Space

Crusts, cracks and other geologic features on sand dunes near the Martian equator are leading researchers to believe there may have been water there much more recently than previously thought.

The features, likely caused by the movement of thawed, salty water, turned up in images taken by China’s Zhurong rover. A chemical analysis from the rover shows that they may have formed as recently as 400,000 years ago, researchers report April 28 in Science Advances.

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The results could help guide future missions to find life on Mars. Atmospheric conditions on Mars 400,000 years ago were similar to what’s seen now, suggesting it’s possible that there’s still liquid, salty water at the planet’s low latitudes, says Xiaoguang Qin, a geologist at the Chinese Academy of Sciences in Beijing.

The Zhurong rover — China’s first Mars rover — landed on the Red Planet in May of 2021 in a region called Utopia Planitia, just north of the Martian equator (SN: 5/19/21). Over nine months, the rover gathered images and information on the chemical composition of the region’s dunes and took measurements of the cracks found along the sandy surfaces.

When Qin and his team first saw the rover images they were surprised. The crust’s features appeared to be related to water activity. Wind wouldn’t leave those geologic tracks; it would instead erode the crust. Nor would dioxide frost; it wouldn’t exist at lower latitudes. Melting pockets of frozen water best explained the features found on the dunes, the team concluded.

Mapping the number and size of meteorite impact craters in the area gave a rough estimate of the dunes’ age — they likely formed 1.4 million to 400,000 years ago. That suggests there was water in the region as recently as hundreds of thousands of years ago, not billions of years ago, as previously speculated.

It’s the combination of the features seen in the dunes with the age which makes the new research special, says Aditya Khuller, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “We’ve seen these features before,” says Khuller. “But they’re usually much older.”

Scientists also have previously found evidence for current-day water ice in the mid-latitude gullies of Mars. And data from NASA landers hint that liquid brines can exist on the planet at middle to high northern latitudes, although it would be too cold for life (SN: 5/11/20).  

Qin says the findings from the Zhurong rover point to comparatively mild ground temperatures, which suggests the low-latitude sand dunes of Mars could be hospitable to life. More

Rocky planets might have been forming since the beginning of the universe. A stellar nursery in a neighboring galaxy has the right materials for such planet formation, researchers report April 24 in Nature Astronomy.

The overall chemical makeup of the tiny galaxy, called the Small Magellanic Cloud, is akin to that of the early universe. The finding suggests that rocky planets might have been able to develop in the relatively pristine chemical environment that pervaded the cosmos just a couple billion years after the Big Bang.

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The Small Magellanic Cloud is one of the Milky Way’s nearest galactic neighbors, though it’s very different from our galaxy. The tiny galaxy has a much lower abundance of heavy metal elements — such as iron, magnesium and aluminum — which are all crucial to the formation of rocky planets. This low-metal environment also mimics that of the early universe, an epoch before stars had enough time to forge the heavy elements and blow them out into space.

Because of the lack of these elements, astronomers have been unsure if rocky planets are able to form in the Small Magellanic Cloud. And previous telescopes did not have the ability to really probe young stars with a mass less than or equal to that of the sun, so astronomers couldn’t measure the star systems’ dust content, which is needed to infer if planets could be being born. But with the sensitivity of the James Webb Space Telescope, or JWST, astronomers can now gather more light and see smaller, fainter stars in greater detail (SN: 12/7/22).

Astrophysicist Olivia Jones and colleagues used an infrared camera on JWST to look at a region of the Small Magellanic Cloud called NGC 346, where young stars are forming. “It’s the first time ever we’ve really been able to look at how solar-size stars form in an environment akin to the early universe,” says Jones, of the Royal Observatory, Edinburgh.

The team detected signatures that suggest that lots of dust is orbiting and falling toward hundreds of stars in the region. As these dust grains orbit, they could begin to stick together and eventually accrete to create rocky planets.

“One of the things we would love to understand better is how the environmental context impacts star formation and then, later on, the planet-forming populations around those young, forming stars,” says Michael Meyer, an astronomer at the University of Michigan in Ann Arbor who was not involved in the research.

Because the Small Magellanic Cloud is the nearest example of a cosmic region with a much different chemical composition than the Milky Way, he says, it provides the first touchstone to study how star and planet formation depend on the stellar environment.

