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    5 cool things to know about NASA’s Lucy mission to the Trojan asteroids

    For the first time, a spacecraft is headed to Jupiter’s odd Trojan asteroids. What Lucy finds there could provide a fresh peek into the history of the solar system.

    “Lucy will profoundly change our understanding of planetary evolution in our solar system,” Adriana Ocampo, a planetary scientist at NASA Headquarters in Washington, D.C., said at a news briefing October 14.

    The mission is set to launch from the Kennedy Space Center at Cape Canaveral, Fla., as early as October 16. Live coverage will air on NASA TV beginning at 5 a.m. EDT, in anticipation of a 5:34 a.m. blast off.

    The Trojan asteroids are two groups of space rocks that are gravitationally trapped in the same orbit as Jupiter around the sun. One group of Trojans orbits ahead of Jupiter; the other follows the gas giant around the sun. Planetary scientists think the Trojans could have formed at different distances from the sun before getting mixed together in their current homes. The asteroids could also be some of the oldest and most pristine objects in the solar system.

    The mission will mark several other firsts, from the types of objects it will visit to the way it powers its instruments. Here are five cool things to know about our first visit to the Trojans.

    1. The Trojan asteroids are a solar system time capsule.

    The Trojans occupy spots known as Lagrangian points, where the gravity from the sun and from Jupiter effectively cancel each other out. That means their orbits are stable for billions of years.

    “They were probably placed in their orbits by the final gasp of the planet formation process,” the mission’s principal investigator Hal Levison, a planetary scientist at Southwest Research Institute in Boulder, Colo.,  said September 28 in a news briefing.

    But that doesn’t mean the asteroids are all alike. Scientists can tell from Earth that some Trojans are gray and some are red, indicating that they might have formed in different places before settling in their current orbits. Maybe the gray ones formed closer to the sun, and the red ones formed farther from the sun, Levison speculated.

    Studying the Trojans’ similarities and differences can help planetary scientists tease out whether and when the giant planets moved around before settling into their present positions (SN: 4/20/12). “This is telling us something really fundamental about the formation of the solar system,” Levison said.

    2. The spacecraft will visit more individual objects than any other single spacecraft. 

    Lucy will visit eight asteroids, including their moons. Over its 12-year mission, it will visit one asteroid in the main asteroid belt between Mars and Jupiter, and seven Trojans, two of which are binary systems where a pair of asteroids orbit each other.

    “We are going to be visiting the most asteroids ever with one mission,” planetary scientist Cathy Olkin, Lucy’s deputy principal investigator, said in the Oct. 14 briefing.

    The spacecraft will observe the asteroids’ composition, shape, gravity and geology for clues to where they formed and how they got to the Lagrangian points.

    The spacecraft’s first destination, in April 2025, will be an asteroid in the main belt. Next, it will visit five asteroids in the group of Trojans that orbit the sun ahead of Jupiter: Eurybates and its satellite Queta in August 2027; Polymele in September 2027; Leucus in April 2028; and Orus in November 2028. Finally, the spacecraft will shift to Jupiter’s other side and visit the twin asteroids Patroclus and Menoetius in the trailing group of space rocks in March 2033.

    The spacecraft won’t land on any of its targets, but it will swoop within 965 kilometers of their surfaces at speeds of 3 to 5 meters per second relative to the asteroids’ speed through space.

    There’s no need to worry about collisions while zipping through these asteroid clusters, Levison said. Although there are about 7,000 known Trojans, they’re very far apart. “If you were standing on any one of our targets, you wouldn’t be able to tell you were part of the swarm,” he said.

    The Trojan asteroids trail and follow Jupiter in its orbit around the sun, but they’re actually quite far from the giant planet. In fact, Earth is closer to Jupiter than either swarm of Trojans is.NASA, adapted by T. TibbittsThe Trojan asteroids trail and follow Jupiter in its orbit around the sun, but they’re actually quite far from the giant planet. In fact, Earth is closer to Jupiter than either swarm of Trojans is.NASA, adapted by T. Tibbitts

    3. Lucy will have a weird flight path.

    In order to make so many stops, Lucy will need to take a complex path. First, the spacecraft will swoop past Earth twice to get a gravitational boost from our planet that will help propel it onward to its first asteroid.

