After decades of searching for extraterrestrial intelligence, the nonprofit SETI Foundation has an announcement. "A new study by researchers at the SETI Institute suggests stellar 'space weather' could make radio signals from extraterrestrial intelligence harder to detect." Stellar activity and plasma turbulence near a transmitting planet can broaden an otherwise ultra-narrow signal, spreading its power across more frequencies and making it more difficult to detect in traditional narrowband searches. For decades, many SETI experiments have focused on identifying spikes in frequency — signals unlikely to be produced by natural astrophysical processes. But the new research highlights an overlooked complication: even if an extraterrestrial transmitter produces a perfectly narrow signal, it may not remain narrow by the time it leaves its home system... "If a signal gets broadened by its own star's environment, it can slip below our detection thresholds, even if it's there, potentially helping explain some of the radio silence we've seen in technosignature searches," said Dr. Vishal Gajjar, Astronomer at the SETI Institute and lead author of the paper. The researchers created "a practical framework for estimating how much broadening could occur for different types of stars" — and accounting for space weather — by "using radio transmissions from spacecraft in our own solar system, then extrapolated to other stellar environments." The study's co-author (a SETI Institute research assistant) suggests this coud lead to better-targetted SETI searches. (M-dwarf stars — about 75% of stars in the Milky Way — actually have the highest likelihood that narrowband signals would get broadened before leaving their system...)

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Colliding black holes were detected through spacetime ripples for the first time in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO), notes Space.com: Since then, LIGO and its partner gravitational wave detectors Virgo in Italy and KAGRA (Kamioka Gravitational Wave Detector) in Japan have detected a multitude of gravitational waves from colliding black holes, merging neutron stars, and even the odd "mixed merger" between a black hole and a neutron star... During the first three observing runs of LIGO, Virgo and KAGRA, scientists had only "heard" 90 potential gravitational wave sources. But now they've published new data from the LIGO-Virgo-KAGRA (LVK) Collaboration that includes 128 more gravitatational wave sources — some incredibly distant: [Gravitational-Wave Transient Catalog-4.0, or GWTC-4] was collected during the fourth observational run of these gravitational wave detectors, which was conducted between May 2023 and Jan. 2024... Excitingly, GWTC-4 could technically have been even larger, as around 170 other gravitational wave detections made by LIGO, Virgo and KAGRA haven't yet made their way into the catalog. One aspect of GWTC-4 that really stands out is the variety of events that created these signals. Within this catalog are gravitational waves from mergers between the heaviest black hole binaries yet, each about 130 times as massive as the sun, lopsided mergers between black holes with seriously mismatched masses, and black holes that are spinning at incredible speeds of around 40% the speed of light. In these cases, scientists think the extreme characteristics of the black holes involved in these mergers are the result of prior collisions, providing evidence of merger chains that explain how some black holes grow to masses billions of times that of the sun... GWTC-4 also includes two new mixed mergers involving black holes and neutron stars. [LVK member Daniel Williams, of the University of Glasgow in the U.K., said in their statement] "We are really pushing the edges, and are seeing things that are more massive, spinning faster, and are more astrophysically interesting and unusual." The catalog also demonstrates just how sensitive the LVK detectors have become. Some of the neutron star mergers occurred up to 1 billion light-years away, while some of the black hole mergers occurred up to 10 billion light-years away. Einstein's theory of general relativity can be tested with these detections, and "So far, the theory is passing all our tests," says LVK member Aaron Zimmerman, of the University of Texas at Austin. "But we're also learning that we have to make even more accurate predictions to keep up with all the data the universe is giving us." And LVK member Rachel Gray, a lecturer at the University of Glasgow, says "every merging black hole gives us a measurement of the Hubble constant, and by combining all of the gravitational wave sources together, we can vastly improve how accurate this measurement is." In short, says LVK member Lucy Thomas of the California Institute of Technology (Caltech), "Each new gravitational-wave detection allows us to unlock another piece of the universe's puzzle in ways we couldn't just a decade ago."

