Earth-like exoplanet discovered

16 November 2017
Posted by Chris Smith.

Space scientists have confirmed the discovery of an Earth-sized planet orbiting a cool, calm star about 11 light years away.

As names go, Ross-128b belies the exciting potential of this remote, Earth-sized planet to harbour life.

Perched in orbit around the dimly-glowing Class M red dwarf star called Ross 128, which is about one fifth of the size of the Sun, Ross 128b has taken researchers at the European Southern Observatory (ESO) more than a decade to detect.

Xavier Bonfils and his colleagues, who have published the findings in the journal Astronomy and Astrophysics, used an instrument called HARPS - short for High Accuracy Radial velocity Planet Searcher - at the La Silla Observatory, in Chile, to spot regular tiny dips in the intensity of the light reaching the Earth from the Ross 128 star.

These dips, which occurred roughly every 10 days, correspond to the planet passing in front of the parent star, blocking the path of some of its light and making it momentarily dimmer. The orbiting planet also pulls on the host star as it moves around it, producing a warping effect that slightly alters the colour of the light reaching us. And because the researchers know how big the star is, this colour shift can be used to calculate the size and mass of the planet.

The measurements put the planet's mass at about 1.35 times that of the Earth. It's also orbiting very close to the parent star at a distance of just 0.049 astronomical units (AU), which is roughly one twentieth of the Earth-Sun distance. But because Ross 128 is smaller, 220 times dimmer and therefore much cooler than the Sun, the amount of energy reaching the newly-identied planet is quite similar (about 1.38 times) to the amount of energy that reaches Earth from the Sun.

Liquid water could well exist under these conditions, because the planet is sitting either just inside, or on the cusp of what is dubbed the habitable zone. This is the "Goldilocks" section of space around a star where the temperature is just right to sustain life processes. The observations for Ross 128b suggest average surface temperatures of somewhere between -60°C and +20°C.

Whether there is water there, and the prospect for finding life too, will depend heavily upon the existence of an atmosphere, which the researchers have not been able to measure yet. And before they do, they need to resolve what are the best molecules to look for as hallmarks of life itself. 

Likely candidates are oxygen, water and methane, but finding them is likely to hinge on more powerful instruments like the ESO's "Extremely Large Telescope (ELT)" and NASA's James Webb Space Telescope (JWST), which are still being built. So we have a few more years to wait before ET can give himself away, if he's there...


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