J
ust over 10 , 000 days have passed since
the discovery of the first exoplanet, and
the 4 , 000 so far confirmed among the
3 , 000 known extrasolar systems have re-
vealed an unpredicted variety of planetary
systems. After the first random discover-
ies, researchers gained experience with
those planets easiest to detect − the
giant ones orbiting very small stars.
Then, more targeted programs were
launched, such as the prolific Kepler,
to discover Earth-size planets orbit-
ing in the habitable zones of solar-
type “dwarf” stars, a term that
includes spectral classes F, G and
K. At the same time, more hum-
ble projects were also devel-
oped that continued using the
easiest way to discover planets- find those that pass in front
of the discs of the most clas-
sic dwarf stars, the so-called
“red dwarfs” or M-types.
For many years,
we have believed
that M dwarfs were
the ideal stars around
which to look for the first
signs of extraterrestrial life.
Now we have realized that
planets in M dwarf habitable
zones are subjected to extreme
conditions and phenomena for a
time incompatible with life as we
know it. Researchers’ attention has
therefore moved towards K dwarfs,
but we have yet to figure out where
to point the telescopes.
A
lmost all 4 , 000
exoplanets so
far discovered and
confirmed are cer-
tainly unsuitable
for hosting life as
we know it. Kepler-
421 b, represented
in the background,
is an example of an
inhospitable planet
orbiting a solar-
type star (G 9 /K 0 ).
[Harvard-Smithson-
ian, Center for As-
trophysics/D. A.
Aguilar]K type star EN_l'Astrofilo 29/08/2019 15:46 Page 5