TRAPPIST-1's Outer Planets May Harbor Water, New Study Finds

Nettie James
September 2, 2017

And the latest results from the Hubble Information Centre have suggested that the outer planets of the system may harbour floods of water, needed to support life.

However, as far as finding signs of hydrogen surrounding the TRAPPIST-1 worlds, the results on that were inconclusive.

This artist's rendition shows the planets of the TRAPPIST-1 system. "As in our own atmosphere, where ultraviolet sunlight breaks molecules apart, ultraviolet starlight can break water vapour in the atmospheres of exoplanets into hydrogen and oxygen". But it's possible that the planets were initially so rich in liquid water that, even with the water loss caused by UV radiation, they haven't dried up, according to one of the study's authors, Michaël Gillon, an astronomer at the University of Liège in Belgium. The odds of water still being on these planets surfaces are slim to none. All these planets are similar in size to Earth and Venus, or slightly smaller, and have very short orbital periods. At the same time, measurements of the amount of ultraviolet light hitting these planets allow scientists to estimate the rate at which their atmospheres are bleeding into space. All of them are tidally locked.

The team wrote in their paper that observing the TRAPPIST-1 planets over a broad wavelength range from the ultraviolet to the infrared would provide insights into the current state and the dominant physical processes shaping these planets' atmospheres. This creates a perpetual night side and perpetual day side on each TRAPPIST-1 planet.

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. "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".

As the study paper claimed, it is possible that the six innermost planets of the TRAPPIST-1system, coated with the maximum levels of ultraviolet radiation, could have lost almost worth of 20 Earth's Ocean water some 8 billion years ago.

"In terms of habitability, this is a positive step forward to say that hopes are still high", said study co-author Julien de Wit, in a statement from MIT.

The astronomers sought to predict how much water each planet may have lost over its history. "But we need to gather more information and actually see a hint of water, which we haven't found yet".

"It depends a lot on their initial water content", Dr. Bourrier added. The results suggest that the outer planets of the system might still harbour substantial amounts of water.

Using the STIS, the researchers could detect any escaped hydrogen gas around the atmosphere of each planet, which helped them determine the likelihood of atmospheric water vapor.

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