The low-metal stellar environment in the Small Magellanic Cloud is comparable to that of faraway galaxies that were developing around 11 billion years ago. During this time, a period called “cosmic noon,” there was a surge of star formation throughout the cosmos. If rocky planets could be accreting around stars in the Small Magellanic Cloud, the researchers suggest, such worlds could have been forming in the early years of the universe as well.

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The young stars in NGC 346 are also relative lightweights. One reason scientists are interested in studying the possibility of planet formation around low-mass stars is because they are the most common type of stars in the universe and the longest-lived, says Penn State astronomer Kevin Luhman, who was not involved in the research.

“They offer the longest period of time in which life might form and survive on any planets around them,” Luhman says. “If the most common star in the universe lived for only a million years, then exploded, that would be kind of bad for life.” The fact that these types of stars can potentially form rocky planets, he says, is a good sign for life developing elsewhere in the universe.

Follow-up research will focus on determining what chemical signatures can be found developing around the stars, Jones says. This could clue the researchers in to what the chemical elements are that make up any rocky planets. More

Uracil, a building block of life, has been found on the asteroid Ryugu.

Yasuhiro Oba and colleagues discovered the precursor to life in samples collected from the asteroid and returned to Earth by Japan’s Hayabusa2 spacecraft, the team reports March 21 in Nature Communications.

“The detection of uracil in the Ryugu sample is very important to clearly demonstrate that it is really present in extraterrestrial environments,” says Oba, an astrochemist at Hokkaido University in Sapporo, Japan.

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Uracil had been previously detected in samples from meteorites, including a rare class called CI-chondrites, which are abundant in organic compounds. But those meteorites landed on Earth, leaving open the possibility they had been contaminated by humans or Earth’s atmosphere. Because the Ryugu samples were collected in space, they are the purest bits of the solar system scientists have studied to date (SN: 6/9/22). That means the team could rule out the influence of terrestrial biology.

Oba’s team was given only about 10 milligrams of the Ryugu sample for its analysis. As a result, the researchers were not confident they would be able to detect any building blocks, even though they’d been able to previously detect uracil and other nucleobases inmeteorites (SN: 4/26/22).

Nucleobases are biological building blocks that form the structure of RNA, which is essential to protein creation in all living cells. One origin-of-life theory suggests RNA predated DNA and proteins and that ancient organisms relied on RNA for the chemical reactions associated with life (SN: 4/4/04).

The Japanese spacecraft Hayabusa2 collected these samples of Ryugu on two separate touchdowns on the asteroid. The sample on the left contains 38.4 milligrams of material and the one on the right, 37.5 milligrams. Analysis of about 10 milligrams of the sample revealed the presence of uracil, a key building block of life.Y. Oba et al/Nature Communications 2023, JAXA

The team used hot water to extract organic material from the Ryugu samples, followed by acid to further break chemical bonds and separate out uracil and other smaller molecules.

Laura Rodriguez, a prebiotic chemist at the Lunar and Planetary Institute in Houston, Texas, who was not involved in the study, says this method leaves the possibility that the uracil was separated from a longer chain of molecules in the process. “I think it’d be interesting in future work to look at more complex molecules rather than just the nucleobases,” Rodriguez says.

She says she’s seen in her research that the nucleobases can form bonds to create more complex structures, such as a possible precursor to the nucleic acid which may lead to RNA formation. “My question is, are those more complex structures also forming in the asteroids?”

Oba says his team plans to analyze samples from NASA’s OSIRIS-REX mission, which grabbed a bit of asteroid Bennu in 2020 and will return it to Earth this fall (SN: 10/21/20). More

In August 2021 on a lonely crater floor, the newest Mars rover dug into one of its first rocks.

The percussive drill attached to the arm of the Perseverance rover scraped the dust and top several millimeters off a rocky outcrop in a 5-centimeter-wide circle. From just above, one of the rover’s cameras captured what looked like broken shards wedged against one another. The presence of interlocking crystal textures became obvious. Those textures were not what most of the scientists who had spent years preparing for the mission expected.

