Space

TRAPPIST planets may have too much water to be habitable

TRAPPIST planets may have too ...
An artist's rendition of the surface of one of the TRAPPIST-1 planets
An artist's rendition of the surface of one of the TRAPPIST-1 planets
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An artist's rendition of the surface of one of the TRAPPIST-1 planets
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An artist's rendition of the surface of one of the TRAPPIST-1 planets

Life as we know it can't exist without water, so the search for extraterrestrial life often begins as a search for water. A new study on the density of the seven planets in the nearby TRAPPIST-1 system has found that these worlds may have even more water than Earth does, but in a cruel case of having too much of a good thing, that might be enough to drown out any hopes of finding life there.

TRAPPIST-1's seven planets were discovered just over a year ago, and since then they've been the subject of intense study. Astronomers have calculated the diameters and densities of the planets, what they might be made of, how the closely-knit group avoids crashing into each other, and of course, what the chances are of finding life.

Judging by existing data, the TRAPPIST-1 planets are surprisingly light for their mass and volume. At a glance, the most obvious explanation to astronomers is that the worlds must be quite gassy, with thick atmospheres – but that doesn't quite line up with observations.

"The TRAPPIST-1 planets are too small in mass to hold onto enough gas to make up the density deficit," says Cayman Unterborn, co-author of the study. "Even if they were able to hold onto the gas, the amount needed to make up the density deficit would make the planet much puffier than we see."

The next candidate to plug the hole is water, either in the form of liquid or ice. So the scientists on the new study set out to determine the composition of the worlds. Using a physics calculator program known as ExoPlex, the researchers plugged in as much of the available data as possible on the star and planets in the system, as well as comparisons to other stars.

The team found that water appears to account for as much as 15 percent of the mass of the innermost planets, TRAPPIST-1b and 1c, and over 50 percent for the planets 1f and 1g. That's an absolutely huge amount of water – by comparison, Earth is only 0.02 percent water by mass. That may sound like a promising start to the search for life, but the scientists warn against getting your hopes up.

"We typically think having liquid water on a planet as a way to start life, since life, as we know it on Earth, is composed mostly of water and requires it to live," says Natalie Hinkel, co-author of the study. "However, a planet that is a water world, or one that doesn't have any surface above the water, does not have the important geochemical or elemental cycles that are absolutely necessary for life."

Interestingly, the planets also appear to be too close to the star for ice to have formed there in the first place. They lie inside what's known as the "ice line," the distance from a star where water builds up on a planet in the form of solid ice. According to the study, the planets of TRAPPIST-1 most likely formed at least twice as far out, before migrating inwards.

Of course, it's always wise to keep in mind that these calculations are incomplete, and are estimations at best. Another recent study on the composition of the TRAPPIST-1 planets found that the worlds were at most only 5 percent water by mass. The discrepancy is likely due to different datasets and methods.

The latest research was published in the journal Nature Astronomy.

Source: Arizona State University

8 comments
Bob
Just plug the numbers into "six sigma". It should give the number of dolphins per square mile on each water planet. In industry we found that adding a variable for the water temperature at Miami beach greatly improved our quality numbers. Math is amazing. It will always give you an answer. Whether or not it means anything is another subject. Only a few of you will know what I mean. Everyone else believes that math purifies the data and must be true.
SimonClarke
Just because there is no land doesn't mean there can't be life. If the planet is geothermicly active then there will still be the nutrients introduced into the water column.
Douglas Bennett Rogers
These planets would be great targets for colonization, as they have enormous amounts of easily recoverable fusion fuel.
McDesign
A great phrase i just heard - "we tend to over-value that which we can quantify"
WilliamSager
For oceans to truly be filled with life there must be a large area where the bottom of the ocean is at least close to the surface for sunlight feeding plants to grow that other life forms can feed upon.
Jean Lamb
"It's life, Jim, but not as we know it". Sighs...
Ralf Biernacki
I think they are wrong. They are assuming that for the nutrient cycles to work, volcanoes must recycle onto land surface, and then the eroded material will fertilize the ocean. But you don't need land exposed to atmosphere for that. You can have a working plate tectonics cycle with volcanoes spewing directly into the ocean, way below the surface, to recycle mineral nutrients. As long as currents can carry dissolved nutrients into the photic area, you're in the black; or perhaps you don't even need that, if the life is based on autotrophs other than photosynthetic ones.
Ralf Biernacki
@William Sager: You're assuming that autotrophs need a solid substrate. But even if we limit ourselves to photosynthetic autotrophs, algae do not need a solid substrate to live. Many species survive as planktonic, floating forms. And there is nothing impossible about multicellular, nectonic plants---even on our Earth, some kelps maintain flotation via blisters filled with sythesized gas, viz. the Sargasso. I think a purely planktonic/nectonic biosphere is quite viable. Stuff falls to the bottom, of course, but even if biology won't find a way to recycle sediment from the hadal plain, plate tectonics will do it free of charge.