Reid: Space agencies spend a lot of time and money on asteroids. Sure, they're focused on how to avoid getting *hit* by the asteroids, but they also think about the value of the rocks themselves. In fact, several missions have been completed with the sole intention of interacting with asteroids. In this SciShow compilation video, we'll explore asteroids from every angle, starting with the all-important, "Why do we care about them at all?"

[slide: "Mining Asteroids for Space Treasure"]

If we as a species ever want to get off this planet, we're going to need to find stuff we can use to build things and survive in space. Lucky for us, there's a lot of it; I'm talking about water, iron, platinum, gold - you name it. It's...just locked up in asteroids. And a growing number of people believe that if we want to live in space, we have to mine them.

Most of the asteroids in our solar system are in the asteroid belt, which is between Mars and Jupiter. But there are 14,000 NEOs, or "Near Earth Objects," which are asteroids floating around a lot closer to home. Right now, we're most interested in carbonaceous chondrite asteroids, or "C-type" asteroids; they're mostly made of life-friendly stuff like carbon, phosphorus, and nitrogen. Any future space settlement will need a lot of these elements because that's what makes up breathable air and fertilizer for growing crops. But the best thing about C-type asteroids is that they're basically chunks of clay, so you've got all these organic elements stuck together with water. And in space, water is more valuable than gold.

We need to drink it, obviously, but we can also separate it into hydrogen and oxygen for rocket fuel. You know, for those interplanetary gas stations. And due to its density, water can even protect us from radiation, which is one of the biggest dangers of spending a long time in space. Launching a single gallon of water from Earth into orbit costs about 83,000 US dollars, not to mention the astronauts have to bring up all the water they'll need for their entire stay in space. So if we could just mine our water from asteroids, that would be *way* better.

There are also S-type asteroids, which are made of rocky minerals and some metals, and M-type, which have a -

- which have a bunch of metals. Since they're both denser than C-type asteroids, they'd be more difficult to mine. But more important than precious metals, they hold materials we need to build machinery or tools in space. Iron, nickel, cobalt, and silicon can make semiconductors and glass, and platinum-group metals can make ultra-conductive parts that won't corrode. Try to imagine anything cooler than putting a 3D printer in space, filling up its cartridges with materials mined from asteroids, and printing out pieces of a space station.

So, what's stopping us? Why is Babylon 5 not already a thing? Well, the first thing we need to do is survey the asteroids. To do that, we need telescopes. Lots of telescopes, like, hundreds of them, that we can send out to look at our NEOs and tell us what we can find inside of them. And simple optical telescopes aren't good enough; we need spectrometers, which are special instruments that can tell us what elements are present in a sample by looking at how they reflect light and heat. Ideally, these telescopes would be able to latch onto an asteroid's surface and do a chemical analysis on the spot. We *do* have the technology to do that now.

Curiosity, the Mars rover, has an onboard lab called the "ChemCam" for analyzing the composition of Martian soil, but the ChemCam was expensive to build and get to Mars, and it's one of a kind. Mass producing hundreds of spectrographic chemistry labs/ telescopes and *then* sending them up into space...? It's not something we know how to do in a cost-efficient way. 

There *are* people working on those instruments though. Two American companies - Planetary Resources and Deep Space Industries - are looking to crack into the asteroid-mining business. The country of Luxembourg wants in on the asteroid boom, too. It's offered to 200 million Euro line of credit to any asteroid mining company that wants to set up headquarters inside it's border, and NASA is launching a mission in September 2016 to send a spectrometer-equipped, sample-collecting space lab to a nearby C-type asteroid. 

This is the OSIRIS-REx Mission, and one of its goals is to tell us how accurate spectrometers are. The OSIRIS-REx spacecraft will measure a bunch of stuff, including the materials on the surface of the asteroid, then collect a sample to send back to Earth. If the spectrometers -

If the spectrometers say that there are compounds in the asteroid clay that aren't actually there, then we'll need to figure out how to improve our technology. But if the instruments turn out to be right, we're in business. 

Once we know how to find asteroids and figure out what's *inside* them, we can start thinking about ways to mine those materials and use them for our space technologies. If asteroid mining pans out, especially if we have more water in space for drinking, refueling, and radiation protection, the frontier of the solar system will really start to open up. And space stations, lunar colonies, and Mars settlements start to sound like something that could happen in our lifetime.