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Astronomers have spotted a galaxy they believe is made of 99.9% dark matter, reports CNN — and it's so faint, it's almost invisible: CDG-2, which is about 300 million light-years from Earth, appears to be so rich in dark matter that it could belong to a hypothesized subset of low surface brightness galaxies called "dark galaxies," which are believed to contain few or no stars.... [Post-doctoral astrophysics/statistics fellow Dayi Li at the University of Toronto was lead author on a study about the discovery, and tells CNN] There is no strict definition of dark galaxies... but their existence is predicted by dark matter theories and cosmological simulations. "Where exactly do we draw the line in terms of how many stars they should have is still ambiguous, because not everything in astronomy is as clear-cut as we like," he said. "To be technically correct, CDG-2 is an almost-dark galaxy. But the importance of CDG-2 is that it nudges us much closer to getting to that truly dark regime, while previously we did not think a galaxy this faint could exist." To observe CDG-2, the researchers used data from three telescopes — Hubble, the European Space Agency's Euclid space observatory and the Subaru Telescope in Hawaii — along with a novel approach that involved looking for objects called globular clusters. "These are very tight, spherical groupings of very olds stars, basically the relics of the first generation of star formation," Li said. Globular clusters are bright even if the surrounding galaxy is not, and previous observations have shown a relationship between them and the presence of dark matter in a galaxy, Li added. Because CDG-2 appears to have very few stars, there must be something else providing the mass that the clusters need to hold themselves together. Li and his colleagues assume that the source of the mass is dark matter. The researchers found a set of four globular clusters in the Perseus Cluster, a group of thousands of galaxies immersed in a cloud of gas and one of the most massive objects in the universe. Further observations revealed a glow or halo around the globular clusters, suggesting the presence of a galaxy... Astronomers believe, Li explained, that after the formation of the clusters early in the galaxy's existence, larger surrounding galaxies stripped it of the hydrogen gas required to make more individual stars like our sun. "The material that this galaxy needed to continue to form stars was no longer there, so it was left with basically just a dark matter halo and the four globular clusters." The process, he added, would leave behind a skeleton or ghost of "a galaxy that pretty much just failed." As a result of this formation mechanism, the galaxy only has 0.005% of the brightness of our own galaxy, Li said... Studying potential dark galaxies is important because they provide nearly pristine views of the behavior of dark matter, according to Neal Dalal, a researcher at the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, Canada, who was not involved with the study. Robert Minchin, an astronomer at New Mexico's National Radio Astronomy Observatory, told CNN that "it seems likely that other very dark galaxies will be found by this method in the future."

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NASA is eyeing an April launch window for the upcoming Artemis II mission after it repaired a helium-flow issue on the Space Launch System upper stage rocket. "Work on the rocket and spacecraft will continue in the coming weeks as NASA prepares for rolling the rocket out to the launch pad again later this month ahead of a potential launch in April," NASA wrote in an update on Tuesday. Space.com reports: The repair work occurred inside the huge Vehicle Assembly Building (VAB) at NASA's Kennedy Space Center (KSC) in Florida. Artemis 2's SLS and Orion crew capsule have been in the VAB since Feb. 25, when they rolled back to the hangar from KSC's Launch Pad 39B. Just a few days earlier, the Artemis 2 stack successfully completed a wet dress rehearsal, a two-day-long practice run of the procedures leading up to launch. In the wake of that test, however, NASA noticed an interruption in helium flow in the SLS' upper stage. That was a significant issue, because helium pressurizes the rocket's propellant tanks. Rollback was the only option, as the affected area in the upper stage was not accessible at the pad. The problem took a potential March launch out of play for Artemis 2, which will send four astronauts on a roughly 10-day flight around the moon. It will be the first crewed flight to the lunar neighborhood since Apollo 17 in 1972. The next Artemis 2 launch window opens in April, with liftoff opportunities on April 1, April 3-6 and April 30. And those options apparently remain in play, thanks to recent work in the VAB. That work centered on a seal in an interface through which helium flows from ground equipment into the SLS upper stage. That seal was obstructing the interface, which is known as a quick disconnect.

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"Saturn and some of its 274 moons are pretty weird," writes Smithsonian magazine: [Saturn moon] Titan has strangely few impact craters, Hyperion is tiny and misshapen, and Iapetus has a tilted orbit. What's more, planets tend to wobble along their rotational axes as they spin, like an off-kilter spinning top in the moments before it topples over. Formally called precession, scientists have long thought that Saturn's wobble rate should match Neptune's because they're probably gravitationally linked. However, data from NASA's Cassini spacecraft, which studied the ringed planet from 2004 to 2017, revealed that Saturn's precession rate is slightly speedier than Neptune's. In 2022, some researchers suggested that the destruction of a hypothetical moon, called Chrysalis, around 160 million years ago may have knocked Saturn out of sync and formed the pieces that became the planet's rings. But this work implied that Chrysalis probably would've crashed into Titan, posing a major problem, study co-author Matija Äuk, an astronomer at the SETI Institute, tells New Scientist's Leah Crane. In that case, Chrysalis' debris couldn't have become the rings, he says. So, Äuk and his colleagues used computer simulations to investigate what would happen if Chrysalis did smack into Titan. If that happened around 400 million years ago, they found, the crash would've wiped away Titan's craters and made its orbit more elliptical. The altered path may have slowly pushed the trajectories of other moons, which then scraped against one another and left chunks of ice and rock that now make up Saturn's rings. The timing seems to align with the rings' estimated age of roughly 100 million years. Additionally, one piece of kicked-up debris may have formed the weird moon Hyperion, which may have subsequently tilted the orbit of the moon Iapetus, according to the analysis. The scenario could also resolve Saturn's unexpected wobble, which is currently "a little bit too fast," Äuk tells Jacopo Prisco at CNN. The study has been accepted for publication in the Planetary Science Journal, and is already available on the preprint server arXiv.

