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 planets
in habitable 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 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 15% to 50%.
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 Milky Way, could life survive there?
The answer is: we don't know, but we do know it's very complicated, and that's
a good start.
Astronomers have been studying the question, and in just 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 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 had lots of usable fuel in the other layers, it just had no way to get it 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 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 could 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.
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 5 years.
Microorganisms would receive 100 times the lethal dose of ultraviolet from every superflare.
But it gets worse.
Those flares might actually remove the raw materials for life in a red dwarf system.
Astronomers working with the Very Large Telescope and the Hubble Space Telescope studied the
red dwarf star AU Microscopii.
They discovered that huge blobs of material are being ejected out of the protoplanetary
disk, acting like a huge snowplow 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 superflares.
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 their 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 4 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 Manasvi 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 400-750
nanometer range to convert energy from the Sun into, uh, 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 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?
We'll get to that in a second, but first I'd like to thank:
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I know I've been a total buzzkill 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 Barnard's Star.
This red dwarf is the second closest star to the Sun, only 6 light-years away, compared
to 4.3 for Alpha Centauri.
This planet wouldn't qualify as being in the habitable zone.
It orbits around distance of Mercury and has an average surface temperature of -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 could 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 we're 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
ten 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.
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For more infomation >> Noticias Telemundo Mediodía, 24 de enero de 2019 | Noticias Telemundo - Duration: 21:37. 
For more infomation >> 23/01/2019 19:25 (120 Leigham Ct Rd, London SW16 2RW, UK) - Duration: 9:50. 
For more infomation >> Flamingo Kero Kero Bonito sub español - Duration: 3:23. 
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