[slide]

Turns out asteroid innards have a lot of potential uses: from rocket fuel to construction materials. So, great! Let's chart a course to the asteroid belt and snag a few. But as Caitlin will tell you, that might not be as simple as you think.

[slide: "The Asteroid Belt: Not What You Think!"]

Caitlin: It's one of the most fascinating areas of the solar system, and it's also probably the one that's most often portrayed inaccurately in media. The asteroid belt is usually depicted as a perilous obstacle course of flying rocks. Even in the Cosmos reboot, Neil deGrasse Tyson is shown darting around it in a spaceship of the imagination like he's steering the Millenium Falcon through the Hoth asteroid field. But it turns out that if you're in the asteroid belt, it's easier to fly through safely than it is to actually find an asteroid.

Located between the orbits of Mars and Jupiter the belt covers an *enormous* region - about two to three times the size of the Earth's distance from the Sun; that's around 50 *trillion* cubic kilometers. And while most of that is empty space, it does contain *trillions* of space rocks ranging in sizes from bits of dust to a quarter the size of our moon. And together, they have perplexed astronomers for centuries.

So, where did the asteroid belt come from? Astronomers used to think that it held the remnants of a planet that was destroyed by a comet or a collision with some other protoplanet in the earliest days of the solar system's formation. But it turns out that there's not enough mass in the asteroid belt to account for even a small terrestrial planet. So far, we've only found four objects in it that are more than 400 km in diameter: the asteroids Vesta, Pallas, Hygiea, plus the dwarf planet, Ceres. Together, those four objects contain more than *half* of the total mass of the asteroid belt, with Ceres -

- accounting for most of that. 

There are also too many chemical differences among the asteroids for them to have originated from a single object. Most of them are composed of rocky minerals, for example, while a few contain mostly metals like iron and nickel. So more than likely, the asteroids are remnants of the solar system's formation 4.5 billion years ago.

As our System's giant disk of gas and dust slowly accreted into larger and larger particles, eventually forming planets, some swaths of the material weren't able to collect into anything. In the asteroid belt's case, the enormous gravitational pull of Jupiter likely prevented those particles from coalescing into even a small planet. And they're not the only leftovers we've found from those early days; the asteroid belt is sometimes referred to as the "main belt" to distinguish it from the Kuiper belt - that's the big band of debris out past Neptune where Pluto and other dwarf planets hang out, and is thought to have similar primordial origins.

To learn more about the messages of the solar system's birth still floating around in the main belt, NASA has sent the Dawn spacecraft to investigate. In 2011, Dawn orbited Vesta, where it mapped the giant asteroid's entire surface and found that it's more geologically complex than we thought originally. With a crust, mantle, and an iron core - more like a protoplanet than just a chunk of rock. And now, Dawn has moved to Ceres, the largest object between Mars and Jupiter, which has already been found to have water ice on its surface and even a thin atmosphere. It'll take up orbit there in 2015.

And, by the way, Dawn joins more than a dozen other spacecraft that have navigated safely through the asteroid belt, in case you needed any more proof that it wasn't just some celestial minefield. Pioneer 10 became the first to make its way through in 1972, with no laser cannons needed.

[slide]

Reid: Despite the relatively sparse presence of asteroids in the belt, we have successfully traveled there to explore some awesome asteroids. Here's Hank to describe what we found inside one of the biggest asteroids in the belt. And...a dwarf planet, while we're at it.

[slide: "What We've Learned From the Dawn Mission So Far"]

Hank: We spend a lot of time visiting other planets and moons, but other places in the solar system can teach us plenty about the history of our neighborhood.

So in 2007, NASA launched the Dawn spacecraft to investigate the two largest objects in the asteroid belt between Mars and Jupiter - a giant asteroid called "Vesta" and an icy dwarf planet -

- named "Ceres." Dawn was the first mission to orbit something in the asteroid belt and the first to orbit two bodies besides Earth. The mission was supposed to end a year ago, but NASA voted to keep it going, and today marks the one-year anniversary of Dawn's extended mission.

In the last decade, Dawn has taught us a lot more about Vesta and Ceres than we expected, and there's still way more discoveries on the way. Vesta and Ceres were selected as targets because they're so different from each other; Vesta is dense and rocky like the planets closer to the sun, but Ceres is icy like the smaller worlds in the outer solar system. So visiting both of them was like getting double the science in one mission.