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A start-up called Reflect Orbital "proposes to use large, mirrored satellites to redirect sunlight to Earth at night," reports the Washington Post, "with plans to bathe solar farms, industrial sites and even entire cities in light that could, if desired, reach the intensity of daylight...." Slashdot noted their idea in 2022 — but Reflect Orbital now expects to launch its first satellite in April, according to the article. "But its grand vision is largely 'aspirational,' as its young founder, Ben Nowack, told me..." Reflect Orbital's Nowack describes a scene right out of sci-fi: An extremely bright star appears on the northern horizon and makes its way across the sky, illuminating a 5-kilometer circle on Earth, then setting on the southern horizon about five minutes later, just as another such "star" appears in the north. To make the night even brighter, a customer could make 10 "stars" appear at once in the north by ordering them on an app. Two such artificial stars are in development in Reflect Orbital's factory. Nowack showed them to me on a Zoom call. The first to launch is 50 feet across, but he plans later to build them three times that size. If all goes according to plan, he'll have 50,000 of them circling the Earth in 2035 at an altitude of around 400 miles. Nowack plans to start selling the service "in mostly developing nations or places that don't have streetlights yet." Eventually, he thinks, he can illuminate major cities, turn solar fields and farms into round-the-clock operations for any business or municipality that pays for it. He likened his technology to the invention of crop irrigation thousands of years ago. "I see this as much the same thing," he said, arguing that people would no longer have to "wait for the sun to shine." The article adds that Elon Musk's SpaceX "wants to launch as many as a million satellites to serve as orbiting data centers — 70 times the number of satellites now in orbit." (America's satellite-regulation Federal Communications Commission grants a "categorical exclusion" from environmental review to satellites on the grounds that their operations "normally do not have significant effects on the human environment.") The public comment periods for the two proposals close on March 6 and March 9.

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A start-up called Reflect Orbital "proposes to use large, mirrored satellites to redirect sunlight to Earth at night," reports the Washington Post, "with plans to bathe solar farms, industrial sites and even entire cities in light that could, if desired, reach the intensity of daylight...." Slashdot noted their idea in 2022 — but Reflect Orbital now expects to launch its first satellite in April, according to the article. "But its grand vision is largely 'aspirational,' as its young founder, Ben Nowack, told me..." Reflect Orbital's Nowack describes a scene right out of sci-fi: An extremely bright star appears on the northern horizon and makes its way across the sky, illuminating a 5-kilometer circle on Earth, then setting on the southern horizon about five minutes later, just as another such "star" appears in the north. To make the night even brighter, a customer could make 10 "stars" appear at once in the north by ordering them on an app. Two such artificial stars are in development in Reflect Orbital's factory. Nowack showed them to me on a Zoom call. The first to launch is 50 feet across, but he plans later to build them three times that size. If all goes according to plan, he'll have 50,000 of them circling the Earth in 2035 at an altitude of around 400 miles. Nowack plans to start selling the service "in mostly developing nations or places that don't have streetlights yet." Eventually, he thinks, he can illuminate major cities, turn solar fields and farms into round-the-clock operations for any business or municipality that pays for it. He likened his technology to the invention of crop irrigation thousands of years ago. "I see this as much the same thing," he said, arguing that people would no longer have to "wait for the sun to shine." The article adds that Elon Musk's SpaceX "wants to launch as many as a million satellites to serve as orbiting data centers — 70 times the number of satellites now in orbit." (America's satellite-regulation Federal Communications Commission grants a "categorical exclusion" from environmental review to satellites on the grounds that their operations "normally do not have significant effects on the human environment.") The public comment periods for the two proposals close on March 6 and March 9.

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