Name: 炎熱的木星正在洩漏金屬!| 科學秀新聞 (This Hot Jupiter Is Leaking Metal! | SciShow News)
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In the world of exoplanets, the easiest to find are the Hot Jupiters

-- large gas giants that orbit super close to their host stars.

For years, those were the only planets beyond

Even though our technology can now hunt for more

Earth-like worlds, studying Hot Jupiters is still

important for learning about how planetary systems evolve.

So astronomers are still hard at work learning

all they can about these first-gen exoworlds.

And this month in the Astronomical Journal,

they've announced that the Hubble Space telescope

has found the first planet with metal gas escaping

its atmosphere -- which offers us further insight

The planet in question is known as WASP-121b,

whose discovery was announced back in 2016.

It's about 20% more massive than Jupiter,

but has nearly twice the diameter, so it's... puffier.

It's located about 900 light-years away from us

orbiting an F-type star, one slightly more massive,

There's been previous research studying water

in 121b's atmosphere, but for this study,

They did this by looking at the wavelengths of light

coming from the star that passed through the planet's

atmosphere during a transit -- those are the times when

the planet passed in front of the star relative to us.

Whatever light's missing clues us into the elements

The team detected ions of magnesium and iron.

Finding metals in Hot Jupiter atmospheres isn't new,

but they usually hang out in the lower atmosphere as clouds.

For WASP-121b, these metals were not just located

in the atmosphere -- they were also found so far away

from the planet they're no longer bound to it by gravity.

The reason for this is because WASP-121b is so stinkin' hot.

Its upper atmosphere clocks in at around 2500 degrees Celsius,

10x hotter than any other known exoplanet.

And it gets to that toasty temperature because it's less than

four million kilometers away from its star, WASP-121a.

The planet's year is only 1.3 Earth days long!

WASP-121a emits more ultraviolet light than our Sun,

The magnesium and iron also help heat the planet

giving the stuff further away from the core an easier job

Basically, the hydrogen and helium in the upper atmosphere

are flying off the planet, taking the magnesium and iron with them.

Hot Jupiter evolution -- they form further out in the solar system,

but migrate inward and lose their outer atmosphere

So WASP-121b is a great piece of evidence

But looking at things on an even bigger scale,

a new 3D map of the Milky Way was published last week

in the journal Science, which revealed that

It's hard to figure out how far away stuff is in space.

But one tried and true method since the early 1900s

involves a class of young, bright stars called Cepheids.

Those are stars that are varying in brightness over time,

but their variation is incredibly regular.

In 1912, astronomer Henrietta Swan Leavitt discovered

that the brightness of a Cepheid was directly tied

The brighter the star, the longer it took to vary in brightness.

So by measuring a Cepheid's period, you know how bright

By comparing that against how bright it looks

in the night sky, you can determine how far away it is.

There's a bit more to it, but that's the gist.

University of Warsaw put together data from

2,431 Cepheids located within our galaxy,

collected by a variety of survey missions,

and determined their location within the Milky Way

And when they plotted these stars in a three-dimensional map,

they discovered that the so-called disk of our galaxy is not flat.

It's warped, starting at a distance of around

10 kiloparsecs out, up the edge of the galaxy at 20.

And our side of the Milky Way is warping in the

opposite direction as what's happening on the

In other words, if you look at it edge on,

Near the edges, our disk also flares out.

While nearer the center it's only about 500 light-years thick,

out in the galactic boonies stars can be up to

5000 light-years away from the galactic plane.