K2-141b: a hellish planet! Before we found the first exoplanets — planets
orbiting other stars — it seemed reasonable to suppose that other planetary systems looked
like ours: small, rocky planets close to a Sun-like star,
a big Jupiter and a few other gas giants farther out.
But after a quarter-century of discovery revealing thousands of exoplanets in our galaxy, things
look very different. In a word, we (our solar system) are “weird” — at least among
the planetary systems found so far. Just how weird is still a matter of debate.
And weirdness is relative. In fact, we found:
Planets made of water, planets with a diamond core;
Planets too hot, planets too cold; Planets that shouldn't exist;
Earth-like planets.
Since the discovery of 51 Pegasi b, the first ever-known planet orbiting around a star similar
to our Sun, we learned to find exoplanets by combining different techniques and instruments.
We have been amazed by the variety of exoplanets that exist, and we are learning that every
exoplanet is unique. This appears to be a new challenge for astronomers, like the one
they had when they first started studying the different type of stars.
The problem's that it will take time to have some good theories of planetary formations
because planets are way more numerous than stars: astronomers estimate that every star
in our galaxy has (almost) a planet orbiting around it.
This means that they are literally everywhere in the universe! They are thousand of billions!
Can you imagine such a huge number? We found even many planetary systems, like
our solar system, in which some planets orbit a star similar to our Sun.
Today we want to talk about one of the most bizarre planets we discovered: K2-141b.
This is a planet where it rains rock.
We know what you are thinking: how is it possible it rains rock?
Well, later in the video you will have the answer to this question.
Ladies and Gentlemen, fasten your seatbelt and follow us on this journey through the
universe: we will bring you far away, around the K2-141 star, to introduce to you the planet
K2-141b. Are you ready?
Many ancient philosophers, as Epicuro and Democrito, guessed that other worlds might
exist, basing their thoughts on a philosophical point of view rather than physical demonstrations.
Much later, in the sixteenth century, the Italian philosopher Giordano Bruno was the
first to assert that:
“There are therefore countless suns and an infinite number of worlds orbiting around
them, like the seven worlds orbiting our Sun”. (Giordano Bruno, On the Infinite Universe
and Worlds, 1584)
About 2300 years after Epicuro's ideas, and 400 years after Giordano Bruno, scientists
Michel Mayor and Didier Queloz found the first extra-solar planet: 51 Pegasi b. For this
discovery, they were awarded The Nobel Prize in Physics in 2019. Since then, the hunt for
extra-solar planets started, and astronomers all around the world became planet hunters.
Although we have still a long way to go before we get a well-built statistic for exoplanets,
we can study each of them, understanding how different they are.
Until now, there are 4301 confirmed exoplanets and 3192 planetary systems.
One of them is K2-141b, the hellish planet.
In these images, you can see that, if there's something that resembles hell, this is certainly
the case of K2-141b. On his surface, the temperature reaches extreme
peaks, and everything is somehow reddish. But...who found it? And how did he reach hell?
It was detected in 2018 by Luca Malavolta, from the Physics and Astronomy department
of the University of Padua, using the so-called “transit method”.
This method was our...highway to hell! The transit method measures the light curve
of distant stars for periodic dips in brightness, that are the result of exoplanets passing
in front of the star relative to the observer. These changes in brightness are characterized
by very small dips and for a fixed period of time.
These changes are also periodic, causing the same dips in brightness each time they occur,
for the same amount of time. Using the transit-detecting-method in order
to find an exoplanet it's like attempting to watch a lighthouse with binoculars from
hundred thousand of kilometres in order to find a small moth that flies around it.
One of the greatest advantages of the transit method is the way it can provide accurate
constraints on the size of detected planets. Think about a lamp: if we put an object between
us and the lamp, some of the light will be stopped by the object. The larger the object,
the larger the amount of light that will be blocked.
That's why a small planet will cause a small change in brightness, a larger planet will
cause a more noticeable change. One of the disadvantages of the transit method
is that planetary transits are observable only when the planet's orbit happens to be
perfectly aligned with the astronomers' line of sight.
As a result, this method cannot guarantee that a particular star being observed does
indeed host any planets.
But let's talk about our weird planet. K2-141b is thought to be a massive rocky exoplanet
orbiting extremely close to an orange main-sequence star.
It was classified as a Super-Earth, being larger than Earth but not as large as ice
giants Uranus and Neptune. It has a radius of 1.51 terrestrial radio.
