HOTTEST
Meteorites offer tantalizing clues about what the early solar system was like. But finding them is far from rocket science. Often, researchers simply fan out across a landscape and walk for hours while staring at the ground. Now, some scientists are turning to drones and machine learning to help spot freshly fallen meteorites much more efficiently.
A team of six people on a meteorite-hunting expedition can search about 200,000 square meters per day, says Seamus Anderson, a planetary scientist at Curtin University in Perth, Australia. But since the area over which a cluster of meteorites falls typically can’t be pinpointed to better than a few million square meters, searching can take a while, he says. “It’s quite slow.”
Seamus Anderson (pictured) and his colleagues used a drone to find a meteorite in Western Australia in 2021.The Desert Fireball Network
Around 2016, Anderson began toying with the concept of using drones to take pictures of the ground to look for meteorites. That idea blossomed into a Ph.D. project. In 2022, he and his colleagues reported their first successful recovery of a meteorite spotted with a drone. They’ve since found four more meteorites at a different site, the team reported August 17 in Los Angeles at a meeting of the Meteoritical Society.
Drone-based searches are much faster than the standard way of doing things, Anderson says. “You’re going from about 300 days of human effort down to about a dozen or so.” It’s also fun and exciting work, he says, but there are challenges too.
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}Anderson and his collaborators have used drones to search for meteorites in remote parts of Western Australia and South Australia. The team is tipped off about a fall site by networks of ground-based cameras that track meteoroids flashing through Earth’s atmosphere. Then, the hunt is on.
The researchers pack a four-wheel drive vehicle with drone and computer equipment, battery charging stations, generators, fuel, food, camping equipment, tables, chairs and more. The drive to the fall site can take more than a day, often on rough or nonexistent roads, Anderson says. “You hope you don’t pop a tire.”
After arriving, the team flies its primary drone at an altitude of about 20 meters. Its camera takes an image of the ground once every second, and the researchers download the data every 40 minutes or so when the drone lands to receive fresh batteries.
A typical day of flying can net over 10,000 images, which are then divided digitally into 100 million or so smaller sections. Those “tiles,” each 2 meters on a side, are fed into a machine learning algorithm that has been trained to recognize meteorites based on images of the real thing or terrestrial rocks spray-painted black. The latter are convincing stand-ins for real meteorites, Anderson says.
The algorithm is good but not perfect. It automatically discards most tiles — typically upwards of 99 percent — that don’t contain any meteorite-looking objects. But that still leaves roughly 50,000 or so tiles after a day’s worth of flights that must be manually checked by a human, Anderson says.
A machine learning algorithm, trained to identify potential meteorites in drone images, can mistake sleeping kangaroos (indicated with yellow squares) for space rocks. Researchers are working on improving the algorithm further.The Desert Fireball Network
Most of the time, those tiles contain things that decidedly aren’t meteorites: animal poop, tin cans, snakes or sleeping kangaroos, for instance. Those objects get flagged as potential meteorites simply because the algorithm isn’t familiar with them, Anderson says, and it’s up to the team to winnow out those false positives.
For objects that still look convincing to the human eye, the researchers send out a smaller drone that flies much lower — about a meter off the ground — to investigate. Finally, the team goes out in person to examine promising candidates.
The researchers plan to train their algorithm to better avoid flagging things like poop and kangaroos as meteorites. And the team is working on making its computer code open-source so that other researchers can freely use it.
Anderson also hopes to see drones make an appearance in Antarctica, a hotbed of meteorite sleuthing (SN: 1/26/22). But the icy environment will present a whole new slew of challenges, Anderson says, such as making sure sensitive electronic equipment fares well in the frigid conditions and overcoming the logistics of working in such a remote place. “Antarctica is a whole different beast.” More
NASA’s Perseverance rover took off at 7:50 a.m. EDT on July 30 from Cape Canaveral, Fla., and is now on its way to Mars with a suite of instruments designed to search for ancient life. The launch is the third this month of spacecraft en route to the Red Planet.
This is the 22nd spacecraft NASA has aimed at Mars (16 of those missions were successful). But Perseverance will be the first mission to cache rock samples from the Red Planet for a future mission to bring back to Earth.
It will also be the first NASA mission in more than 40 years to directly search for life on Mars. The rover will land in a region called Jezero crater (SN: 7/28/20). That crater was once an ancient lake bed, and scientists think its rocks and sediments could preserve signs of life, if life was ever there (SN: 7/29/20). The spacecraft will take video and audio recordings of its own landing as it touches down — another first for a NASA Mars mission.
“This mission has more cameras on it than any we’ve ever sent before,” said Lori Glaze, director of NASA’s Planetary Science Division, on July 30 during a news conference. “It’s going to feel like we’re actually there, riding along with Perseverance on the way down.”
