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    These are our top space images of all time

    We’ve never seen images of space as astounding as those from the James Webb Space Telescope, which shared its first cosmic vistas in July. The pictures have left us dazzled, awestruck and excited for more. They also inspired us to reflect on the top space images past and present. These images have moved us because of their drama, beauty or significance. Here’s how eight Science News staffers answered the question: What’s your favorite space image of all time?

    Apollo 8 Earthrise, taken in 1968

    The Apollo 8 crew orbited the moon 10 times during late December of 1968, capturing this view of Earth.NASA

    Lisa Grossman, astronomy writer, chose Apollo 8’s Earthrise as her top space image. She says: The you-are-there, sci-fi-but-it’s-real feeling of seeing Earth over the edge of the moon gets my imagination going. And something about having the surface of the moon in the image gives me deep chills. I can imagine my own feet in those gray craters, my own eyes looking back at my own Earth. It’s wild. It’s eerie. I love it.

    I feel similarly about the selfie images from the Mars rovers; here’s NASA’s Curiosity rover at Mont Mercou in 2021.

    NASA’s Curiosity rover used a camera on its head and one on its robotic arm to create this selfie with Mont Mercou in March 2021.NASA, JPL-Caltech, MSSS

    You can see the rover and the landscape behind it. That’s our robotic avatar on that planet, rolling around doing our work. Though I’m lukewarm about sending people to do extraterrestrial exploration – I think the risks outweigh the scientific benefits – I have always been a sucker for imagining living on another world. Or at least visiting.

    JWST’s close-up of Neptune, taken in 2022

    Neptune and its rings glow in infrared light in this image from the James Webb Space Telescope. It’s the first direct look at Neptune’s rings in more than 30 years.NASA, ESA, CSA, STSCI, JOSEPH DEPASQUALE/STSCI

    Nikk Ogasa, staff writer for physical sciences, says: There are so many awe-inspiring space images out there, but my favorite from this year was the James Webb Space Telescope’s heavenly shot of Neptune. It is stunning. The image captures the planet’s near-infrared glow in unprecedented detail. Not only can you see the glorious rings, but you can also pick out high-flying methane clouds as bright streaks. It blows my mind that we can see clouds on another world that is billions of miles away.

    Pillars of Creation, first captured in 1995

    After capturing the Pillars of Creation in 1995, the Hubble Space Telescope imaged them for a second time in late 2014 (the image in visible light is shown here).NASA, ESA and the Hubble Heritage Team, STSCI/AURA

    Two members of our team selected the Hubble Space Telescope’s second view of the Pillars of Creation, taken in 2014, as their top space image.

    Design director Erin Otwell says: My top space image is the Pillars of Creation in the Eagle Nebula. It’s my choice because of the awe-inspiring details and the painterly quality of the composition. To me, this image sums up the feeling of studying the cosmos and of creation itself. The towers of gas and dust where new stars are being born compose an almost solid-looking figure. It looks more like a hand than pillars.  

    Maria Temming, assistant editor at Science News Explores, says: I know that claiming the Pillars of Creation as my favorite space image is like saying Starbucks is my favorite coffee. But I don’t care! I love it. I have something of a sentimental attachment to this vista, since it was on the cover of the Great Courses intro to astronomy DVD set that first sparked my interest in space science.

    In an infrared light view of the Pillars of Creation, taken by the Hubble Space Telescope in late 2014, stars in and behind the towers of gas and dust are visible.NASA, ESA, Hubble and the Hubble Heritage Team

    The iconic, candy-colored images of the pillars in visible light are not the only versions that Hubble has captured. In 2014, the space telescope also took a ghostly picture of the scene in infrared light (above). Light at infrared wavelengths shines through the pillars’ gas and dust, revealing the baby stars swaddled inside these clouds.

    Thomas Digges’ view of the universe, published in 1576

    In this image published in 1576, English astronomer Thomas Digges depicts stars extending far beyond the solar system.Wellcome Collection

    Tom Siegfried, contributing correspondent, chose this diagram as his favorite space image. He says: When Copernicus displaced the Earth from the center of the universe, he pictured the stars as occupying a sphere surrounding the planets that orbited on smaller spheres surrounding the sun. But Thomas Digges, an English astronomer who defended Copernicus, believed the stars extended far beyond the solar system.

    In this image, published in 1576, Digges depicted numerous stars beyond the spheres of the planets, suggesting that the universe was “garnished with lights innumerable and reaching up in spherical altitude without end.” With these words Digges was the first follower of Copernicus to suggest that the universe encompassed an infinite expanse of space.

    The Milky Way’s black hole, released in 2022

    In May 2022, the Event Horizon Telescope collaboration released this first image of the black hole at the heart of the Milky Way.EVENT HORIZON TELESCOPE COLLABORATION

    Helen Thompson, associate digital editor, says: Is it extremely blurry? Yes. Is it not even the first time we’ve imaged a black hole? Also yes. But it’s the black hole in our galactic backyard, and we’d never seen it before. There’s something mind-blowing and kind of heartwarming about seeing it for the first time. The Event Horizon Telescope’s first image of Sagittarius A* might not be as pretty as James Webb’s fancy-schmancy pictures, but all of the difficulties that come with imaging black holes and especially this black hole make it so compelling.

    Gravitational lensing of quasar 2M1310-1714, captured in 2021

    Thanks to gravitational lensing, predicted by Einstein’s general theory of relativity before it was observed, quasar 2M1310-1714 appears as four points of light sitting on a ring around two bright galaxies.ESA, Hubble, NASA, T. Treu

    Elizabeth Quill, special projects editor, says: Within the ring of light at the center of this image are a pair of distant galaxies and a much more distant quasar behind them. The mass of the galactic duo is warping the fabric of spacetime, bending and magnifying the quasar’s light to form what are four separate images of the quasar, each sitting around the ring. It’s a visually powerful example of a phenomenon known as gravitational lensing, which was predicted by Einstein’s general theory of relativity before it was ever observed.