    The closest Earth flyby, in October 2022, will take it within 300 kilometers of the planet’s surface, closer than the International Space Station, the Hubble Space Telescope and many satellites, Olkin said. Observers on Earth might even be able to see it. “I’m hoping to go near where it flies past and look up and see Lucy flying by a year from now,” she said.

    Then in December 2030, after more than a year exploring the “leading” swarm of Trojans, Lucy will come back to the vicinity of Earth for one more boost. That final gravitational slingshot will send the spacecraft to the other side of the sun to visit the “trailing” swarm. This will make Lucy the first spacecraft ever to venture to the outer solar system and come back near Earth again.

    4. Lucy will travel farther from the sun than any other solar-powered craft.

    Another record Lucy will break has to do with its power source: the sun. Lucy will run on solar power out to 850 million kilometers away from the sun, making it the farthest-flung solar powered spacecraft ever.

    To accomplish that, Lucy has a pair of enormous solar arrays. Each 10-sided array is more than 7.3 meters across and includes about 4,000 solar cells per panel, Lucy project manager Donya Douglas-Bradshaw said in a news briefing on October 13. Standing on one end, Lucy and its solar panels would be as tall as a five-story building.

    “It’s a very intricate, sophisticated design,” she said. The advantage of using solar power is that the team can adjust how much power the spacecraft needs based on how far from the sun it is.

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    5. The inspiration for Lucy’s name is decidedly earthbound.

    NASA missions are often named for famous scientists, or with acronyms that describe what the mission will do. Lucy, on the other hand, is named after a fossil.

    The idea that the Trojans hold secrets to the history of the solar system is part of how the mission got its unusual name. To understand, go back to 1974, when paleoanthropologist Donald Johanson and a graduate student discovered a fossil of a human ancestor who had lived 3.2 million years ago. After listening to the Beatles song “Lucy in the Sky with Diamonds” at camp that night, Johanson’s team named the fossil hominid “Lucy.” (In a poetic echo, the first asteroid the Lucy spacecraft will visit is named Donaldjohanson.)

    Planetary scientists hope the study of the Trojans will revolutionize our understanding of the solar system’s history in the same way that studying Lucy’s fossil revolutionized our understanding of human history.

    “We think these asteroids are fossils of solar system formation,” Levison said. So his team named the spacecraft after the fossil. 

    The spacecraft even carries a diamond in one of its instruments, to help split beams of light. Said planetary scientist Phil Christensen of Arizona State University in Tempe at the Oct. 14 briefing: “We truly are sending a diamond into the sky with Lucy.” More

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    Earth is reflecting less light. It’s not clear if that’s a trend

    The amount of sunlight that Earth reflects back into space — measured by the dim glow seen on the dark portions of a crescent moon’s face — has decreased measurably in recent years. Whether the decline in earthshine is a short-term blip or yet another ominous sign for Earth’s climate is up in the air, scientists suggest.

    Our planet, on average, typically reflects about 30 percent of the sunlight that shines on it. But a new analysis bolsters previous studies suggesting that Earth’s reflectance has been declining in recent years, says Philip Goode, an astrophysicist at Big Bear Solar Observatory in California. From 1998 to 2017, Earth’s reflectance declined about 0.5 percent, the team reported in the Sept. 8 Geophysical Research Letters.

    Using ground-based instruments at Big Bear, Goode and his colleagues measured earthshine — the light that reflects off our planet, to the moon and then back to Earth — from 1998 to 2017. Because earthshine is most easily gauged when the moon is a slim crescent and the weather is clear, the team collected a mere 801 data points during those 20 years, Goode and his colleagues report.

    Much of the decrease in reflectance occurred during the last three years of the two-decade period the team studied, Goode says. Previous analyses of satellite data, he and his colleagues note, hint that the drop in reflectance stems from warmer temperatures along the Pacific coasts of North and South America, which in turn reduced low-altitude cloud cover and exposed the underlying, much darker and less reflective seas.

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    “Whether or not this is a long-term trend [in Earth’s reflectance] is yet to be seen,” says Edward Schwieterman, a planetary scientist at University of California, Riverside, who was not involved in the new analysis. “This strengthens the argument for collecting more data,” he says.

