as astronomers find more and more
planets around other stars
the big question we want to know is are
they habitable
could there be life there
the vast majority of stars in the milky
way are red dwarf stars
and most of the planet's inhabitable
zones have been
found orbiting these cooler less massive
stars
what are the chances that life could get
going on these worlds
at the time that i'm recording this
video in early 2019 almost
50 planets have been discovered orbiting
within their star's habitable zone
this is the region around a star where
liquid water can be present
too close to the star and water on the
surface of the planet will vaporize and
blow off into space
like mercury here in our solar system
too distant from the star
and water freezes like the icy moons of
jupiter and saturn
most of the stars found with planets in
their habitable zone
have been red dwarfs these are stars
with a fraction of the mass of the sun
from fifteen percent to fifty percent
conditions around these stars would be
very different from what we have here in
the solar system
since these are probably the most common
planets in the milky way
could life survive there the answer is
we don't know
but we do know that it's very
complicated and that's a good start
astronomers have been studying the
question and in the last few weeks
several interesting pieces of research
have come out addressing it
because red dwarf stars have much less
mass than stars like our sun
they have a very different internal
structure our sun
has the core where stellar fusion
happens and this is surrounded
by the radiative zone where photons are
emitted and absorbed
over and over as light makes its way
from the core
to the sun's surface outside the
radiative zone
is the convective zone where the sun
acts more like a lava lamp
where blobs of stellar material rise up
releasing heat
to the surface when the sun
runs out of fuel in the core it'll begin
to die
bloating up into a red giant and then
shrinking down into a white dwarf
it has lots of usable fuel in the outer
layers it just had no way to get them
into the core
red dwarfs on the other hand don't have
a radiative zone
they have the core and stellar fusion
which is surrounded by the convective
zone
the convection constantly mixes up
material
in the entire star bringing new fuel to
the core
when a red dwarf finally dies after
billions trillions
or even tens of trillions of years it
will have used up
all the hydrogen in the star
this incredibly long lifespan means that
whatever happens on the planets around
red dwarfs
they'll have a long time to work out the
details while life on earth
seems to have arrived a few hundred
million years after our planet formed
life orbiting a red dwarf star can take
a few hundred
billion years before it can get going
but actually
it might want to hurry the problem is
that red dwarfs generate incredibly
powerful flares
far worse than anything our sun does
this happens because red dwarfs rotate
more rapidly than larger stars
this causes more extreme magnetic fields
which can release an
enormous amount of energy when they snap
and reconfigure
in the first 100 million years or so of
a red dwarf's life
these flares can release 10 000 times
the energy of a typical flare on the sun
young red dwarfs can release flares like
this every day
even several times a day
if those flares were happening on the
sun they would strip away our planet's
ozone layer within about five years
microorganisms would receive 100 times
the lethal dose of ultraviolet
from every super flare
but it gets worse those flares might
actually remove the raw materials for
life in a red dwarf system
astronomers working with a very large
telescope and the hubble space
telescope studied the red dwarf star au
microscopie they discovered that huge
blobs of material are being ejected
out of the protoplanetary disk acting
like a huge snow plow
that pushes ice and organic molecules
away from the inner system
it looks like the flares might be so bad
they clear out all the useful material
before the planets can
even form even though planets might be
in the habitable zone they'd be bone dry
without all the water that was delivered
to earth in its early history
any life that did get going in the dry
environment would then continue to
suffer extreme super flares
but let's say that life did find a way
to get started on a planet orbiting a
red dwarf
and survive the first hundred million
years of extreme flare activity
then does it have a chance it's believed
that the planets orbiting closely to the
red dwarf stars
are tidally locked like the moon is
tidally locked to the earth
one side of the planet is blasted by
constant radiation
while the other side is in eternal
darkness
only regions around the edge might get
enough variation in temperature
to allow life to survive on the surface
of the planet
the trappist-1 system contains four
planets which are all within the
habitable zone of their star
but they're probably all tidally locked
to their star
according to another paper from savi
lingam and avi loeb
the challenges continue although a
planet might be warm enough to have
liquid water on its surface
they calculated that red dwarf stars
don't give off enough photons in the
right frequency range
to support photosynthesis
here on earth the base of the food chain
is plants
which use photons in the 400 to 750
nanometer range
to convert energy from the sun into the
plant stuff
and then animals eat the plants it's one
of those circle of life kind of things
even if a planet is in the habitable
zone around a red dwarf star
the majority of photons are in the
longer wavelengths infrared and red
light
and less of the shorter wavelengths as
well as ultraviolet
according to lingam and loeb all of the
habitable zone planets found around red
dwarf stars
aren't getting enough of the right kind
of photons to support a biosphere like
earth
and right now i'm sure you're thinking
what about a biosphere that isn't
anything like earth
well we'll get to that in a second but
first i'd like to thank squigglenut arc
titan
jason williams frank x harris stephen
tucker andrew harmsworth ryan androsoff
and the rest
of our 799 patrons for their generous
support
if you love what we're doing you want to
get in on the action head over to
patreon.com
universetoday i know i've been a total
buzz kill so far
just depressing you with news about all
these cool planets
we're finding in the habitable zone so
let me throw you a bone
a recent study from villanova university
looked at the habitability of the
super-earth planet
that was recently found orbiting bernard
starr this red dwarf
is the second closest star to the sun
only six light years away compared to
4.3 for alpha centauri
this planet wouldn't qualify as being in
the habitable zone
it orbits around the distance of mercury
and has an average surface temperature
of
minus 170 degrees centigrade but it also
has 3.2 times the mass of the earth with
1.366
earth radii so it's a large planet with
probably a large
hot iron nickel core and a lot of
geothermal activity
which gives it a similar environment to
jupiter's moon europa
it can have a thick shell of ice
surrounding liquid oceans which have
enough geothermal activity to support an
ecosystem
that doesn't depend on radiation from
the star in fact
worlds like this could be much more
common across the milky way
than the traditional habitable zone
planets were hoping to find
the best piece of good news i think is
the reality that red dwarf stars will
last an incredibly long time
while our own sun only has a few billion
years left red dwarfs can last a
trillion or even 10 trillion years
if life can somehow survive underground
or under the ice protected from those
early flares
they'll have trillions of years to
evolve adapt and improve
we're still in the early days of the
universe when you consider how long
these stars are going to live
maybe slow and steady will win the race
what do you think let me know your
thoughts in the comments once a week i
gather up all my space news into a
single email newsletter
and send it out it's got pictures brief
highlights about the story
and links so that you can find out more
go to universetoday.com
newsletter to sign up all of my videos
are also available in a handy audio and
video podcast format
so that you can have our latest episodes
show up right on your audio device
go to universetoday.com audio or
universetoday.com
video to get the one you want and i'll
put the links in the show notes and
finally
here's a playlist