cast iron skillet full of Brussels sprout halves and bits of bacon sits on a wooden surface

What happens when you season a cast iron pan

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<p>Ahh, cast iron pans. Love ‘em or hate ‘em, they’ve been around for hundreds of years. With proper maintenance, they can last long enough to become family heirlooms. A cornerstone of this pan’s upkeep is seasoning, the process of baking oil onto the pan. Contrary to the name, you won’t need salt and pepper, but fat. </p><p>To season, you heat the pan covered in fat to scalding temperatures in an oven. What is left behind is a somewhat nonstick surface that not only helps with cooking but <a href="https://www.youtube.com/watch?v=8uaoCPxJa3Q&amp;list=PLnNZYWyBGJ1G82dSY0lEGClN4Ma3oTkWm&amp;index=4">protects the pan from rust</a>.</p><p>You can use the fat of your choice, but one thing to keep in mind is the smoke point, the temperature at which it starts to smoke. That temperature varies from oil to oil. For example, virgin avocado oil has a smoke point of 520 F, but coconut oil smokes at just 350 F. As soon as that temperature is reached, the seasoning process begins. </p><p>There are multiple hypotheses about what’s happening at the molecular level inside that hot oven. The predominant one is that the oil is polymerizing. Fats are made up of different fatty acids, like saturated and unsaturated. When heated, those acids break down into smaller molecules called monomers. And when monomers join together, they form larger molecules <a href="https://www.pbs.org/wgbh/nova/video/beyond-the-elements-indestructible/">called polymers</a>. When this joining happens over and over in an iron skillet, the polymers form a protective layer that keeps water at bay. </p>
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<p>A group of researchers from Chongqing University <a href="https://www.sciencedirect.com/science/article/pii/S2589965120300416">studied this phenomenon</a> in the context of another cast iron cooking tool: the wok. Woks, mainly used in Chinese-style cuisine, are usually round-bottomed. The team hypothesized that the slick surface formed during seasoning is due more to the iron than the oil. To test their hypothesis, the researchers coated a wok with beef tallow and heated it up. As the temperature increased, the fat started to reduce. And the scientists, using X-ray technology, started to see oxygen molecules sneaking into the places where iron was present. With this unexpected guest, iron atoms had to shuffle around to make space, creating small lumps along the surface. The final product is what the team called “iron nanoballs.” </p><p>They point out that these nanoballs didn’t make the wok completely nonstick, but rather made the surface conditionally hydrophobic. That means that it repels water when there isn’t much around, but gets wet when there’s a lot of it. The study authors claim this property comes in handy during cooking, because if the pans are <a href="https://www.pbs.org/wgbh/nova/article/pfas-synthetic-chemicals-water-toxic/">completely nonstick</a>, the fat will lump together, causing uneven cooking. If the surface can get wet, it creates an even layer, and the food can cook evenly as the water evaporates, creating less charring.</p>
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<p data-block-key="lvieb">Here is how oil and heat can form a durable coating.</p>

About a dozen thin, crispy homemade potato chips in a black metal air fryer basket

Homemade potato chips in an air fryer. Image Credit: Ali Majdfar, Getty Images

How air fryers work, scientifically speaking

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<p>In recent years, air fryers have exploded in popularity thanks to their promise: You can make crispy, fried food with little to no oil. But what’s really happening inside those countertop machines?  </p><p>Frying generally refers to the process of cooking food in some amount of oil. When you heat up oil in a pan, the “strings” that form are a telltale sign of <a href="https://www.pbs.org/wgbh/nova/video/secrets-of-the-sun/">convection</a>, or “movement of fluid due to temperature and density differences,” says Kevin Keener, an engineer at the University of Guelph who studies thermal food processing methods. As the oil swirls, it slips through the food’s crevices, transferring heat. The temperature of the food rises to the point that the water inside it boils, causing dehydration, a key step in achieving crispiness.</p><p>Air fryers emulate this process with air rather than oil. A fan situated above the food tray (near the heating element) blows hot air around the small chamber, accelerating convection and increasing the amount of heat that gets transferred to the food. This transfer is called heat flux: the amount of energy in a unit of area and time. The heat flux of convection that occurs naturally in a traditional oven might peak at 50 to 100 watts per square meter, Keener says. But adding a fan, like that of an air fryer, could increase the heat flux to a few hundred, or even a few thousand watts per meter, he says.</p>
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<p>In a sense, both deep-frying and air frying work through convection, but with different fluids: oil and air. And that’s a key difference, Keener says. The heat flux of deep-frying is around 30,000 watts per square meter, whereas with hot air, the best you might get are values in the range of 5,000 watts per square meter. That’s because an air fryer can’t go above 450 or 500 F for safety reasons, so the heat flux is capped. This, in turn, affects how crispy your food can get. </p><p>“Crispiness is directly correlated to heat flux value. Higher heat flux, the crispier it’s going to get,” Keener says.</p><p>Although an air fryer’s heat flux and crisping effect don’t match that of deep-frying, that particular quality may be less important to home cooks for some foods, like a steak, Keener says. “You would still want to be at 5,000, but you don't necessarily need to be at 30,000,” he says. “Because people don't generally eat steak because of the crispiness.” </p>
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A small spacecraft with outstretched solar panels approaches two large rocks

