This Week on PlanetWatch

As is true of every week, there have been quite a few new extrasolar planets detected.  This week’s batch is a mix of the weird and wonderful, so as part of a new running segment I’ll be describing the latest finds.

First off, let’s talk about my friend David Kipping’s latest work on the darkest world ever discovered.  They used data from the Kepler Space Telescope to study the Jupiter type planet TrES-2b.  Watching how the light from the star varies as the planet moves around and behind the star allows them to measure how much light the planet itself is either emitting or reflecting both at “day” and at “night”.  They find that this world is very dark indeed – the albedo (or what fraction of starlight is reflected by the planet) is less than 1% .  Just to compare, Earth reflects around 30% of the Sun’s light in the non-ice regions.

Artist's impression of the Darkest Planet

As David says, this makes the planet “blacker than coal”.  A well roasted planet, its surface temperature is 1200C  – partly because of its extremely low albedo, but also because it’s about 300 times closer to its star than Earth is to the Sun.  How could it be so black? Probably some exotic chemistry is at work, but we’ll need to revisit this system with more upcoming Kepler data to be sure.

Back on the less weird side of things, the HARPS (High Accuracy Radial Velocity Planetary Search) project has made some exciting discoveries of very low mass planets (ranging from 2.7 to 4.8 Earth masses) around sunlike stars.  While these are all a little closer to their stars than Earth is (about 0.13 to 0.4 times the Earth-Sun distance), one in particular (the snazzily named HD 85512b) is an extremely good candidate for habitability, provided it has at least 50% cloud cover.  In fact, the authors of another paper on the subject say that

HD 85512 b is…[one of ] the best candidates for exploring habitability to date, a planet on the edge of habitability.

The Telescopio Nazionale Galileo in the Canary Islands, destination of the HARPS-North instrument (Source: University of St. Andrews)

Very exciting! Even more exciting is that Edinburgh is now a member of the HARPS-North collaboration, which will be attempting to make similar discoveries in the Northern Hemisphere of the sky.  It will be able to study the same patch of sky that Kepler is looking at right now, and allow us to confirm and hone their discoveries.  One day, I’ll hopefully be writing a PlanetWatch with an amazing planet discovery from Edinburgh astronomers!


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