Computing and Planet-Finding

October 17, 2012 in blog, blog-general, blog-technical

An Earth-sized planet has been found around the star closest to the Sun, Alpha Centauri – and while the astronomers used a telescope, it was only with big computing that they could first “see” the planet.

Since astronomers don’t know ahead of time which stars will turn out to harbour planets, modern exoplanet searches carefully monitor huge numbers of stars looking for the subtle “back-and-forth” motions that the gravitational pull of the orbiting planet causes.    But these motions are just a small part of what is going on with the star – stars are constantly in motion, with star-wide rotation and local stellar storms.   So astronomers must gather huge haystacks of data and then sift through them searching carefully for any needles.   The plot in the header of this article, from the Nature paper describing the Alpha Centauri finding,  shows you what astronomers are up against – they are looking for very subtle trends in very noisy data.

To do this, the researchers construct periodograms of their data, looking for signals that occur regularly at some particular period; the periodograms from the Alpha Centauri paper are to the left.   There is a strong peak at just a little over 3 days, of the right size to come from a very close-in planet.

But constructing these periodograms from data taken from a particular star can be extremely time consuming, taking up to a day on a modern computer workstation; and the Kepler project, for instance, is monitoring a quarter of a million stars!  This amount of data simply can’t be processed on individual scientists’ desktop computers; this requires dedicated computing — the sort of significant resources that cloud computing or a supercomputing centre can provide.  In this case, ESO’s HARPS dedicated pipeline computer does much of the heavy lifting.

 

For more on computing and planet finding, here are some good resources:

  • A good, informal, overview of the Alpha Centauri story can be found at the “Bad Astronomy” blog;
  • The European Southern Observatory (ESO)’s exoplanets page has information on this story and the search for exoplanets generally;
  • NASA’s Kepler satellite is another exoplanet-finding machine, and the Kepler Page is full of great information
  • The Astronomy Computing Today blog by practicing astronomers has a post giving some hard numbers about using cloud computing for planet-searching