    My top space image wows me every time. How incredible that the universe works this way. How incredible that the human mind, a motley product of the universe, could foresee it. And not only foresee it; today’s scientists use gravitational lensing as a tool to study otherwise inaccessible regions of space. It’s both humbling and empowering.

    Pale Blue Dot, taken in 1990

    NASA’s Voyager 1 spacecraft took this parting image of Earth after completing its tour of the solar system in 1990.NASA, JPL-Caltech

    Christopher Crockett, associate news editor, says: My favorite space image of all time isn’t of a colorful nebula, or a glittering galaxy, or even a certain supermassive black hole. It’s a single dot, seemingly ensconced in a shaft of light.

    After completing its tour of the solar system in 1990, NASA’s Voyager 1 looked back and took a series of parting images – a “family portrait,” it was called – of several planets orbiting our sun. One of the images, which came to be known as the “pale blue dot” photo, captured Earth as seen from roughly 6 billion kilometers away — the most distant image of home anyone has ever taken.

    The image, updated with modern image-processing software and re-released in 2020 (above), remains a reminder of why we explore the universe. Yes, we want to better understand how space and time, stars and planets, galaxies and superclusters work, because we’re curious. But all those questions ultimately come back to trying to understand where we come from and how we fit into all that surrounds us.

    As Carl Sagan emphasized, nothing better captures just how tiny we are in the grand scheme of things than seeing our entire planet reduced to a mere speck of light.

    When I used to give public talks about astronomy, I almost always closed with this image. And I would usually read from Sagan’s reflections on it:

    “Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives.… on a mote of dust suspended in a sunbeam.… There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known.” More

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    Over time, Betelgeuse changed color. Now it’s also lost its rhythm

    The star Betelgeuse has always been a diva.

    Astronomers from antiquity through the present day have watched the red supergiant pulsing at the shoulder of the constellation Orion, and the star has continually put on a show, two new studies suggest. Betelgeuse may still be recovering from a deep dimming episode a few years ago, one team reports. And the star appears to have put on its reddish stage makeup just 2,000 years ago, before which it wore yellow, another team says.

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    Together, these studies could tell researchers about how stars spew their guts into space and hint at how long it will be before Betelgeuse explodes in a supernova.

    “This star always fools you,” says astronomer Edward Guinan of Villanova University in Pennsylvania, who has studied Betelgeuse for decades and was not involved in the new works. “You think you have it, and all of a sudden, it changes.”

    The “Great Dimming”

    In late 2019, Betelgeuse captured astronomers’ attention when it suddenly grew dark for several months — an event astronomers now call the Great Dimming. Months of subsequent observations led researchers to an explanation: The star had coughed out a big bubble of plasma. That material cooled, condensed into dust and blocked the star’s face from the perspective of Earth months later (SN: 11/29/20). The surface of the star also cooled down, contributing to the dimming (SN: 6/16/21).

    But what happened next was equally surprising, astrophysicist Andrea Dupree and colleagues report in a paper submitted August 2 to The star’s regular pulsating brightness, it seems, went completely out of whack.

    In its non–Great Dimming life, Betelgeuse’s brightness was on a quasi-periodic dimmer switch. As the star breathed in and out — ballooning out before shrinking back down — its brightness went up and down. “For 200 years, it had a nice, 400-day oscillation in brightness,” says Dupree, of the Harvard & Smithsonian Center for Astrophysics in Cambridge, Mass. “But that’s gone now.”

    That regular drumbeat has since grown erratic. Instead of a regular thrum, the oscillations are “like an unbalanced washing machine, going ‘wonka wonka wonka,’” Dupree says.

    The wonkiness is a sign of the star struggling to recover from the loss of material in 2019, Dupree says. She calculates that Betelgeuse ejected several times the mass of the moon from its surface, leaving a large cool spot behind. The star’s surface plasma is sloshing around as it returns to equilibrium.

    If this picture is correct, it means red supergiants like Betelgeuse can spray material into interstellar space in discrete bursts, rather than a continuous stream. That’s important to know because many of the elements that make up planets and people were formed in stars undergoing what Betelgeuse is going through right now. Studying Betelgeuse’s growing pains and death throes can tell us about our own origins.

    But while this picture of Betelgeuse holds together, it is still speculative, Guinan cautions.

    One confounding factor is a new set of observations of Betelgeuse during the four-month period when it’s usually out of view. From May through August every year, Betelgeuse is too close to the sun from Earth’s perspective to be seen at night. Usually that leaves a hole in the datasets of astronomers who track its periodic behavior.

    But amateur observer Otmar Nickel of Mainz, Germany, developed a technique to measure Betelgeuse’s brightness using multiple images taken during the day. Dupree’s paper is the first to include those daytime data.

    “That’s cool,” Guinan says. “You can follow the star all year round.”

    Those extra observations might reveal recurring changes that have always been there, rather than picking up on something truly new. “Those little variations you’re seeing…could easily be present right before the Great Dimming,” Guinan says.

    Dupree’s team predicts that the dust Betelgeuse lost could become visible to some telescopes on Earth in 2023. “That would be proof” that the brightness changes were due to a single outburst, Guinan says.

    Seeing yellow

    The Great Dimming isn’t the first time humans have recorded a major change in Betelgeuse’s personality. Two millennia ago, the star was a completely different color, astrophysicist Ralph Neuhäuser and colleagues report in a paper in press in Monthly Notices of the Royal Astronomical Society.

    The team analyzed ancient descriptions of more than 200 stars whose colors should have been visible to the naked eye in the past few thousand years. Most stars observed over human history had the same color recorded in the past as they display today, the team found. But not Betelgeuse.

    The ancient Roman astronomer Gaius Julius Hyginus, who lived from about 64 B.C. to A.D. 17, and is thought to have written the Latin work De Astronomia, described the star in the right shoulder of Orion has having a similar color to Saturn ­— which is yellow. Astrologer and archivist Sima Qian, working during the Chinese Han dynasty around 100 B.C., independently described the star as yellow. Observers from other ancient cultures conspicuously left Betelgeuse out of their lists of red stars.

