Hi, there!

It's been a few weeks since we did a proper Space News episode, and that's because we've been working really hard to cover the pandemic over on the main channel. We've still got lots of content coming out over there soon, but this week, we decided to take a step away from Earth and bring you some news about stars and the planets.

So, enjoy. [♩INTRO]. Nothing in space is more important to our daily lives than the Sun. Next time you look out the window and don't see a lifeless, frozen wasteland, you know our favorite ball of gas is still chugging along.

But, seriously, life on Earth depends on the steady nature of our star. Here's the thing, though: We don't know if the Sun was always this consistent. Scientists have only been able to track its activity back thousands of years, and it's been around for almost 4.6 billion.

So is the Sun going to stay this steady in the future? Or are we just in the middle of a convenient calm period? At this point, it's impossible to know, but recently, an international team of scientists searched thousands of other stars to try and find out.

And their work, which was published on May 1st in the journal Science, reveals just how much we still don't understand about this fundamental object. One tool they used in this study might surprise you:. NASA's Kepler Space Telescope, which was retired in 2018.

We usually talk about Kepler finding planets outside the solar system, but some of its most important work was understanding the stars those planets orbit. After all, Kepler found planets using the transit method, which watched for a dip in a star's light as a planet moved in front of it. But that really only works if you understand the star's natural variations in brightness.

Kepler could watch around 150,000 stars at the same time, making it a hero for researchers — including those from this new paper. In the study, astronomers searched Kepler's dataset, plus some supplementary data from the Gaia spacecraft, looking for stars that closely resemble the Sun. And they ended up with 369 that roughly matched the Sun's combination of temperature, age, composition, and rotation period.

That last one is actually especially important because a star's rotation is responsible for the creation of its magnetic field. And the Sun's magnetic field produces sunspots, which are a big factor in driving changes in brightness. On the Sun, these fluctuations are small, averaging around 0.07 percent.

But the average fluctuation in the similar stars was around five times bigger than that. From this, you might conclude that our Sun is at some sort of activity minimum and that we should expect things to get more unpredictable in the future. But there's another piece to the puzzle.

The team also looked at another 2500 stars that matched the Sun's age, temperature, and composition, but whose rotation periods. Kepler wasn't able to estimate. And the activity on those stars was much more like what we see on the Sun.

So, what gives? Well, it's possible that this larger group, and the Sun, are somehow fundamentally different than their more active counterparts. Or it could be that stars like the Sun are usually pretty quiet, but are capable of periods of more intense activity.

Either way, there's no need to go out and build a bunker. As best as astronomers can tell, these are changes that play out over thousands or even millions of years. So it's important to know in the grand scheme of things, but your weekend sunbathing in the backyard is going to be just fine.

Speaking of the search for exoplanets, astronomers are starting to look not just for planets in general, but specifically for ones that might be habitable. That word might conjure visions of blue skies and oxygen-rich air, but… that's probably not always true. According to a study published Monday in Nature Astronomy, maybe scientists ought to be looking in more exotic places.

This work is part of the field of astrobiology, which tries to understand what life off Earth might be like and how we could detect it. For now, since there's not a way to get to faraway planets, that detection is most likely going to have to come from biosignatures, which are chemical byproducts produced by life. Like, around here, cows and bacteria make methane, so if you've detected a bunch of methane over a field, you could infer something lived there.

A big goal of NASA's upcoming James Webb Space Telescope is to search for these signatures in the atmospheres of nearby exoplanets. But there are a lot of exoplanets so which ones should we consider habitable enough to study? To find out, this team took common microbes and put them in weird environments to see if they could grow.

They used E. coli and yeast, which represent two big classes of single-celled organisms, and they put them onto growth mediums inside glass bottles. In one bottle, they left ordinary air, but in the others, they replaced that with either pure hydrogen, pure helium, or a mix of nitrogen and carbon dioxide. Importantly, these test environments didn't contain free oxygen, a key element most living things use to get energy.

After allowing the microbes time to grow, they checked the bottles to see what happened. And amazingly, in every case, both the yeast and E. coli could reproduce. E. coli can switch to an alternate metabolism that doesn't require oxygen, so it fared the best, producing a little less than half the growth seen in the regular-air bottle.

Yeast did substantially worse — but it still grew! The most exciting takeaway, though, is that both could grow in an all-hydrogen atmosphere. That's what makes up most of the atmosphere for planets like Jupiter and Saturn, and it's also probably a key component in the atmospheres of many large, rocky exoplanets.

What's even better is that, since hydrogen is so light, the atmospheres containing it are usually large and fluffy, making them easier for telescopes like the James Webb to study. Also, when the team looked at the gasses released by E. coli during the experiment, they found dozens of different molecules, including several already considered prime biosignatures. All this doesn't mean that we're likely to find E. coli on another planet, but it does suggest life is even more adaptable than we thought.

Which is great news for astrobiologists, because so far, we haven't found a ton of truly Earth-like planets. But maybe we didn't need to, after all! Thanks for watching this episode of SciShow Space News!

If you want to learn more about exoplanets and the life that could thrive on them, you might enjoy our Exoplanets playlist. Right now, it's got more than forty episodes in it… so if you're looking for a break from Earth these days, we've got you covered. [♩OUTRO].