Guest post by David Middleton

They must have used the RCP 8.5 Death Star…

The announcement of the Trappist-1 system in February, with seven rocky planets orbiting an ultracool dwarf star, sent ripples of excitement through astrobiologists everywhere.

At least three of the planets looked like they were within the star’s “habitable zone” – the region in which water will remain liquid. On that level, at least, the trio seemed like very good candidates for hosting life.

Now, however, 3D climate modelling is dampening expectations, suggesting that at most only one of Trappist-1’s satellites could support life.

The modelling has been completed by Eric Wolf from the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. In doing so, he made the assumption that the seven planets are – or had once been – ocean-covered, with atmospheres comprising nitrogen, carbon-dioxide and water vapour. Orbital and geophysical properties were derived or deduced from collected data.

When Wolf ran the numbers, the results were rather depressing.

“Model results indicate that the inner three planets presently reside interior to the inner edge of the traditional liquid water habitable zone,” he writes in a paper lodged on pre-print site arxiv.

“Thus if water ever existed on the inner planets, they would have undergone a runaway greenhouse and lost their water to space, leaving them dry today.”

The outer three planets, he adds, “fall beyond the maximum CO2 greenhouse outer edge of the habitable zone” and will have entered a lifeless snowball state.

Thus, only the middle planet remains a candidate for hosting life. It could maintain “at least some habitable surface”, Wolf notes, depending on the atmospheric nitrogen levels. If the planet is, in fact, covered in ocean, then “near present day Earth surface temperatures can be maintained”.

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Cosmos

Don’t get me wrong, I find the entire field of exoplanetary science and the Kepler mission to be really cool.  The application of a remote sensing method to detect and even describe likely planetary bodies in other solar systems is just about the coolest science on this planet… But, are they really “discovering” exoplanets?  It seems to me that this would be analogous to oil companies booking reserves on the basis of high-quality seismic hydrocarbon indicators, without ever drilling them.

Clearly, there are a series of anomalies in the Trappist-1 system which could very well be planets in the habitable zone… But, isn’t this an case of jumping the gun?

NEWS & TECHNOLOGY 1 March 2017

How we’re already seeking life on TRAPPIST-1’s rocky planets

By Leah Crane and Joshua Sokol

WE ARE already taking the first steps toward learning if there could be life on TRAPPIST-1’s newly discovered planets – and what that life might look like.

Last week, a team led by Michaël Gillon at Belgium’s University of Liege announced that TRAPPIST-1, a small, faint star some 40 light years away, has four more rocky planets to join the three we already knew about.

All are less than 20 per cent bigger than Earth, and all orbit well within the distance at which Mercury circles our sun. Despite this closeness, the planets may be candidates to search for life. That’s because TRAPPIST-1 is much smaller and dimmer than the sun, so three of the planets may be cool enough to host liquid water on the surface, putting them in the habitable zone

(see diagram)

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As usual, any and all sarcasm was purely intentional.