of light seen by Kepler when it crosses in front of (transits) its parent star.
o But as it travels around the star and just before it disappears behind it, its face is illuminated by the star, and it reflects that light back to us.
o We know how big the planet is from the transit data, so measuring how much light it reflects back tells us its albedo, or reflectivity.
o We know the temperature of the planet’s surface, so we know whether it is hot enough to glow and thereby contribute to the light we see coming from it.
o The planet in question is not hot enough to glow (a lot) in visible light.
o So what we see has to be mostly reflected light.
o The planet’s albedo is 0.6 (60% of the light hitting it is reflected); that of the Earth is 0.3.
o The only things that reflective in our solar system are Venus (clouds) and Enceladus, a moon of Saturn covered with ice.
o Kepler-10b is too hot for ice, so…
o CLOUDS!!
o What are they made of? Kepler-10b is really hot, especially on the side facing its star, so the clouds are probably suspended droplets of molten rock!
o There is a really cool depiction of this system and what Kepler sees here: http://kepler.nasa.gov/Mission/discoveries/kepler10b/
• Key point of this session: the power of Kepler is in the size of the data set. It allows us to say something meaningful about planetary systems in general, not just the particular few we happen to know about.
There were other sessions, but I’ll leave those for future posts!
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