Understanding better the composition of comets

One of the hypotheses circulating in the astrophysics community is that the comets could have contributed to the appearance of the oceans and of life on Earth. Studying the chemical composition of comets will enable a better understanding of the conditions of the formation and the history of the comets themselves, as well as that of our solar system and of our planet. ‘Besides their role in the creation of the planets,’ explains Emmanuël Jehin, a F.R.S-FNRS research associate, science manager and main investigator for the comets within the framework of the TRAPPIST project, ‘one theory has it they could have contributed to the appearance of the oceans on our planet and to the provision of organic compounds. At the beginning of the history of the Earth, 4.5 billion years ago, the Sun was a lot more luminous than it is today, which allows us to suppose that any liquids were vaporised and that the Earth was just a rocky planet, with no life. It was only later, 3.8 billion years ago, that some volatility in the solar system generated a rain of several billions of comets and meteorites, of which many smashed into our planet. Given their ice and organic molecule composition, we could argue that they are at the origin of our oceans and thus contributed to the appearance of life on Earth.’ TRAPPIST will contribute indirectly to checking this theory. Astrophysicists are currently trying to determine the isotopic ratios of deuterium (D) to hydrogen (H) and to see if there are similarities between the comets and our oceans. To do so it is necessary to use powerful telescopes such as the ESO’s VLT (Very Large Telescope) (Read also the article Where does the water in the oceans come from?). The Liège telescope will enable a series of comets to be identified, which are of potential observational interest from the point of view of this goal.

TRAPPIST will in effect enable the Liège astrophysicists to deepen our knowledge of comets. Thanks to special filters developed by NASA, the telescope will study the chemical composition at the moments they both approach and become more distant from the Sun. ‘With a large telescope you can study comets for only one or two nights a year,’ points out Emmanuël Jehin. ‘Here we can do what astronomers who work in this field dream about: track and study each one from week to week as they near and grow more distant from the Sun. We can in this way determine their evolution and composition and observe if the abundance changes according to their distance from the Sun. In accumulating measurements on a dozen or so comets per year we can highlight the different classes of comet from the point of view of their composition and try to link that to the place in the solar system they were formed.’