Astronomer and Associate Curator of Astrophysics at the American Museum of Natural History Dr. Ruth Angus joins WIRED to answer the internet’s burning questions about exoplanets. What is the most extreme exoplanet? Have we discovered any habitable planets yet? How are the waves on Miller’s planet ( Interstellar ) so big? Answers to these questions and many more await on Exoplanet Support.
Image Credit: HR 8799 Orbiting Exoplanets by Jason Wang (Caltech)/Christian Marois (NRC Herzberg), licensed under Creative Commons Attribution 3.0 Unported (CC BY 3.0).
Source: https://commons.wikimedia.org/wiki/File:HR_8799_Orbiting_Exoplanets.gif
License: https://creativecommons.org/licenses/by/3.0/
For information about the American Museum of Natural History, visit https://amnh.org or connect with the Museum on YouTube: https://www.youtube.com/c/AmericanMuseumofNaturalHistory .
I'm an astronomer and an associate curator
at the American Museum of Natural History.
Let's answer some questions from the internet.
Scientists believe there is a super-Earth
but the way things are going around here,
even a slightly above-average Earth would be welcome.
for what is actually a slightly pedestrian thing,
that is a little bit more massive than the Earth.
Do we have a super-Earth beyond Neptune?
a potential ninth planet in our solar system.
we think that it might be tugging on other objects out there
right at the edge of the solar system.
If it's out there, it's extremely far away,
because it doesn't reflect much sunlight.
And it's also moving extremely slowly.
Nobody's found it yet, but it's hypothesized.
realscientists asks, How do we find exoplanets?
of exoplanets has been around for a long time,
they have only been confirmed in the last 30 years.
They are really hard to find. They are really hard to find.
So there are a couple of main ways that we detect them.
We can't directly image them most of the time.
They're just too faint compared to their host star.
And trying to photograph an exoplanet is like trying
to photograph a firefly next to a lighthouse.
of a planet based on the influence it has
One of the main techniques we use to find exoplanets
This is where a planet passes in front of its host star
and blocks out a little bit of light.
If we measure the brightness of a star
to get a little bit more dim as the planet passes
in front of it, and then it brightens again
once the planet has passed all the way past it.
We've found more than 3,000 planets this way.
There's another technique that is also pretty successful,
and it's called the radial velocity method,
This is where we actually see the star moving in space.
but we can see that the star moves,
and we infer that there's a planet orbiting it,
dragging it around with its gravity.
What we can do is actually measure the Doppler shift
and when it's moving away, its light is red-shifted.
So we infer that the star is moving
and it's being yanked around by a planet.
kaycie_hall asks, My toddler makes me read about space,
watch things about space, talk about space.
I'm just out here pretending I have any clue.
Well, I also have a toddler, so I can totally relate.
An exoplanet is just a planet outside
It's a planet that orbits another star.
And we found thousands of these exoplanets.
We're up to over 6,000. They're everywhere in our galaxy.
Probably every star has an exoplanet.
FinancialSun6933 asks, Is a planet orbiting two suns
Yes, it is. And we have found planets just like this.
This is actually a pretty unlikely configuration,
and they're very difficult to find.
So these are called circumbinary planets.
The star itself, the double star, is called a binary.
Kepler-16b, for example, is a circumbinary planet.
It's one of the first ever discovered.
If you've seen Star Wars, like the original film,
on Tatooine, there's an image of two suns rising.
So Tatooine is actually a circumbinary planet.
It orbits both stars at the same time.
stars that have another star for a companion,
are actually the most common type of star in the galaxy.
Our sun is actually slightly unusual,
StarTalkRadio asks, What is the most extreme exoplanet?
We could talk about the hottest exoplanet,
which orbits its star extremely close in,
and it's basically as hot as a star is.
It's so hot, in fact, that on its day side,
molecular hydrogen, like H2 molecules,
Most exoplanets sort of orbit in a circular way,
like the Earth has a very circular orbit,
they orbit in a sort of oval shape, like an ellipse.
And these planets have extreme temperature swings.
that are actually kind of disintegrating as we watch.
So these are planets very close to their host star
that have a big, extended, puffy atmosphere,
which actually seems like it's kind of being blown away
A few different options for extreme planets there.
FluorescentLightbulb asks, Explain like I'm five,
what makes the Earth so gosh darn livable?
How is it different from the other planets
in our solar system, or viewable planets in our galaxy?
because Earth's in the habitable zone,
and also because it's small and rocky,
But there are a lot of other qualities
that make Earth pretty perfect for habitability and life.
It has a pretty strong magnetic field,
and that magnetic field shields us from solar radiation.
which we think is essential for life.
Plate tectonics, we think, might be important for life,
to actually almost moderate the amount of carbon
And this kind of keeps the planet in equilibrium,
called the faint young Sun paradox.
Our sun used to be fainter and dimmer,
has sort of always maintained roughly
As the planet gets warmer, there's more rain,
more evaporation, more weathering of rock,
and rock weathering removes carbon.
Another thing that makes our planet special
And without it, axial tilt might change,
and it would send the seasons sort of totally out of whack,
would experience massive climactic swings.
