Tue, 04 May 2010
I'm at the European Geosciences Union (EGU) General Assembly, 2010, the biggest gethering of European geoscientists, in Vienna, May 2-7. This is my first time here and its huge: over 9000 participants. Merely finding the talks and posters is a challenge (they supply a USB stick with the abstracts and agendas as they can't print them all!
The first day I spent mostly at the exoplanet stream (and putting up my own poster). Some neat stuff on show: summaries by Borucki on Keplers findings (on the Hot Jupiters they found :" these things glow like a blast furnace; forget life"). He points out that when they look for Earth sized planets, radial velocity confirmation would take 1000s of hours on 10M telescopes - so it won't happen. hmm.
Steve Unwin on SIM: neat astrometric mission for planet hunting and galaxy measurement. A targeted mission list, unlike the Gaia survey; to fly in 2016 if the Decadal survey says yes. 20% of time available under the general observer program, so get proposals ready ?
Nestest poster idea: Anomalous night-time temps on Mars, Gonzales et al.. Finding hot spots on Arsia Mons, a volcano. Explained by air rising from 100km long lava tubes. We've seen pit entrances to caves on Mars with HiRISE, etc. here they model heat output from a pit entrace/exit and imply 100km caves. Oh to go exploring...
Tinetti points out that we lack proper spectra, both experimental and theoretical, for high temperature and pressure gases such as methane, etc. Hmm, I know a group in Galway that might be able to help ...
Helmut Lammer raised an interesting point at the poster session, that many groups ignore the stellar wind when looking at H2 atmospheres around exoplanets. Theis grossly inflates the apparent H2 atmosphere. Without taking this into acount it would be easy to mistake H2 detections with a Neptune-like atmosphere. He points to a 1.7M UV telescope that the Russians are planning to launch that would help do UV measurements when Hubble is gone.
Lena Noack gave a talk on convection in tidally-locked planets (with related poster Low-lid formation on Super-Earths and implications for the habitability of Super-Earths and Sub-Earths). They argue that no covection can be expected in the mantle, and hence no geodynamo or magnetosphere. This could be a problem for holding an atmosphere. Time to check for planetary magnetic fields. Break out the polarimeter ?
Oh, and it seems that That Damned Volcano is closing Irish airspace on Tuesday. Might be an idea to go to the meeting about it. Hope it clears by Friday ...
Thu, 20 Aug 2009
In this weeks Astronomy & Astrophysics was a paper by M. Reidemeister et al., A possible architecture of the planetary system HR 8799.
This revisits HR 8799, one of the few planetary systems seen by direct imaging, actually observing the planets.
These are believed to be three Jupiter-sized planets (of about 5, 7 and 7 times the mass of Jupiter: the exact numbers depend on the precise viewing angle from Earth; Reidmeister think this is nearly pole-on). They were discovered last year by Marois et al..Summarizing all available data, they decide that HR 8799 is less that 50 Million years old, practically still forming. Their proposed layout of the system has at least three dust rings, still coalescing and cooling. By comparison, our Solar system at that stage had formed the main planets but the four outer giants were still moving into position, working their way through the remains of a dusty, gassy disk : another 500 million years or so before Jupiter and Saturn settled into their current orbits, and bombarding the inner system as they did so, leading to the cratering we see on the moon and resurfacing Mars, Earth and Venus.
What makes the HR 8799 system so interesting is that its a good test for theories of planetary or stellar formation. Its unclear whether it formed as a 'planetary system', with the planets formed in the debris disk of the star, or as a "multiple star" system; for the latter. Modelling the formation of HR 8799 will be a good test of Alan Boss's 'Gravitational Instability' theory, vs the 'core accretion' model which has been gaining ground in recent years.
In the meantime for non-theorists, its pole-on orientation gives us a good view of planets in formation. Roll-on the clearer images of the James Webb Space Telescope.
Tue, 21 Apr 2009
From the exoplanets mailing list:
Gliese 581d is now more solidly inside the habitable zone; it was considered before to be on the outer edge of the habitable zone (this work moves its believed semi-major axis from 0.25 AU to 0.22 AU). Gliese 581d was a maybe for habitability (see this Centauri dreams article for example), depending on cloud cover, etc. Now its definitely in. The new Gl 581e is beyond the classical habitable zone.
These planets are quite close in: Rory Barnes and colleagues at Lunar and Planetary Laboratory in Arizona did some good work on the habitability of Gliese 581 c (paper online) and concluded that it would be tidally heated to such a degree it was probably never habitable. Such tidal heating might make Gl 581e habitable; time to run the model again.
Correction: On reading the ESO Press release and paper (via) it appears that Gl 581e is inside the orbit of Gl 581b, and too close to the star to be habitable. To date, planets have been labelled b, c, d .. as they are discovered, and they've been discovered shortest-period first, so 'b' also meant closest to the star. Now Gl 581e is closest to the star, with a period of 3 days.