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Then the scientists watched on a video conference as the rover’s two spectrometers revealed the chemistry of those meshed textures. The visible shapes along with the chemical compositions showed that this rock, dubbed Rochette, was volcanic in origin. It was not made up of the layers of clay and silt that would be found at a former lake bed.

Nicknamed Percy, the rover arrived at the Jezero crater two years ago, on February 18, 2021, with its sidekick helicopter, Ingenuity. The most complex spacecraft to explore the Martian surface, Percy builds on the work of the Curiosity rover, which has been on Mars since 2012, the twin Spirit and Opportunity rovers, the Sojourner rover and other landers.

But Perseverance’s main purpose is different. While the earlier rovers focused on Martian geology and understanding the planet’s environment, Percy is looking for signs of past life. Jezero was picked for the Mars 2020 mission because it appears from orbit to be a former lake environment where microbes could have thrived, and its large delta would likely preserve any signs of them. Drilling, scraping and collecting pieces of the Red Planet, the rover is using its seven science instruments to analyze the bits for any hint of ancient life. It’s also collecting samples to return to Earth.

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Since landing, “we’ve been able to start putting together the story of what has happened in Jezero, and it’s pretty complex,” says Briony Horgan, a planetary scientist at Purdue University in West Lafayette, Ind., who helps plan Percy’s day-to-day and long-term operations.

Volcanic rock is just one of the surprises the rover has uncovered. Hundreds of researchers scouring the data Perseverance has sent back so far now have some clues to how the crater has evolved over time. This basin has witnessed flowing lava, at least one lake that lasted perhaps tens of thousands of years, running rivers that created a mud-and-sand delta and heavy flooding that brought rocks from faraway locales.

Jezero has a more dynamic past than scientists had anticipated. That volatility has slowed the search for sedimentary rocks, but it has also pointed to new alcoves where ancient life could have taken hold.

Perseverance has turned up carbon-bearing materials — the basis of life on Earth — in every sample it has abraded, Horgan says. “We’re seeing that everywhere.” And the rover still has much more to explore.

On the floor of the Jezero crater (shown on July 28, 2021), Perseverance found rocks that were volcanic in nature, not the sedimentary rocks that scientists expected from a dry lake bed.JPL-CALTECH/NASA, ASU, MSSS

Perseverance finds unexpected rocks

Jezero is a shallow impact crater about 45 kilo­meters in diameter just north of the planet’s equator. The crater formed sometime between 3.7 billion and 4.1 billion years ago, in the solar system’s first billion years. It sits in an older and much larger impact basin known as Isidis. At Jezero’s western curve, an etched ancient riverbed gives way to a dried-out, fan-shaped delta on the crater floor.

That delta “is like this flashing signpost beautifully visible from orbit that tells us there was a standing body of water here,” says astrobiologist Ken Williford of Blue Marble Space Institute of Science in Seattle.

Perseverance landed on the crater floor about two kilometers from the front of the delta. Scientists thought they’d find compacted layers of soil and sand there, at the base of what they dubbed Lake Jezero. But the landscape immediately looked different than expected, says planetary geologist Kathryn Stack Morgan of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Stack Morgan is deputy project scientist for Perseverance.

Closeup images of an abraded rock from the floor of the Jezero crater show a distinct crystalline structure.JPL-CALTECH/NASA, MSSS

For the first several months after the landing, the Mars 2020 mission team tested the rover’s movements and instruments, slowly, carefully. But from the first real science drilling near the landing location, researchers back on Earth realized what they had found. The texture of the rock, Stack Morgan says, was “a textbook igneous volcanic rock texture.” It looked like volcanic lava flows.

Over the next six months, several more rocks on the crater floor revealed igneous texture. Some of the most exciting rocks, including Rochette, showed olivine crystals throughout. “The crystal fabric was obviously cooled from a melt, not transported grains,” as would be the case if it were a sedimentary sample, says Abigail Allwood of the Jet Propulsion Lab. She leads the rover’s PIXL instrument, which uses an X-ray beam to identify each sample’s composition.

Mission scientists now think the crater floor is filled with igneous rocks from two separate events — both after the crater was created, so more recently than the 3.7 billion to 4.1 billion years ago time frame. In one, magma from deep within the planet pushed toward the surface, cooled and solidified, and was later exposed by erosion. In the other, smaller lava flows streamed at the surface.

