NARRATOR: This episode is supported by LegalZoom.
Last week in a NASA press release,
we learned about an amazing new discovery.
A nearby red dwarf star was discovered
to have not one, but seven Earth-like planets,
and any of them may be capable of supporting life.
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The TRAPPIST-1 planetary system was
discovered by Dr. Michael Gillon and team
and reported in the journal, "Nature."
The discovery of three planets in the system
was made in 2015, with the Transiting Planets
and Planetesimals Small Telescope, TRAPPIST,
at the La Silla Observatory in Chile.
Follow up with the Spitzer Space Telescope
has now revealed an additional four planets.
Both telescopes use the transit method,
watching for the dimming of the central star
as the planets pass in front of it.
Never before have we seen so many Earth-like planets
in one place.
Any one of them could bear liquid water, maybe even life.
The TRAPPIST-1 system lies 39 and 1/2 light years away
in the constellation of Aquarius.
The star, TRAPPIST-1a, is an ultra cool dwarf
star, about 10% the sun's diameter and less than 10%
its mass.
It's also much colder, about 2,500 Kelvin compared
to the sun's 5800 Kelvin.
The seven planets huddle extremely close to this star--
all within one fifth of Mercury's orbit.
That makes a year on a TRAPPIST-1 planet
very short, from a day and a half
on the innermost TRAPPIST-1b to three weeks on TRAPPIST-1h.
That's a lot of birthday cake.
The planets live so close together that they all tug
on each other gravitationally.
It's enough to slightly vary the length of their years.
The gravitational influence on each other
allows us to figure out their masses,
between 0.4 and 1.4 times Earth's mass.
This, combined with the depth of the eclipses which
gives their sizes, we can know their densities and so
their compositions.
They are very likely rocky or watery worlds
just like our own.
The planets have now settled into stable orbital resonances
with each other, and that's a hint
that they may have formed further out
and then migrated inwards.
It's also unlikely that enough material resources
would have been available for so much planet forming
so close to the star.
Because different chemicals condense
at different temperatures, planets' distance
from the star during formation largely
determines the planet's chemical makeup.
If they did form further out, then the TRAPPIST-1 septuplets
may have a lot of water and other volatiles.
Maybe the TRAPPIST-1 planets started out
as mixtures of rock and ice.
However, three of them now occupy
their star's habitable zone, where
planet's surface temperature would
be just right for liquid water.
We can estimate the location of the habitable zone
for a given star based on the intensity of its photon flux
and the effect of atmospheric greenhouse gases.
Our solar system's habitable zone extends from roughly 1
astronomical unit-- so Earth's orbit--
to 1 and 1/2 AU, covering Earth and Mars.
The same calculation for TRAPPIST-1
forms a smaller, thin band.
But in that densely packed system,
it covers three of the planets.
Gillon and team have done some climate modeling,
which indicate that the three innermost planets may
be more Venusian, so overheated due to a runaway greenhouse
effect.
However, that's really hard to predict at this point.
The outermost planet, which orbits past the snow line,
should be icy.
However, it may be that internal heat left over from formation
and generated by tidal interactions with its star
and the other planets could warm it to liquid water temperatures
as well.
In fact, any of the seven planet could host liquid water.
Should we pack our bags and move to TRAPPIST-1?
What would it be like there?
We've already established that the temperature
could be to our liking.
Wein's law tells us that the 2,500 Kelvin TRAPPIST-1
star shines brightest at infrared wavelengths.
It would look pink on the sky to us,
but there will be no day and night so an eternal sunrise.
See, because the planets are so close to the star,
they're probably tidally locked, like our moon.
One side of each planet will always
face the star, the other away.
That could be OK for habitability
if they have sufficiently thick atmospheres to mix the heat
from their sun globally.
These planets would be huge in each other's skies.
I'm talking No Man's Sky huge.
At closest approach, some will appear larger
than the full moon, up to twice that size.
So they could easily see each other's continents
if they have them.
Partial eclipses of the central star by sister planets
may be common, but there would be no full eclipses.
The TRAPPIST-1a star is just too close by,
standing a whopping 5 and 1/2 degrees on the sky if you're
standing on the innermost planet,
and a degree on the sky for the outermost.
For comparison, our sun and moon span around half a degree
on the sky.
On the inner planets' sunny side,
the star will provide about as much visible light as our sun.