    Decreased cloudiness over the eastern Pacific isn’t the only thing trimming Earth’s reflectance, or albedo, says Shiv Priyam Raghuraman, an atmospheric scientist at Princeton University. Many studies point to a long-term decline in sea ice (especially in the Arctic), ice on land, and tiny pollutants called aerosols — all of which scatter sunlight back into space to cool Earth.

    With ice cover declining, Earth is absorbing more radiation. The extra radiation absorbed by Earth in recent decades goes toward warming the oceans and melting more ice, which can contribute to even more warming via a vicious feedback loop, says Schwieterman.

    Altogether, Goode and his colleagues estimate, the decline in Earth’s reflectance from 1998 to 2017 means that each square meter of our planet’s surface is absorbing, on average, an extra 0.5 watts of energy. For comparison, the researchers note in their study, planet-warming greenhouse gases and other human activity over the same period boosted energy input to Earth’s surface by an estimated 0.6 watts of energy per square meter. That means the decline in Earth’s reflectance has, over that 20-year period, almost doubled the warming effect our planet experienced. More

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    NASA’s Perseverance rover snagged its first Martian rock samples

    The Perseverance rover has captured its first two slices of Mars.

    NASA’s latest Mars rover drilled into a flat rock nicknamed Rochette on September 1 and filled a roughly finger-sized tube with stone. The sample is the first ever destined to be sent back to Earth for further study. On September 7, the rover snagged a second sample from the same rock. Both are now stored in airtight tubes inside the rover’s body.

    Getting pairs of samples from every rock it drills is “a little bit of an insurance policy,” says deputy project scientist Katie Stack Morgan of NASA’s Jet Propulsion Lab in Pasadena, Calif. It means the rover can drop identical stores of samples in two different places, boosting chances that a future mission will be able to pick up at least one set.

    The successful drilling is a comeback story for Perseverance. The rover’s first attempt to take a bit of Mars ended with the sample crumbling to dust, leaving an empty tube (SN: 8/19/21). Scientists think that rock was too soft to hold up to the drill.

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    Nevertheless, the rover persevered.

    “Even though some of its rocks are not, Mars is hard,” said Lori Glaze, director of NASA’s  planetary science division, in a September 10 news briefing.

    Rochette is a hard rock that appears to have been less severely eroded by millennia of Martian weather (SN: 7/14/20). (Fun fact: All the rocks Perseverance drills into will get names related to national parks; the region on Mars the rover is now exploring is called Mercantour, so the name Rochette — or “Little Rock”  — comes from a village in France near Mercantour National Park.)

    Rover measurements of the rock’s texture and chemistry suggests that it’s made of basalt and may have been part of an ancient lava flow. That’s useful because volcanic rocks preserve their ages well, Stack Morgan says. When scientists on Earth get their hands on the sample, they’ll be able to use the concentrations of certain elements and isotopes to figure out exactly how old the rock is — something that’s never been done for a pristine Martian rock.

    Rochette also contains salt minerals that probably formed when the rock interacted with water over long time periods. That could suggest groundwater moving through the Martian subsurface, maybe creating habitable environments within the rocks, Stack Morgan says.

    “It really feels like this rich treasure trove of information for when we get this sample back,” Stack Morgan says.

    Once a future mission brings the rocks back to Earth, scientists can search inside those salts for tiny fluid bubbles that might be trapped there. “That would give us a glimpse of Jezero crater at the time when it was wet and was able to sustain ancient Martian life,” said planetary scientist Yulia Goreva of JPL at the news briefing.

    Scientists will have to be patient, though — the earliest any samples will make it back to Earth is 2031. But it’s still a historic milestone, says planetary scientist Meenakshi Wadhwa of Arizona State University in Tempe.

    “These represent the beginning of Mars sample return,” said Wadhwa said at the news briefing. “I’ve dreamed of having samples back from Mars to analyze in my lab since I was a graduate student. We’ve talked about Mars sample return for decades. Now it’s starting to actually feel real.” More

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    50 years ago, astronomers were chipping away at Pluto’s mass

    The shrinking mass of Pluto — Science News, August 28, 1971

    Pluto was the last of the planets to be discovered (in 1930). If astronomers continue to make it lighter, it may be the first to disappear.… [The latest measurement] brings Pluto down to 0.11 of Earth’s mass, less than an eighth of its former self.… The wide discrepancies among the figures presented for the mass of Pluto illustrate the particular difficulties of measuring its mass.… If a planet has satellites, its mass can be determined from studying their motions.… But Pluto has no known satellites.

