News Item

Discovery of Earth-like planet

We are excited that two astronomers in our School have played a crucial role in the discovery of a new planet which is believed to be the most Earth-like found to date.

Artists impression of the new planet, courtesy of ESO. This illustrates the frozen surface, thin atmosphere, and dim red dwarf star that have been inferred from the studies.

The new planet, designated by the unglamorous identifier OGLE-2005-BLG-390Lb, has a mass five times that of Earth and is approximately 20,000 light years from us near the centre of the Milky Way where it orbits its parent star, a red dwarf some five times less massive than the Sun.

OGLE-2005-BLG-390Lb is a small cold world, too cold to support life, but its discovery using the technique of gravitational microlensing has been hailed as a groundbreaking result in the search for extra-terrestrial life.

The planet's discovery is an international effort, reported in Nature as the joint result of three independent microlensing campaigns – PLANET/Robonet (Probing Lensing Anomalies Network) OGLE (Optical Gravitational Lensing Experiment) and MOA (Microlensing Observations in Astrophysics) -using a worldwide network of telescopes and involving 73 collaborators from 32 institutions across 12 countries.

The technique of microlensing, first noted by Einstein in 1912, relies upon light from a background star being bent by the gravitational field of a dim foreground star acting as a gravitational lens.

This results in an observable brightening and fading of the observed star over a few weeks. With their smaller masses, planets orbiting the lens star can cause an additional blip, lasting from hours to days. In the graph shown below you can see both variations, as determined by various different telescopes in the collaboration

The light curve for this star and its earth-like planet. The main peak caused by lensing due to the star magnifies the light by a factor of three for a few weeks. The lensing by the planet magnifies the detected light by 15% for 12 hours. The inset at rop right shows more detail of this important peak.


OGLE-2005-BLG-390Lb is only the third planet to be detected by this technique. Dr Martin Dominik of the University of St Andrews is co-leader of the PLANET collaboration while Professor Keith Horne leads the microlensing efforts of the RoboNet project. “The new planet confirms that with microlensing we can now find small cool planets down to the mass of the Earth,” said Prof. Horne. “Our next goal is to find more of them, with lower masses, in order to measure the abundance of cool Earths and determine if habitable planets like Earth are abundant or rare.

“If the abundance is high, the next step is to search for life on those planets.” Dr Dominik said : “We saw a 12-hour flash in the light curve on August 10th 2005. Monitoring this anomaly with two of our telescopes, together with a dense coverage of the peak, allowed us to conclude that it was caused by a low-mass planet orbiting the lens star.

“The chance that an observed background star is magnified by more than 30% at a given time is only about one in a million. However, with more than 100 million stars routinely monitored by the OGLE and MOA microlensing surveys there are about 120 ongoing events where the lens star can be probed for surrounding planets.”

Roughly five times the mass of Earth, OGLE-2005-BLG-390Lb is probably the lowest mass exo-planet so far detected around an ordinary star.

Both our scientists featured on TV news bulletins on 25 January.

University press release

Press release from the European Southern Observatory

PPARC Press Release

The journal Nature

BBC News Online Article

New Scientist


The Times Online

The Sun

The Herald

The Scotsman

First posted BDS 25.1.06, 18.30
Updated 15.00, 26.1.06