HARPS, Chile

By Matthew Owens

The European Southern Observatory (ESO) is an intergovernmental astronomy organisation, now marking the 50th year after its inception, supported by many countries including the UK, with three sites in Chile: La Silla, Paranal and Chajnantor. The site at La Silla at 2,400 metres above sea level in the Atacama Desert was ESO’s first site. The 3.6 metre ‘planet hunter’ telescope at La Silla is home to the High Accuracy Radial velocity Planet Search (HARPS) whose precision has lead to many discovery firsts including the smallest ever detected exoplanet (a planet lying outside the solar system). New results from HARPS has recenlty been published revealing that planets around red dwarf stars, which are very common cool stars in the Milk Way (accounting for about 80% of all stars), with a mass at least half that of our sun. The prevalence of so-called Super-Earths (planets with a mass between 1 and 10 times that of our planet) orbiting red dwarfes in the habitable zone has for the first time been estimated and the results are astounding:

Tean leader Xavier Bonfils explained, “Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet…Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.

The Southern sky

If such exoplanets have a rocky surface and contain water on the surface, then the prospect of some form of life existing on the planet, perhaps in abundance, is tantalising for us all. The new estimates also allow for a calculation of how many super-Earth planets may exist in the habitable zone around red dwarfs in close proximity to the sun; there may number as many as 100 within 30 light years.

One such planet discoverd by HARPS in Chile, Gliese 667 Cc, may well have water on the surface and so could support life. An artist’s impression of the planet is shown below. Before we start packing our bags for an exo-holiday though, it should be remembered that the planet lies some 22 light years away from us, that is 22 years of travel at 186,000 miles per second!



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