flowing liquid water on the surface of Mars.

But now, some scientists aren't so sure.

According to a paper published on Monday in Nature Geoscience, it might just be… sand.

Which is way less fun.

Y'know, sand is coarse... and rough.. and gets everywhere.

Since life on Earth relies on liquid water, we're always searching for it in other parts

of the solar system, in case it contains alien bacteria or can teach us more about our planet.

And thanks to previous missions, we've found that Mars has plenty of water frozen in polar

ice caps or floating around as water vapor.

But in 2015, researchers announced that they'd found liquid water trickling down hills on

Mars' surface.

Specifically, they found hydrated salts, which are just salt molecules attached to some water molecules.

And these hydrated salts created dark, flowing lines on Mars' surface called recurring

slope lineae, or RSLs.

On the off-chance life was hanging out in those RSLs, we didn't want to send the Curiosity

rover to check them out, because it's contaminated with material from Earth.

But scientists have been analyzing them with satellites.

In this new paper, they used the HiRISE satellite orbiting Mars to study the slopes of more

than 150 RSLs at 10 different sites.

They found that, on average, almost all of the RSLs ended when a hill got between 28

and 35 degrees steep.

And, according to measurements of Martian sand dunes, that's about the same angle

where flowing sand stops moving.

The scientists argue that, if the RSLs do contain liquid water, some of them should

flow past that roughly 30-degree mark.

Still, that's not the only reason they're questioning the liquid water idea.

For one, if RSLs were filled with salty water, they should be depositing dry salt piles when

the water eventually evaporates, but scientists haven't found any yet.

Also, one of the arguments for RSLs containing water is that they appear seasonally, like

water is freezing and melting.

But this team observed that sand flows can also change seasonally, based on how dust

blows around on Mars' surface.

Still, this definitely isn't a perfect hypothesis: The researchers admitted that seasonal sand

flow happens more easily on certain dunes that are constantly replenished by new sand

blowing onto them.

And the hills where we've seen RSLs aren't all like that.

And sand can't explain the hydrated salts, either.

But there are other possibilities!

Previous studies, like one published last year in Geophysical Research Letters, have

suggested that they could be caused by carbon dioxide frost instead, which would form when

gas condenses and freezes on the surface.

So before you throw your swimsuit into your bag and put it on your Mars rocket, maybe

wait a little while until we know a little more.

But don't abandon your suitcase entirely!

Because last week, astronomers announced that they've found a new, nearby exoplanet that

might be one of the most welcoming yet.

It's called Ross 128 b, and it was spotted using HARPS, an instrument attached to a telescope

in Chile.

HARPS is one of our most successful tools for finding new worlds.

It discovers planets by measuring wobbles in stars, which suggest that something — like

a planet — is pulling on them.

And that's how we found 128 b.

This new planet orbits a red dwarf star only 11 light-years away, making it the second

closest Earth-like exoplanet we've found.

Proxima Centauri b is just about 4 light-years away.

Red dwarfs are the most common stars in the universe, and they can be great exoplanet

parents.

They're only half the size of the Sun at most, and aren't too bright or hot.

And, while some of them can give off the occasional violent burst of radiation, the star 128 b

orbits seems especially calm.

From what we know so far, Ross 128 b doesn't seem too different from Earth.

It's about the same size, and its temperature probably ranges from -60 to 20 degrees Celsius.

But since its star is so small, 128 b orbits it a lot more closely than we do the Sun — about

20 times closer.

This helps it stay nice and warm, but it also means a year there lasts a little less than

10 days.

But if you don't mind birthday cake, that's not so bad.

Right now, even though the planet seems homey, we're not sure what its atmosphere is like,

or if it has liquid water on its surface.

So that's the next thing to figure out.

But when the European Southern Observatory's Extremely Large Telescope comes online in

2024, it should be able to figure out if 128 b has any oxygen in its atmosphere.

For now, it's still the most temperate planet we've ever found around such a calm star,

so that's still pretty awesome.

And we'll be learning more about it soon.

Plus, 128 b's star is currently cruising toward our solar system, and in around 70,000

years, it'll be the closest star to Earth besides the Sun.

So if we're still around in 70,000 years, but still haven't got warp drive figured

out, at least the trip will be a little shorter if we do decide to go.

Alright, exciting announcement!

I've been telling everybody about this.

The SciShow team and I were talking about a problem that many of us have.

Often, people will ask us what we want for Christmas, or for our birthdays and we won't

know what to say because we don't care about stuff that much.

But then I was thinking: there are things that I would like to get, or that I've bought

for myself, or that people have given to me that I really love because I love the world,

I love the universe, the existence of biology...that kind of thing.

So we put together a collection of artifacts of this universe...we got a limited number

of each of those things, and we have put them up at a store called SciShow Finds.

The SciShow Finds are curated by me, they are things that I would love to get in my

stocking.

It's a very small list of just six cool things of varying price points.

I did my best to only include one science book.

It's the book that I read this year that affected me the most, it's called "What is

Life" and it makes an extremely compelling case that biology is a chemical inevitability.

Which is a really important thought for having there be life out there in the universe.

As time progresses, we're probably going to add some new finds.

And as we add new ones, they will replace the ones, so all of these products are only

around for a limited time.

You're bound to have friends or family who would love some Mars Socks, trilobite fossils,

or maybe this Space Shuttle lapel pin.

And, if not, you might just want to get them for yourself or just slide the link in if

anybody's like, “What do you want, man?”

Just be like, “SciShowFinds.com!”

And know that when you go to SciShowFinds.com or send somebody there, you're also supporting

SciShow.

So, thank you!

Thank you for doing that, in that way, and also for doing that by watching this video.

You're the best!