    “I thought, ‘Oh, how can this be?’” says Neuhäuser, of AIU Jena in Germany. “I was not expecting such a result … to find a star to change color in historical time.”

    A star’s color is a sign of its evolutionary stage (SN: 7/23/21). When stars burn through the hydrogen fuel in their cores, they puff up and expel gases into space. That expansion makes their surface temperatures drop, and they change color from blue to red in fairly short order — about 10,000 years for a giant star like Betelgeuse, which is around 14 times as massive as the sun.

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    Measuring a star’s age isn’t as easy as you’d think. Here’s how scientists get their ballpark estimates.

    That relatively recent color change suggests Betelgeuse has just reached the end of its hydrogen-burning life and became the red supergiant we know it as today while human observers were watching.

    “It’s fully consistent with astrophysical knowledge,” Neuhäuser says. “It could have been expected, but no one really checked.”

    That result means anyone waiting for Betelgeuse to go supernova will have a very long wait. If the star just became a supergiant in the last few millennia, it has more than 1 million years to go before the boom. More

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    How balloons could one day detect quakes on Venus

    The balloon was floating over the Pacific Ocean when the first sound waves hit. For 11 seconds, a tiny device dangling beneath the large, transparent balloon recorded sudden, jerky fluctuations in air pressure: echoes of an earthquake more than 2,800 kilometers away.

    That scientific instrument was one of four hovering high above the Malay Archipelago on December 14, 2021. That day the quartet became the first network of devices to monitor an earthquake from the air, researchers report in the Aug. 16 Geophysical Research Letters.

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    The finding could help scientists track earthquakes in remote areas on Earth, and also opens the door to one day sending specially equipped balloons to study the geology of other worlds, including our closest planetary neighbor.

    “Venus is the sister planet of Earth, but it’s the evil twin sister,” says David Mimoun, a planetary scientist at the University of Toulouse in France. “We don’t know why the two planets are so different. That’s why we need measurements.”

    The idea of using balloons to study far-off rumblings on Earth has its roots in the Cold War. In the 1940s, the U.S. military launched a top secret project to spy on Soviet nuclear weapons testing using microphones attached to balloons floating high in the atmosphere. When the ground shakes, it releases low-frequency sound waves that can travel long distances in the atmosphere. The military planned on using the microphones to pick up on the sound of the ground shaking from a nuclear explosion. But the project was eventually deemed too expensive and dropped — though not before one of the balloons crashed in New Mexico, launching the Roswell conspiracy.

    For decades after, balloon science stayed mostly in the realm of meteorology. Then in the early 2000s, Mimoun and his colleagues started experimenting with using balloons for space exploration, specifically for studying extraterrestrial quakes.

    Analyzing temblors is one of the main ways that scientists can learn about a planet’s interior. On worlds with thin atmospheres, such as Mars or Earth’s moon, this generally means sending a lander to the surface and measuring quakes directly on the ground (SN: 5/13/22).

    But doing that on Venus isn’t really an option. The dense atmosphere means that the planet’s surface has about the same pressure as Earth’s deep ocean, with temperatures averaging around 450° Celsius — hot enough to melt lead. “Basically, it’s hell,” Mimoun says.

    Landers have made it to the surface of Venus before (SN: 6/19/76). But these probes lasted only a few hours before succumbing to the extreme heat and pressure. The chances of measuring a quake in that short time frame are slim, says Siddharth Krishnamoorthy, a research technologist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., who wasn’t involved in the study. So while radar images of Venus have revealed a world dotted with volcanoes, scientists still don’t know for sure if Venus is geologically active, he says.

    Scientists have previously experimented with the idea of detecting quakes on Venus using orbiters (SN: 9/02/05). But quake-detecting balloons have better resolution, says Mimoun, meaning they could provide the key to revealing the planet’s interior life. But first Mimoun and his colleagues had to show that they could design devices small enough to be carried by balloons but sensitive enough to pick up earthquakes far below.

    In 2021, the team attached micro-barometers to 16 balloons launched from the Seychelles Islands, off the coast of East Africa. In December, four balloons — having drifted thousands of kilometers apart — recorded similar, low-frequency sound waves. These changes in air pressure resembled ground readings of a 7.3 magnitude earthquake near the Indonesian island of Flores, indicating that the sound waves were produced by the earthquake. The researchers were able to use the changes in air pressure to pinpoint the epicenter of the quake and calculate its magnitude.

    “This is a huge step forward in demonstrating the utility of this technology,” says Paul Byrne, a planetary scientist at Washington University in St. Louis, who was not involved with the study.

    Even without being able to pick up quakes, the balloons, if designed to survive in the Venusian atmosphere, might be able to detect changes in air pressure that reveal clues about the planet’s volcanic eruptions and mysterious highlands, Byrne says.

    Venus is entering a renaissance of interest from space agencies. At least two NASA missions to visit the planet are planned for the end of this decade (SN: 6/2/21). Mimoun is hoping that earthquake-detecting balloons will feature in the next major mission, emphasizing that their data could help researchers understand why Earth and Venus — alike in size and distance from the sun, relative to the other planets — have gone down such different paths.

     “We have no clue,” Mimoun says. “So we need to go back.” More

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    How Mars rovers have evolved in 25 years of exploring the Red Planet

    Few things are harder than hurling a robot into space — and sticking the landing. On the morning of July 4, 1997, mission controllers at the Jet Propulsion Laboratory in Pasadena, Calif., were hoping to beat the odds and land a spacecraft successfully on the Red Planet.

    Twenty-five years ago that little robot, a six-wheeled rover named Sojourner, made it — becoming the first in a string of rovers built and operated by NASA to explore Mars. Four more NASA rovers, each more capable and complex than the last, have surveyed the Red Planet. The one named Curiosity marked its 10th year of cruising around on August 5. Another, named Perseverance, is busy collecting rocks that future robots are supposed to retrieve and bring back to Earth. China recently got into the Mars exploring game, landing its own rover, Zhurong, last year.

