WASP 76b: Hot Jupiter Exoplanet that Rains Iron at Night

WASP 76b: Hot Jupiter Exoplanet that Rains Iron at Night


Hello Space Fans and welcome to another edition
of Space Fan News. In this episode astronomers at the European
Southern Observatory have observed an exoplanet that is tidally locked around it’s star
and because of this has extreme temperatures on the daytime and nighttime side. The temperatures are so hot that on the day
side, iron is a gas and at night that gas condenses into molten iron rain. It seems the more we look for and at exoplanets,
the stranger some of them become. We tend to be really focused on the Earth-like
ones because we like to fantasize that somehow, someday we could live on one of those. But Earth-like planets are elusive compared
to all the others that are out there and this week, astronomers using ESO’s Very large
Telescope and associated instruments have found a really strange exoplanet. The planet is called WASP-76b and it orbits
its star WASP-76 once every 1.81 days. That’s its year folks! The system is located some 640 light years
away in the areas of the sky bounded by the constellation Pisces. WASP-76b itself is what astronomers call a
hot-jupiter, meaning its about the size of jupiter and, well, it’s hot. It’s about1.8 times larger in radius than
Jupiter and is a little less massive (about .9 times the mass of Jupiter). Now a really large planet the size of Jupiter
going around it star once every couple of days is strange enough but because it’s
year is so short, that also means it’s pretty close to the star, which makes it very hot. Being so close also grabs it pretty strongly
to the star. WASP-76 is an F7 star that is about 1.7 times
bigger than our sun and 1.5 times as massive and because of all these factors, WASP-76b
is tidally locked to the star in its orbit around it. Tidally-locked means that the rate at which
the planet rotates matches its orbit around the star making one side of the planet always
facing the star and the other side facing away. So here we have a planet that’s way bigger
and more massive than Jupiter, going around an F7 star – which are known to, among other
things, emit large amounts of UV radiation – going around that star every couple of day
AND it has one side always facing the star and the other facing away… Well that’s a party where you know weird
stuff’s gonna happen. Astronomers looking at this system using ESO’s
VLT and specifically the spectral imager known as ESPRESSO, a fiber optics high resolution
spectrograph, and when they looked at the planet at various spots in the transit (that’s
the part where the planet passes between us and the star), on the day side of the planet
where temperatures were around 2400K, which means the daytime side of this star is comparable
to some of the cooler stars out there. Looking at the spectral images, they were
able to closely follow the neutral iron in the atmosphere as the daytime on the planet
progressed. Because different parts of the planet were
visible to us as the planet went around and correcting for all the motions of the planet
rotation and orbital motion, the team look at what was happening to the iron content
in the atmosphere. They noticed that when they could see more
of the daytime-side disk, they say more Iron and because we’re talking about 2400K, it
had to be gaseous. Then looking at the evening terminator as
it became less visible but was still there, the iron content went down and on the dark
side of the planet and the morning terminator, they couldn’t see any iron. So they concluded that since they could see
neutral iron on the dayside and the evening terminator, but not the nightside and the
morning terminator, the gaseous iron in the atmosphere condensed as it moved to the night
side (or the dark side as I like to say) and since the nighttime temps are still pretty
hot, of around 1600k, that’s still hot enough for iron to be a liquid. And it rains. Iron. Molten Iron. Here’s what they think that would look like. This is iron condensing into rain. This wasn’t in the paper but it makes me
wonder about the oceans on WASP-76b. Would need a helluva boat to sail on molten
seas. Or maybe it’s like a giant version of Mustafar
system in Star Wars. Who knows, we could have just found the birthplace
of Darth Vader. Alright enough of that. I want to thank all Deep Astronomy Patreon
Patrons who keep these episodes coming and I want to thank all of you for watching and
as always Keep Looking Up!

How do we know it rains IRON on WASP-76b?

How do we know it rains IRON on WASP-76b?


I’m sure we’ve all heard of exoplanets
where some pretty bizarre stuff goes on, like evaporating exoplanets, whose orbits have
taken them too close to their parent star. Or a planet orbiting a pulsar, likely to be
composed of crystalline carbon, which would be similar, but denser than diamond. However, a newly discovered exoplanet called
WASP-76b, discovered using ESO’s VLT, has been found to have a very special characteristic:
on this planet, temperatures are so hot that instead of water rain, it rains molten iron. How can this be? And how can researchers know this from an
object 640 light years away? Exoplanets are pretty difficult to detect. Most exoplanets are only observed when the
planet’s orbit is aligned just right so that it transits in front of its parent star
from our perspective. Any whose orbits don’t align with our perspective
are exceptionally hard to discover, so chances are that there’s a lot more out there in
our relatively near vicinity that we don’t know about. Exoplanets that are very close to their stars,
with very small orbits, are the easiest to discover, because we can see a very clear
pattern on the star’s light curve over a short period of time. WASP-76b is one such planet. Plus, it is huge, way bigger than Jupiter,
and combine this with the fact that it only takes 1.8 Earth days to make one orbit, it
made it comparatively easy to detect. But detecting the presence of an exoplanet
is one thing, how do astronomers know anything about its physical characteristics? Interestingly, the first thing astronomers
do is find out the physical characteristics of the parent star, WASP-76. The distance to the star is first determined,
and then the star is classified based on its brightness and colour. Knowing the distance helps us determine how
bright it is, and we measure its colour simply by observing it, which helps us determine
how hot it is. If the star is on the main sequence, then
this chart also helps us know the radius and mass of the star, as they all tend to follow
a pattern. Once we have that information, we can determine
the characteristics of the orbiting planet itself. Knowing the mass and radius of the star means
we can measure the mass of the orbiting planet using some clever equations, based on the
Law of Universal Gravitation. As it happens, WASP-76b is a super-Jupiter,
way bigger than our Jupiter. That means that although it is massive, this
mass is spread out across a large volume, likely making it a gas giant. Orbiting this close to the star means the
planet is probably tidally locked, only one side faces the star at any given time. Also, due to the proximity of the planet,
it orbits within the star’s atmosphere, the physics of which we really don’t understand
yet. However, the star facing side will be extremely
hot, estimated to be around 2,400°c, easily hot enough to vaporise metals. Models go on to suggest the night side is
about 1500°c, still blisteringly hot, but much cooler. To really find out what WASP-76b is made of
though, we need to go back to the light curve of the transit. Scientists look for differences in the light
when the planet passes in front of the star, as light from the star will shine through
the planet’s atmosphere. Certain atoms block certain wavelengths of
light, so any reduced wavelengths help us know what is in the atmosphere. This is known as spectroscopy. For WASP-76b, the biggest surprise that scientists
detected was an abundance of iron in the atmosphere! Based on what we know about the planet so
far, it seems like iron exposed to the day side of the planet is vaporised, where it
is transported through strong wind processes to the terminator line between the day and
the night side of the planet. Here, the temperature is low enough for the
iron the cool and condense, producing iron raindrops which fall deeper into the atmosphere. By the time the wind has reached the “morning”
side of the planet, iron can no longer be detected. This remarkable measurement, taken by the
ESPRESSO instrument on ESO’s VLT, is the first time variations have been spotted like
this on an ultra-hot gas giant. Although it probably won’t be the last time! So, there we have it. How it can rain iron on WASP-76b. I have no doubt we’ll be hearing about more
astonishing exoplanet discoveries in the future, there are a lot of missions that have either
launched or will be launched in the not too distant future, helping us get a better understanding
of the universe around us. So, if you enjoyed this video and want to
learn about new discoveries as they come, subscribe so you don’t miss out! Also, a big thanks to my patrons and members
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