Bad astronomy | Exoplanet WASP-121b is warmer than some stars


More than 4,200 exoplanets have now been found – foreign worlds orbiting other stars – we are bound to see some that are extreme.

But there is extreme, and there is Extreme. WASP-121b is the latter. Hard core. Heavy metal, even.

WASP-121 is a star about 880 light years away from the Sun. We call it the F6 star, which means that it is larger, warmer and brighter than the Sun; About four times brighter.

The planet orbiting the planet was discovered in 2015 by Wide-Angle Search for Planets or WASP with a series of cameras with telephoto lenses that cover a vast swath of the sky in search of transit: when a planet When revolving, it passes directly in front of it, reducing the light of the star by a fraction.

WASP-121b, as the planet is called, is simply terrible. It is slightly more massive than Jupiter (1.2 times), but 1.9 times larger in diameter. This is because it is bloated. And just why is it inflated?

because it is hot. It orbits the star at a distance of less than 4 million kilometers – comparing it to the Sun around 150 million km from Earth’s orbit. The WASP-121b is so close that it screams around the star in just 1.27 days, which is just 30.5 hours! Its year is barely more than the day of the earth.

It is so close to the star that it sinks; The average temperature is around 2100 ° C (3800 ° F). And this is the average. Cooks in the hottest place of the day 3000 ° C (5400 ° F). It is hotter than some stars!

The chemistry at that temperature is … interesting. Most of the molecules are destroyed apart from heat, so there is no water, no oxygen on Earth. The atmosphere dominates hydrogen, and even atoms are hydrogen; Molecular hydrogen (H2) as we see it on Earth like temperature cannot exist. Even weirder, free electrons (free of other atoms like sodium and potassium) combine with hydrogen atoms to form H-, a species we do not actually see on Earth. This atom is really good at absorbing light, so it heats up efficiently and is another reason why the atmosphere is so unsightly.

Planets like these are called Ultra hot jupiter, And it is expected that their atmospheric behavior dominates this hydrogen ion. However, observations of WASP-121b showed that its air contained other chemicals, so a team of astronomers obtained extremely high-resolution spectra of the atmosphere.

They found that very good (or hot?): Magnesium, sodium, calcium, chromium, iron, nickel and vanadium – as astronomers Metals. That last one is a bit funny. Vanadium is not a very common element, but when heated to the right temperature it becomes very good at absorbing light, making it easier to spot in the spectra.

When I studied brown dwarfs for a time – objects on a much larger scale than planets, but much less than stars, and what we usually find are much warmer – I was surprised to learn that Vanadium is commonly seen in their environments for this reason, as is titanium. They actually appear together, but only the vanadium appears in WASP-121b. He is strange in himself. But titanium can make molecules even at high temperatures, and at temperatures of WASP-121b these molecules can actually run out of the atmosphere … it is really raining! Vanadium is a gas at these temperatures, so it is still seen in the upper atmosphere.

The conclusion to be made here is that planetary atmospheres are not as simple as we might think, even when the situation (such as being flown by their stars) should do so.

I know it all sounds strange, but in a way it is. Planets like WASP-121b are very common, and they are very different from Earth. Heck, they are different from Jupiter, and they generally have more than the vastness of gas of our neighborhood.

There is one more thing I want to point out. When the planet passes in front of its star, some stars pass through the planet’s atmosphere. Different elements absorb different wavelengths (colors) of light, so a spectrum can reveal their presence. Call it a The transfer Spectrum.

But the planet is so hot that it really shines itself, like a star does! When it is behind the star, on the other side of its orbit, we cannot see it, the overall brightness of the system decreases somewhat (though not nearly as much as the planet blocks a star). A spectrum taken then shows only the star. If you compare our distance to the star of the planet on a spectrum, you can find out which elements are shining in its atmosphere. Call it a Emission Spectrum.

It tells us about things going on in the atmosphere, including wind speed; As the wind moves, the air color changes slightly due to the Doppler shift. They measured wind speeds in WASP-121b’s atmosphere at over 30 kilometers per second – enough to survive the planet! So the air there is so hot that it literally goes away from the planet… to the tune of 1000 tons per second! This is a lot, although smaller than the total mass of the atmosphere; It will take trillions of years to complete the planet’s air supply.

There is more than pure scientific interest for all this (apart from the general) Holy wow-Looking at its amazement). The devices used to probe this incredibly alien world can also be used to learn more about planets like Earth. They are harder to find (they are smaller and cooler, and have less impact on their host stars, making them more difficult to detect) but finding who we are. The characterization of their atmosphere can be very interesting indeed. This is one way we will seek life on other worlds.

Holy Wow!

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