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    Other Mars spacecraft have done amazing science from a standstill, such as the twin Viking landers in the 1970s that were the first to photograph the Martian surface up close and the InSight probe that has been listening for Marsquakes shaking the planet’s innards (SN Online: 2/24/20). But the ability to rove turns a robot into an interplanetary field geologist, able to explore the landscape and piece together clues to its history. Mobility, says Kirsten Siebach, a planetary scientist at Rice University in Houston, “makes it a journey of discovery.”

    Each of the Mars rovers has gone to a different place on the planet, enabling scientists to build a broad understanding of how Mars evolved over time. The rovers revealed that Mars contained water, and other life-friendly conditions, for much of its history. That work set the stage for Perseverance’s ongoing hunt for signs of ancient life on Mars.

    Each rover is also a reflection of the humans who designed and built and drove it. Perseverance carries on one of its wheels a symbol of Mars rover tracks twisted into the double helix shape of DNA. That’s “to remind us, whatever this rover is, it’s of human origin,” says Jennifer Trosper, an engineer at the Jet Propulsion Lab, or JPL, who has worked on all five NASA rovers. “It is us on Mars, and kind of our creation.”

    The little microwave that could

    Sojourner, that first rover, was born in an era when engineers weren’t sure if they even could get a robot to work on Mars. In the early 1990s, then-NASA Administrator Daniel Goldin was pushing the agency to do things “faster, better and cheaper” — a catchphrase that engineers would mock by saying only two of those three things were possible at the same time. NASA had no experience with inter­planetary rovers. Only the Soviet Union had operated rovers — on the moon in 1970 and 1973.

    JPL began developing a Mars rover anyway. Named after the abolitionist Sojourner Truth, the basic machine was the size of a microwave oven. Engineers were limited in where they could send it; they needed a large flat region on Mars because handling a precision landing near mountains or canyons was beyond their abilities. NASA chose Ares Vallis, a broad outflow channel from an ancient flood, and the mission landed there successfully.

    Sojourner spent nearly three months poking around the landscape. It was slow going. Mission controllers had to communicate with Sojourner constantly, telling it where to roll and then assessing whether it had gotten there safely. They made mistakes: One time they uploaded a sequence of computer commands that mistakenly told the rover to shut itself down. They recovered from that stumble and many others, learning to quickly fix problems and move forward.

    In 1997, NASA’s first rover, Sojourner, rolled down a landing ramp and became the first mobile Mars robot. Solar panels provided power throughout its 12-week mission.JPL-CALTECH/NASA

    Although Sojourner was a test mission to show that a rover could work, it managed to do some science with its one X-ray spectrometer. The little machine analyzed the chemical makeup of 15 Martian rocks and tested the friction of the Martian soil.

    After surviving 11 weeks beyond its planned one-week lifetime, Sojourner ultimately grew too cold to operate. Trosper was in mission control when the rover died on September 27, 1997. “You build these things, and even if they’re well beyond their lifetime, you just can’t let go very easily, because they’re part of you,” she says.

    Jennifer Trosper, an engineer at the Jet Propulsion Laboratory, is part of a small group of people who have worked on all five NASA Mars rovers. Here she is in 2021 with a model of Perseverance.CHRISTOPHER MICHEL/WIKIMEDIA COMMONS (CC BY-SA 4.0)

    Twin explorers

    In 1998 and 1999, NASA hurled a pair of spacecraft at Mars; one was supposed to orbit the planet and another was supposed to land near one of the poles. Both failed. Stung from the disappointment, NASA decided to build a rover plus a backup for its next attempt.

    Thus were born the twins Spirit and Opportunity. Each the size of a golf cart, they were a major step up from Sojourner. Each had a robotic arm, a crucial development in rover evolution that enabled the machines to do increasingly sophisticated science. The two had beefed-up cameras, three spectrometers and a tool that could grind into rocks to reveal the texture beneath the surface.

    But there were a lot of bugs to work out. Spirit and Opportunity launched several weeks apart in 2003. Spirit got to Mars first, and on its 18th Martian day on the surface it froze up and started sending error messages. It took mission controllers days to sort out the problem — an overloaded flash-memory system — all while Opportunity was barreling toward Mars. Ultimately, engineers fixed the problem, and Opportunity landed safely on the opposite side of the planet from Spirit.

    Both rovers lasted years beyond their expected three-month lifetimes. And both did far more Martian science than anticipated.

    Spirit broke one of its wheels early on and had to drive backward, dragging the broken wheel behind it. But the rover found plenty to do near its landing site of Gusev crater, home to a classic Mars landscape of dust, rock and hills. Spirit found rocks that appeared to have been altered by water long ago and later spotted a pair of iron-rich meteorites. The rover ultimately perished in 2010, stuck in a sand-filled pit. Mission controllers tried to extract it in an effort dubbed “Free Spirit,” but salts had precipitated around the sand grains, making them particularly slippery.

    Opportunity, in contrast, became the Energizer Bunny of rovers, exploring constantly and refusing to die. Immediately after landing in Meridiani Planum, Opportunity had scientists abuzz.

    The pale rock at center, seen beneath the Opportunity rover’s robotic arm in 2013, was one of many at the rover’s landing site that held long-awaited evidence that liquid water once flowed on Mars.

    “The images that the rover first sent back were just so different from any other images we’d seen of the Martian surface,” says Abigail Fraeman, a planetary scientist at JPL. “Instead of these really dusty volcanic plains, there was just this dark sand and this really bright bedrock. And that was just so captivating and inspiring.”

    Right at its landing site, Opportunity spotted the first definitive evidence of past liquid water on Mars, a much-anticipated and huge discovery (SN: 3/27/04, p. 195). The rover went on to find evidence of liquid water at different times in the Martian past. After years of driving, the rover reached a crater called Endeavour and “stepped into a totally new world,” Fraeman says. The rocks at Endeavour were hundreds of millions of years older than others studied on Mars. They contained evidence of different types of ancient water chemistry.

