spaceSpace and Physics

The TRAPPIST-1 Planets May Actually Have Too Much Water For Life


Jonathan O'Callaghan

Senior Staff Writer

Water, water, everywhere, but possibly too much to drink. NASA/JPL-Caltech

A new study published in Nature Astronomy today suggests that some of the TRAPPIST-1 planets could have a huge amount of water – but that might not necessarily be great news for life.

Led by Cayman Unterborn from Arizona State University, the researchers examined the mass densities of the seven planets in the TRAPPIST-1 system, 40 light-years from Earth, to work out how much water they have.


We have been able to work out the planets’ characteristics by watching them pass in front, or transit, their host red dwarf star. Each world is about the size of Earth, but orbits closer than Mercury does to our own Sun.

The researchers found that two of the outermost planets, TRAPPIST-1f and g, were likely composed of more than 50 percent water; for comparison, Earth’s mass is just 0.1 percent water. The innermost planets, TRAPPIST-b and c, are likely drier but still up to 15 percent water.

They note that it’s possible planets f and g formed beyond the “snow line” – the region beyond which ice can form in a system – before migrating inwards to the star’s habitable zone, where liquid water can exist. The planets b and c, meanwhile, likely formed within the snow line.

“We find that, compared with planets in our Solar System that also formed within the snow line, TRAPPIST-1b and c contain hundreds more oceans of water,” the team wrote in their paper.


While all this water might sound quite good for life, there are a few problems, as notes. Some theories suggest that a planet entirely encased in water, devoid of any land, might struggle to develop life.

The planets orbit well within the orbit of Mercury in our own Solar System. NASA/JPL-Caltech

There are also some question marks over the structures of the planets themselves. TRAPPIST-1f, for example, could have liquid water extending down 200 kilometers (125 miles) – 20 times the depth of the Mariana Trench.

Below that would be a layer of ice, then a layer of magnesium silicate, and finally a liquid iron core. This composition wouldn’t be great for regulating the planet’s temperature via geological processes.

“Rocky planets with water mass fractions greater than that of Earth may not behave geochemically and geophysically similar to the Earth,” the team wrote.


“With no exposed land, key geochemical cycles including the drawdown of carbon and phosphorus into oceanic reservoirs from continental weathering will be muted, thus limiting the size of the biosphere.”

They go on to add that despite looking habitable, it might be difficult to actually detect any life in the system – and this may hold true for other red dwarf stars too.

Of course, we don’t know how important land was for life on Earth yet. But this latest study adds to others that suggest we shouldn’t get too excited about the TRAPPIST-1 system just yet.


spaceSpace and Physics
  • tag
  • water,

  • earth,

  • life,

  • habitable,

  • search for life,