ASTROBIOLOGY 7numberof “candidate Earths” have been
discovered around this type of dwarf.
Among the 18 Earth-size exoplanets known
today, one was discovered around a G
dwarf, two around K dwarfs, and 15 around
M dwarfs.
At first glance, it doesn’t matter if host
stars are solar-type dwarfs or red dwarfs.
What is important is that the planets are
in the habitable zone, although in the case
of M dwarfs, this means being very close
to the star surface. Conversely, especially
in recent years and through mostly theo-retical studies, researchers have realized
that things are not as obvious as they ap-
peared up-to a few years ago. If the goal
is to discover potentially habitable or in-
habited planets, the worst places to look
for them might just be M dwarf systems.
They have evolutionary characteristics that
conflict with the possibility of hosting life.
During the first billion years of existence,
in their pre-main sequence phase, these
stars are much brighter and warmer than
they are after reaching the main sequence.
Moreover, for a few billions of years afterF
amiliar bright
stars and se-
lected exoplane-
tary host stars
within 65 light-
years of our Sun.
Names of host
stars appear in
turquoise; names
of stars without
known planets
appear in violet.
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