There could be water on multiple Earth-sized planets orbiting the recently discovered TRAPPIST-1 dwarf star – making them potentially habitable – according to an international collaboration of researchers, including the University of Warwick.
Using the NASA/ESA Hubble telescope to estimate whether there might be water on the surface of the seven planets around TRAPPIST-1, the researchers found that although the innermost planets must have lost most – if not all – of their water, the outer planets of the system might still harbour substantial amounts.
The researchers measured the ultraviolet (UV) irradiation that the planets receive from TRAPPIST-1, as these UV rays cause water molecules to break apart into their constituent hydrogen and oxygen atoms – making them vulnerable to being driven off into space by the X-ray radiation from the star.
Professor Peter Wheatley, from the University of Warwick’s Astronomy & Astrophysics Group in the Department of Physics, played a significant part in the project, measuring the X-ray irradiation of the planets by their parent star.
The observed amount of ultraviolet radiation emitted by TRAPPIST-1 suggests that the planets could have lost gigantic amounts of water over the course of their history.
This is especially true for the innermost two planets of the system, TRAPPIST-1b and TRAPPIST-1c, which receive the largest amount of UV energy, and could have lost more than twenty Earth-oceans-worth of water during the last eight billion years.
However, the outer planets of the system — including the planets e, f and g which are in the habitable zone — should have lost much less water, suggesting that they could have retained some on their surfaces.
According to Professor Wheatley, “It is exciting that we can now study the environments of individual Earth-sized planets. Our results suggest that water, and potentially life, could have survived in the TRAPPIST-1 system, despite the relatively intense ultraviolet and X-ray irradiation of the planets.”
In February 2017, astronomers announced the discovery of seven Earth-sized planets orbiting the ultracool dwarf star TRAPPIST-1, 40 light-years away. This makes TRAPPIST-1 the planetary system with the largest number of Earth-sized planets discovered so far.
This study was led by the Swiss astronomer Vincent Bourrier from the Observatoire de l’Université de Genève.