First, Dawn traveled to 2.8 billion km to get to Vesta, where it arrived in 2011. Before Dawn, we already knew a little bit about the asteroid - thanks to the Hubble Space Telescope - like, that it has a massive crater on it's south pole. The crater is almost as wide as the asteroid itself; if Earth had a crater that big relative to its size, it would fill the entire Pacific Ocean basin. The crater also has a huge mountain on the edge, which Dawn eventually confirmed is about 22 km higher than the surrounding terrain. That makes it almost 3x taller than Mount Everest and one of the tallest mountains in the entire solar system.

But besides taking some sweet pictures of the crater, one of Dawn's biggest accomplishments at Vesta was confirming a hypothesis we had that some meteorites we found on Earth came from Vesta. Vesta is unusual for an asteroid because it's a lot like a mini planet. It has a liquid metal core, a mantle, and crust made out of lava, which we were able to figure out using instruments like Hubble. We haven't really seen an asteroid like that anywhere else in the solar system.

About 6% of the meteorites we've collected on Earth look a lot like they could be from those unique, different layers of Vesta, and we call them "HEAD" meteorites, or "Howardite, Eucrite, and Diogenite" meteorites. Based on the composition, eucrites could have come from the hardened lava on Vesta's surface, diogenites could have come from the inside of the asteroid, and howardites look like a mix of the two, which could have happened when Vesta's crater was formed. And Dawn -

And Dawn pretty much confirmed that was right. Using its different spectrometers, Dawn confirmed the data we'd measured from father away was correct. And Vesta is probably responsible for a while class of meteorites all by itself, which is a pretty big accomplishment for one asteroid. After 14 months at Vesta, Dawn packed up its bags and started a 1.5 billion km, almost three-year journey to the dwarf planet, Ceres, where it arrived in 2015, and it's been there ever since.

As we were approaching Ceres, one of the first things we noticed were these bright spots, like, big, shiny reflectors stuck all over the surface. These spots were a huge mystery for a while. Were they water, ice, clay, salt, aliens? After analyzing how these spots absorbed light, astronomers concluded that they were probably magnesium sulfate, or as we call it here on Earth, "Epsom salt." So you can think of Ceres the next time you're preparing to drink an Epsom salt laxative.

The salt deposits were probably created when asteroids smashed into Ceres' surface, exposing the salt-filled ice that was hidden beneath. Then, the exposed ice turned into a vapor, and the salt deposits were left behind. We suspected from previous research that Ceres had a lot of water ice, but Dawn helped confirm that during its other observations. And the ice seems like it's everywhere, even if it's hiding underneath the surface.

But this February, Dawn found something that we didn't expect - organic molecules, which are the building-blocks of life. Although it couldn't detect exactly what the molecules were, the spacecraft observed tar-like compounds made of carbon and hydrogen on Ceres' surface in an area about 1,000 square kilometers. Because the concentration of molecules is so high, it seems unlikely that the molecules came from an outside source, like an asteroid impact, since the impact usually scatters molecules all over the place. Instead, they probably formed from water and heat-based chemical reactions on Ceres, which could mean it used to have a warm, watery environment.

We might investigate that more in the future, but for now, Dawn's main job in its extended mission is to give us a clearer picture of Ceres' surface and composition. When cosmic rays from the Sun hit Ceres, they create -

- they create radiation and neutrons that Dawn can use to identify the different molecules on and even underneath the surface. Dawn did a lot of this during its mission, but since we got some extra time, we're hoping to get the clearest data we can. The mission will officially end when Dawn runs out of fuel, which could happen around the end of 2018. After that, it'll probably just keep orbiting around Ceres like a permanent little travel buddy.

[slide]

Reid: So we can learn a lot just from orbiting asteroids, but we can get an even better idea of what's inside by sampling them. That's what Hayabusa did in the first ever asteroid-sampling mission.

[slide: "Hayabusa: The Artificial Meteor Launched From an Asteroid"]

The moon landings brought back samples of an extraterrestrial body, but it would be 36 years before we could land on anything else and bring bits of it home. The goal was to bring home a new kind of sample, one that might date back to the birth of our solar system and teach us a thing or two about early days on Earth. For this mission, the Japanese team set their sights on the asteroid Itokawa, and the spacecraft given this task was named Hayabusa. It had a pretty rocky time, but ultimately, it was a huge success despite the setbacks.