Overall, we're at a pretty steady state.
And we think that this is probably a prerequisite for life.
Have we discovered any habitable planets yet,
because I'd really just like to start over.
Unfortunately, we haven't discovered anything
that we know for sure is habitable.
is the existence of a liquid water on the surface.
This means a planet has to be about the right distance
from its star to be the right sort of temperature
that the planet has to be relatively small like Earth,
because big planets like Jupiter, Saturn,
they tend not to have a discernible surface,
they're actually mostly made of gas,
but there are a lot of other criteria probably
For us on Earth, we have a stabilizing moon,
which stops our orbit from changing too much.
from irradiating the surface of Earth.
We have an atmosphere. We have plate tectonics.
Have we found planets in this habitable region,
the distance that makes liquid water possible?
orbit stars that are very different from our sun.
Most of these planets orbit little stars,
K-dwarfs are a little smaller than the sun,
and M-dwarfs are a lot smaller than the sun.
is that M-dwarfs are very magnetically active.
Think solar flares, they have coronal mass ejections,
high-energy particles leaving their surfaces
and potentially blasting these exoplanets.
The James Webb Space Telescope has been looking
on habitable-zone exoplanets orbiting M-dwarfs,
So we're now starting to wonder whether, actually,
maybe the star has to be just right as well
Which exoplanet do you think has the greatest chance
One of the main targets in the search for life
is the TRAPPIST-1 planetary system.
is that it is a very active M-dwarf star
with an extremely strong magnetic field.
And the planets orbiting TRAPIST-1 are blasted
Now, TRAPIST-1 has three planets in the habitable zone,
and we don't yet know whether or not they have atmospheres,
but the James Webb Space Telescope is working on it.
I think a better candidate is a star called TOI-700.
It has two exoplanets in its habitable zone,
so it's a small star with a strong magnetic field.
TOI-700 d and e are probably my bet
for the place most likely to have life.
Old stars tend to be more stable, more peaceful,
more sanguine, more calm, a bit like our own sun.
doesn't have so much strong radiation blasting its planets.
A Reddit user asks, Explain like I'm five.
If the sun is getting hotter in billions of years,
does that mean that planets further away from us
may become suitable for life while Earth may not?
and the habitable zone in our solar system
And it's actually been doing this for a really long time.
the Earth's oceans might evaporate,
and the Earth itself will not be habitable.
Humans have only been around for like 300,000 years,
so we've got a lot of time to figure it out.
It does mean that Mars is going to get warmer and warmer,
and it's gonna move into the habitable zone even more,
and it will stay in the habitable zone
jobmegens1 asks, Can't help but wonder
if an alien civilization would have detected Earth
that's called the Earth Transit Zone, which is like a plane,
which is where an alien would have to be
Probably if there are aliens out there scanning the skies,
looking for Earth-sized exoplanets,
if they live in that Earth Transit Zone.
If an alien has seen us, why haven't they said hello yet?
haven't really noticed our presence yet
because human technology hasn't been around
for all that long in the grand scheme of things.
bl4ck4nti asks, How do we know what exoplanets look like?
because we can measure the radial velocity,
or Doppler shift, of the star as the planet orbits.
And if you have radius, you have size,
then you know something about the density of your planet.
Maybe a planet's around the right density
or maybe it's around the right density
to be extremely heavy, like mostly made of metals and rock.
Mostly I've talked about exoplanets transiting their stars,
but planets can also pass around the back.
and they glow brightly in infrared,
we can actually see when they pass behind the star,
And we can even map the hotspots on the surface of a planet,
and we can figure out what the winds might be doing,
and understand, relatively speaking,
So some of those exoplanets that we've discovered
are actually pretty bizarre-looking.
ProudReaction224 asks, Explain like I'm five
how scientists can figure out the composition
is by observing a planet as it transits its host star.
Most of the light coming from the star
is gonna pass directly through space into our telescopes,
but some of the light is gonna filter
as it passes through a planet's atmosphere, it's changed.
Gas molecules in the atmospheres of planets absorb light
Carbon dioxide, for example, removes certain colors,
And we can infer the presence of these molecules
by seeing where those colors are missing
as a planet passes in front of its host star.
It's much easier to do this for a big, puffy planet,
because you get more light passing through the atmosphere.
the atmosphere is actually just a teeny,
tiny layer on top of the rocky core,
and so you don't really get very much starlight passing
It's really difficult to do this for Earth-like planets.
Just learned there's an exoplanet nearly the size
I wonder, are there planets bigger than stars?
You could try adding mass to Jupiter,
but what you would actually do is just increase its density
The smallest stars, M-dwarfs, can be extremely small,
So can you get a star that's smaller than a planet?
Actually, in certain circumstances, perhaps you could.
that are very close to their host star
are actually irradiated so strongly that they are so hot
that they actually puff up a little bit.
that is a little bit bigger than Jupiter.
adhamaloka asks, What does it take for us to be able
You need to have a planetary system
from the star using something called a coronagraph.