llustration of NASA’s DART spacecraft and the Italian Space Agency’s  LICIACube prior to impact at the Didymos binary system. Image Credit: NASA/Johns Hopkins APL/Steve Gribben

DART spacecraft slams into asteroid

<p>Tonight, around 6.8 million miles away from Earth, NASA slammed a spacecraft into an asteroid in a bid to change the rock’s trajectory. This is the agency’s first test of a technology designed to defend Earth against <a href="/wgbh/nova/article/asteroid-dust-ice-age/">asteroids or comets</a> that might one day threaten to collide with our planet. </p>
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<p>“Humans: one, asteroids: zero!” declared NASA communications strategist Tahira Allen amid celebration and cheering at Johns Hopkins University's Applied Physics Laboratory, over a NASA livestream.</p><p>From “Armageddon” to “Don’t Look Up,” Hollywood has long imagined how scientists could redirect an asteroid headed toward Earth. With lower stakes, NASA is testing its own theory with the <a href="https://www.pbs.org/wgbh/nova/video/can-humans-deflect-asteroid/">Double Asteroid Redirection Test (DART)</a>. The mission launched <a href="https://www.pbs.org/wgbh/nova/article/nasa-dart-deflect-hazardous-asteroid-didymos/">10 months ago</a>, carrying with it an autonomous guiding system called SMART Nav to help it maneuver and target an asteroid. </p><p>For the test, scientists chose Dimorphos, a 525-foot asteroid “moonlet” that circles a larger asteroid called Didymos. "We needed something with a moon that was small enough that we could move it with a strike from a spacecraft, but not so small that we would wreck the moon,” Andy Rivki, a scientist working on the DART mission said in a livestream leading up to the impact. (Neither Dimorphos nor Didymos poses any threat to Earth) </p>
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<p>The spacecraft itself had a camera that transmitted its approach live. As it blazed toward Dimorphos at 4 miles per second, the asteroid grew from a tiny white dot in the video feed to a detailed view of gray rocks and rubble that filled the screen. And then: nothing.</p><p>“We’ve made impact!” DART mission members shouted as the room erupted into cheers. </p><p>“Now is when the science starts,” said Lori Glaze, director of NASA's planetary science division, after the impact. It will be days before scientists can calculate if, and by how much, the asteroid’s trajectory was altered. As Dimorphos circles around, telescopes on Earth can help capture variation in its orbit, and hence, the success of the mission.</p><p>In the next 100 years, a scenario like the one in “Armageddon” is highly unlikely. But DART may be proof that if Earth were to be <a href="/wgbh/nova/video/day-the-dinosaurs-died/">threatened by an asteroid</a>, humans could do something about it. “We are embarking on a new era of humankind, an era in which we potentially have the capability to protect ourself from something like a dangerous, hazardous asteroid impact,” Glaze said.</p><p><i>Correction: An earlier version of this article attributed quotes from Lori Glaze to Laurie Leshin.</i></p>
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<p data-block-key="vqnhb">The mission is a test to see if NASA could knock an Earth-bound asteroid off its path, should we ever need to.</p>

A bright orange vertical flame and billows of steam against a black night sky

The Artemis I flight test mission begins as NASA’s Space Launch System rocket, carrying the Orion spacecraft, launches from Florida's Kennedy Space Center. Image Credit: NASA/Keegan Barber