Normally for the chance to study asteroids, we have to let them come to us, but in 2003, the Institute of Space and Astronautical Science - the predecessor to the Japanese space agency, JAXA - said, "Why wait?" and planned the complicated trip for a probe to intercept Itokawa. The asteroid was named after one of the fathers of Japanese rocket development, Dr. Hideo Itokawa. And Hayabusa, whose name means "falcon" in Japanese, was designed to fly up to that asteroid, touch down, collect samples, and bring them back home.

But it didn't have to make that journey alone; Hayabusa traveled with a mini-lander on board, MINERVA, which had its own goals to image Itokawa and take readings of its temperature. While MINERVA's work would happen only once it reached Itokawa, Hayabusa would pioneer new technology -

- to get there in the first place and land safely, like autonomous navigation and electrical propulsion.

And being the first mission to bring back asteroid samples, not all of these new technologies worked perfectly. In its first year of travel, Hayabusa encountered a solar flare that degraded its solar panels. That meant Hayabusa's ion engines didn't have the power they were anticipated to have. All in all, it was a bump in the road, but nothing that Hayabusa couldn't handle. Because two years after its launch, Hayabusa made it to the Itokawa asteroid only a few months delayed.

Then came the landing. Or, multiple landings. On November 4th, 2005, Hayabusa initiated its landing protocol and was nearing touchdown, until its sensors detected some kind of interference above the asteroid surface. It's not clear what it was, so rather than risking a crash into an unexpected object, Hayabusa aborted its first attempted landing.

One week after the first try, Hayabusa made it far enough along the landing protocol to launch Minerva. But MINERVA never made it. Hayabusa launched MINERVA a little too far from Itokawa's surface, and right after the deployment, Hayabusa automatically ascended away from the asteroid, so neither of the robots touched Itokawa on that attempt.

Hayabusa still hadn't landed on Itokawa, until the lucky third try one week after saying goodbye to MINERVA. In what was becoming the true Hayabusa fashion, the landing was technically a success because it landed on the asteroid, but it still didn't go as planned. Hayabusa lost contact with the team on Earth during touchdown, and when the spacecraft came back online, they realized that it had bounced twice and ended up 30 meters off target. Don't get me wrong: This was a huge success as the first ever controlled landing on an asteroid, but it didn't hit the target it needed to, so the landing was promptly followed by the first ever *ascent* from an asteroid 28 minutes after landing.

Now, some explorers -

- would've had to make do with the previous attempt, but Hayabusa was prepared to try again. This spacecraft had several fuel options to pull from, so the solar panel issue didn't completely drain the onboard fuel reserves required for another landing on Itokawa.

Finally - six days later on November 25th, attempt number four - Hayabusa landed and fired two sampling bullets into the asteroid. Those bullets collected samples totalling less than one gram and held them in the reentry capsule. After all that trial and error, Hayabusa finally had what it came for. But that tiny capsule of precious dust still had to make it back to Earth.

By 2010, Hayabusa had returned and ejected the reentry capsule to parachute down to Austrailia. When it did, scientists analyzed it to find that Itokawa was less dense than they thought, with porous insides. They even found evidence was water in the minerals that made up the return samples. That's a far cry from liquid water, but it supports the idea that impacts from similar objects could've been the source for up to half of Earth's water.

But Hayabusa itself would only get so close to those sweet shores of home. See, Hayabusa was never intended to return in one piece; it had a bigger, brighter destiny - it was an opportunity to create an artificial meteor. When meteors reach our atmosphere, we don't have any way of knowing what they're made of; we just see something burning up before our eyes. So, researchers took the opportunity to observe the light given off an object with a known composition. They knew Hayabusa's size, its weight, and what it was made of, so they watched it burn for science.

They observed Hayabusa as it hit the atmosphere and broke up into fragments. Each fragment was accompanied by a large burst of light. But the fragments didn't each lead to one burst of light alone; instead, they each produced an additional ghost light that was smaller, dimmer, and farther away from the pieces of Hayabusa themselves.

And that will help scientists understand what it looks like when other objects break up, too. So, Hayabusa got to go out in a blaze of glory, and even it's final moments had something to tell us.