The planet's mass confirms that it is rocky: it has a mass of 5.08 terrestrial masses,
which gives us a mean density of 8.2 g/cm^3, about 1.48 times the density of Earth.
This high density implies a composition with a large iron core.
We said that K2-141b orbits an orange main-sequence star.
A K-type main-sequence star also referred to as a K dwarf or orange dwarf, is a main-sequence
(hydrogen-burning) star of spectral type K and luminositty class V (to the voiceover:
V here is a Roman Number). These stars are intermediate in size between
red M-type-main-sequence stars("red dwarfs") and yellow G-type-main-sequence stars. They
have masses between 0.5 and 0.8 times the mass of the Sun and surface temperatures between
3,900 and 5,200 K. These stars are of particular interest in the search for extraterrstrial
life. Well-known examples include Alpha Centauri B (K1 V) and Epsilon Indi (K5 V). Our star,
K2-141, is about 61 parsecs away in K2 Campaign 12, within the constellation Aquarius.
It is smaller than our Sun (0.708 solar masses) and has a temperature of 4599 K.
It is aged between 1.6 and 12.9 billion years old.
For comparison, the Sun has a temperature of 5778K and is 4.5 billion years old.
How's K2-141b orbit? The planet orbits at a distance of about 0.00716
AU (1.071.000 km) from its star: it is very close to it!
For example, the Earth lies at 1 AU (149.597.870 km) from the Sun.
And, for comparison, our Mercury's Perihelion is 0.307499 AU more than 41 times farther away
from our Sun. The extremely small distance from its star
it's what makes this planet unique: it has one of the shortest known orbital periods
of any confirmed exoplanet. One orbit takes just 0.28 Earth Day to complete
(6.7 hours). If the Earth itself took that small amount
of time to make a complete orbit around the Sun, we will have the seasons changing from
Winter to Summer in something like 3.35 hours: it would be necessary to bring with you boots
as well as flip-flops! While analyzing the planet's illumination
pattern, scientist found that about two-thirds of the planet experiences perpetual daylight.
In fact, at this proximity, K2-141b is tidally locked with its host star, meaning that the
same side of the planet always faces the star. The scorching hot part of the planet reaches
temperatures of over 5.400 degrees Fahrenheit. It's not enough to only melt rocks, but also
vaporize them, creating a thin, inhospitable atmosphere.
The rest of the planet is cloaked in never-ending darkness, reaching frigid temperatures of
negative 328 degrees Fahrenheit. This means that the two sides of the planet
are completely different places, yet both are similar: K2-141b is hostile and creepy
in both sides. Of course, such weird discoveries amazed scientists
all over the world, because models of planetary formation don't predict the existence of such
planets: they are too close to their host star and they move way too fast.
As a consequence of this,
What can we say about K2-141b atmosphere and climate?
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If there is one thing we can say for sure, it is that K2-141b it's not a habitable planet,
due to its extremely close proximity to its host star.
K2-141b is believed to have both an atmosphere and oceans, which are magma oceans, maybe
tens of kilometres deep. Temperatures are high enough to make the magma
vaporize into the atmosphere. In Earth's water cycle, water evaporates,
rises up into the atmosphere, condenses, and returns to the surface as rain. Now imagine
that process, but instead of water, K2-141b only has rocks to work with.
At the upper edge of the atmosphere, the temperature drops and the vaporized magma liquifies, resulting
in rain. From there, rocks "rain" back down into
the 60-mile-deep magma ocean, which flows to the bright side to restart the cycle.
This is a very hostile planet. Every human being, every animal, every form of life on
his surface would be immediately vaporized by the high temperature.
The planet likely won’t be like this forever, though, says Professor Nicolas Cowan: “All
rocky planets, including Earth, started off as molten worlds but then rapidly cooled and
solidified. Lava planets give us a rare glimpse at this stage of planetary evolution.”
Although sometimes life on Earth may seem hard, remember that planets like K2-141b exist.
And the Earth is the only planet where you can have ice cream.
Professor Giang Nguyen from York University, Canada, stated that this research “is the
first step to understand how to study the weather and to make a prediction for exoplanets
like K2-141b.” This is a way to test our models over some conditions that could be
only confirmed by the new-generation telescopes that will be launched in the following years,
like the James Webb Space Telescope.
"This video ends here! Thanks for watching everyone! What do you think about K2-141b
planet? Do you have a favourite exoplanet? What do you think about this video? Was it
useful to you? Let us know in the comments below!
See you on the channel, and remember to get an ice cream before it's too late!