New source for planetary water explored

Water is essential for life on Earth, but where does water on planets come from? Previously it had been suggested that water was delivered by comets, but new findings published in Nature Astronomy by an international team of astronomers, including researchers from the University of St Andrews, reveal that some planets may have had water since their creation.

Simulations carried out as part of the new study, which was led by Professor Sean Raymond at the University of Bordeaux, show that the seven rocky planets orbiting nearby star TRAPPIST-1 would have been torn apart by the impact of the number of comets required to deliver the present amount of water.

For at least one of these planets water must therefore have been present since its formation, which sets fundamental environmental conditions for the emergence and evolution of life.

By contrast, our home planet Earth was born much less water-rich and experienced a massive bombardment that eventually formed the Moon as a result of a large impactor of a size comparable to that of Mars.

The potential diversity of planetary environments that could have supported the emergence of life is most remarkable. Rather than focusing on planets that look pretty much identical to Earth, it is well worth studying such environments and their potential co-evolution with life in detail.

Patrick Barth, a PhD student at the Centre for Exoplanet Science at the University of St Andrews, said: “We found that planet TRAPPIST-1 g has about 100 times more water than Earth, which was outgassed from its molten interior when the planet was still very young rather than coming from impactors at a later stage.”

Could a thick water ocean have formed on TRAPPIST-1 g? Is this good or bad for the emergence of life? Does such an ocean still survive until today, or is the water buried deep in the interior? Upcoming large space telescopes like NASA’s JWST will look at the TRAPPIST-1 system more closely, particularly aiming at measuring the chemical composition of its atmosphere.

Royal Society University Research Fellow, Dr Ludmila Carone, whose work follows the source of water on alien worlds and Earth and who is set to join the University of St Andrews, also worked on the research.

She said: “The TRAPPIST-1 planets show us that other worlds can be truly unique and very alien compared to our own Earth.”

Patrick added: “If life did emerge on the alien world TRAPPIST-1 g, it must have faced conditions vastly different from those encountered by life on early Earth. Where would evolution have taken it?”