NASA’s Artemis I moon rocket finally launches

<p>After months of delays, fuel leaks, and hurricanes, NASA launched the world’s most powerful rocket from Kennedy Space Center just before 2 a.m. This uncrewed mission, dubbed Artemis I, is designed to test the massive rocket and technologies aboard the new Orion spacecraft.</p>
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<p>“We rise together, back to the Moon and beyond,” said NASA launch commentator Derrol Nail as the rocket lifted off.</p><p>Minutes after launch, the rocket boosters and <a href="/wgbh/nova/video/how-do-you-get-a-rocket-to-land-back-on-earth/">core stage fell away</a>, and Orion continued on what will be a 25-day mission around the Moon and back. The spacecraft will travel roughly 1.3 million miles, at one point coming within 62 miles of the lunar surface, and splash down in the Pacific Ocean on December 11. </p><p>Artemis I is the first mission in the Artemis program, which aims to put <a href="/wgbh/nova/video/back-to-the-moon/">a crew on the Moon</a>, including the first woman and person of color, and pave the way for eventual <a href="/wgbh/nova/video/the-planets-mars/">exploration of Mars</a>.</p><p>To launch the Orion spacecraft, including a crew and payload in a single trip to the Moon, NASA and its collaborators designed the Space Launch System rocket. This SLS core stage alone stands 212 feet tall. In this first configuration, the rocket can produce 8.8 million pounds of thrust.</p><p>The mission will also test Orion’s large heat shield. NASA estimates that upon reentry the spacecraft will experience temperatures as high as 5,000 F, half as hot as the surface of the Sun.</p>
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<p>"The heat shield actually has to withstand the fastest and hottest reentry we’ve ever seen in human spaceflight,” NASA astronaut Kayla Barron said in a pre-launch broadcast.</p><p>When Orion splashes down, the heat shield tiles will absorb seawater, and engineers will need to change them out for the next mission. </p><p>Orion is also equipped to test radiation exposure, one of the hazards Artemis crews will face on future missions. Orion’s sensors will measure radiation as the craft transits to and from the Moon. The spacecraft is carrying mannequins dressed in radiation protection vests, and upon its return, scientists will measure the vests’ radiation damage to better understand what Artemis crews will need to endure. </p><p>The next mission is Artemis II, which currently aims to send four astronauts to the Moon in 2024, more than 50 years after the <a href="/wgbh/nova/video/apollos-daring-mission/">Apollo program</a> ended.</p><p>“Artemis is different than Apollo because we are returning to the Moon, but this time we are going to stay,” Barron said.</p>
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<p data-block-key="fzq82">NASA’s massive SLS rocket and Orion spacecraft kick off a series of missions to put humans back on the Moon.</p>

Silhouette of a spacecraft with panels extended against giant white moon, with Earth off in the distant night sky

An artist rendering of NASA's Orion spacecraft doing a lunar flyby during the Artemis 1 mission. Image credit: NASA/Liam Yanulis, Flickr

