In one of the most complex cosmic dances astronomers have yet spotted, three rings of gas and dust circle a trio of stars.
The star system GW Orionis, located about 1,300 light-years away in the constellation Orion, includes a pair of young stars locked in a close do-si-do with a third star making loops around both. Around all three stars is a broken-apart disk of dust and gas where planets could one day form. Unlike the flat disk that gave rise to the planets in our solar system, GW Orionis’ disk consists of three loops, with a warped middle ring and an inner ring even more twisted at a jaunty angle to the other two.
The bizarre geometry of this system, the first known of its kind, is reported in two recent studies by two groups of astronomers. But how GW Orionis formed is a mystery, with the two teams providing competing ideas for the triple-star-and-ring system’s birth.
In a Sept. 4 study in Science, astronomer Stefan Kraus of the University of Exeter in England and colleagues suggest that gravitational tugs and torques from the triple-star ballet tore apart and deformed the primordial disk. But in a May 20 study in the Astrophysical Journal Letters, Jiaqing Bi of the University of Victoria in Canada and colleagues think that a newborn planet is to blame.
“The question is how do you actually form such systems,” says theoretical physicist Giuseppe Lodato of the University of Milan, who was not on either team. “There could be different mechanisms that could do that.”

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Astronomers have seen tilted disks of gas and dust around binary star systems, but not systems of more than two stars (SN: 7/30/14). Around half of the stars in the galaxy have at least one stellar companion, and their planets often have tilted orbits with respect to their stars, going around more like a jump rope than a Hula-Hoop (SN: 11/1/13). That misalignment could originate with the disk in which the planets were born: If the disk was askew, the planets would be too.
About a decade ago, astronomers first realized that GW Orionis has three stars and a planet-forming disk, and the scientists scrambled to get a closer look. (At the time, it was impossible to tell if that disk was a single loop or not.) Bi’s team and Kraus’ team aimed the Atacama Large Millimeter/submillimeter Array in Chile at the triple-star system.
Both groups spotted the trio of stars: one about 2.5 times and another about 1.4 times the sun’s mass orbiting each other once every 242 days, and another 1.4 solar mass star orbiting the inner pair about every 11 years.
The observations also revealed three distinct rings of dust and gas encircling the stars. The closest ring to the star trio lies about 46 times the distance from Earth to the sun; the middle one about 185 times the Earth-sun distance; and the outermost ring about 340 times that distance. For perspective, Neptune is about 30 times the distance from Earth to the sun.
That innermost ring is strongly misaligned with respect to the other rings and the stars, the teams found. Kraus’ group added observations from the European Southern Observatory’s Very Large Telescope to show the shadow of the inner ring on the inside of the middle loop. That shadow revealed that the middle ring is warped, swooping up on one side and down on the other.
Astronomers looked at GW Orionis with the ALMA telescope array (left, blue) and the SPHERE instrument on the Very Large Telescope (right, red), both in Chile. The ALMA observations revealed the disk’s tri-ringed structure, while the SPHERE images showed the shadow cast by the innermost ring, allowing scientists to describe the rings’ deformed shapes in detail.Left image: ALMA/ESO, NAOJ, NRAO; Right image: ESO, S. Kraus et al, Univ. of Exeter
Next, both groups ran computer simulations to figure out how the system formed. This is where their conclusions begin to differ, Bi says. His team suggests that a newly formed, not-yet-discovered planet cleared its orbit of gas and dust, splitting the inner ring off from the rest of the disk (SN: 7/16/19). Once the disk was split, the inner ring was free to swing around the stars, settling into its skewed alignment.
Simulations from Kraus’s team, though, found that the chaotic gravity from the triple stars’ orbital dance alone was enough to break up the disk, a phenomenon called disk tearing. Each star tends to keep the disk aligned with itself, and the tug-of-war warped and sheared the disk, and twisted the inner ring even further. Theoretical studies had suggested disk tearing might happen in multiple star systems, but this is the first time it’s been seen in real life, Kraus contends.
“I think it’s plausible that there could be planets somewhere in the system, but they’re not needed to explain the misalignment,” he says. “We don’t need to invoke undiscovered planets to explain what we see.”
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A trio of stars in GW Orionis are surrounded by an enormous, warped disk of gas and dust, new observations reveal. This animation, which is based on computer simulations and observational data, shows the complex geometry of the deformed and broken-apart disk.
The difference may lie in the assumptions that the groups made about the disk’s properties, in particular its viscosity, says astrophysicist Nienke van der Marel, Bi’s colleague at the University of Victoria. A more viscous disk would tear like how Kraus and colleagues propose, but a less viscous disk needs a planet to break apart, she says. She thinks her team’s work is more realistic based on observations of other star systems. But with current technology, there’s no way to tell what the properties of GW Orionis’ disk are really like.
And neither group could explain what made the disk split into three. “We don’t really know what’s causing the outer ring,” Klaus says.
Lodato, who predicted the disk-tearing effect in 2013, thinks GW Orionis is proof that the phenomenon really exists. Back then, Lodato and colleagues were “very worried” that their simulations showed an effect that was introduced by the computations, not real physics, he says. “Now observations tell us that it does happen in reality.”
Future telescopes may also be able to spot the planet if it exists, van der Marel says. More

