Our corner of the galaxy teems with alien worlds. In the 25 years since the discovery of the first planets beyond our solar system, astronomers have found more than 3,600 worlds orbiting other stars. A
select few have become tantalizing targets in the search for
life despite orbiting stars that are much smaller, cooler — and
in many ways harsher — than the sun.
Just 39 light-years away, seven planets, all roughly the size
of Earth, whirl around a dim red star dubbed TRAPPIST- 1,
astronomers announced in February (SN: 3/18/17, p. 6). Three
are potentially habitable. In April, a team reported the discovery
of another world snuggled up to a red sun, LHS 1140b, described
by researchers at the European Southern Observatory as perhaps the best candidate in the search for signs of life. And last
August, astronomers revealed that not only does a small planet
named Proxima b orbit the star closest to the sun, a red neighbor, but it too could support life (SN: 9/17/16, p. 6).
All of these worlds orbit faint ruddy stars known as M dwarfs,
the most common type of star in the galaxy. Of the roughly 200
planets that have been spied around M dwarfs, dozens are in
the coveted habitable zone. It’s this region around a star where
a planet could have temperatures
that support liquid water, widely
considered an essential ingredient
But M dwarfs are quite different
from the sun, and their planets might
be rough places to eke out a living — “the low-rent district
of the galaxy,” says Victoria Meadows, an astrophysicist at the
University of Washington in Seattle. Harsh flares, bright begin-
nings and a tight gravitational grip on the innermost planets
could be disastrous for any liquid water that’s available.
Many more planets are expected to be found in habitable
zones around M dwarfs. So researchers want to get a better
handle on what these planets are up against. New observations
and computer simulations reveal that, while it’s difficult for
M dwarf planets to hold on to substantial amounts of water,
not all hope is lost.
“There are always ways around these things,” says astro-
physicist Rory Barnes, also at the University of Washington.
M dwarfs and their planet families are plentiful, and there are
many conditions in which these worlds can grow and evolve.
Exoplanets found in a narrow
band around M dwarf stars
could host a very different
kind of life By Christopher Crockett
TRAPPIS T- 1 (illustrated)
is on a growing list
of dim red suns with
planets that could
support life. Three of its
seven planets are in the
Mars Earth Venus
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