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Every week is great for getting excited about planets, but this past one has been especially exciting! I mean, planets!

What would we do without them? From launching a new satellite, to finding diamonds from a lost world, researchers have been hard at work transforming how we think about our planet, the solar system, and the rest of the universe. It’s been a big week.

First up, earlier this week, NASA launched its Transiting Exoplanet Survey Satellite, or TESS, from the Kennedy Space Center in Florida. Like its name suggests, TESS will hunt for exoplanets using the transit method, which relies on watching a planet cross in front of its star. When that happens, the brightness of the star dims by a certain amount, depending on how big and how close the planet is.

Over time, if the brightness keeps changing by the same amount at regular intervals, that’s a good indication that there’s a planet there. Researchers can then extrapolate details about the planet’s size and orbit based on the magnitude and regularity of that dip. The Kepler Mission, which ran from 2009 to 2013, also used this method.

It focused in on a small patch of sky, which allowed it to get lots of data from dimmer, farther stars. TESS is gonna do almost the exact opposite: It’ll look at about 85% of the sky and observe over 200,000 targets, focusing only on the brightest stars within 200 light-years of Earth. But that brightness will allow it to do something Kepler can’t.

See, when transiting exoplanets move in front of their stars, they don’t just block out light because they’re in the way. The chemicals in their atmospheres also absorb some of the light. Specific chemicals absorb specific wavelengths of light, and when scientists spread that starlight out into a spectrum, they can see that chemical footprint.

It shows up as a pattern of dark lines at specific wavelengths. Based on this pattern, they can tell what’s in that planet’s atmosphere. And based on that, they can figure out some of what’s happening on the planet’s surface, even maybe assess how habitable the world is.

The thing is, if a star is dim, its spectrum is also dim, and the spectral lines aren’t well-defined. And since Kepler focused on dimmer targets, it’s really hard to extract that chemical info. That’s not to badmouth Kepler, of course, it did lots of amazing things, lots of great measurements, found tons and tons of planets!

But spectrally, it’s kind of lacking. We have gotten good spectra from some of its targets, but most of them are just too dim. Because TESS will look at super bright stars, we’re going to be able to do lots of follow-up using ground-based telescopes, and when it launches, NASA’s James Webb Space Telescope.

We’re going to get much more detailed and complete portraits of the kinds of planets in the galaxy than we did with Kepler. We’ll be able to learn not just their size and orbit, but their compositions, and what kinds of processes are happening on and inside them! So far, TESS is expected to find tens of thousands of new worlds, including at least a few dozen around the size of Earth.

And when they do, you can bet we will be here to tell you about them. Speaking of planets, scientists published a paper this week in Nature Communications describing the first evidence of a whole new planet in our solar system. Or rather, one that used to be around here billions of years ago.

This isn’t, like, a sneaky Planet 9 announcement, you probably would’ve heard about that. For a while, researchers believed that the early solar system was full of protoplanets. These were bodies around the size of Mars or Mercury that smashed into each other to form today’s planets and moons, including Earth’s Moon.

We think they should exist based on what we can see around us, but we haven’t really had any tangible proof, at least, not until this new paper. Now, researchers have announced they’ve found concrete evidence for a lost protoplanet in the Almahata Sitta meteorite, which exploded over Sudan in 2008. Specifically, this rock is a ureilite, which is a kind of meteorite that’s been exposed to intense pressures and temperatures, and has lots of magnesium, iron, and carbon.

We think all ureilites came from one original parent body, but we’re not totally sure. Either way, they definitely formed under some extreme conditions, like the kind of conditions on par with the inside of Earth. Now, we’ve found this kind of rock before, but Almahata Sitta is special.

Because when scientists took a close look at some of its fragments, they found diamonds inside! Which is not actually the special part. We know diamonds form inside the Earth, and since ureilites formed in similar environments, the presence of diamonds wasn’t a huge surprise.

But the information contained in them was. Diamonds are minerals, which means they have regular, repeating crystalline structures. And that structure reflects the pressure and temperature conditions under which the mineral formed.

Analysis of the diamonds in this meteorite showed that its parent body formed under pressures that exceeded 20 gigapascals, which is a whole lot; the kind of pressures seen in the Earth’s upper mantle. That means that the rocks must have originally formed in a body big enough to have sustained a mantle like the Earth, something about the size of Mercury or Mars, but with a different composition. The problem is, there isn’t a direct match anywhere in our solar system.

But there probably used to be. Based on its composition, scientists now think Almahatta Sitta came from a Mercury- or Mars-sized protoplanet that existed billions of years ago. That means the diamonds in these rocks are some of the last remains of a world that no longer exists, at least, not in the way it used to.

These days, it might just be a bunch of asteroids. We already knew that ureilites happen under extreme conditions, but now, we have some pretty clear pointers to their origin: protoplanets. Or maybe even just one protoplanet.

As always, it would be helpful to do more research to look for supporting evidence. But one way or another, these rocks are telling a pretty great story. Thank you for watching this episode of SciShow Space!

Scientists are learning new stuff about the universe every week, and if you want to keep learning about that and getting excited about it with us, you can subscribe at youtube.com/scishowspace. [♪ OUTRO].