It’s a scientific first: the discovery of an atmosphere around an Earth-like planet in the habitable zone.

Now, if that sounds like a jumble of words, in simple terms that’s a bunch of ingredients that play into life as we know it.

Here’s what’s cool about finding that.

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Back to the basics: What’s an atmosphere?

Most fundamentally, it’s a layer of gases surrounding a planet.

On Earth, our atmosphere provides us with a few things:

• Air: The oxygen that humans and animals need to breathe, and the carbon dioxide that plants need.
• A sun shield: Protects against harmful rays, like ultraviolet radiation.
• Keeps us warm: Traps in heat and keeps us from getting too cold.
• Creates weather: Everything from wind and clouds to rain and snow.

So, it’s possible this other planet, known as LHS 1140 b, could have some of those things too. (It’s pretty big by the way, roughly 5.6 times Earth's mass.)

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We don’t know yet if it has oxygen, carbon dioxide, water vapor or other gases to create life-supporting conditions.

The scientists discovered the planet’s atmosphere by finding helium gas leaking into space.

(MORE: 6 cool space experiments)

How they found it is pretty cool. As the planet crossed in front of its star, a sliver of starlight filtered through the planet's atmosphere on its way to Earth. The team then looked for a small dip in the star’s light at the exact wavelength of infrared light that helium blocks. 

And what does the habitable zone mean?

The habitable zone is a specific distance from a star that allows liquid water to be present on its surface — if water is actually there is different, though.

In Earth terms, the temperatures are quite comfortable. But being too close to the sun has Venus boiling, and being too far away makes Mars very frigid. 

For this planet, about 48 light-years away from Earth, it’s also in the sweet spot of its orbit around a small, cool red dwarf star. It receives less than half the sunlight Earth does.

Before accounting for this newly discovered atmosphere, scientists estimated a surface temperature of around minus 53 degrees Fahrenheit, which makes it cold but potentially habitable.

Challenging assumptions

Stars like the one this planet orbits can emit high-energy radiation that can strip nearby planets' atmospheres over time.

Scientists also haven’t been able to find an atmosphere on a neighboring planet, LHS 1140 c, where specific conditions — being smaller and less gravitationally bound — should make that easier to spot.

That’s a signal that the neighboring planet’s atmosphere was stripped away long ago, but LHS 1140 b has maintained its own, since it’s in a place with cooler, calmer conditions.

This all opens the door to the possibility that planets can hold onto atmospheres longer than we had previously assumed.

(MORE: Some of space’s weirdest planets)

What’s next is to determine the rest of the composition of the planet's atmosphere and whether it has any oceans or other things that we have which indicate further habitability.

But for now, this is astronomers’ strongest evidence yet that a rocky planet beyond our solar system has maintained an atmosphere over time.

"Twenty years ago we wondered whether other terrestrial-type planets even existed,” said Robin Wordsworth, Gordon McKay Professor of Environmental Science and Engineering and Professor of Earth and Planetary Sciences at Harvard and one of the lead authors' dissertation advisors. “Then we learned they're common, and found some in the habitable zone. The next question was whether any of them had managed to keep an atmosphere. Now we know at least one has."

Content writer Ada Wood enjoys exploring the stories that science and climate teach us about our natural world and how it influences the way we live in it.