    Opportunity ultimately drove farther than any rover on any extraterrestrial world, breaking a Soviet rover’s lunar record. In 2015, Opportunity passed 26.2 miles (42.2 km) on its odometer; mission controllers celebrated by putting a marathon medal onto a mock-up of the rover and driving it through a finish line ribbon at JPL. Opportunity finally died in 2019 after an intense dust storm obscured the sun, cutting off solar power, a must-have for the rover to recharge its batteries (SN: 3/16/19, p. 7).

    The twin rovers were a huge advance over Sojourner. But the next rover was an entirely different beast.

    Mission project scientist Ashwin Vasavada stands with several rovers, which learn to traverse various surfaces in the Mars Yard at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.JPL-Caltech/NASA

    The SUV of rovers

    By the mid-2000s, NASA had decided it needed to go big on Mars, with a megarover the size of a sports utility vehicle. The one-ton Curiosity was so heavy that its engineers had to come up with an entirely new way to land on Mars. The “sky crane” system used retro-rockets to hover above the Martian surface and slowly lower the rover to the ground.

    Against all odds, in August 2012, Curiosity landed safely near Mount Sharp, a 5-kilometer-high pile of sediment within the 154-kilometer-wide Gale crater (SN: 8/25/12, p. 5). Unlike the first three Mars rovers, which were solar-powered, Curiosity runs on energy produced by the radioactive decay of plutonium. That allows the rover to travel farther and faster, and to power a suite of sophisticated science instruments, including two chemical laboratories.

    Curiosity introduced a new way of exploring Mars. When the rover arrives in a new area, it looks around with its cameras, then zaps interesting rocks with its laser to identify which ones are worth a closer look. Once up close, the rover stretches out its robotic arm and does science, including drilling into rocks to see what they are made of.

    When Curiosity arrived near the base of Mount Sharp, it immediately spotted rounded pebbles shaped by a once-flowing river, the first close­up look at an ancient river on Mars. Then mission controllers sent the rover rolling away from the mountain, toward an area in the crater known as Yellowknife Bay. There Curiosity discovered evidence of an ancient lake that created life-friendly conditions for potentially many thousands of years.

    Curiosity then headed back toward the foothills of Mount Sharp. Along the way, the rover discovered a range of organic molecules in many different rocks, hinting at environments that had been habitable for millions to tens of millions of years. It sniffed methane gas sporadically wafting within Gale crater, a still-unexplained mystery that could result from geologic reactions, though methane on Earth can be formed by living organisms (SN: 7/7/18, p. 8). The rover measured radiation levels across the surface — helpful for future astronauts who’ll need to gauge their exposure — and observed dust devils, clouds and eclipses in the Martian atmosphere and night sky.

    Shimmering clouds of ice crystals appear in the sky above Gale crater on Mars, as seen by the Curiosity rover in March 2021. The ability to drive across Mars gives rovers a humanlike ability to interact with the landscape.
    MSSS, JPL-Caltech/NASA

    “We’ve encountered so many unexpectedly rich things,” says Ashwin Vasavada of JPL, the mission’s project scientist. “I’m just glad a place like this existed.”

    Ten years into its mission, Curiosity still trundles on, making new discoveries as it climbs the foothills of Mount Sharp. It recently departed a clay-rich environment and is now entering one that is heavier in sulfates, a transition that may reflect a major shift in the Martian climate billions of years ago.

    In the course of driving more than 28 kilometers, Curiosity has weathered major glitches, including one that shuttered its drilling system for over a year. And its wheels have been banged up more than earthbound tests had predicted. The rover will continue to roll until some unknown failure kills it or its plutonium power wanes, perhaps five years from now.

    Over nearly 10 years of driving on Mars’ rocky surface, Curiosity’s wheels have taken more of a beating than its designers expected.
    MSSS, JPL-Caltech/NASA

    A rover and its sidekick

    NASA’s first four rovers set the stage for the most capable and agile rover ever to visit Mars: Perseverance. Trosper likens the evolution of the machines to the growth of children. “We have a preschooler in Sojourner, and then … your happy-go-lucky teenagers in Spirit and Opportunity,” she says. “Curiosity is certainly a young adult that’s able to do a lot of things on her own, and Perseverance is kind of that high-powered mid­career [person] able to do pretty much anything you ask with really no questions.”

    Perseverance is basically a copy of Curiosity built from its spare parts, but with one major modification: a system for drilling, collecting and storing slender cores of rock. Perseverance’s job is to collect samples of Martian rock for future missions to bring to Earth, in what would be the first robotic sample return from Mars. That would allow scientists to do sophisticated analyses of Martian rocks in their earthbound labs. “It feels, even more than previous missions, that we are doing this for the next generation,” Siebach says.

    The rover is working fast. Compared with Curiosity’s leisurely exploration of Gale crater, Perseverance has been zooming around its landing site, the 45-kilometer-wide Jezero crater, since its February 2021 arrival. It has collected 10 rock cores and is already eyeing where to put them down on the surface for future missions to pick up. “We’re going to bring samples back from a diversity of locations,” says mission project scientist Kenneth Farley of Caltech. “And so we keep to a schedule.”

    Perseverance went to Jezero to study an ancient river delta, which contains layers of sediment that may harbor evidence of ancient Martian life. But the rover slightly missed its target, landing on the other side of a set of impassable sand dunes. So it spent most of its first year exploring the crater floor, which turned out to be made of igneous rocks (SN: 9/11/21, p. 32). The rocks had cooled from molten magma and were not the sedimentary rocks that many had expected.

    Scientists back on Earth will be able to precisely date the age of the igneous rocks, based on the radioactive decay of chemical elements within them, providing the first direct evidence for the age of rocks from a particular place on Mars.

    Perseverance collected its 9th rock core, barely the size of a pinky finger, on July 7. Future missions will return the stored samples to Earth for study.

    Once it finished exploring the crater floor in March, the rover drove quickly toward the delta. Each successive NASA rover has had greater skills in autonomous driving, able to identify hazards, steer around them and keep going without needing constant instructions from mission control.

