Ice at the bottom
of the global ocean:
the astrophysicists determined
the water content of the planets orbiting their small host star
in the habitable zone. They
found that considering all the cases, around
90% of the planets are harbouring more than
10% of water. For comparison: The
Earth has a fraction of water of only about
0.02%. So most of these alien planets are literally
water worlds in comparison. The situation could be even
more extreme if the protoplanetary
disks in which these planets form live longer than assumed
in the models. In any case, these planets would be covered by
very deep oceans at the bottom of which, owing to the huge pressure,
water would be in form of ice.
Water is required
for life as we know it. So could these planets be habitable indeed?
"While liquid water is generally
thought to be an essential ingredient, too much of a good thing
may be bad," says Willy
Benz. In previous studies the scientists in
Bern showed that too much water may prevent the regulation
of the surface temperature and destabilizes the climate.
"But this is the case for the Earth, here we deal with considerably
more exotic planets which might be subjected to a much harsher
radiation environment, and/or be in synchronous "
growth of planetary embryos:
To start their
calculations, the scientists considered a series of a few hundreds
to thousands of identical, low mass stars and around each of
them a protoplanetary disk
of dust and gas. Planets are formed by
accretion of this material.
Alibert and Benz assumed
that at the beginning, in each disk there were
10 planetary embryos with an initial mass equal to the
mass of the Moon. In a few
day's computer time for each system the model calculated how
these randomly located embryos grew and migrated. What kind of
planets are formed depends on the structure and evolution of
the protoplanetary disks.
or not, the study of planets orbiting very low mass stars will
likely bring exciting new results, improving our knowledge of
planet formation, evolution, and potential habitability,"
summarizes Willy Benz.
Because these stars are considerably less luminous than the sun,
planets can be much closer to their star before their surface
temperature becomes too high for liquid water to exist. If one
considers that these type of stars also represent the overwhelming
majority of stars in the solar neighbourhood and that close-in
planets are presently easier to detect and study, one understands
why the existence of this population of
Earth-like planets is really of importance.
Alibert, Yann and W. Benz: Formation and composition of planets
around very low mass stars, A&A October 2016, https://arxiv.org/abs/1610.03460
What do you think
of 'them' apples?
Yep. Ah ha. You bet. There you go.