PlanetWatch: Milestone by Milestone

This week’s hottest news is of course the “Tatooine” type planet Kepler 16-B, a Saturn-like planet orbiting two stars. Detected using the Kepler Space Telescope, it orbits a closely packed binary system (with total mass about the same as our Sun).  The whole system is aligned on the same plane to within about half a degree, suggesting that the whole system formed out of a single disc of material – this is by no means the only possible way, but it is certainly the simplest, and we should apply Occam’s Razor in the absence of other data.  This is a somewhat serendipitous discovery – the planet is due to stop transiting star A in 2018, and star B in 2014, not to do so again for a few decades.  In astronomical terms, the team caught this planet just in time!

Schematic of the Kepler-16 system (taken from Doyle et al 2011, Science, in press)

The discovery of such an unusual system illustrates the progress of planet detection.  Detecting a planetary transit signal amongst the din of stellar transit signals (after all, star A will transit star B and vice versa) is a real achievement, and a testament to the Kepler instrumentation.  With the Extreme Solar Systems conference taking place this past week, we’ve seen a whole raft of announcements about planet discoveries.  The HARPS team have announced an interesting crop of 50 exoplanets, with a surprisingly large fraction of Super-Earths in the mix.  We’ve also had the recent discovery of the controversial “diamond planet“, which is most likely a stellar remnant rather than a bona fide planet.  This doesn’t make the discovery any less exciting – after all, this planet is probably the core of a white dwarf with its atmosphere stripped away, something we’ve never seen in the wild before.  Any details we can glean from this gives us vital forensic evidence regarding the last stages of a star’s life.

All these milestones edge us closer to the Holy Grail of planet detection – an Earth analogue, orbiting a solar type star in the habitable zone.  We’re still not quite there yet, but each of these unusual discoveries sharpens our tools (both instrumental and theoretical), bringing us closer to seeing the first of our planet’s cousins.


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