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Habitability Primer: The search for and study of other Earths


Detecting planets similar to Earth and analysing their physicochemical properties is one of Science's current challenges. Researchers at the UAM contribute to a review of this fascinating field of Astrobiology.

Swiss astronomers Michelle Mayor and Didier Queloz announced in 1995 the discovery of a planet similar to Jupiter orbiting the star 51 Peg; that is, it is only 15 years since we learnt, without ambiguity, that there are planets orbiting stars similar to the Sun, thus answering a question that Humanity has asked itself for more than 2,000 years. We currently know of more than 450 extrasolar planets. These planets have some similarities, but also significant differences, with the planets of the Solar System.

Moreover, none of the known exo-planets have characteristics that are similar to Earth, because current instruments do not have the sensitivity necessary to detect them. Detecting an “Earth” outside the Solar System is a highly complex task, technologically and scientifically. A planet like ours is around one billion times weaker than its star and the separation of both bodies in the sky is approximately one tenth of a second of arc, assuming that it is a nearby star. So the challenge of observing it is clearly enormous. Furthermore, we must know where to observe: not all stars have planets with the suitable conditions to potentially develop life. Therefore, success depends on different factors that require a rigourous evaluation.

The observation method must be based on an instrument able to detect and analyse an extremely weak body, literally stuck to a star that is a million times brighter. Nowadays the viable solution identified is an interferometer (several telescopes that combine the light received), in space (to avoid the disturbances in our atmosphere), that is capable of suppressing the light from the star and that operates in the infrared (electromagnetic waves with which we can identify molecules intimately connected to life).

From a scientific point of view, we must at least know: i) where to observe, which entails a thorough knowledge of the formation and evolution of planetary systems, and which are the most likely stars to host “Earths” in the so-called habitability zone, or the region of space around a star where water in liquid form can exist; ii) what are the stability conditions of the planets, to allow a sufficiently stable and persistent environment which would enable eventual development of life; iii) what are the conditions in the atmospheric and geophysical evolution, which make a planet habitable; iv) what are the traces in the atmosphere of a planet that reflect the presence of life; v) what is the origin and evolution of life on terrestrial planets; and vi) what is the co-evolution of a planet's atmosphere, the climate and life.

Volume 10/1 of 2010 of the journal Astrobiology presents the results of the study carried out over several years by the “Terrestrial Exoplanet-Scientific Advisory Group” committee of the European Space Agency (ESA), with the collaboration of many other scientists, among them researchers from the Department of Theoretical Physics of the UAM. The different contributions indicate that it is possible to detect “Earths” and to build the tools to analyse and characterise them.

  Habitability Primer: La búsqueda y estudio de otras Tierras