Three planets in the Kepler-11 system as they simultaneously transit their star as imagined by by a NASA artist (Image credit: NASA). From http://ciera.northwestern.edu/Research/highlights/research_highlights.php#ForeignWorlds.
Great finish to the meeting, and thankfully no big disasters at my special session.
Lots of excellent talks, but the talk that stood out for me was Sarah Ballard’s, in which she addressed an impressively simple but compelling question: Is there a difference between planetary systems where we’ve only found one planet and systems where we’ve found more than one?
This question is important because such a difference could point to different formation and/or evolutionary processes in these systems, and so comparison of these systems could elucidate subtle but significant aspects of planet formation.
In fact, Ballard did find the two types of planetary system are different, and that, for some reason, about half of M-dwarf stars that host planets have only one.
She also found modest but intriguing differences in the stars that host single planet: their features suggest they may be older than stars with multi-planet systems. Does that mean that single-planet stars used to have multiple planets but enough time has passed that the system became dynamically unstable, leaving behind a single planet?
Blue glacial ice. From http://upload.wikimedia.org/wikipedia/commons/1/10/JoekullsarlonBlueBlockOfIce.jpg.
I really enjoyed Aomawa Shields‘s dissertation talk in the “Extrasolar Planets: Host Stars and Interactions” session, in which she discussed how different stellar types could influence the climates of putative Earth-like planets.
She highlighted how the ice-albedo feedback would operate differently on planets orbiting M-dwarfs as compared to those orbiting F-stars. Since they are so cool, M-dwarfs shine primarily in infrared (IR) wavelengths, while F-stars are much hotter and emit in the visible and ultraviolet (UV). At the same time, water ice primarily absorbs IR but reflects visible light.
Therefore, around an M-dwarf, the ice on an Earth-like planet’s surface would absorb a lot of the stellar insolation, heating the planet, while around an F-star, the ice would reflect it, keeping the planet cool. As a consequence, Shields argued that M-dwarf planets have climates more stable against global ice ages than F-star planets. So although there may be other challenges to life on an M-dwarf planet, climate stability is probably not one of them.
The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. From http://en.wikipedia.org/wiki/Doppler_spectroscopy#mediaviewer/File:ESO_-_The_Radial_Velocity_Method_%28by%29.jpg.
Another great day at the AAS meeting. One talk that stuck out for me was the dissertation talk from Ben Nelson (PSU). I was amazed at how much he was able to squeeze into his 15 minutes and still not lose the audience.
Among the things he covered was his new MCMC code, RUNDMC, specially suited to analyze radial velocity (RV) observations of planetary systems and thoroughly but quickly sample the sprawling parameter space associated with these systems. He applied his code to several systems to understand how robustly different planetary configurations could be detected in those systems, including whether the RV data favored additional planets in a system or other kinds of variability.
Lots of amazing presentations today, running the gamut from transmission spectroscopy of hot Neptune-like planets to the detailed and puzzling architectures of multi-planet systems. But two talks really stuck out for me.
The first one, by Prof. Dan Baker at U Colorado, covered recent developments in the study of the Van Allen radiation belts (which Van Allen preferred to call “zones” — when asked by a reporter what was the function of Van Allen belts, he said they hold up Van Allen’s pants). As a member of the Radiation Belt Storm Probe mission, Baker explained what we understand and what remains mysterious about these powerful celestial phenomena suspended above our heads, including a bizarre “glass wall” that keeps charged particles at bay.
The European Space Agency’s Rosetta spacecraft captured these photos of the Philae lander descending toward, and then bouncing off, the surface of Comet 67P/Churyumov–Gerasimenko during its historic touchdown on Nov. 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/ID — http://www.space.com/27788-philae-comet-landing-bounce-photos.html
In the afternoon, Dr. Paul Weissman gave the most recent updates on the Rosetta mission, still in orbit around Comet Churyumov-Gerasimenko (which Weissman called “comet CG”). Following up on the more-exciting-than-expected landing of the Philae spacecraft, Weissman explained that the lander struck a surprisingly hard sub-surface layer (comparable in strength to solid ice), which probably contributed to the lander’s unplanned ballistic trajectory around the comet. Lots of other interesting science, including more evidence about the origin of Earth’s water.
Day 2 of the workshop was just as great as day 1. Lots of great resources, but the one that really stood out for me was the seaborn plotting module for matplotlib — just produces some amazing plots, have a look.
Onto the rest of the conference!
The new year finds me in Seattle two days before the AAS 225 meeting officially begins to attend the Software Carpentry workshop. This workshop is put on by a volunteer organization that teaches scientists how to write and maintain robust code.
On the first day, we covered some shell scripting, basic python, and the ipython notebook. Just the first few lessons are already hugely useful for me, and the teachers are doing a great job explaining things clearly. They are also using a variety of tools to record and document the workshop. I’ve pasted links to those records below.
Very much looking forward to Day 2.
Useful links and particularly useful notes: