Discovery of icy planet brings astronomers one step closer to the discovery of other Earths

Researchers from Liverpool John Moores University’s Astrophysics Research Institute working as part of an international team of experts have made an exciting discovery that could help in the ongoing search for ‘other Earths’.

Mike Bode, LJMU’s Professor in Astrophysics, explained: “Until the 1990s, the only planets we knew of were the ones that orbited the Sun in our Solar System. Over the last 10 years, we have discovered around 170 planets around other stars, known as ‘exoplanets’. Most of these have been gas giants like the planet Jupiter. The discovery of this new planet constitutes a major leap forward because it is significantly more like Earth than any other planet found to date.”

The planet – so far known only as OGLE-2005-BLG- 390Lb – is located around 25,000 light years from Earth, close to the centre of our galaxy, the Milky Way. It is about five times as massive as Earth and though this sounds enormous, in astronomical terms this makes it a very small planet compared to those exoplanets discovered so far.

Like Earth, the newly discovered planet is orbiting a star. Whereas the Earth completes an orbit around the Sun approximately every 365 days, the new planet takes a decade to circle its star. The planet’s star is also smaller than our sun, approximately one fifth its size and much cooler, and is classified as a Red Dwarf.

Given how far away it is from its star – three times the distance of Earth from the Sun – the planet’s surface is much colder than ours and at around 220 degrees Centigrade below zero it’s too cold for liquid water, a requirement for the development of life.

The LJMU astronomers think that it may a thin atmosphere, like our own, but that its rocky surface is probably buried deep beneath frozen oceans. They believe that the planet may in fact more closely resemble a massive version of Pluto, rather than one of the inner planets, such as Earth or Venus.

Professor Bode continued: “This new exoplanet lends weight to the leading theory of how planetary systems form. This states that planets close to their sun – like Earth – form from the accumulation of small grains of dust, sand and pebbles, whereas planets further away from their parent star form from material in the form of snowballs. This planet is precisely in the range of mass and distance from its parent star that the theory predicts.”

Detecting such exoplanets is very difficult because of their distance from the Earth, coupled with their faintness against the glare of their parent star. Until recently, such planets were only detected by either the tiny “wobble” they induced as they orbit their parent star, or the very small dip they induce in the star’s light as they orbit in front of it. These techniques are however only sensitive to revealing “hot Jupiters” – planets very unlike the Earth.

The new planet was detected using a special technique that measures changes in star light that is being bent by the gravitational pull of another object.

Professor Bode explained: “In 1915, Albert Einstein predicted that gravity can bend light. This new planet revealed its existence by means of the combination of its gravitational field with that of its parent star bending the light of an observed background star, and acting as a lens. Such bending of light, known as ‘microlensing’, results in an observable brightening of the background star which may last for weeks as the ‘lensing’ star crosses the line of sight to the background star. The presence of the planet is given away by a much shorter ‘blip’ superimposed on the light variation due to the lensing star.”

He continued: “This is the third extrasolar planet to be discovered using this technique. The first two planets found were bigger than Jupiter. This new discovery proves that the technique works for smaller, harder to detect planets, and means we can step up the search for even more Earth-like planets.”

In order to be able to catch and characterize a planet, the international team had to carry out a nearly-continuous round-the-clock monitoring of microlensing events using the OGLE (Optical Gravitational Lensing Experiment) and MOA (Microlensing Observations in Astrophysics) telescope networks which monitor millions of stars. The OGLE network reported a high magnification event, and alerted the PLANET and RoboNet global networks which began monitoring in detail. An anomaly lasting only a few hours was noticed which turned out to be the signature of the new planet.

Led by astronomers at LJMU, on behalf of a consortium of 10 UK universities, RoboNet is a network of the largest fully-robotic telescopes built to-date. It currently comprises the Liverpool Telescope in La Palma in the Canaries and further telescopes in Hawaii and Australia. All three of these giant robotic telescopes were designed and manufactured in Merseyside by Telescope Technologies Ltd, harnessing LJMU expertise. In its first year of operation, RoboNet has already helped to discover two of the three planets identified using the gravitational microlensing technique.

The operation of RoboNet relies on the sophisticated “e-STAR” software developed in a collaboration between Exeter University and LJMU.

Dr Iain Steele, who leads the LJMU end of e-STAR, explained: “Using e-STAR technology, this network of telescopes can detect and respond to the rapidly changing universe much faster than any human. Our ‘virtual astronomers’ collect, analyse and interpret data 24 hours a day, every day of the year, alerting us only when they make a discovery.”

Dr Martin Bergdorf, LJMU’s RoboNet Project Scientist, concluded: “Together with our collaborators, RoboNet shows that the microlensing effect is currently the only way to detect low-mass, cool planets – a fundamental step on the path to discovering other Earths. We are now working to intensify our search and push the boundaries of extra-solar planet detection.”

A report on the research has been published in the January 26 edition of the leading journal Nature, entitled ‘Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing’.

(1) The planetary discovery is a joint effort of three independent microlensing campaigns: PLANET/RoboNet, OGLE, and MOA, involving a total of 73 collaborators affiliated with 32 institutions in 12 countries (France, United Kingdom, Poland, Denmark, Germany, Austria, Chile, Australia, New Zealand, United States of America, South Africa, and Japan).

(2) The network of telescopes included:
The PLANET network of 1m-class telescopes consisting of the ESO 1.54m Danish at 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).

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). The Faulkes Telescope South is due to join RoboNet later in 2006. The Faulkes Telescopes were funded by the Dill Faulkes Educational Trust and are now owned and operated by the Las Cumbres Observatory, USA. The Liverpool Telescope is run by LJMU as a National Facility for astronomy on behalf of the Particle Physics and Astronomy Research Council, who also provided the funding for the RoboNet project.