[slide]

Hayabusa had some surprises under the surface, but this next asteroid's surprises threw a real wrench into the whole sampling process. Savannah is going to tell us why OSIRIS-REx almost didn't make it home.

[slide: "The Asteroid That Nearly Swallowed OSIRIS-REx"]

Savannah: There's something about a giant ball pit that strikes fear in the hearts of children and maybe some adults, that you'll jump in, sink to the bottom, and never be seen or heard from again. The fear of ball pits may be unfounded here on Earth, but out in space, it turns out it's kind of justified, because we could've lost a spacecraft when it tried to touch an asteroid.

Bennu - or 101955 Bennu, if you're fancy - is a rubble pile asteroid usually found somewhere between the orbits of Earth and Mars. The term "rubble pile" is used for asteroids like Bennu which are built up from individual chunks of rocks, but there isn't enough mass or gravitational attraction to fuse them into one solid rocky body. Scientists hypothesized that between 700 million and 2 billion years ago, a larger asteroid was smashed into bits after colliding with another space rock, and some of those bits later reformed as Bennu. But the raw materials, the basic minerals inside of Bennu, are *way* older, forming just 10 million years into our solar system's life. It's a cosmic time capsule astronomers can study to learn about our origins, which started over four and a half billion years ago.

So back in 2016, humanity sent the spacecraft OSIRIS-REx not just to visit Bennu, but to bring samples back to Earth for analysis. OSIRIS-REx arrived in 2018, collecting data in orbit for a couple years. Then, on October 20th, 2020, it descended upon a site dubbed "Nightingale." The probe was supposed to touch the solid surface of Bennu for several seconds and release a burst of nitrogen gas to kick up a small collection of pebbles and dust into its sample collector.

The mission was called a "touch and go," or TAG, but the real "touch" was more like a "sink," almost 50 centimeters beneath the surface. And the "go" part was a little more dramatic, too, because the probe ended up leaving not a delicate footprint, but a crater eight to nine meters wide. 

While the sample collection was a success, the weird results demanded a follow-up. The mission team ordered an extra flyby to snap photos of the TAG site to collect more data, and the data revealed that the rocks on and just under Bennu's surface have near zero cohesion - the force that helps things like water or flour grains stick together. That means that Bennu's surface rocks are held together solely by their very, very weak mutual gravitational pull. That explains why OSIRIS-REx's departure made such a large crater; the rocks were way more susceptible to being flung away by the oomph of OSIRIS-REx's thrusters.

Before the TAG, scientists knew Bennu's surface wouldn't have a whole lot of cohesion, at least compared to other rocky bodies in the solar system. But based on the asteroid's overall shape, they expected there to be *some.* And the fine particles that scientists expected to be in Bennu's near-subsurface weren't there; they had either sunk deeper into Bennu's interior or been flung off into space.

So instead of rocks and dust working together to form a solid surface, the individual rocks just jostled around, sliding over one another when they got disturbed, like molecules of a liquid. Or like balls in a ball pit. According to the accelerometers on board, the spacecraft kept sinking throughout its sample collection, so if OSIRIS-REx hadn't fired its thrusters to back off when it did, it would've tumbled down into Bennu's cosmic ball pit, and been lost to us. The unexpected lack of cohesion is probably not just localized to Nightingale, and it may apply to other rubble pile asteroids out there, too. So, pinning down how these rubble pile asteroids actually work is going to be important for future missions, whether it's to touch down on their surface again, or to stop one from colliding with Earth.

OSIRIS-REx, meanwhile, is currently on its way back to Earth, -

- and in 2023, is scheduled to deliver its precious cargo: some of the oldest minerals in the solar system. Then, it'll move on to its next target, the asteroid Apophis. But it's just a flyby, so any fear of ball pits will have to wait for the next spacecraft.

[slide]

Reid: The more explore asteroids, the better we'll get at it. Each of these missions has taught us more about what we can expect next time, and how can actually benefit from these space rocks. So there's a lot more to asteroids than just...Armageddon.

Thanks for watching this SciShow compilation. If you love space content, you might be interested in our SciShow pin-of-the-month. Every month in 2023, we're highlighting a different rocket. May's pin features Nell, the first liquid-fueled rocket ever launched. You can watch the story of that rocket on SciShow and get your Nell pin at dftba.com/scishow.

[outro]