    Update

    The discovery of Pluto’s moon Charon in 1978 (SN: 7/15/78, p. 36) finally allowed astronomers to accurately calculate the planet’s mass: about 0.2 percent of Earth’s mass. Decades after scientists resolved Pluto’s heft, the planet received arguably the greatest demotion of all — a downgrade to dwarf planet (SN: 9/2/06, p. 149). Some astronomers have since proposed alternate definitions for the term “planet” that, if widely adopted, would restore Pluto to its former rank. More

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    See some of the most intriguing photos from NASA’s Perseverance rover so far

    In February, NASA’s Perseverance rover touched down on Mars and went to work. The rover has seen the first flight of a Martian robot, gotten its drill bit dirty and begun traversing the floor of Jezero crater, thought to be the remains of an ancient lake (SN: 4/30/21).

    And what Perseverance is finding isn’t exactly what scientists expected. “The crater floor is super interesting,” says planetary scientist Briony Horgan of Purdue University in West Lafayette, Ind., one of the mission’s long-term science planners. “We didn’t really know what we were getting into from orbit.”

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    Perseverance is getting views of enormous boulders that may have been transported by ancient floods, fine rock layers that look like they settled in calm waters, and rocks with large crystals that look volcanic. The rover’s landing site may include a volcanic lava flow from long ago, or signs of an earlier episode of water — or something else.

    “It’s not as obvious as we thought,” Horgan says. “Whatever it is, it’s cool.”

    Here are some of the image highlights from the rover so far.

    Taking the long view

    Before the rover landed, the Perseverance team knew that Jezero crater looked like the dry basin of an ancient lake, with a river delta flowing into it. The prospect of finding preserved lake floor sediments made the site good for searching for past life, one of the mission’s primary goals.

    This picture, taken March 17, is a mosaic of five images taken with Perseverance’s Remote Microscopic Imager camera. The tilted layers of sedimentary rock (arrows) and other textures in this escarpment were probably formed by interaction between an ancient river and a lake.JPL-Caltech/NASA, LANL, CNES, CNRS, ASU, MSSS

    Perseverance took this snapshot March 17 of a steep slope in a part of Jezero’s delta, from more than two kilometers away. The rover probably won’t reach that spot until sometime next year. But already, the rover’s Remote Microscopic Imager camera is uncovering details that could reveal new insight into the crater’s watery past.

    For example, the tilted layers of sedimentary rock and cementlike mixtures of coarse sand and pebbles in this rock feature, nicknamed “Delta Scarp,” confirm the delta’s wet history. There are also individual large boulders cemented into the front of the scarp, suggesting that the region saw high floods, says Perseverance deputy project scientist Katie Stack Morgan of NASA’s Jet Propulsion Lab in Pasadena, Calif.

    Closer to home

    Even eroded outcrops close to Perseverance’s landing site look like they had a watery history. This image of a remnant of part of the delta rising out of the crater floor was taken with Perseverance’s Mastcam-Z camera February 22.

    Perseverance’s Mastcam-Z camera took this image (shown in false color) February 22 of a relatively nearby escarpment, which probably preserves ancient lake sediments. Click to enlargeJim Bell/ASU, Mastcam-Z

    “Many of us expected these outcrops to be quite uninteresting, based on orbital data,” Stack Morgan says. But images from the ground showed beautiful layers, just like what you would find in a deep-lake deposit.

    “We weren’t expecting to find them here, but maybe they’re right next door to our landing site,” she says. These outcrops could be remnants of the edge of the lake that used to fill Jezero crater or could represent an even older lake that was replaced.

    Even closer

    Perseverance is taking close-ups of the rocks around it too. This closeup image of a rock nicknamed “Foux” was taken July 11 using the WATSON camera on the end of the rover’s robotic arm. The area in the image is only about 4 centimeters by 3 centimeters.

    This close-up image of a larger rock was taken with Perseverance’s WATSON camera, part of the SHERLOC instrument on the rover’s robotic arm. It shows textured rocks with an interesting coating that might indicate interaction with water. JPL-Caltech/NASA, MSSS

    The textures in this image are fascinating, as are the “crazy red coatings” that are more purple than typical Mars dust, Horgan says. “What rocks are these?” The coatings probably imply alteration by water, and the purple color suggests that they contain some iron, she adds.