A new look at the nitrogen on Venus may overturn a decades-old assumption about the planet’s atmosphere. Scientists long thought that atmospheric turbulence would create a uniform mixture of gases in Venus’s atmosphere below an altitude of about 100 kilometers. That’s how it works on Earth. But data from NASA’s MESSENGER spacecraft now indicate that […] More

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

When the first-ever image of a black hole was released in April 2019, it marked a powerful confirmation of Albert Einstein’s theory of gravity, or general relativity.
The theory not only describes the way matter warps spacetime, but it also predicts the very existence of black holes, including the size of the shadow cast by a black hole on the bright disk of material that swirls around some of the dense objects. That iconic image, of the supermassive black hole at the center of the galaxy M87 about 55 million light-years away, showed that the shadow closely matched general relativity’s predictions of its size (SN: 4/10/19). In other words, Einstein was right — again.
That result, reported by the Event Horizon Telescope Collaboration, answered one question: Is the size of M87’s black hole consistent with general relativity?
But “it is very difficult to answer the opposite question: How much can I tweak general relativity, and still be consistent with the [black hole] measurement?” says EHT team member Dimitrios Psaltis of the University of Arizona in Tucson. That question is key because it’s still possible that some other theory of gravity could describe the universe, but masquerade as general relativity near a black hole.

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In a study published October 1 in Physical Review Letters, Psaltis and colleagues have used the shadow of M87’s black hole to take a major step toward ruling out those alternative theories.
Specifically, the researchers used the size of the black hole to perform what’s known as a “second-order” test of general relativity geared toward boosting confidence in the result. That “can’t really be done in the solar system” because the gravitational field is too weak, says EHT team member Lia Medeiros of the Institute for Advanced Study in Princeton, N.J.
So far so good for relativity, the researchers found when they performed this second-order test.
The results are on par with those from gravitational wave experiments like the Advanced Laser Interferometer Gravitational-Wave Observatory, which has detected ripples in spacetime from the merger of black holes smaller than M87’s (SN: 9/16/19). But the new study is interesting because “it’s the first attempt at constraining a [second-order] effect through a black hole observation,” says physicist Emanuele Berti of Johns Hopkins University, who was not involved in the new work.
Generally, physicists think of general relativity as a set of corrections or add-ons to Isaac Newton’s theory of gravity. General relativity predicts what those add-ons should be. If measurements of how gravity works in the universe deviate from those predictions, then physicists know general relativity is not the full story. The more add-ons or factors added to a test, the more confidence there is in a result.
In weak gravitational fields, like within the solar system, physicists can test whether “first-order” additions to Newton’s equations are consistent with general relativity or not. These additions are related to things like how light and mass travel in a warped spacetime, or how gravity makes time flow more slowly.
Those aspects of gravity have been tested with the way stars’ light is deflected during a solar eclipse for example, and the way laser light sent to spacecraft flying away from the sun takes longer than expected to return to Earth (SN: 5/29/19). General relativity has passed every time.
But it takes a strong gravitational field, like the one around M87’s black hole, to kick the tests up a notch.
The new result is slightly disappointing for the physicists hoping to find cracks in Einstein’s theory. Finding a deviation from general relativity could point the way to new physics. Or it could help unite general relativity, the physics of the very large, and quantum mechanics, the leading theory that describes the physics of the very small, like subatomic particles and atoms (SN: 3/30/20). The fact that general relativity still refuses to bend is “worrying for those of us who are old enough that we were hoping to get an answer in our lifetime,” Psaltis says.
But there is some hope that general relativity might still fail around black holes. The new study makes the box of possible ways for the theory to break down smaller, “but we haven’t made it infinitesimal,” Medeiros says. The study is “a proof of concept to show that the EHT could do this… But it’s really just step one of many.”  
Future observations from the EHT will make for even more precise tests of general relativity, she says, especially with yet-to-be-released images of Sgr A*, the black hole at the center of the Milky Way. With much more precise measurements of Sgr A*’s mass than any other supermassive black hole, that image may make the possible box around the theory even smaller — or blow it wide open. More

On Mars, the speed of sound depends on its pitch.