5 reasons why humans are going back to the Moon

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<p>Fifty years after the last <a href="/wgbh/nova/video/how-nasas-apollo-8-left-earths-orbit/">Apollo mission</a>, NASA is embarking on a new age of lunar exploration. With the <a href="https://www.pbs.org/wgbh/nova/article/artemis-launch-nasa-sls-orion-moon/">launch of Artemis 1</a>, the agency has begun testing technologies designed for this era, including the massive SLS moon rocket and the Orion spacecraft, which will carry crews on future missions. But why go back at all? NOVA’s “<a href="https://www.pbs.org/wgbh/nova/video/back-to-the-moon/">Back to the Moon</a>” explores five reasons scientists and entrepreneurs alike have their sights set on the Moon once again:</p><h3><b>To study its water </b></h3><p>Water is essential for life on Earth and a critical ingredient for outer space exploration. The Moon would be an ideal space pitstop to gather this resource, but for a long time it was unclear whether it had water at all. After researchers analyzed lunar samples from the Apollo mission, they concluded that the Earth and the Moon are formed from the same materials. This hypothesis raised an intriguing possibility: Might the Moon also have once been wet?</p>
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<h3><b>The Moon is a record of solar system history (5:20 - 7:45)</b></h3><p>The Moon preserves a complete geologic record that dates back nearly to the formation of the solar system. NASA’s moon-mapping spacecraft, the Lunar Reconnaissance Orbiter, has been orbiting the Moon since 2009. It was designed to gather new insight into the Moon’s geological record and scout the surface for future human exploration. </p>
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<h3><b>To harness resources to build lunar bases (7:45 - 11:23)</b></h3><p>After scientists uncovered the Moon’s mineral wealth, some suggested it could be harnessed to build bases on the Moon. Hauling materials from Earth to build on the Moon could cost billions of dollars. But if the raw materials are already available in space, then all kinds of construction activities become conceivable.</p>
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<h3><b>Lunar ice could be a fuel source (29:03 - 32:15)</b></h3><p>Water is made up of hydrogen and oxygen, and if those two atoms can be separated and stored, they can fuel a rocket. That’s because hydrogen and oxygen are highly flammable, and when they are burned together, they release a huge amount of energy–enough to propel a rocket. That means that, at least in theory, lunar ice could provide water to drink, air to breathe, and a source of propellant for spaceships to fuel up and head out.</p>
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<h3><b>Lava tubes could be lunar shelter (46:12 - 49:03)</b></h3><p>To live on the Moon, humans will need to shield themselves from radiation coming from the Sun and deep space. One way to do this might be to live <i>in</i> the Moon, inside lava tubes that formed billions of years ago. Scientists have yet to discover what’s inside them, but similar tubes on Earth might offer clues. </p>
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<p data-block-key="r5y64">Earth’s natural satellite could be a jumping-off point for future space exploration.</p>

Looking down on a black 4-burner induction cooktop with a boiling pot of pasta. A hand pushes a button; raw shrimp and vegetables sit on either side of the stove.

A pot of pasta boils on an induction cooktop. Image Credit: Juan Algar, Getty Images

How do induction stoves work?

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<p>Some 110 million U.S. households use a range–or cooktop and oven–for cooking. About <a href="https://www.eia.gov/consumption/residential/data/2020/hc/pdf/HC%203.1.pdf">two-thirds of those</a> are powered by electricity, while one-third use natural gas or other fuels. But of the electric-powered majority, only a tiny percentage use what’s called induction. Though induction stoves might look like other electric stovetops, there’s some fascinating science that sets them apart from both gas and traditional electric stoves. </p><p>In a gas stove, natural gas or another fuel like propane is ignited to create a flame that can quickly be turned to the desired level. Electric ranges, on the other hand, come in a variety of styles, but all rely on a heating coil. Once the power is turned on, alternating current sends a rush of electrons around the coil. But the electrons aren’t on a slip-n-slide: The coil itself is designed to resist the electron flow, priming the particles to release their energy as heat. This process of building up the heat means it takes longer for an electric burner to reach the desired temperature than an instantly adjustable gas burner.</p><p>At a glance, induction cooktops may resemble traditional electric ones—both can have smooth, glass tops with coils powered by electricity. But induction cooktops use electricity in a slightly different way to heat up your pans.</p>
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<p>In contrast to traditional electric stoves, the coil inside an induction cooktop does not itself generate heat. In fact, the coil is designed with metals that conduct electricity rather than resist it. As the alternating current flows from the power socket into the metal coil, it forms a magnetic field. This magnetic field can interact with ferromagnetic materials, like the iron in a <a href="https://www.pbs.org/wgbh/nova/article/season-cast-iron-skillet-polymerization/">cast iron skillet</a> or the alloys in a stainless steel pan, to create small currents in those metals. The pan itself then acts like a traditional heating coil, resisting those currents and causing the electrons to release their energy as heat.</p><p>This method of heating is possible because ferromagnetic materials have magnetic domains, or groups of atoms that are aligned in such a way that they can be collectively influenced by a magnetic field. This is why induction stovetops only work with pots and pans made of magnetic materials—and they won't directly heat up other things, like aluminum pans or the skin on your hand.</p><p>Like a gas stove, an induction stove can be adjusted up and down immediately, heating food quickly and efficiently. According to <a href="https://www.energystar.gov/about/2021_residential_induction_cooking_tops#:~:text=The%20per%20unit%20efficiency%20of,times%20more%20efficient%20than%20gas">Energy Star</a>, roughly about 85% of the electricity consumed by induction stovetops actually goes toward heating your food. By contrast, traditional electric stoves have an efficiency of 75-80%, and gas stoves are 32% efficient.</p>
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<p data-block-key="o5d6c">Here’s how a magnetic field can heat up your pans.</p>