    Volcanic grains?

    Perseverance has also found evidence of igneous, or volcanic, rocks on Jezero’s crater floor. That wasn’t surprising — observations from orbit suggested that volcanic rocks should be there, and scientists hoped to pick up some to help researchers back on Earth figure out the rocks’ absolute ages. Right now, the timing of past events on Mars is based on the sizes of craters and the ages of rocks from the moon, and it’s not extremely precise.

    This image, taken August 2, shows mysterious holes and light and dark patches that are potential crystals. The Perseverance rover abraded the rock to prepare for drilling into it. JPL-Caltech/NASA

    Igneous rocks on Mars tend to be old and preserve a record of their ages well. “If you want to figure out when things happened on Mars, you want an igneous rock,” Stack Morgan says.

    On the ground, though, things are a little more complicated. This rock was the first that Perseverance cleared dust from in preparation for taking a sample. The image shows mysterious holes, which could have been formed by erosion or by air bubbles trapped in lava as it cooled. And the surface is divided into light and dark patches that could be individual crystals, or cemented grains.

    If they’re crystals, that suggests volcanic activity, Stack Morgan says — but these crystals are bigger than expected for lava that would have cooled at the planet’s surface. Similar crystals form deep in the subsurface of Earth, where magma solidifies slowly. When lava cools at Earth’s surface, the crystals “don’t have time to grow big,” Stack Morgan says. The next step, she says, is “thinking through how rocks like this could have formed here, if they are indeed igneous or volcanic rocks. How would we get a rock that looks like this?” Maybe this rock formed underground and was transported to the surface, but it’s not clear how.

    First sample attempt

    That same rock carried more surprises when the rover team tried to drill into it August 6. The drill worked perfectly, to the team’s elation. “One of the most complex robotic systems ever designed and executed worked perfectly with no faults the first time,” Stack Morgan says. “We were like ‘Oh my god, this is amazing.’”

    But when they looked inside the tube that was meant to capture the rock sample, it was empty.

    “It’s been a bit of an emotional roller coaster,” Stack Morgan says.

    Perseverance’s shadow (left) looms over the borehole that the rover made on its first attempt to drill into the Red Planet. The rover’s WATSON imager took a close-up of that hole (composite image at right). These images were taken August 6.JPL-Caltech/NASA, MSSS

    The team thinks that the rock was more crumbly than expected, and essentially turned to dust. “The rock was not able to keep its act together,” Stack Morgan says. The drill is designed to sweep the small grains produced in the drilling process, called cuttings, up and out of the sample tube. Stack Morgan thinks the entire sample was treated as cuttings and ended up in a pile of dust on the ground.

    There is a silver lining: Now the rover has a sealed sample of Martian atmosphere. And the rover will attempt to take another sample of a hardier rock sometime soon, Stack Morgan says.

    In the wind

    Mars may have had lakes and rivers in its past, but today the dry, dusty landscape is shaped mostly by wind (SN: 7/14/20). Perseverance has seen a number of dust devils and windstorms sweep through Jezero crater as a beautiful reminder of how environments are always changing, even on a dried-up planet like Mars.

    A dust devil swirls across the Martian landscape. This image was captured with the Perseverance rover’s left Mastcam-Z camera June 15.JPL-Caltech/NASA, ASU

    “We often think of Mars as this barren wasteland where not much happens today,” Stack Morgan says. “But when you see these dust devils move across the images, you’re kind of reminded that Mars, even though not Earthlike, is its own very active planet still.” More

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    Jupiter’s intense auroras superheat its upper atmosphere

    Jupiter’s upper atmosphere is hundreds of degrees warmer than expected. After a decades-long search, scientists may have pinned down a likely source of that anomalous heat. The culprit, a new study suggests, is the planet’s intense auroras, Jupiter’s version of Earth’s northern and southern lights (SN: 6/8/21).

    The temperature of the upper atmosphere of Jupiter, which orbits an average distance of 778 million kilometers from the sun, should be about –73° Celsius, says James O’Donoghue, a planetary scientist at the JAXA Institute of Space and Astronautical Science in Sagamihara, Japan. That’s largely due to the feeble illumination of the sun there, which amounts to less than 4 percent of the energy per square meter that hits Earth’s atmosphere. Instead, the region several hundred kilometers above the planet’s cloud tops has an average temperature of about 426° C.

