More to life than the habitable zone

July 13, 2017
Two separate teams of scientists from the CfA have identified major challenges for the development of life in TRAPPIST-1. The TRAPPIST-1 system, depicted here in an artist's conception, contains seven roughly Earth-sized planets orbiting a red dwarf, which is a faint, low-mass star. This star spins rapidly and generates energetic flares of ultraviolet radiation and a strong wind of particles. The research teams say the behavior of this red dwarf makes it much less likely than generally thought that the three planets orbiting well within the habitable zone could support life. Credit: NASA/JPL-Caltech/R. Hurt

Two separate teams of scientists have identified major challenges for the development of life in what has recently become one of the most famous exoplanet systems, TRAPPIST-1.

The teams, both led by researchers at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass., say the behavior of the star in the TRAPPIST-1 system makes it much less likely than generally thought, that there could support life.

The TRAPPIST-1 star, a , is much fainter and less massive than the Sun. It is rapidly spinning and generates energetic flares of ultraviolet (UV) radiation.

The first team, a pair of CfA theorists, considered many factors that could affect conditions on the surfaces of planets orbiting red dwarfs. For the TRAPPIST-1 system they looked at how temperature could have an impact on ecology and evolution, plus whether ultraviolet radiation from the central star might erode atmospheres around the seven planets surrounding it. These planets are all much closer to the star than the Earth is to the Sun, and three of them are located well within the .

"The concept of a habitable zone is based on planets being in orbits where liquid water could exist," said Manasvi Lingam, a Harvard researcher who led the study. "This is only one factor, however, in determining whether a planet is hospitable for life."

Lingam and his co-author, Harvard professor Avi Loeb, found that planets in the TRAPPIST-1 system would be barraged by UV radiation with an intensity far greater than experienced by Earth.

"Because of the onslaught by the star's radiation, our results suggest the atmosphere on planets in the TRAPPIST-1 system would largely be destroyed," said Loeb. "This would hurt the chances of life forming or persisting."

Lingam and Loeb estimate that the chance of complex life existing on any of the three TRAPPIST-1 planets in the habitable zone is less than 1% of that for life existing on Earth.

In a separate study, another research team from the CfA and the University of Massachusetts in Lowell found that the star in TRAPPIST-1 poses another threat to life on planets surrounding it. Like the Sun, the red dwarf in TRAPPIST-1 is sending a stream of particles outwards into space. However, the pressure applied by the wind from TRAPPIST-1's star on its planets is 1,000 to 100,000 times greater than what the solar wind exerts on the Earth.

The authors argue that the star's magnetic field will connect to the magnetic fields of any planets in orbit around it, allowing particles from the star's wind to directly flow onto the planet's atmosphere. If this flow of particles is strong enough, it could strip the planet's atmosphere and perhaps evaporate it entirely.

"The Earth's acts like a shield against the potentially damaging effects of the ," said Cecilia Garraffo of the CfA, who led the new study. "If Earth were much closer to the Sun and subjected to the onslaught of particles like the TRAPPIST-1 star delivers, our planetary shield would fail pretty quickly."

While these two studies suggest that the likelihood of life may be lower than previously thought, it does not mean the TRAPPIST-1 system or others with are devoid of life.

"We're definitely not saying people should give up searching for around red dwarf stars," said Garraffo's co-author Jeremy Drake, also from CfA. "But our work and the work of our colleagues shows we should also target as many as possible that are more like the Sun."

The paper by Lingam and Loeb was published in the International Journal of Astrobiology and is available online. The paper by Garraffo et al, also available online, has been published by The Astrophysical Journal Letters.

Explore further: Astrophysicists identify composition of earth-size planets in TRAPPIST-1 system

More information: Manasvi Lingam et al. Physical constraints on the likelihood of life on exoplanets, International Journal of Astrobiology (2017). DOI: 10.1017/S1473550417000179

The Threatening Environment of the TRAPPIST-1 Planets, arXiv:1706.04617 [astro-ph.SR] lanl.arxiv.org/abs/1706.04617

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TopCat22
1.5 / 5 (4) Jul 13, 2017
The authors argue that the star's magnetic field will connect to the magnetic fields of any planets in orbit around it, allowing particles from the star's wind to directly flow onto the planet's atmosphere. If this flow of particles is strong enough, it could strip the planet's atmosphere and perhaps evaporate it entirely.

... Then based on this statement we should be trying to hook to the suns magnetic field to obtain unlimited amounts of free energy here on earth...
thingumbobesquire
4 / 5 (2) Jul 13, 2017
Better yet fully fund a crash program for nuclear fusion the power of the sun itself.
tblakely1357
not rated yet Jul 13, 2017
Is the behavior of this red dwarf star representative of most red dwarf stars?
bobbysius
not rated yet Jul 13, 2017
Not really. Trapist-1 is a VERY low mass red dwarf (any smaller and it would be a brown dwarf). Most red dwarfs are more massive which means their flare activity after the first few billions year should abate. Also their habitable zones will be further away, so less chance of the stars magnetic field connecting with those of its planets.
EarthlingToo
not rated yet Jul 14, 2017
So then, is the fact that Life has only been observed here perhaps make it (Earth)... special?
jonesdave
not rated yet Jul 14, 2017
So then, is the fact that Life has only been observed here perhaps make it (Earth)... special?


No. It just means that we haven't quite yet got the ability to detect it elsewhere. For exoplanets, we would need a very, very powerful telescope, capable of taking the spectrum of an earth-like planet's atmosphere when it passes in front of its star, and looking for the signals that would indicate life. As for the solar system; we have barely scratched the surface. If there is life on Mars it is almost certainly underground. On Europa and Enceladus, it would be under kilometres of ice. There is no reason to believe the Earth is particularly special at the moment.
tblakely1357
5 / 5 (1) Jul 14, 2017
Well except for the surprisingly high percentages of chaotic planetary systems which would doom life, especially complex life. The need for an extraordinary large moon to stabilize the planets rotation which without would doom complex life. The need for the system to be in the 'Goldilocks' area in a galaxy. And whether the vast amounts of water on this planet is common or not.

I'm not saying intelligent life elsewhere is impossible but the more we see out there the more rare it looks to be.
jonesdave
not rated yet Jul 14, 2017
Well except for the surprisingly high percentages of chaotic planetary systems which would doom life, especially complex life. The need for an extraordinary large moon to stabilize the planets rotation which without would doom complex life. The need for the system to be in the 'Goldilocks' area in a galaxy. And whether the vast amounts of water on this planet is common or not.

I'm not saying intelligent life elsewhere is impossible but the more we see out there the more rare it looks to be.


The poster didn't mention intelligent life - some would say it has yet to arise on Earth - just whether or not the Earth was special. Certainly, the situation with the moon would probably make it rare.
Osiris1
not rated yet Jul 16, 2017
Many red dwarf stars in all galaxies there is. Making sweeping generalizations about all on the basis of too small a sample of red dwarves we cannot. We are left like the likeable robot on the movie: "Number 5"!: "Neeed input!"

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