Discovery of earth-like planet

Two scientists at the School of Physics and Astronomy of the University of St Andrews, Scotland have played a crucial role in the discovery of a new planet which astronomers believe is the most Earth-like found to date.

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.

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.

Its relatively cool parent star and large orbit mean its surface temperature is estimated to be only 50 to 100 Kelvin. OGLE-2005- BLG-390Lb is too cold to harbour liquid water on its surface and therefore cannot support life.

It is likely to have a thin atmosphere, like Earth, but its rocky surface is probably deeply buried beneath frozen oceans. It more closely resembles a more massive version of Pluto, like the icy cores of Neptune and Uranus, rather than the inner rocky planets like Earth or Venus.

The nearest other Earth-like contender found to date is GJ 876d, a planet 7.5 times the mass of Earth, separated from its star by just 1/50th of the Earth-Sun distance. By contrast, GJ 876d has a surface temperature of 2000 Kelvin and is too hot to support life.

“We have not yet found a true analogue of the Earth, but at least we know that small planets exist that are either hotter and cooler than the Earth,” added Dr Dominik.

“While other techniques are better at finding hot planets, the microlensing method specialises in finding cool planets. The discovery of a rocky/icy sub- Neptune mass planet already as the third microlensing detection is a strong hint for these objects being common.

“In fact, this finding is in agreement with the prediction of a strong population of cool planets below 10 Earth masses.

“Microlensing appears to be ideally suited to probe it, with its currently unique sensitivity to Earth-mass planets.”

An artist’s impression of OGLE- 2005-BLG-390Lb is available from the Press Office, University of St Andrews, e-mail ns30@st- andrews.ac.uk, gec3@st- andrews.ac.uk, cg24@st- andrews.ac.uk Media are kindly asked to credit the European Southern Observatory.

Issued by Beattie Communications on behalf of the University of St Andrews. Contact : Niall Scott, tel 01334 462244/, mobile 07711 223062, e- mail [email protected]

Notes to Editors

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. (France, United Kingdom, Poland, Denmark, Germany, Austria, Chile, Australia, New Zealand, United States of America, South Africa, Japan).

The ability to catch and characterize a planet requires round-the-clock, high-precision monitoring. These demands are met by the PLANET network of 1m-class telescopes including the Danish 1.54m at the ESO La Silla (Chile), the Canopus Observatory 1.0m (Hobart, Tasmania, Australia), the Perth 0.6m Bickley, Western Australia), the Boyden 1.5m (South Africa), and the SAAO 1.0m (Sutherland, South Africa).

PLANET is operating a common campaign with RoboNet, a UK operated network of 2m fully- robotic telescopes currently comprising the Liverpool Telescope (Roque de Los Muchachos, La Palma, Spain) and the Faulkes Telescope North (Haleakala, Hawaii, USA). This network will be enhanced with the Faulkes Telescope South (Siding Springs, Australia) from 2006.

Links:

Univ of St Andrews, Physics & Astronomy: http://www.st- andrews.ac.uk/~physics/

Scottish Universities Physics Alliance: http://www.supa.ac.uk

PLANET (Probing Lensing Anomalies Network): http://planet.iap.fr

RoboNet: http://www.astro.livjm.ac.uk/RoboNe t/

Dr Martin Dominik is supported on a PPARC rolling grant awarded to Prof Andrew C Cameron. The RoboNet telescopes receive funding from PPARC

Contacts:

Dr. Martin Dominik Phone: +44-1334-463066 (office) +44-1334-470305 (home) E-mail: [email protected]

Prof. Keith Horne Phone: +44-1334-463322 (office) E-mail: [email protected]

Niall Scott Director Press Office University of St Andrews Tel 01334 462244, mobile 07711 223062 E-mail [email protected]