All sound travels slower through Mars’ air compared with Earth’s. But the higher-pitched clacks of a laser zapping rocks travels slightly faster in the thin Martian atmosphere than the lower-pitched hum of the Ingenuity helicopter, researchers report April 1 in Nature.

These sound speed measurements from NASA’s Perseverance rover are part of a broader effort to monitor minute-by-minute changes in atmospheric pressure and temperature, like during wind gusts, on the Red Planet.

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“The wind is the sound of science for us,” says astrophysicist Baptiste Chide of Los Alamos National Laboratory in New Mexico.

To listen to the wind, Perseverance carries two microphones. One was meant to record audio during the mission’s complex entry, descent and landing, and while it didn’t work as hoped, it is now turned on occasionally to listen to the rover’s vitals (SN: 2/22/21; SN: 2/17/21). The other microphone is part of the rover’s SuperCam instrument, a mast-mounted mishmash of cameras and other sensors used to understand the properties of materials on the planet’s surface.

But these microphones also pick up other sounds, such as those made by the rover itself as its wheels crunch the surface, and by Perseverance’s flying companion, the robotic helicopter Ingenuity. The SuperCam instrument, for example, has a laser, which Perseverance fires at interesting rocks for further analysis (SN: 7/28/20). The microphone on SuperCam captures sounds from those laser shots, which helps researchers learn about the hardness of the target material, says planetary scientist Naomi Murdoch of the Institut Supérieur de l’Aéronautique et de l’Espace in Toulouse, France.

Murdoch, Chide and their colleagues listened to the laser’s clack-clack when zapping rocks. (“It doesn’t do, really, ‘pew pew,’” Murdoch says). When the laser hits a target, that blast creates a sound wave. Because scientists know when the laser fires and how far away a target is, they can measure the speed at which that sound wave travels through the air toward the SuperCam microphone.

The speed of this sound is about 250 meters per second, the team reports. That’s slower than on Earth, where sound travels through the air at about 340 m/s.

The slower speed isn’t surprising. What we hear as sound is actually pressure waves traveling through a medium like air, and the speed of those waves depends on the medium’s density and composition (SN: 10/9/20). Our planet’s atmosphere is 160 times as dense as the Martian atmosphere, and Earth’s air is mostly nitrogen and oxygen, whereas the Martian air is predominately carbon dioxide. So sound on Mars travels slower in that different air.

The team also used the SuperCam microphone to listen to the lower-pitch whirl of Ingenuity’s helicopter blades (SN: 12/10/21). From this lower-pitched sound, the researchers learned that there is a second speed of sound at the Martian surface at frequencies below 240 hertz, or slightly deeper than middle C on a piano: 240 m/s.

In contrast, at Earth’s surface, sound moves through the air at only one speed, no matter the pitch. The two speeds on Mars, the researchers say, are because of its carbon dioxide–rich atmosphere. Carbon dioxide molecules behave differently with one another when sound waves with frequencies above 240 hertz move through the air compared with those below 240 hertz, affecting the waves’ speed.

“We’ve proved that we can do science with a microphone on Mars,” Chide says. “We can do good science.”

The SuperCam microphone captures thousands of sound snippets per second. Those sounds are affected by air pressures, so the researchers can use that acoustic data to track detailed changes in air pressures over short timescales, and, in doing so, learn more about the Martian climate. While other Mars rovers have had wind, temperature and pressure sensors, those could sense changes only over longer periods.

“Listening to sounds on another planet is another way that helps all of us place ourselves as if we were there,” says Melissa Trainer, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., who was not part of this work.

The team is focusing on next collecting acoustic data at different times of day and different seasons on Mars.

“The pressure changes a lot on Mars throughout the year with the seasons,” Trainer says. “I’m really excited to see how the data might change as it gets collected through proceeding seasons.” More