    Perseverance has a separate computer processor to run calculations for autonomous navigation, allowing it to move faster than Curiosity. (It took Curiosity two and a half years to travel 10 kilometers; Perseverance traveled that far in a little over a year.) “The rover drives pretty much every minute that we can give it,” Farley says.

    In April, Perseverance set a Martian driving record, traveling nearly five kilometers in just 30 Martian days. If all goes well, it will make some trips up and down the delta, then travel to Jezero crater’s rim and out onto the ancient plains beyond.

    Perseverance has a sidekick, Ingenuity, the first helicopter to visit another world. The nimble flier, only half a meter tall, succeeded beyond its designers’ wildest dreams. The helicopter made 29 flights in its first 16 months when it was only supposed to make five in one month. It has scouted paths ahead and scientific targets for the rover (SN Online: 4/19/22). Future rovers are almost certain to carry a little buddy like this.

    An engineer at NASA’s Jet Propulsion Laboratory measures light on the Perseverance rover during a 2019 test. The rover landed on Mars last year and has been exploring it ever since.JPL-CALTECH/NASA

    China’s debut

    While the United States has led in Mars rover exploration, it is not the only player on the scene. In May 2021, China became the second nation to successfully place a rover on Mars. Its Zhurong rover, named after a mythological fire god, has been exploring part of a large basin in the planet’s northern hemisphere known as Utopia Planitia.

    The landing site lies near a geologic boundary that may be an ancient Martian shoreline. Compared with the other Mars rover locations, Zhurong’s landing site is billions of years younger, “so we are investigating a different world on Mars,” says Lu Pan, a planetary scientist at the University of Copenhagen who has collaborated with Zhurong scientists.

    In many ways, Zhurong resembles Spirit and Opportunity, in size as well as mobility. It carries cameras, a laser spectrometer for studying rocks and ground-penetrating radar to probe underground soil structures (SN Online: 5/19/21).

    After landing, Zhurong snapped pictures of its rock-strewn surroundings and headed south to explore a variety of geologic terrains, including mysterious cones that could be mud volcanoes and ridges that look like windblown dunes. The rover’s initial findings include that the Martian soil at Utopia Planitia is similar to some desert sands on Earth and that water had been present there perhaps as recently as 700 million years ago.

    In May, mission controllers switched Zhurong into dormant mode for the Martian winter and hope it wakes up at the end of the season, in December. It has already traveled nearly two kilometers across the surface, farther than the meager 100 meters that Sojourner managed. (To be fair, Sojourner had to keep circling its lander because it relied on that lander to communicate with Earth.)

    The China National Space Administration released this image on June 11, 2021 of Zhurong with its landing platform on Mars.CNSA/Handout via Xinhua

    From Sojourner to Zhurong, the Mars rovers show what humankind can accomplish on another planet. Future rovers might include the European Space Agency’s ExoMars, although its 2022 launch was postponed after Russia attacked Ukraine (SN: 3/26/22, p. 6). Europe terminated all research collaborations with Russia after the invasion, including launching ExoMars on a Russian rocket.

    Vasavada remembers his sense of awe at the Curiosity launch in 2011: “Standing there in Florida, watching this rocket blasting off and feeling it in your chest and knowing that there’s this incredibly fragile complex machine hurtling on the end of this rocket.… It just gave me this full impression that here we are, humans, blasting these things off into space,” he says. “We’re little tiny human beings sending these things to another planet.” More

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    Amateur astronomers’ images of a rare double aurora may unlock its secrets

    What happens when two different kinds of auroras get together? One spills the other’s secrets.

    Amateur astronomers have captured a strange combination of red and green auroras on camera, and physicists — who had never seen such a thing before — have now used these images to learn what may trigger the more mysterious part of the lightshow.

    Photographer Alan Dyer was in his backyard in Strathmore, Canada, when he saw the lights dancing overhead and started filming. “I knew I had something interesting,” says Dyer, who also writes about astronomy. What he didn’t know was that he had just made the most complete recording of this rare phenomenon.

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    At a glance, Dyer’s video looks like a celestial watermelon. The rind, a rippling green aurora, is well understood: It appears when the solar wind energizes protons trapped within Earth’s magnetic field, which then rain down and knock electrons and atoms around (SN: 12/10/03).  

    The swath of fruity magenta is more mysterious: Though scientists have known about these “stable auroral red arcs” for decades, there’s no widely accepted proof of how they form. One popular theory is that part of Earth’s magnetic field can heat up the atmosphere and, like proton rain, jostle particles.   

    But until now, researchers had never seen both of these red and green auroras side by side, says Toshi Nishimura, a space physicist at Boston University. “This strange combination,” he says, “was something beyond our expectations.”

    [embedded content]
    Alan Dyer’s footage of this rare double aurora, a time lapse captured over 33 minutes on October 12, 2021, is helping physicists tease out clues to what causes the red glow.

    Along with satellite observations, Dyer’s images and similar ones captured by other amateur astronomers in Canada and Finland show that the two phenomena are related, Nishimura’s team reports in the July JGR Space Physics. Thin rays in the red aurora are the smoking gun as to how. Those lines trace the paths of electrons as they fall along the Earth’s magnetic field. So just as proton rain triggers the green aurora, electron rain appears to trigger the red one, with the solar wind powering both at the same time. Since the electrons carry less energy than the protons, they make for a more reddish color. 

    But electron rain might not be the only way to produce these red glows, cautions Brian Harding, a space physicist at the University of California, Berkeley. Either way, he says, the results are exciting because they show what’s going on is more complicated than researchers thought.

    Those complications are important to understand. The auroras Dyer saw, though beautiful, are danger zones for radio communication and GPS systems (SN: 8/13/17). As Nishimura puts it: If you were driving under a subauroral red arc, your GPS might tell you to veer into a field.

    Until scientists better understand these red glows, they won’t be able to forecast space weather like they do normal weather, Harding explains. “You want to make sure that you can predict stuff like this,” he says.

    The new results would not have been possible without the citizen scientists who took the photos, Nishimura says. “This is a new way of doing research…. When they take more and more cool images, they find more and more things that we don’t know about.”

