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[ intro ]
Earth is the way we see it today largely thanks to plate tectonics.
As these massive plates slide around, they create Earth’s defining geologic features,
like oceans and mountains.
Many scientists believe tectonic activity may have even been an enabling factor for
the emergence of life.
So, it’s no surprise that astronomers are looking for this activity elsewhere in the
galaxy, too.
And in a paper published late last month in The Astrophysical Journal Letters,
one team proposed that they might have found it.
They looked at a planet called LHS 3844 b,
and found that it may not just have tectonic activity — it may also be half-covered in
volcanoes.
LHS 3844 b is about 45 light-years away,
and it appears to be a rocky world about twice as large as Earth, with no atmosphere.
It also orbits its star really closely, so much so that it’s tidally locked,
meaning gravity causes it to always keep the same side facing its star.
This causes an extreme temperature dichotomy, where the star-facing side cooks at up to
800 degrees Celsius,
while the far side drops below negative 250 degrees.
In their study, these researchers wondered how this difference might affect the inside
of the planet.
So they built a computer model to find out.
First, they figured that the region underneath the planet’s surface, called the mantle,
may experience heat from several sources.
There’s warmth coming from the surface on the dayside of the planet,
but there may also be heat from the core, as well as energy from the breakdown of radioactive
elements inside the planet.
But, since they don’t know what the planet is made of,
or the exact combination of these heat sources, the team ran their simulations under various
conditions.
In a few cases, they found that material from the mantle would rise or sink kind of evenly
across the planet.
But more often, they discovered that all the upwelling would happen on one side of the
planet and all the downwelling on the other.
And mantle upwellings drive volcanic activity.
So, it’s possible that one side of this world is just covered in volcanoes,
spewing material from underground!
If it is, that wouldn’t necessarily teach us about tectonic motion,
but it could help astronomers determine what’s going on deep inside the planet, which could
continue to inform models.
The big thing, though, is that in all their simulations, this planet’s crust seemed
to move, much like it does on Earth.
So, there seems to be tectonic motion!
Unfortunately, it’s currently impossible to see that directly from 45 light-years away.
But by exploring planets with models like this,
we can at least get some insight into what tectonics can be like elsewhere in the galaxy.
Last week also brought news of another exoplanet, called Gliese 486 b.
It was featured in a paper published last week in the journal Science.
And at first glance, it looks remarkably similar to the last planet we talked about.
It’s a rocky world about 2.5 times the size of Earth, and it also orbits close to its
star.
But it’s different in one important way: It might have an atmosphere.
Or at least, it might give us our best chance yet of really studying an atmosphere around
a rocky exoplanet.
See, there are two main ways of studying an exoplanet’s atmosphere.
The first is transmission spectroscopy,
and it involves observing a star’s light as it passes through a planet’s atmosphere
—
or is transmitted by it.
If you know what the star’s light looks like before it enters the air,
you can compare that to how it looks after it passes through.
And any changes will tell you something about what atoms and molecules are around that planet.
The problem is, rocky planets tend to be smaller, so it’s hard to pick those signals out.
The other method here is emission spectroscopy, and it works by directly observing the light
produced by the planet’s atmosphere — or emitted by it.
Everything emits light at some level, whether it’s visible or not.
And that light can uniquely identify the atom or molecule that produced it.
But again, rocky planets are small, and way dimmer than their stars.
So, finding an atmosphere around a planet like this, let alone saying anything definitive
about it, has been kind of an ongoing quest.
But Gliese 486 b might be the perfect place to keep looking.
According to the authors, it’s the best rocky planet we know of for emission spectroscopy
and the second-best for transmission spectroscopy.
And that’s based on a number of things.
For one, the planet is 430 degrees Celsius,
so any atmosphere would be big and fluffy.
And bigger things are just easier to observe.
A hot atmosphere would also emit brighter light,
making emission observations easier to make.
Meanwhile, the transmission side would benefit from the fact that the planet goes around
the star in less than a day and a half,
creating lots of chances to see starlight go through an atmosphere.
The star itself is relatively inactive, too, without a lot of things like big flares.
For transmission observations, that would create fewer complications when researchers
are making comparisons.
And to top it all off, the whole system is just 26 light-years away, and closer objects
are always easier to study.
At this point, astronomers haven’t definitively found an atmosphere yet.
This paper was mostly about gathering detailed information on the planet.
But that’s something they’re hoping to do soon —
because if we want to understand what exoplanets are like, we’re going to need good, clear
data.
That’s also true in our search for tectonic activity on other worlds!
And in that regard, both of these planets seem like goldmines.
Understanding exoplanets like this requires an incredible amount of data analysis.
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[ outro ]