A large sphere with varied blue and white bands fills most of the frame, with sections of its golden rings visible on either side

A false-color image of Saturn based on near-infrared data from the Cassini spacecraft, which orbited the planet for 13 years. Image Credit: NASA/JPL-Caltech/SSI/CICLOPS/Kevin M. Gill

8 Mind-Blowing Space Documentaries to Watch Now on NOVA

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<p>For almost 50 years, NOVA has explored the cosmos, taking viewers across our solar system, into distant galaxies, and right up to the “edge” of a black hole. From a Mars rover swooping down to the red planet, to a probe’s daring encounter with an asteroid, we’ve followed NASA and other space missions as they’ve revealed the universe to humanity. Now we present a curated selection of space documentaries from the past five years so you can explore the universe alongside the scientists who make the journey possible.</p>
<h3>New Eye on the Universe (2023)</h3><p>In July 2022, NASA’s James Webb Space Telescope released its first images, looking further back in time than ever before to show our universe in <a href="/wgbh/nova/video/how-nasa-colors-images-of-the-universe/">stunningly beautiful detail</a>. But that was just the beginning: With tons of new data and spectacular images flooding in, Webb is allowing scientists to peer deep in time to try to answer some of astronomy’s biggest questions. When—and how—did the first stars and galaxies form? And can we see the fingerprints of life in the atmospheres of distant worlds–or even within our own solar system?</p>
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<h3><a href="https://www.pbs.org/wgbh/nova/video/star-chasers-of-senegal/"><b>Star Chasers of Senegal</b></a><b> (2023)</b></h3><p>A NASA spacecraft named <a href="/wgbh/nova/article/nasa-lucy-mission-trojan-asteroids/">Lucy blasts off</a> from Cape Canaveral on a mission to the Trojans, a group of asteroids over 400 million miles from Earth thought to hold important clues about the origins of our solar system. Just hours before, in Senegal, West Africa, a team of scientists sets out to capture extraordinarily precise observations vital to the success of the Lucy mission—crucial data needed to help NASA navigate Lucy to its asteroid targets across millions of miles of space. The team’s leader, Senegalese astronomer Maram Kaire, takes viewers on a journey to investigate his nation’s rich and <a href="/wgbh/nova/video/how-to-calculate-time-with-an-islamic-astrolabe/">deep history of astronomy</a>, reaching back <a href="/wgbh/nova/video/these-ancient-stones-helped-track-seasons/">thousands of years</a>—and the promising future ahead.</p>
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<h3>Ultimate Space Telescope (2022)</h3><p>How did NASA engineers build and launch the most ambitious telescope of all time? Follow the dramatic story of the James Webb Space Telescope—the most complex machine ever launched into space. If it works, scientists believe that this new eye on the universe will <a href="/wgbh/nova/video/nasa-reacts-to-the-james-webb-space-telescope-images/">peer deeper back in time and space</a> than ever before to the birth of galaxies, and may even be able to “sniff” the atmospheres of exoplanets as we search for signs of life beyond Earth. But getting it to work is no easy task. The telescope is far bigger than its predecessor, the famous <a href="/wgbh/nova/article/hubble-space-telescope-best-images/">Hubble Space Telescope</a>, and it needs to make its observations a million miles away from Earth—so there will be no chance to go out and fix it. That means there’s no room for error; the most ambitious telescope ever built needs to work perfectly. Meet the engineers making it happen and join them on their high stakes journey to uncover new secrets of the universe. </p>
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<h3><a href="https://www.pbs.org/wgbh/nova/video/nova-universe-revealed-alien-worlds/"><b>NOVA Universe Revealed: Alien Worlds</b></a><b> (2021)</b></h3><p>In the five-part series <a href="https://www.pbs.org/wgbh/nova/series/nova-universe-revealed/">NOVA Universe Revealed</a>, we delve into the vastness of space to capture moments of high drama when the universe changed forever. In this episode, we tackle an age-old question: Are we alone? Or do other lifeforms and intelligences thrive on worlds far beyond our own? Ultra-sensitive telescopes and dogged detective work are transforming <a href="/wgbh/nova/video/how-to-find-an-exoplanet/">alien planet-hunting</a> from science fiction into hard fact. Join NOVA on a visit to exotic worlds <a href="/wgbh/nova/video/planets-two-stars/">orbiting distant suns</a>, from puffy planets with the density of Styrofoam to thousand-degree, broiling gas giants. Most tantalizing of all are the Super-Earths in the “Goldilocks zone,” just the right distance from their sun to support life, and with one of them signaling life’s essential ingredient, water, in its atmosphere. Are we on the brink of answering that haunting question?</p>