    According to Dyer, more photos are exactly what’s coming. “We can make a unique contribution to science,” he says.  After all, “you never know what’s going to appear.” More

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    Binary stars keep masquerading as black holes

    As astronomy datasets grow larger, scientists are scouring them for black holes, hoping to better understand the exotic objects. But the drive to find more black holes is leading some astronomers astray.

    “You say black holes are like a needle in a haystack, but suddenly we have way more haystacks than we did before,” says astrophysicist Kareem El-Badry of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “You have better chances of finding them, but you also have more opportunities to find things that look like them.”

    Two more claimed black holes have turned out to be the latter: weird things that look like them. They both are actually double-star systems at never-before-seen stages in their evolutions, El-Badry and his colleagues report March 24 in Monthly Notices of the Royal Astronomical Society. The key to understanding the systems is figuring out how to interpret light coming from them, the researchers say.  

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    In early 2021, astronomer Tharindu Jayasinghe of Ohio State University and his colleagues reported finding a star system — affectionately named the Unicorn — about 1,500 light-years from Earth that they thought held a giant red star in its senior years orbiting an invisible black hole. Some of the same researchers, including Jayasinghe, later reported a second similar system, dubbed the Giraffe, found about 12,000 light-years away.

    But other researchers, including El-Badry, weren’t convinced that the systems harbored black holes. So Jayasinghe, El-Badry and others combined forces to reanalyze the data.

    To verify each star system’s nature, the researchers turned to stellar spectra, the rainbows that are produced when starlight is split up into its component wavelengths. Any star’s spectrum will have lines where atoms in the stellar atmosphere have absorbed particular wavelengths of light. A slow-spinning star has very sharp lines, but a fast-spinning one has blurred and smeared lines.

    “If the star spins fast enough, basically all the spectral features become almost invisible,” El-Badry says. “Normally, you detect a second star in a spectrum by looking for another set of lines,” he adds. “And that’s harder to do if a star is rapidly rotating.”

    That’s why Jayasinghe and colleagues misunderstood each of these systems initially, the team found.

    “The problem was that there was not just one star, but a second one that was basically hiding,” says astrophysicist Julia Bodensteiner of the European Southern Observatory in Garching, Germany, who was not involved in the new study. That second star in each system spins very fast, which makes them difficult to see in the spectra.

    What’s more, the lines in the spectrum of a star orbiting something will shift back and forth, El-Badry says. If one assumes the spectrum shows just one average, slow-spinning star in an orbit — which is what appeared to be happening in these systems at first glance — that assumption then leads to the erroneous conclusion that the star is orbiting an invisible black hole.

    Instead, the Unicorn and Giraffe each hold two stars, caught in a never-before-seen stage of stellar evolution, the researchers found after reanalyzing the data. Both systems contain an older red giant star with a puffy atmosphere and a “subgiant,” a star on its way to that late-life stage. The subgiants are near enough to their companion red giants that they are gravitationally stealing material from them. As these subgiants accumulate more mass, they spin faster, El-Badry says, which is what made them undetectable initially.

    “Everyone was looking for really interesting black holes, but what they found is really interesting binaries,” Bodensteiner says.

    These are not the only systems to trick astronomers recently. What was thought to be the nearest black hole to Earth also turned out to be pair of stars in a rarely seen stage of evolution (SN: 3/11/22).

    “Of course, it’s disappointing that what we thought were black holes were actually not, but it’s part of the process,” Jayasinghe says. He and his colleagues are still looking for black holes, he says, but with a greater awareness of how pairs of interacting stars might trick them. More

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    How Russia’s war in Ukraine hinders space research and exploration

    Space exploration may seem like a faraway endeavor from Earth’s surface, but events on the ground ripple into space. The Russian war on Ukraine is no exception.

    From a rocket launch system to a rover set to explore Mars, a wide range of space missions is facing postponements or cancelations due to escalating tensions on the ground in the wake of Russia’s full-scale invasion into Ukraine on February 24. The European Union, United States and others have imposed sanctions on Russia; Russia, as a result, is continually changing and canceling its space-related plans. The shifts are having an impact on everything from international collaborations to missions that rely on Russian rockets to get to space.

    Here’s a closer look at some of those projects.

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    ExoMars rover

    The ExoMars mission is a partnership between the European Space Agency and the Russian space agency Roscosmos. This is a two-part mission to Mars consisting of an orbiter and a rover. The orbiter has been at the Red Planet since late 2016, but the Rosalind Franklin rover was supposed to launch this September (SN: 10/18/16).

    “The sanctions and the wider context make a launch in 2022 very unlikely,” the European Space Agency, or ESA, said in a February 28 statement in response to Russia’s invasion of Ukraine.

    Due to Earth’s and Mars’ orbital geometry, the most direct trajectory for a spacecraft from our planet to Mars repeats every two years, and that launch window remains open for less than two weeks. The ExoMars rover, which will look for signs of past life, was originally to launch in 2020, but due to the pandemic and technical issues, it slipped to 2022 (SN: 3/12/20). Now it’s at risk of slipping again to 2024.

    The eROSITA telescope

    Spectrum-Roentgen-Gamma is a space-based X-ray observatory, run jointly by Germany and Russia, that has been mapping the large-scale structure of the universe for the last two and a half years (SN: 7/8/20). The probe’s main telescope, eROSITA, has discovered hundreds of celestial objects, including a bizarre stellar explosion known as a “cow” (SN: 1/21/22). On February 26, the Germans placed eROSITA into safe mode as an action to “freeze co-operation with Russia,” according to a statement from SRG leadership at the Max Planck Institute in Garching, Germany.  

    “This is a standard, reversible, operation mode of the telescope, in which we do not take data, but keep the vital subsystems on,” says Andrea Merloni, an astronomer at the Max Planck Institute for Extraterrestrial Physics, also in Garching, and eROSITA’s project scientist. He declined to comment on any other aspect of the mission or collaboration with Russia.