    Scientists first noticed this mismatch more than 40 years ago. Since then, researchers have come up with several ideas about where the upper atmosphere’s thermal boost might originate, including pressure waves or gravity waves created by turbulence lower in the atmosphere. But observations by O’Donoghue and his colleagues now provide convincing evidence that the auroras pump heat throughout the planet’s upper atmosphere.

    The researchers used the 10-meter Keck II telescope atop Hawaii’s dormant Mauna Kea volcano to observe Jupiter on one night each in 2016 and 2017. Specifically, the team looked for infrared emissions that betray the presence of positively charged hydrogen molecules (H3+). Those molecules are created when charged particles in the solar wind, among other sources, slam into the planet’s atmosphere at hundreds or thousands of kilometers per second, painting polar auroras.

    Measuring the intensities of these molecules’ infrared emissions let the team pin down how hot it gets high above the cloud tops. In those polar regions, temperatures in the upper atmosphere likely top out at about 725° C, the team reports in the Aug. 5 Nature. But at equatorial latitudes, the team’s heat map showed that the temperature falls to about 325° C. That pattern of a gradual drop-off in temperature toward lower latitudes bolsters the notion that Jupiter’s auroras are the source of anomalous heat in the upper atmosphere and that winds disperse that warmth from the polar regions.

    One of the nights the team observed Jupiter — January 25, 2017 — was particularly well-timed because Jupiter was experiencing a strong solar flare at the time. Besides an intense aurora, data revealed a broad swath of warmer-than-normal gases at mid-latitudes, which the researchers interpret as a wave of warmth rolling southward. “It was pure luck that we captured this potential heat-shedding event,” says O’Donoghue.

    The team’s observations “are close to a ‘smoking gun’ for the redistribution of auroral energy,” says Tommi Koskinen, a planetary scientist at the University of Arizona in Tucson. The next challenge, he notes, is to understand the underlying mechanisms of heat production and heat transfer and to then incorporate them into researchers’ simulations of Jupiter’s atmospheric circulation. More

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    Marsquakes reveal the Red Planet boasts a liquid core half its diameter

    Mars has had its first CT scan, thanks to analyses of seismic waves picked up by NASA’s InSight lander. Diagnosis: The Red Planet’s core is at least partially liquid, as some previous studies had suggested, and is somewhat larger than expected.

    InSight reached Mars in late 2018 and soon afterward detected the first known marsquake (SN: 11/26/18; SN: 4/23/19). Since then, the lander’s instruments have picked up more than a thousand temblors, most of them minor rumbles. Many of those quakes originated at a seismically active region more than 1,000 kilometers away from the lander. A small fraction of the quakes had magnitudes ranging from 3.0 to 4.0, and the resulting vibrations have enabled scientists to probe Mars and reveal new clues about its inner structure.

    Simon Stähler, a seismologist at ETH Zurich, and colleagues analyzed seismic waves from 11 marsquakes, looking for two types of waves: pressure and shear. Unlike pressure waves, shear waves can’t pass through a liquid, and they move more slowly, traveling side to side through solid materials, rather than in a push-and-pull motion in the same direction a wave is traveling like pressure waves do.

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    Of those 11 events, six sets of vibrations included shear waves strong enough to stand out from background noise. The strength of those shear waves suggests that they reflected off of the outer surface of a liquid core, rather than entering a solid core and being partially absorbed, Stähler says. And the difference in arrival times at InSight for the pressure waves and shear waves for each quake suggest that Mars’ core is about 3,660 kilometers in diameter, he and colleagues report in the July 23 Science.

    That’s a little more than half of the diameter of the entire planet, larger than most previous estimates. The Red Planet’s core is so big, in fact, that it blocks InSight from receiving certain types of seismic waves from a large part of the planet. That, in turn, suggests that Mars may be more seismically active than the lander’s sensors can detect. Indeed, one of the regions in the lander’s seismic blind spot is the Tharsis region, home to some of Mars’ largest volcanoes. Volcanic activity there, as well as the motion of molten rock within the crust in that region, could trigger quakes or seismic waves.