Perseverance, shown here in an artist’s illustration, will seek signs that Mars once hosted alien life.JPL-Caltech/NASA
Mars launches tend to come in clumps thanks to Mars’ and Earth’s orbits. The planets line up on the same side of the sun every two years, so scientists have narrow windows to launch for the most efficient trip. All three of this year’s missions will arrive in February 2021.
The other missions launched in July represent firsts for their respective countries. The United Arab Emirates’ first interplanetary mission, which carries an orbiter called the Hope Probe, launched from Japan on July 19. Hope will measure Mars’ weather, from daily temperature changes to the significance of dust in the planet’s atmosphere (SN: 7/14/20).Sign Up For the Latest from Science News
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Next up was China’s first Mars mission, Tianwen-1, which means “questions to heaven” and launched on July 23. China has previously sent spacecraft to orbit and land on the moon (SN: 1/3/19). And it is the first nation to send an orbiter, lander and rover all at once on its first attempt to reach Mars. “No planetary missions have ever been implemented in this way,” mission scientists wrote July 13 in Nature Astronomy. “If successful, it would signify a major technical breakthrough.”
Tianwen-1’s lander and rover will touch down in Utopia Planitia in April 2021. Instruments on the rover and lander will test Mars’ soil composition and magnetic and gravitational fields and will probe Mars’ interior.
Utopia Planitia is the same region where the first long-lived Mars lander, NASA’s Viking 1, touched down in 1976 (SN: 7/20/16). Viking was the first spacecraft to search for life on Mars, but its results were inconclusive. Perhaps with the rush of spacecraft this year, and the plans to bring red rocks home, scientists will finally learn whether Mars ever did — or does — host alien life. MoreTo practice searching for extraterrestrial life, researchers have run a dress rehearsal with the one world they know to be habitable: Earth.
While Earth was between the sun and moon for a lunar eclipse in January 2019, the Hubble Space Telescope observed how chemicals in Earth’s atmosphere blocked certain wavelengths of sunlight from reaching the moon. That observing setup mimicked the way astronomers plan to probe the atmospheres of Earthlike exoplanets as they pass in front of their stars, filtering out some starlight.
“We basically pretend we’re alien observers looking at our planet,” says Giada Arney, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.
Using Hubble, the researchers focused on spotting the effects of atmospheric ozone. Because ozone is both a chemical by-product of oxygen produced in photosynthesis and a shield that protects life from the sun’s harmful ultraviolet rays, astronomers think atmospheric ozone could be a key indicator that a distant world is habitable. During the lunar eclipse, Hubble examined sunlight that had passed through Earth’s atmosphere and reflected off of the moon for signatures of ozone.Sign Up For the Latest from Science News
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“It’s safer for Hubble to observe sunlight reflected off the moon” than to look directly at the backlit Earth, explains Allison Youngblood, an astronomer at the University of Colorado Boulder. The telescope’s instruments are so sensitive and Earth is so bright that “even the nightside would fry Hubble’s detectors.”
Those observations revealed prominent dips in particular wavelengths of ultraviolet sunlight that had been absorbed by the ozone, Youngblood, Arney and colleagues report online August 6 in the Astronomical Journal.
The data help confirm that chemicals in the Earth’s atmosphere filter light as expected, based on researchers’ understanding of atmospheric chemistry. That finding gives astronomers more confidence that they will be able to recognize potentially habitable exoplanets. MoreMars 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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There was a problem signing you up.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
The greatest puzzle in cosmology just got even more puzzling.
Images from the James Webb Space Telescope have confirmed that the universe appears to be expanding significantly faster than it should be, researchers report in a study accepted in the Astrophysical Journal. The observation is in conflict with an esteemed theory, the standard model of cosmology, that describes how the universe has evolved since the first moments after the Big Bang.
The conflict comes down to calculations of the Hubble constant, a number that describes how fast everything in the universe is flying apart. One calculation, based on Planck satellite observations of the oldest light in the universe in conjunction with the standard model of cosmology, suggests the Hubble constant is 67.4 kilometers per second per megaparsec (a megaparsec is about 3 million light-years). Hubble Space Telescope images of stars at various distances from us provide a fundamentally incompatible value — 73 kilometers per second per megaparsec.
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}The discrepancy is known as the Hubble tension, and new JWST data hasn’t done anything to ease it (SN: 7/30/19). The telescope took images of the same stars as the Hubble telescope and calculated a very similar Hubble constant. Although the Planck number disagrees from the Hubble telescope and JWST number by less than 10 percent, the discrepancy in the measurements implies that there’s something terribly wrong with our understanding of the universe. Unless an error turns up in one of the measurements, it will take strange new physics to explain the tension.
“Papers in the literature over the last 10 years have invoked anything from weird dark matter to weird dark energy, to another [exotic] particle, to a magnetic field in the early universe to a new field, all kinds of things” to explain the Hubble tension, says cosmologist Adam Riess of Johns Hopkins University.