    The Russian News Agency TASS reported March 1 that Roscosmos intends to estimate the financial loss of that safe-mode action and other European space-related sanctions, and the Russian space agency will then bill “the European side” of the projects.

    ESA, meanwhile, is “assessing the consequences on each of our ongoing programmes conducted in cooperation with the Russian state space agency,” the agency said in its February 28 statement.

    Navigation satellites

    In response to international sanctions against Russia, the head of Roscosmos announced February 26 that the agency was suspending cooperation with the European spaceport in Kourou, French Guiana, and withdrawing its dozens of employees from the site. Several space missions were set to launch from this location via a Russian Soyuz rocket in the next year, including a pair of European navigation satellites in early April.

    These satellites would have joined with the already-launched two dozen that make up the Galileo navigational system, the European answer to the United States’ GPS system. Two additional Galileo satellites are also in orbit, but they were placed incorrectly and instead focus on science and search and rescue (SN: 12/10/18).

    OneWeb internet network

    The U.K. company OneWeb, which is building a space-based internet network with hundreds of low-Earth satellites, is also facing a launch postponement.

    A Soyuz rocket was scheduled to send up a few dozen OneWeb satellites March 4, one of a series of launches aimed at completing the network in 2022. But in the early hours of March 2, the head of Roscosmos tweeted the space agency wouldn’t launch the satellites without a guarantee from the company that they wouldn’t be used for military purposes. He also demanded the U.K. government sell its share of the mission, which it has refused to do.

    Venera-D mission to Venus

    The Russian-Ukraine war has also affected U.S. space activities, but to a lesser extent than its impact on its European counterparts. NASA has relationships with several commercial partners, so the agency relies less on Roscosmos. But NASA is still feeling some effects.

    For instance, in retaliation to U.S. sanctions, the head of Roscosmos tweeted on February 26 that NASA’s participation in the Russian-led Venera-D mission to Venus would be “inappropriate.” This mission will include an orbiter, lander and surface station, and it will focus on understanding Venus’s former and present habitability.

    However, Venera-D won’t launch until late this decade, and NASA has been involved only in some planning groups. The U.S. space agency already has two of its own Venus missions in the works (SN: 6/02/21).

    International Space Station

    While many areas of cooperation in space with Russia are fraying, the International Space Station collaboration so far remains unchanged. “NASA continues working with all our international partners, including the State Space Corporation Roscosmos, for the ongoing safe operations of the International Space Station,” NASA public affairs officer Joshua Finch, at Kennedy Space Center in Cape Canaveral, said in an e-mailed statement.

    Currently, there are two Russian cosmonauts, four NASA astronauts and one ESA astronaut aboard the station. Later this month, a Russian Soyuz capsule is set to return the two cosmonauts and one of the NASA astronauts to Earth, landing in Kazakhstan as scheduled, Finch said.

    However, during a March 1 NASA Advisory Council meeting, Wayne Hale, a former NASA associate administrator, recommended the U.S. space agency consider contingencies in case Russia no longer collaborates on the space station. At the same meeting the following day, former U.S. representative Jane Harman recommended that NASA think about what cooperation with Russia will look like going forward. More

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    A space rock called Kamoʻoalewa may be a piece of the moon

    The moon’s violent history is written across its face. Over billions of years, space rocks have punched craters into its surface, flinging out debris. Now, for the first time, astronomers may have spotted rubble from one of those ancient smashups out in space. The mysterious object known as Kamoʻoalewa appears to be a stray fragment of the moon, researchers report online November 11 in Communications Earth & Environment.

    Discovered in 2016, Kamoʻoalewa — also known as 2016 HO3 — is one of Earth’s five known quasisatellites (SN: 6/24/16). These are rocks that stick fairly close to the planet as they orbit the sun. Little is known about Earth’s space rock entourage because these objects are so small and faint. Kamoʻoalewa, for instance, is about the size of a Ferris wheel and strays between 40 and 100 times as far from Earth as the moon, as its orbit around the sun weaves in and out of Earth’s. That has left astronomers to wonder about the nature of such tagalong rocks.

    “An object in a quasisatellite orbit is interesting because it’s very difficult to get into this kind of orbit — it’s not the kind of orbit that an object from the asteroid belt could easily find itself caught in,” says Richard Binzel, a planetary scientist at MIT not involved in the new work. Having an orbit nearly identical to Earth’s immediately raises suspicions that an object like Kamoʻoalewa originated in the Earth-moon system, he says.

    Researchers used the Large Binocular Telescope and the Lowell Discovery Telescope, in Safford and Happy Jack, Ariz., respectively, to peer at Kamoʻoalewa in visible and near-infrared wavelengths. “The real money is in the infrared,” says Vishnu Reddy, a planetary scientist at the University of Arizona in Tucson. Light at those wavelengths contains important clues about the minerals in rocky bodies, helping distinguish objects such as the moon, asteroids and terrestrial planets.

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    Kamoʻoalewa reflected more sunlight at longer, or redder, wavelengths. This pattern of light, or spectrum, looked unlike any known near-Earth asteroid, Reddy and colleagues found. But it did look like grains of silicate rock from the moon brought back to Earth by Apollo 14 astronauts (SN: 2/20/71).

    “To me,” Binzel says, “the leading hypothesis is that it’s an ejected fragment from the moon, from a cratering event.”

    Martin Connors, who was involved in the discovery of Earth’s first known quasisatellites but did not participate in the new research, also suspects that Kamoʻoalewa is a chip off the old moon. “This is well-founded evidence,” says Connors, a planetary scientist at Athabasca University in Canada. But, he cautions, “that doesn’t mean it’s right.”

    More detailed observations could help confirm Kamoʻoalewa is made of moon stuff. “If you really wanted to put that nail in the coffin, you’d want to go and visit, or rendezvous with this little quasisatellite and take a lot of up-close observations,” says Daniel Scheeres, a planetary scientist at the University of Colorado Boulder not involved in the work. “The best would be to get a sample.”

    China’s space agency has announced plans to send a probe to Kamoʻoalewa to scoop up a bit of rock and bring it back to Earth later this decade. More