red dwarfs are the most common type of
star in the universe with their ubiquity
low temperatures lifetime spanning
trillions of years and a bounty of rocky
planets in their habitable zones red
dwarfs may seem like the most likely
place in the universe to find life but
red dwarfs are known for unleashing
ultra powerful flares that could
potentially destroy a closed planet's
atmosphere however the two closest red
dwarfs to our solar system Proxima
Centauri and Barnard's star each host
potentially habitable planets as our
technology improves these systems will
become the first natural laboratories to
see if living with a red dwarf star is
possible welcome back to launchpad I'm
Christian Reddy your friendly
neighborhood astronomer in a previous
video we talked about the lifespans of
red dwarf stars they're certainly the
most common type of star in the universe
and they are home to planets many of
which exist in their so-called habitable
zones as red dwarfs age they become more
luminous and warmer reaching sun-like
luminosities for up to several billion
years but that's trillions of years down
the road what about today can red dwarfs
support life now if they can that would
make life a relatively common occurrence
in the universe it's estimated that
anywhere from 10 to 50 percent of all
red dwarf stars have at least one planet
in their habitable zone this is the
range of distances where liquid water
could be stable on the planet's surface
in fact the closest star to our Sun
Proxima Centauri is only 4.2 light-years
away and is host to a planet in its
habitable zone as the planet revolves
around the star its spectrum shifts from
red to blue wavelengths and then back
again
this repeated oscillation revealed the
presence of Proximus planet and also
showed that the planet has an overall
period of about eleven point two days
from Kepler's third law we know that the
planet must be at an orbital distance of
about 0.05 astronomical units in other
words about five percent the distance
between the Earth and the Sun however
Proxima bees distance an orbital period
are really the only two things that we
know
you're about this planet analysis of its
radial velocity curve suggests that the
planet is at least one point three times
the mass of the Earth but it could be
larger and that's because we don't know
the system's inclination relative to our
line of sight if we're viewing the
system directly edge-on then the planet
is exactly 1.3 times the mass of Earth
but if we're viewing the system at some
intermediate angle then the planet would
have to be much more massive to produce
the radial velocity measurements that we
see if its mass is closer to the minimum
then it is likely a rocky super earth if
it's much greater than it could be a
mini Neptune but a day on Proxima be
would be unlike anything we experience
on earth tidal forces from the star on
the planet would be extremely strong and
would slow the planets rotation down if
Proxima bees O'War Betances are good
that it would be tidally locked to the
star with one side of the planet always
facing the star and the other side in
perpetual night halfway between the day
and night sides of the planet Proxima
Centauri with large and low on the
horizon in a perpetual Twilight Zone now
keep in mind we don't know anything
about Proxima bees composition we don't
know if it has an atmosphere or oceans
or anything but different climate models
have been run involving different
scenarios to assess Proxima bees
potential habitability in one very
simple model Proxima bee is covered in a
global ocean with temperatures at the
sub stellar point reaching 19 degrees
centigrade or 66 degrees Fahrenheit
however the rest of the planet is pretty
much a frozen ice ball in other words
the planet would look kind of like a
frozen eyeball with a liquid ocean at
the substellar point and ice everywhere
else in other scenarios ocean currents
would carry the substellar heat around
the planet but that would leave the sub
stellar region that much colder in most
cases just a few degrees Celsius above
freezing
however Proxima bees orbit may have a
moderate a centricity in that case the
planet wouldn't be tidally locked but
instead completes three rotations on its
axis
for every two revolutions around its
star this is called a three to spin
resonance and it's exactly the kind of
orbit that mercury has in this scenario
the planet rotates on its axis once
every seven and a half days that would
spread the star's heat more evenly
around the planet leaving the planet
with a cold tropical ocean with ice caps
reaching all the way down to mid
latitudes adding land to these models
interrupts the flow of heat around the
planet if there's land on the daytime
side of Proxima B that may increase the
planet's overall habitability
but the models also predict that the
planet would be cloudy most of the time
that's not necessarily bad for life in
general but it would have an effect on
the efficiency of photosynthesis in a
recent paper researchers demonstrated
that red dwarfs with masses less than
20% the Sun just don't produce enough of
the kinds of light that are necessary
for photosynthesis here on earth perhaps
a kind of plant life could evolve along
the shores of Proxima bees oceans with
large black leaves to absorb as many of
próximas low-energy photons as possible
however it's unlikely that such plants
could ever produce enough oxygen to
sustain complex life and then there's
that little matter of the frequent
powerful and ultra deadly flares from
red dwarfs their convective interiors
produce strong magnetic fields and their
short rotation periods twist those
magnetic fields up until they snap
unleashing massive flares of plasma
x-ray and UV radiation Proxima Centauri
flares about once every two to three
days
if Proxima B is going to maintain its
atmosphere it's going to need a really
strong magnetic field to shield itself
but like all red dwarfs Proxima
occasionally unleashes super flares that
are up to 10,000 times more powerful