Sometime after these events, water flowed from the nearby highlands into the crater to form a lake tens of meters deep and lasting tens of thousands of years at least, according to some team members. Percy’s instruments have revealed the ways that water altered the igneous rocks: For example, scientists have found sulfates and other minerals that require water to form, and they’ve seen empty pits within the rocks’ cracks, where water would have washed away material. As that water flowed down the rivers into the lake, it deposited silt and mud, forming the delta. Flooding delivered 1.5-meter-wide boulders from that distant terrain. All of these events preceded the drying of the lake, which might have happened about 3 billion years ago.

Core samples, which Perseverance is collecting and storing on board for eventual return to Earth, could provide dates for when the igneous rocks formed, as well as when the Martian surface became parched. During the time between, Lake Jezero and other wet environments may have been stable enough for microbial life to start and survive.

“Nailing down the geologic time scale is of critical importance for us understanding Mars as a habitable world,” Stack Morgan says. “And we can’t do that without samples to date.”

About a year after landing on Mars, Perseverance rolled several kilometers across the crater floor to the delta front — where it encountered a very different geology.

The delta might hold signs of ancient life

Deltas mark standing, lasting bodies of water — stable locales that could support life. Plus, as a delta grows over time, it traps and preserves organic matter.

Sand and silt deposited where a river hits a lake get layered into sedimentary material, building up a fan-shaped delta. “If you have any biological material that is trapped between that sediment, it gets buried very quickly,” says Mars geologist Eva Scheller of MIT, a researcher with the Percy team. “It creates this environment that is very, very good for preserving the organic matter.”

While exploring the delta front between April 2022 and December 2022, Perseverance found some of the sedimentary rocks it was after.

Sedimentary rocks made of layers of sand and silt turned up in the delta front region (shown on April 16, 2022), which Perseverance has been exploring since April of last year.JPL-CALTECH/NASA, ASU

Several of the rover’s instruments zoomed in on the textures and shapes of the rocks, while other instruments collected detailed spectral information, revealing the elements present in those rocks. By combining the data, researchers can piece together what the rocks are made of and what processes might have changed them over the eons. It’s this chemistry that could reveal signs of ancient Martian life — biosignatures. Scientists are still in the early stages of these analyses.

There won’t be one clear-cut sign of life, Allwood says. Instead, the rover would more likely reveal “an assemblage of characteristics,” with evidence slowly building that life once existed there.

Chemical characteristics suggestive of life are most likely to hide in sedimentary rocks, like those Perseverance has studied at the delta front. Especially interesting are rocks with extremely fine-grained mud. Such mud sediments, Horgan says, are where — in deltas on Earth, at least — organic matter is concentrated. So far, though, the rover hasn’t found those muddy materials.

But the sedimentary rocks studied have revealed carbonates, sulfates and unexpected salts — all materials indicating interaction with water and important for life as we know it. Percy has found carbon-based matter in every rock it has abraded, Horgan says.

“We’ve had some really interesting results that we’re pretty excited to share with the community,” Horgan says about the exploration of the delta front. Some of those details may be revealed in March at the Lunar and Planetary Science Conference.

Perseverance leaves samples for a future mission

As of early February, Perseverance has collected 18 samples, including bits of Mars debris and cores from rocks, and stored them on board in sealed capsules for eventual return to Earth. The samples come from the crater floor, delta front rocks and even the thin Martian atmosphere.

In the final weeks of 2022 and the first weeks of 2023, the rover dropped — or rather, carefully set down — half of the collected samples, as well as a tube that would reveal whether samples contained any earthly contaminants. These captured pieces of Mars are now sitting at the front of the delta, at a predetermined spot called the Three Forks region.

Perseverance deposited a cache of samples in the Three Forks region in December and January. If the rover isn’t operable when a future mission arrives at Mars, the samples can still be collected and returned to Earth.JPL-CALTECH/NASA, MSSS

If Perseverance isn’t functioning well enough to hand over its onboard samples when a future sample-return spacecraft arrives, that mission will collect these samples from the drop site to bring back to Earth.