When we're trying to get these really,
really high-resolution images from the ground,
You know, when you look at a star, you can see it twinkling?
That is because the light from that star passes
through a column of air that's turbulent,
that twinkling messes up your observations basically.
You can't resolve really small distances in your images.
So what you can do is shine a laser through the atmosphere,
that allows you to predict the motion of the air,
and then the starlight falls on a mirror that you distort
to counteract the variations in the air.
And this is called adaptive optics,
and it allows you to focus light really extremely precisely
and get these precise images of exoplanets.
So the Webb telescope already detected water
in the form of steam on an exoplanet already,
and I wonder if we will detect signs of life
Water is a really common molecule in the galaxy,
it turns out, and a lot of exoplanets do have water.
So methane is a molecule that's produced by life,
and it's something that we would call a biosignature gas.
and a number of other single molecules
is that there are lots of ways to make methane
that actually doesn't have to involve life at all.
So methane on its own is not a perfect biosignature.
is that we actually probably wanna look
at a combination of two different molecules,
so, for example, methane and oxygen together,
because the two, methane and oxygen,
and oxygen have to be constantly produced perhaps
PeterCorless asks, Which exoplanet fascinates you most?
One of my favorite exoplanets is called 55 Cancri Ae.
It orbits extremely close to its host star.
Its whole year is shorter than an Earth day.
And it's so hot that we think it's actually a lava world,
and yet, it's held on to an atmosphere.
That atmosphere is probably constantly being outgassed,
Maybe it's being stripped away at the same time.
It's almost like a beacon of hope for me,
because it shows that planets can outgas new atmospheres
even when their host star is doing everything it can
SugarandBlotts asks, I have recently heard
that astronomers have found an exomoon.
I am quite scientifically illiterate.
An exomoon is a moon in another solar system.
We have tons of moons in our solar system.
So if our solar system has so many moons,
if other planetary systems didn't have any.
Moons also present another interesting possibility for life.
we have icy moons, Europa and Enceladus,
and these moons are actually warmer than they should be.
They're outside the habitable zone,
but they have liquid oceans under an icy crust.
The reason for that is that they orbit massive planets
So we think maybe there's life on our own icy moons,
And if icy moons could be a place for life to hang out,
then there's lots of opportunities for icy moons
and another potential host for life.
WTF, no one's concerned about rogue planets.
Rogue planets are these solitary planets
that don't have a host star, they probably once did,
but interactions maybe with other planets
in the planetary system has sent the planet outwards.
So we think that there are thousands and thousands,
of rogue planets out there in space.
How does finding planets in habitable zones affect SETI?
Do we point instruments at these planets?
SETI is the search for extraterrestrial intelligence.
This is really more about technosignatures
It's searching for things like narrowband radio emission.
It's searching for potentially laser signals.
It's searching for also things called Dyson spheres.
A Dyson sphere is where the entire star is covered
It would look like a very dim object
And so, in fact, SETI has really only covered
like a very small number of stars, but it's still searching.
MithandirsGhost asks, How do we know
that exoplanets aren't sunspots or starspots?
are two-dimensional for the most part.
you can see a spot coming into view,
the star a little bit more dim overall,
without being foreshortened on the limb.
So variations in starlight caused by spots tend to be smooth
they almost disappear, they sort of flatten.
they sharply block the star's light.
So transits tend to look like very sharp dips.
When we search for planets using the Doppler method,
the star itself actually has a Doppler signal,
Our Earth orbiting the sun actually makes the sun move
a little bit because both the Earth
and the sun orbit the center of mass
The Earth is dragging it around as it orbits,
The sun itself has its own Doppler signal,
it's shifting and roiling and pulsating,
when we find exoplanets using the Doppler method,
They turn out just to be interference from the spots.
If you've seen the movie Project Hail Mary,
40 Eridani, the planet that Rocky is from,
when Andy Weir was writing the book,
that it was probably not a real planet.
It was probably just some spots on the surface of the star
And unfortunately, Rocky's home world might not be real,
but it still lives on in our hearts and minds.
how is it possible for the waves to be so big
on the water planet if the gravity is stronger?
is a planet that's orbiting a black hole,
and it has extremely strong tidal forces,
and it's tidally locked to the star.
The moon is actually tidally locked to the Earth.
The moon's rotational period, how fast it spins,
is exactly the same as its orbital period,
how long it takes to go around the Earth.
So it always shows the same face to the Earth.
This water planet that orbits a black hole is the same.
It has these big tidal bulges on each side,
and on the side away from the black hole,
into this football or rugby-ball shape,
and the waves on the planet are created
The tidal bulges actually should stay put.
So you'd have a shallow part of the planet,
and you'd have a deep part of the planet,
and you wouldn't necessarily have waves like traveling
and rippling across the planet like you do in the film.
If the planet wasn't quite tidally locked,
if it was moving around just a little bit,
perhaps you could get some sort of sloshing back and forth
and maybe you could make these kinds of exotic waves.
Maybe that is what Kip Thorne was going for in the science.
Those are all the questions for today.
Thank you for watching Exoplanet Support.
