Issue 13 - April 2014

Science Update: Water from RV and More!
By Wes Traub Water from Radial Velocity. Using spectral cross-correlation of radial-velocity (RV) spectra in the L band, the non-transiting orbit of hot Jupiter tau Boo b was improved and, surprisingly, water vapor detected, by Lockwood et al., see http://iopscience.iop.org/2041-8205/783/2/L29/pdf/apjl_783_2_29.pdf . Gemini Planet Imager success! The Gemini Planet Imager (GPI) coronagraph was installed at the 8-meter Gemini South telescope in January, and was an instant success on the sky, according to Bruce Macintosh. Near-infrared images of beta Pic b and the disk around HR 4796 A are visual proof, at http://planetimager.org/. Runaway greenhouse limit. By moving from a 1-D to a 3-D atmospheric model of an Earth-like planet, Leconte et al., in http://www.nature.com/nature/journal/v504/n7479/full/nature12827.html , find that Hadley cell circulation has a stabilizing effect, yielding a value of about 0.95 AU for the inner edge of the habitable zone for the present Earth-Sun system, fortuitously close to older estimates, according to Kasting and Harman: see http://www.nature.com/nature/journal/v504/n7479/full/504221a.html . Mass from spectra. Exploiting the fact that atmospheric scale height varies as the mass of a planet, de Wit and Seager (http://www.sciencemag.org/content/342/6165/1473.full.pdf) found that it should be possible to estimate that mass solely from a transit spectrum, at least in cases where the degeneracy with temperature, radius, and mean molecular weight can be disentangled. Clouds or hydrogen-poor? The lack of spectral features in the near-infrared spectra of GJ 1214b prompts Kreidberg et al. to infer that the planet has high clouds, but a similarly flat spectrum in the same spectral range for GJ 436b encourages Knutson et al. to conclude that that planet has either high clouds or a hydrogen-poor atmosphere, all of which suggests that more data are needed; the side-by-side papers are at http://www.nature.com/nature/journal/v505/n7481/full/nature12888.html and http://www.nature.com/nature/journal/v505/n7481/full/nature12887.html respectively, with commentary by Moses at http://www.nature.com/nature/journal/v505/n7481/full/505031a.html. Plate tectonics redux. A new model of the Archaean era (4 to 3.5 billion years ago) on Earth features numerous volcanic “heat pipes” to the surface, allowing heat to escape while also allowing the surface layer to remain relatively cool. This means that Earth may have switched quickly from a static crust to a plate-tectonic crust around the end of this era, with implications for exoplanets; Moore and Webb report on this at http://www.nature.com/nature/journal/v501/n7468/full/nature12473.html, with commentary by Moresi at http://www.nature.com/nature/journal/v501/n7468/full/501496a.html. Brown Dwarf maps. Crossfield et al. applied the Doppler imaging technique from stars to a nearby brown dwarf to obtain images of the surface through a full rotation period, with about 10 percent brightness variations. The paper is at http://www.nature.com/nature/journal/v505/n7485/full/nature12955.html and a commentary by Showman is at http://www.nature.com/nature/journal/v505/n7485/full/505625a.html