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According to two separate teams of astrophysicists from the Harvard-Smithsonian Center for Astrophysics (CfA) and the Lowell Center for Space Science and Technology, behavior of the parent star in the TRAPPIST-1 planetary system makes it much less likely than generally thought, that planets there could support life.

In February 2017, astronomers announced that the star TRAPPIST-1 hosts at least seven planets — TRAPPIST-1b, c, d, e, f, g and h.

All these planets are similar in size to Earth and Venus, or slightly smaller, and have very short orbital periods: 1.51, 2.42, 4.04, 6.06, 9.21, 12.35 and 20 days, respectively.

Three of these planets lay in the star’s habitable zone, meaning they may harbor suitable conditions for life.

The host star, TRAPPIST-1, is a red dwarf star in the constellation Aquarius, 38.8 light-years away.

The star is barely larger than Jupiter and has just 8% of our Sun’s mass. It is rapidly spinning and generates energetic flares of UV radiation.

In the first study, CfA theorists Manasvi Lingam and Avi Loeb 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 UV 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 habitable zone.

“The concept of a habitable zone is based on planets being in orbits where liquid water could exist,” Dr. Lingam said.

“This is only one factor, however, in determining whether a planet is hospitable for life.”

The team found that the TRAPPIST-1 planets 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,” Professor Loeb said.

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Category: Science