than anything the Sun produces such an
event was witnessed in 2016 when Proxima
suddenly brightened by 68 times it's
estimated the Proxima unleashes about
five to six of these super flares every
year
if Proxima be ever had an ozone layer it
would have been pretty much destroyed
after just a few hundred thousand years
of these flares any life on the surface
it's going to have to adapt to that as
well
assuming of course its atmosphere wasn't
completely destroyed by Proxima Centauri
when it was just a few million years old
au microscope IAM and AD Leonys are
examples of red dwarfs that are about a
hundred million years old and they flare
three to four times a day not only does
a habitable zone planet require an ultra
powerful magnetic field
it also requires huge water inventories
to resist the relentless onslaught from
their host stars approxima B may no
longer have any water red dwarf stars
take very long to form with gestation
periods lasting up to a hundred million
years during this time they are actually
more luminous than they are when they
are reached the main sequence that means
that the planet could be subjected to so
much energy that its atmosphere would
have undergone a runaway greenhouse
effect the result may be a planet that
isn't cold at all but rather an ultra
hot desert wasteland like Venus however
approximate B may have avoided this
early fate if it had formed farther away
from the star and then migrated in after
the star had settled down a little bit
then the plan would only have to contend
with the ultra deadly flares from
Proxima Centauri now none of this is to
say that life is impossible on such a
planet but any life that could evolve on
próxima B would have to be adapted to
resist extreme cold and extreme
radiation but perhaps there's another
scenario that's more favorable to life
around a red dwarf barnard star is the
second closest star system to our Sun at
eight point six billion years it is
nearly twice as old as Proxima Centauri
and therefore a lot less active in 2018
astronomers announced the discovery of a
planet orbiting at zero point four
astronomical units from Barnard star
that's the same distance from Barnard as
mercury is from the Sun however Barnard
star is only 0.33% the luminosity of the
Sun that means this planet is only
getting about two percent the amount of
radiation earth gets from the Sun that
puts Barnard
at a frigid - 168 degrees centigrade
however Barnard B is at least 3.3 times
more massive than Earth that would put
it firmly in the super earth category
and it may also mean that it has a very
large liquid iron core if so that might
provide enough geothermal energy to
sustain life in subsurface oceans it's
tempting to think that maybe some of
that heat could burst through cracks in
the surface and dot the surface of the
planet with warm springs where a more
complex life could survive but we don't
really know enough about super Earths to
begin with they may just not have any
plate tectonics allowing such cracks and
fissures to form still a large liquid
convecting core would armed Barnard B
with a very strong magnetic field
combine that with it's already larger
distance from the star and a thick
enough ice sheet subsurface life could
be very well protected from Barnard's
flares
however after eight point six billion
years Barnard B may no longer have
enough radiogenic heat to prevent the
subsurface ocean from freezing hey what
can I tell you life's hard it might seem
that the chances for life around a red
dwarf star are really not that good but
it may be possible that life still finds
a way to eke out an existence in the
same way it does in the most extreme
environments here on earth but such
environments don't bode well for complex
life the best we may be talking about
are just small microorganisms
however Barnard and Proxima B are both
the closest known exoplanets to earth
that makes them ripe for future study
with our upcoming telescopes Barnard B
is far enough away from its host star
that the James Webb Space Telescope
might be able to directly image it in
the near infrared and the upcoming giant
Magellan 30 meter and extremely large
telescopes may also have a shot at
imaging it using adaptive optics now
mind you these telescopes won't be able
to show us pictures of lardy's oceans
and coastlines but they should be able
to
at least get the color information of
the planet and possibly obtain the
planet spectra if they can do that then
we have a shot at characterizing Barnard
bees atmosphere assuming of course it
has an atmosphere
unfortunately Proxima B is too close to
its host star to be directly imaged by
any of these telescopes but maybe over
time the spectra of the planet will be
able to be teased out from the spectra
of the star fingers crossed it seems
that the likelihood for life around
these red dwarf stars is pretty unlikely
then again life would have plenty of
time to form evolve get destroyed by a
flare and repeat over and over again for
trillions of years with each iteration
the star becomes less active literally
making life easier on those planets and
then in the far future the red dwarf
evolves and in many cases becomes very
hospitable for life to see how a red
dwarf evolves make sure you check out my
video on red dwarf stars I'll have a
link in the description below and I'd
like to take a second to thank my
patreon supporters who are making this
video possible thank you so much for
your help and if you'd like to help out
please visit my patreon page I'd also
like to say thanks to dr. Edward F
Guinan at Villanova University Edie was
one of my professors when I was a wee
undergraduate and he very kindly shared
with me some of his insights about the
habitability of red dwarf stars while I
was researching this video so thank you
dr. Guinan I hope I didn't screw it up
too much and as always if you'd like to
join me on this journey through this
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on any new videos until next time stay
curious my friends
you