Planets further out will receive less light,
but the star's infrared intensity
provides the heat needed for liquid water.
Sounds pretty sci-fi awesome.
But a word of caution.
Being so close to the central star
exposes the planets to stellar activity.
Out here on Earth, our distance and our magnetosphere
protect us from most of the sun's coronal mass ejections.
But within a tenth of an AU of TRAPPIST-1a,
CMEs would be dangerous, and tidal locking
would weaken the planet's protective magnetospheres.
The TRAPPIST-1a's winds may have eroded
its planet's atmospheres, just as the sun did with Mars.
In addition, although this star is now relatively quiet,
when these M dwarfs are young, they are extremely active.
This planetary system probably had a traumatic youth,
which may not have been ideal for starting life.
We don't yet know much about what those planet's atmospheres
are like.
Are they breathable air?
Are they cyanide?
All sorts of fascinating nasty compounds
can end up in exoplanet atmospheres,
all strongly affecting climate temperature and chemistry.
The Hubble Space Telescope has confirmed that the a, b,
and h planets don't have hydrogen helium
atmospheres, which means they aren't
gassy planets like Jupiter.
Future spectroscopy from the James Webb Space Telescope
will hopefully provide us with atmospheric composition data
that may include signatures of chemicals
indicative of the presence of biological activity--
of life.
Finally, I mentioned tidal heating could warm TRAPPIST-1h
above water's freezing point.
However, tidal forces could pose a serious problem
to the inner planets.
Picture Io, squished and stretch so vigorously
by Jupiter and neighbor Europa that it's a hellish volcano
world.
Tidal force between two bodies is
proportional to the product of the masses
and the inverse cube of their distance.
There is so much more mass in the TRAPPIST-1 star planet
system than the Jupiter-Io-Europa system
that, while the tides are about half the magnitude of Io's
on TRAPPIST-1h, they may be up to 100 times
as bad on TRAPPIST-1b.
That could seriously increase temperatures
and volcanic activity and make it a real surfing mecca.
Clearly, not all planets in the habitable zone
are created equal.
Liquid water is just one item on a long list of requirements
for life as we know it.
Tidal locking, stellar activity, atmospheric composition,
and volcanism can all turn an Earth-like planet
uninhabitable.
But this finding tells us that Earth
sized planets are probably common around M dwarf stars.
Remember also that a potentially habitable Earth-like planet
was recently found orbiting the very nearby Proxima Centauri.
Given that M dwarfs are the most numerous stars in the galaxy,
we may have seeing a giant boost in the number
of possible homes for life out there in space time.
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Hey, guys.
Today, we're covering comments from the last two episodes--
Telescopes of Tomorrow and The Eye of Sauron.
So several of you asked why we didn't
cover the European Extremely Large Telescope rather than
the Giant Magellan Telescope.
After all, EELT will have nearly three times the collecting
area of GMT.
The reason is that I wanted to talk about GMT,
and we only had room for three telescopes total.
It's design phase is a little further along,
and it'll see first light a few years earlier than EELT.
That makes it the very first of the new generation
of gigantic telescopes.
EELT will be amazing indeed and may warrant its own episode.
Aaron Craig points out that Galileo did not, in fact,
invent the telescope.
Yep, and that's why I was careful not
to say that he invented it.
That credit is usually given to Dutchman Hans Lippershey, who
filed a patent for an invention, for seeing things
far away as if they were nearby, a few years before Galileo
made his famous observations of Jupiter's moons
and the phases of Venus.
However, Galileo did make massive improvements
in the design and effectively invented the use of telescopes
for astronomy.
SS asks about the distinction between the genes
mass, the genes length, and the genes instability.
So in the original derivation by genes,
the gene's mass is just the mass of a region of size
equal to the gene's length, which itself
is the maximum size region of cloud can be before it
fragments, because local gravitational collapse
happens faster than pressure can equalize across the cloud.
But the gene's mass could also be derived by a simple energy
balance.
As you suggest, it's when inward gravitational forces
and outward gas pressure are in equilibrium.
But at larger masses, the gravity wins and a star forms.
As long as the cloud is still smaller than the gene's length,
it won't fragment further and a single star will form.
Slikrx asks the burning question,
is the planet that was found in the Fomalhaut system
in the Hobbitable zone?
No, I'm absolutely "shire" the planet
is too far out for Hobbits.
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