The Hunt for New Earth

The search for life in the universe began a new phase on Wednesday in Kazakhstan with the launch of Corot, the French space telescope. Corot's role will be to seek and find small rocky planets which have a similar size and composition to that of our own Earth. The European Space Agency (ESA) says that's about as difficult as detecting a candle burning next to a lighthouse from a distance of 1000 kilometres.

Corot is an acronym of “COnvection ROtation and planetary Transits” but the name is also a passing nod to the great French 19th century landscape painter Jean-Baptiste Camille Corot. The spacecraft’s mission will be to look for rocky worlds about twice the size of Earth that lie in what space scientists call habitable zones. These are the regions of space in each solar system where heat from the nearest star is neither too hot nor too cold to sustain liquid water which scientists consider the holy grail for sustaining life. Any planets found by Corot will be studied intensely by future missions scheduled for the next decade. Scientists are hoping to gain a better understanding how planets form and how common other earth-like planets may be.

The study of planets outside our solar system began in 1995 when Swiss astronomer Michel Mayor discovered 51 Pegasi b, a gassy giant that orbits the star 51 Pegasi in the Pegasus constellation. Pegasi’s discovery opened the floodgates. In the last 12 years astronomers have found over 200 “exo-planets” which are all gas giants similar to Jupiter. However the problem with all of these planets is that they have no surface and are therefore incapable of supporting life. Small planets are too difficult to detect from Earth due to our atmosphere which blurs the picture. The Hubble Space Telescope was launched to gain clearer pictures of outer space. But Hubble’s mission is to search for stars in deep space not to look for tiny planets in our immediate neighbourhood. Hence Corot.

The Corot space telescope project is led by CNES (Centre National d'Études Spatiales - the French Space Agency) in conjunction with several European partners and Brazil. The spacecraft is equipped with a 27 cm diameter afocal telescope and a camera sensitive to tiny variations of the light intensity from stars. A Russian rocket lifted the satellite into a circular polar orbit with an altitude of 827 km where it will stay for the next two and half years. It will observe perpendicular to its orbital plane, meaning there will be no Earth eclipse (properly called an “occultation”), allowing 150 days of continuous observation. Beyond 150 days, the Sun's rays can interfere with the results.

Corot will focus on two parts of the universe which are relatively close to Earth. The first is the centre of our own galaxy, the Milky Way; the other is the constellation Orion. Like Hubble, it will measure how much light comes from a star. Corot will be hoping to spot a small eclipse that would indicate a planet crossing in front of the star. So Corot will only be able to indirectly detect the presence of a planet. But it is an important stepping stone in the effort to find habitable, Earth-like planets around other stars.

To verify light variation from a star found by Corot, we will have to wait until Project Darwin, the ESA most ambitious long-term adventure. Darwin is scheduled to launch in 2015 and will comprise of at least four separate components. There will be three, or possibly more, space telescopes, each at least 3 metres in diameter, and another spacecraft will serve as a communications hub. The multiple crafts will be placed in an orbit about 1.5 million kilometres from the Earth. Darwin will require telescope of roughly 30 metres in size and this is way beyond the current limits of technology. By comparison Hubble is barely 2.3 metres. Scientists are using a technique known as interferometry first developed in the 1950s. Inferometry uses a number of smaller telescopes and combines their individual signals to mimic a much larger telescope. The technique will be applied to the infrared telescope to be used by Darwin. It will have a second benefit in that it will cut out the blinding light from the nearby star.

NASA is also planning a mission similar to Darwin. Called the Terrestrial Planet Finder (TPF) it plans to study all aspects of planets outside the solar system. There is no planned launch date at this time and NASA may well decide to combine this project with Darwin. As the 2001 review which recommended the TPF said “"The discovery of life on another planet is potentially one of the most important scientific advances of this century, let alone this decade, and it would have enormous philosophical implications.”

Corot is the first small step to this discovery.