Some of these explanations “look semi-successful, some of them look like failures, some of them would cause other problems,” he says. Developing a theory that might resolve the tension “is still very much in the skunkworks [or extremely speculative] stage of trying to understand what [the tension] could mean.”
JWST looks to the stars to calculate the Hubble constant
With the Hubble telescope and JWST, astronomers calculate the Hubble constant by observing flashing stars known as Cepheid variables. The stars flare up periodically at rates that indicate how much light they’re putting out. Comparing a star’s brightness in telescope images with its expected brightness, based on the flare-up rates, gives a measure of the distance to the stars. Shifts in the color of the light coming from the stars reveal how fast they’re moving. Combining distance and speed observations of Cepheid stars leads to a measure of the expansion of the universe.
But Cepheid variable stars tend to sit deep inside galaxies, surrounded by crowds of other stars. That can make it difficult to get good measurements of the Cepheids’ speeds and locations. One simple resolution for the Hubble tension could have been that the Hubble telescope measurements were simply off.
Enter JWST, which can peer through the stellar crowds to clearly make out the color and brightness of Cepheid variables. The higher-resolution JWST images provide data with dramatically lower uncertainties and reduced confusion with nearby stars than the Hubble telescope could manage. The result: The Hubble telescope measurements have been right all along, Riess and colleagues report in their new paper.
This study alone isn’t enough to convince astronomer Wendy Freedman of the University of Chicago. The two galaxies studied are comparatively close to us, on cosmic scales, with the farthest one about 75 million light-years away, she notes. The relative proximity makes it easier to pick out the Cepheids from the stellar crowds. Freedman suspects it will be harder to distinguish Cepheids from the crowds of surrounding stars in more distant galaxies, even with JWST.
“The problem is only going to be worse,” Freedman says. “Because the resolution, it gets worse as you go to a higher distance.” For very distant galaxies, she suspects, stars could appear too close together to pick out the Cepheids from neighboring stars, even for JWST. As a result, Freedman says that Riess’ confirmation of the higher Hubble constant may crumble with analysis of more distant Cepheids.
Patterns in this Planck satellite image of the cosmic microwave background, the oldest light in the universe, suggest that the universe is expanding at 67.4 kilometers per second per megaparsec, according to the standard model of cosmology.ESA and the Planck Collaboration
JWST’s images leave the Hubble tension untouched
Hints that the measurements might hold up at larger distances arose in a Sept. 12 presentation at a conference in Baltimore dedicated to the first year of JWST science. Riess showed preliminary Cepheid data from four more galaxies. One of them is 140 million light-years away — among the most distant galaxies in the Hubble telescope Cepheid studies. JWST data from those stars also line up with the Hubble telescope measurements. Although still awaiting peer review, the images strongly suggest that the JWST has indeed overcome the uncertainties that resulted when light from Cepheids got mixed up with light from nearby stars in the lower resolution Hubble telescope images.
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University of Cambridge astrophysicist George Efstathiou, who was not involved in the study, is both convinced that Riess has gotten the measurements right and confounded by the implications. “When they showed me all of that [data],” Efstathiou says, “my reaction was, ‘Well, you know, I’m stumped.’”
Efstathiou is a member of the Planck satellite collaboration, which studied the oldest light in the universe, called the cosmic microwave background, and found the lower value for the expansion of the universe. The satellite’s calculation is based on images of the patterns in light from the early universe. Together with the standard model of cosmology, the images show that the universe is expanding with a Hubble constant that’s lower than the JWST measurement by about 5.6 kilometers per second per megaparsec.
As it stands, there doesn’t seem to be anything wrong with the Planck measurement of the Hubble constant or with the JWST observations. The tension between the measurements points a finger at the standard model of cosmology as the problem. But the standard model also appears to be unimpeachable; it’s withstood numerous other challenges without breaking down. The model came about in part due to the discovery of the accelerating expansion of the universe, which earned Riess and others a Nobel Prize in physics (SN: 10/4/11). The revelation was a key piece in shaping the model to include dark matter, dark energy and other factors, making it the simplest theory that can accurately describe the universe.
Now, though, Riess’ Cepheid-based studies of the Hubble constant show that there’s still more to learn.
“This is a crack, or a surprise that doesn’t fit,” Riess says. “It’s left us more in a kind of confused or purgatory state.” The implication, he says, is “there’s a problem with the standard model. You can revise it, but we don’t know how to revise it, which direction or in what way.”
People shouldn’t mistake the tension over the Hubble tension as despair. “It’s more of an opportunity to learn something about the universe with these telescopes,” Riess says.
One possibility is completely new physics.
“If there’s new physics, that’d be fun,” Freedman says. “We’d all like to see something new and interesting…. Either way, I think it’s going to be an exciting result — either confirming the [standard] model or showing that there’s something still in the model that’s missing.” More