    Seismic waves (red lines in this illustration) traveling through Mars from a quake’s source (example, red dot) to the InSight lander (white dot) reveal the Red Planet’s internal structure, including a massive core (yellow-white) more than half the diameter of the planet.Chris Bickel/Science

    While the newly analyzed data confirm the planet’s outer core is liquid, it’s not clear yet whether Mars has a solid inner core like Earth, says study coauthor Amir Khan, a geophysicist also at ETH Zurich. “The signal should be there in the seismic data,” he says. “We just need to locate it.”

    In a separate analysis also published in Science, Khan and colleagues suggest that InSight’s seismic blind spot may also stem, in part, from the way that seismic waves slow down and bend as they travel deep within the planet. Changes in seismic wave speed and direction can result from gradual variations in rock temperature or density, for example.

    Mars’ seismic waves also hint at the thickness of the planet’s crust. As they bounce back and forth within the planet, the waves bounce off interfaces between different layers and types of rocks, says Brigitte Knapmeyer-Endrun, a seismologist at the University of Cologne in Bergisch Gladbach, Germany. In a separate study in Science, she and her team analyzed seismic signals that reflected off several such interfaces near Mars’ surface, making it difficult to determine the depth at which the planet’s crust ends and the underlying mantle begins, she says. The researchers concluded, however, that the average thickness of the crust likely lies between 24 and 72 kilometers. For comparison, Earth’s oceanic crust is about 6 to 7 kilometers thick, while the planet’s continental crust averages from 35 to 40 kilometers thick.

    Together, these seismic analyses are the first to investigate the innards of a rocky planet other than Earth, Stähler says. As such, they provide “ground truth” for measurements made by spacecraft orbiting Mars, and could help scientists better interpret data gathered from orbit around other planets, such as Mercury and Venus.

    The findings could also provide insights that would help planetary scientists better understand how Mars formed and evolved over the life of the solar system, and how the Red Planet ended up so unalike Earth, says Sanne Cottaar, a geophysicist at the University of Cambridge. Cottaar wrote a commentary, also published in Science, on the new research. “Mars was put together with similar building blocks” as Earth, she says, “but had a different result.” More

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    NASA’s Perseverance Mars rover has begun its first science campaign

    NASA’s Perseverance rover on Mars has seen its future, and it’s full of rocks. Lots and lots of rocks. After spending the summer trundling through Jezero Crater and checking out the sights, it’s now time for Percy to get to work, teasing out the geologic history of its new home and seeking out signs of ancient microbial life.

    “We’ve actually been on a road trip,” project manager Jennifer Trosper, who is based at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., said at a July 21 news conference. “And during it, we will take our very first sample from the surface of Mars.”

    Percy is about 1 kilometer south of where it landed on February 18 (SN: 2/17/21). After driving itself around a region of sand dunes, accompanied by its tagalong helicopter Ingenuity (SN: 4/30/21), the robotic explorer has pulled up to its first sampling spot: a garden of flat, pale stones dubbed paver stones. “This is the area where we are really going to be digging in, both figuratively and literally, to understand the rocks that we have been on for the last several months,” said Kenneth Farley, Perseverance project scientist at Caltech.

    The team has been trying to figure out whether these rocks are volcanic or sedimentary. “We still don’t have the answer,” Farley said. Images taken a few centimeters above the surface show what the team is up against: The rocks are littered with dust and pebbles, probably blown in from elsewhere, and the smoother surfaces have a mysterious purplish coating. “All of these factors conspire to prevent us from peering into the rock and actually seeing what it is made out of,” he said.

    In the coming weeks, Percy will bore a smooth cavity in one of those rocks and get below the surface crud. Instruments on its robotic arm will then move in close to produce detailed chemical and mineralogical maps that will reveal the rocks’ true nature. Then, sometime in mid-August, the team will extract its first sample. That sample will go into a tube that will eventually get dropped off — along with samples from other locales — for some future mission to pick up and bring to Earth (SN: 7/28/20).

    Cameras scouting farther afield have turned up future sampling sites. A small far-off hill shows hints of finely layered rock that may be mud deposits. “This is exactly the kind of rock that we are most interested in investigating for looking for potential biosignatures,” Farley said.

    And the way that rocks are strewn about an ancient river delta in the distance suggests that the lake that once filled Jezero Crater went through multiple episodes of filling in and drying up. If true, Farley said, then the crater may have preserved “multiple time periods when we might be able to look for evidence of ancient life that might have existed on the planet.” More