Researchers are currently working on designs for a joint Mars mission between NASA and the European Space Agency that could retrieve the samples. Launching in the late 2020s, it would land near the Perseverance rover. Percy would transfer the samples to a small rocket to be launched from Mars and returned to Earth in the 2030s. Lab tests could then confirm what Perseverance is already uncovering and discover much more.

Meanwhile, Percy is climbing up the delta to explore its top, where muddy sedimentary rocks may still be found. The next target is the edge of the once-lake, where shallow water long ago stood. This is the site Williford is most excited about. Much of what we know about the history of how life has evolved on Earth comes from environments with shallow water, he says. “That’s where really rich, underwater ecosystems start to form,” he says. “There’s so much going on there chemically.”

Perseverance landed on Mars in February 2021. As of early February of this year, the rover had gathered 18 samples — and deposited half for a future potential return to Earth.JPL-CALTECH/NASA More

CHICAGO — An entire ocean of liquid magma, or maybe a hot heart of solid metal, may lurk in Io’s underworld.

The surface of Jupiter’s innermost moon is covered in scorching lava lakes and gored by hundreds of active volcanoes, some spitting molten rock dozens of kilometers high (SN: 8/6/14). Over the years, the moon’s restless, mesmerizing hellscape has attracted the attention of many planetary scientists (SN: 5/3/22).

Now, researchers are digging into the nature of Io’s infernal interior to explain what is driving the spectacular volcanism on the moon’s fiery surface. “It’s the most volcanically active place in the solar system,” says planetary scientist Samuel Howell of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “But it’s not really clear where that energy comes from.”

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Researchers generally agree that Io gets most of its energy from a gravitational tug-of-war between its parent planet Jupiter and its sibling moon Europa. Those grand forces pull on Io’s rocky body, generating tremendous frictional heat in its interior. But how that heat is stored and moved around remains a mystery.

One explanation is that Io’s netherworld may house an enormous ocean of liquid magma, planetary scientist David Stevenson of Caltech said December 15 at the American Geophysical Union’s fall meeting. Though the exact size of the proposed molten sea remains uncertain, it would need to be relatively large, he said. “The magma ocean could be, say, 100 kilometers thick.”

In 2011, researchers reported that Io’s mantle couldn’t be completely solid. Magnetic measurements of Io from the Galileo spacecraft indicated there must be an electrically conductive layer inside the moon. A global underground layer containing molten rock, the scientists wrote, would fit the bill.  

Hot spots speckle the surface of the volcanic moon Io in this infrared image captured by NASA’s Juno spacecraft on July 5, 2022, when the spacecraft was about 80,000 kilometers from the moon.JPL-Caltech/NASA, SwRI, ASI, INAF, JIRAM

But the researchers couldn’t tell whether that layer would consist of a continuous sea of magma or many little pockets of molten rock dispersed throughout solid rock, resembling a soggy sponge.

Building off that previous work, Stevenson and Caltech geophysicist Yoshinori Miyazaki calculated that a mixed layer of magma and solid rock beneath Io’s crust would be fundamentally unstable under the amount of heating they predict occurs inside the moon. The molten rock and solid rock would split into distinct layers, with the molten rock coalescing into a subsurface sea, Stevenson said. “The final conclusion is [that] Io has a magma ocean.”

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But there are other possibilities. “A lot of information is consistent with a large, global conductive layer that could be a magma ocean,” Howell says. “But I wouldn’t say there’s consensus on how to interpret that data.”

Instead, the truth may lie within Io’s heart, where a core made of solid metal may lurk, Howell reported December 15 at the meeting. Previous research has suggested that Io has a core rich in metals. Howell and colleagues calculate that a metal core that’s about as rigid as solid ice and a rocky mantle as viscous as Earth’s could fully dispense the immense quantities of heat that Io is estimated to emit. That would fulfill the energy-shedding role of a magma ocean.

Future measurements collected by NASA’s ongoing Juno mission as well two future spacecraft — NASA’s Europa Clipper and the European Space Agency’s JUICE — may provide the data needed to determine whether either, or some combination, of the hypotheses is correct, Stevenson and Howell said (SN: 12/15/22). Until then, the mystery of what dwells in Io’s dark depths may have to remain in purgatory. More

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

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 arXiv.org. 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.

[embedded content]
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

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