For years, NASA has been working

on an amazing telescope.

It's called the James Webb Space Telescope,

or JWST, and at one point,

it was intended to launch in 2007.

We've been talking about this project

since SciShow started, because James Webb

could transform our understanding of the universe.

But honestly, being a fan of this telescope

is sometimes hard work.

After years of seeing it fail tests and get postponed,

things can feel discouraging.

Today, though, I have some good news!

Last week, after more than a decade of delays,

the two halves of the telescope have

finally been joined together.

Although it won't do identical work,

James Webb is the successor to

the Hubble Space Telescope, which will likely

stop working in the mid-2020s.

And once Webb launches,

it will be charged with a full complement of missions.

Using infrared light, it will study

the composition of exoplanets,

probe the oldest galaxies we can see,

and maybe even answer our questions

about what the universe is made of.

But before it can do any of that,

it needs to launch.

And before it can launch,

it needs to be fully tested.

Until recently, Webb's two main halves

were tested separately.

But now, we can test them together.

One half consists of the telescope itself.

That's the part with gold-coated mirrors

and a suite of instruments.

The other half has the spacecraft,

which will steer the telescope,

along with the giant, five-layer sunshield

that will block light from the Sun, Earth, and Moon.

Blocking this light will help keep the telescope cold

— which is a must, since heat is

a major source of infrared radiation.

So, if it's not cold enough,

an infrared telescope's own heat

can overwhelm its instruments

while it's trying to monitor distant, dim objects.

The sunshield will solve a lot of that problem,

but the telescope will also have a bit of cold helium

to keep some of its instruments extra chilly.

Of course, just because the telescope

is mostly-assembled doesn't mean

it's ready for launch.

Engineers still have to connect

the electronics between the two halves,

and after that, they have to test them all together.

They'll have to make sure they wired

everything correctly and that the equipment

will survive deployment and the vacuum of space.

That means there's still room for error.

But hopefully, things will go well,

and the telescope will finally launch in March 2021.

Thankfully, even if Webb doesn't launch for a while,

there's plenty of other work to do in astronomy.

For example, researchers are still

hunting for the first solid evidence of

an exomoon — a moon orbiting

a planet outside the solar system.

Moons are usually much smaller

than their planets, so even when we find

an exomoon candidate, it's tricky to

isolate the signal and confirm

that it's actually there.

One team of astronomers thinks

there's a way around this, though.

Their paper has been accepted for

publication in The Astrophysical Journal.

And in it, they propose you can find

certain exomoons by studying their planet's chemistry.

And using this method,

they've even found an especially exciting candidate!

This paper focuses on a type of planet

called hot Jupiters.

These are gas giants that orbit

so close to their stars that their year

could be as little as a few days on Earth.

Until recently, there wasn't much evidence

that a moon could exist in a stable orbit

around a planet like this.

So the first thing these scientists did

was use math to confirm moons could live there.

And next, they proposed a way

we could identify them.

Drawing on earlier research,

they suggested you could find some

exomoons by looking for certain gases

in their planets' atmospheres.

This idea is actually based on

what researchers see with Jupiter

and its third-largest moon, Io.

Io has hundreds of active volcanoes

that spew out lava, sulfur-based gases,

and other elements — like sodium and potassium.

And some of those compounds get incorporated

into Jupiter's upper atmosphere.

That's important.

Because at least in our solar system,

elements like sodium and potassium

aren't normally found in

the upper atmospheres of gas giants.

They only seem to get there through

external sources — like volcanic moons.

So, these astronomers hypothesized

that if you detect either sodium

or potassium around a hot Jupiter,

it could have a moon like Io.

This basic idea isn't new,

but these researchers were among

the first to see if it applied to hot Jupiters.

And as it turns out, it might.

In their study, they looked at data

from 14 of these planets,

all of which had sodium or potassium

signatures in their upper atmosphere.

Then, they ran analyses and identified

one that seems most likely to have a moon.

It's called WASP-49b,

and is located 550 light-years away.

If this finding is validated,

it would be the first confirmed exomoon.

But even if it's not, this method is still

a really creative way of studying objects

that are super far from Earth.

It combines the familiar things

that are close to us with alien worlds

hundreds of light-years from here!

At this point, it's unclear if this technique

could be used to find moons like ours

around planets like Earth.

But hey: Maybe we'll need even more

creative methods to do that.

There's a lot to explore in space —

which is part of the reason science fiction is so fun.

You get to think about what would happen if,

say, a bunch of alien robots called Carl

suddenly appeared on Earth.

Okay, let me explain.

About a year ago, Hank, who co-hosts

this channel with me and started SciShow

and does lots of cool things,

released a book that he worked on forever

called An Absolutely Remarkable Thing.

And that book is now available in paperback,

which is just so much more cozy to hold!

So if space, robots, social media,

or just the general state of humanity are things

you're interested in… you can pick up the paperback

of An Absolutely Remarkable Thing

wherever you like to get your books.

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