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<h3>Looking For Life on Mars (2021)</h3><p>Follow along as NASA launches the Mars 2020 Mission, perhaps the most ambitious hunt yet for <a href="/wgbh/nova/video/nasa-mars-perseverance/">signs of ancient life</a> on Mars. In February 2021, the spacecraft blazes into the Martian atmosphere at some 12,000 miles per hour and lowers the Perseverance Rover into the rocky Jezero Crater, home to a dried-up river delta scientists think could have harbored life. Perseverance will comb the area for signs of life and collect samples for possible return to Earth. Traveling onboard is a four-pound helicopter that will conduct a <a href="/wgbh/nova/article/nasa-ingenuity-first-powered-flight-mars/">series of test flights</a>—the first on another planet. During its journey, Perseverance will also test technology designed to produce oxygen from the Martian atmosphere, in hopes that the gas could be used for fuel—or for humans to breathe—on future missions.</p>
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<h3><a href="https://www.pbs.org/wgbh/nova/video/touching-the-asteroid/"><b>Touching the Asteroid</b></a><b> (2020) </b></h3><p>In October 2020, a NASA spacecraft called OSIRIS-REx attempts to reach out and <a href="/wgbh/nova/video/inside-osiris-rexs-mission-to-tag-asteroid-bennu/">grab a piece of an asteroid</a> named Bennu to bring it back to Earth. The OSIRIS-REx team has just three chances to extend its spacecraft’s specialized arm, touch down for five seconds, and collect material from the surface of Bennu. But if they can pull it off, scientists could gain great insight into Earth’s own origins—and even learn to defend against rogue asteroids that may one day threaten our planet.</p>
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<h3><a href="/wgbh/nova/video/back-to-the-moon/"><b>Back to the Moon</b></a> (2019)</h3><p>On the 50th anniversary of the historic Apollo 11 Moon landing, NOVA looks ahead to the hoped-for dawn of a new age in lunar exploration. This time, governments and private industry are working together to reach our nearest celestial neighbor. <a href="https://www.pbs.org/wgbh/nova/article/moon-water-human-space-exploration/">But why go back?</a> The Moon can serve as a platform for basic astronomical research; as an abundant source of rare metals and hydrogen fuel; and ultimately as a stepping stone for human missions to Mars and beyond. Join the next generation of engineers that aim to take us to the Moon, and discover how our legacy of lunar exploration won't be confined to the history books for long.</p>
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<h3>Black Hole Apocalypse (2018)</h3><p>Black holes are the most enigmatic and exotic objects in the universe. They’re also the most powerful, with gravity so strong it can trap light. And they’re destructive, swallowing entire planets, even giant stars. Anything that <a href="/wgbh/nova/video/whats-inside-a-black-hole/">falls into them</a> vanishes…gone forever. Now, astrophysicists are realizing that black holes may be essential to how our universe evolved—their influence possibly leading to life on Earth and, ultimately, us. In this two-hour special, astrophysicist and author Janna Levin takes viewers on a journey to the frontiers of black hole science. Along the way, we meet leading astronomers and physicists on the verge of finding new answers to provocative questions about these shadowy monsters: Where do they come from? What’s inside? <a href="/wgbh/nova/video/take-a-ride-into-a-supermassive-black-hole/">What happens if you fall into one?</a> And what can they tell us about the nature of space, time, and gravity?</p>
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<p data-block-key="z1ikv">Check out some of NOVA’s best space documentaries available for streaming.</p>

Attabey Rodríguez Benítez

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