Posts Tagged ‘space’

FOR DECADES MARS has teased scientists with whispers of water’s presence. Valleys and basins and rivers long dry point to the planet’s hydrous past. The accumulation of condensation on surface landers and the detection of vast subterranean ice deposits suggest the stuff still lingers in gaseous and solid states. But liquid water has proved more elusive. Evidence to date suggests it flows seasonally, descending steep slopes in transient trickles every Martian summer. The search for a big, enduring reservoir of wet, potentially life-giving water has turned up nothing. Until now.

The Italian Space Agency announced Wednesday that researchers have detected signs of a large, stable body of liquid water locked away beneath a mile of ice near Mars’ south pole. The observations were recorded by the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument—Marsis for short. “Marsis was born to make this kind of discovery, and now it has,” says Roberto Orosei, a radioastronomer at the National Institute for Astrophysics, who led the investigation. His team’s findings, which appear in this week’s issue of Science, raise tantalizing questions about the planet’s geology—and its potential for harboring life.

Marsis collected its evidence from orbit, flying aboard the European Space Agency’s Mars Express spacecraft. It works by transmitting pulses of low-frequency electromagnetic waves toward the red planet. Some of those waves interact with features at and below the Martian surface and reflect back toward the instrument, carrying clues about the planet’s geological composition. Conceptually, using the instrument to study Mars’ polar regions couldn’t be more straightforward: Just point it toward the ice and see what bounces back.

In practice, though, it’s a lot more complicated. Marsis spends relatively little time above Planum Australe, the southern polar plane of Mars and the focus of Orosei’s team’s investigation. That meant the researchers could only listen for echoes periodically. It would take many readings—and many years—to get a clear picture of what lies hidden beneath the planet’s southern ice cap. So in May of 2012, on the heels of a software upgrade that enabled Marsis to acquire more detailed data, the researchers began their survey.

Three and a half years and 29 observations later, they had a radiogrammatic map of Mars’ southern polar plane. When they cross-referenced all their measurements, something immediately seized their attention: Bright reflections in the radar signals, corresponding to what Orosei now calls “a well-defined anomaly” some 12 miles across and several feet deep, roughly one mile beneath the surface of the polar ice cap. The surface of an ice cap tends to reflect radar waves more strongly than the regions below it. But on multiple passes, Marsis had detected uncommonly strong echoes originating from beneath the southern pole.

Or rather: Uncommonly strong for a solid material.

Analyses of subglacial lakes on our own planet—like the ones beneath the Antarctic and Greenland ice sheets—have shown that water reflects radar more strongly than rock and sediment. And in fact, the radar profile of this region of Mars’ southern pole resembles those of subglacial lakes here on Earth.

The researchers looked for other explanations for the bright signals. A layer of frozen carbon dioxide above or below the polar cap, for example, could conceivably produce readings like the ones they observed—though the researchers deemed this, and all other explanations that they considered, less likely than the presence of liquid water.

“I can’t absolutely prove it’s water, but I sure can’t think of anything else that looks like this thing does other than liquid water,” says Richard Zurek, chief scientist for the Mars Program Office at NASA’s Jet Propulsion Laboratory, who was unaffiliated with the study. “Maybe that has to do with a shortage of imagination on my part,” he adds, “but it probably has to do with a shortage of data, too.” More radar observations, he says, could give rise to explanations scientists haven’t even thought of yet—and more questions, too.

Not that there’s a shortage of unanswered questions. Still unclear is how the water remains liquid at temperatures tens of degrees below 0° Celsius. Orosei and his team think the answer could be magnesium, calcium, and sodium salts, all of which are present in Martian rock, that have dissolved in the water, lowering its freezing point.

Another question is whether future observations by Marsis and other spacecraft will detect more reservoirs beneath Mars’ southern ice cap. “If this lake is a single occurrence, if there is no other liquid water anywhere else, then the implication would be that we are seeing a quirk of nature—an effect of residual decay, a hydrothermal vent, some thermal irregularity in the crust,” Orosei says. “But, if we were to find that Mars possesses not one subglacial lake, but several, that would change the game.”

More lakes would suggest that the conditions necessary for their existence aren’t so rare. And if those conditions have persisted throughout the planet’s history, then subsurface reservoirs of liquid water could serve as a bridge to the early environment of Mars—a time capsule of sorts from a period billions of years ago, when Mars was a warm, wet planet.

Which, of course, raises the biggest question of all: Could there be life in the waters beneath Mars’ southern ice caps?

It’s certainly possible, says Montana State University glaciologist John Priscu. An expert in the biogeochemistry and microbiology of subglacial environments here on Earth, Priscu led the first team to discover microbial life in a lake beneath the West Antarctic ice sheet. “You need three things for life: liquid water; an energy source, like leaching minerals, which we know Mars has; and a biological seed,” he says. It’s plausible that the lake beneath Mars’ southern pole possesses the first two. As for the whole spark-of-life thing, “I’m not sure we’ll ever know where the seed comes from,” he says. But if Earth got a seed, maybe Mars did, too.

But we’re getting ahead of ourselves. “It’s tempting to think that if life ever evolved on Mars, it would have to be present today,” Orosei says, a subglacial lake like the one his team discovered would be an excellent place to look. But first comes the search for more lakes. And after that, perhaps landers equipped with drills. “Going from zero bodies of water to one is a big change, for sure,” Orosei says, “but the full extent of this discovery depends on what we find next.”

https://www.wired.com/story/large-body-of-liquid-water-on-mars/

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Zinnias such as this one were among the first flowers to be grown on the International Space Station.

Researchers on the International Space Station are growing plants in systems that may one day sustain astronauts traveling far across the solar system and beyond.

Vibrant orange flowers crown a leafy green stem. The plant is surrounded by many just like it, growing in an artificially lit greenhouse about the size of a laboratory vent hood. On Earth, these zinnias, colorful members of the daisy family, probably wouldn’t seem so extraordinary. But these blooms are literally out of this world. Housed on the International Space Station (ISS), orbiting 381 kilometers above Earth, they are among the first flowers grown in space and set the stage for the cultivation of all sorts of plants even farther from humanity’s home planet.

Coaxing this little flower to bloom wasn’t easy, Gioia Massa, a plant biologist at NASA’s Kennedy Space Center in Florida, tells The Scientist. “Microgravity changes the way we grow plants.” With limited gravitational tug on them, plants aren’t sure which way to send their roots or shoots. They can easily dry out, too. In space, air and water don’t mix the way they do on Earth—liquid droplets glom together into large blobs that float about, instead of staying at the roots.

Massa is part of a group of scientists trying to overcome those challenges with a benchtop greenhouse called the Vegetable Production System, or Veggie. The system is a prototype for much larger greenhouses that could one day sustain astronauts on journeys to explore Mars. “As we’re looking to go deeper into space, we’re going to need ways to support astronaut crews nutritionally and cut costs financially,” says Matthew Romeyn, a long-duration food production scientist at Kennedy Space Center. “It’s a lot cheaper to send seeds than prepackaged food.”

In March 2014, Massa and colleagues developed “plant pillows”—small bags with fabric surfaces that contained a bit of soil and fertilizer in which to plant seeds. The bags sat atop a reservoir designed to wick water to the plants’ roots when needed (Open Agriculture, 2:33-41, 2017). At first, the ISS’s pillow-grown zinnias were getting too much water and turning moldy. After the crew ramped up the speed of Veggie’s fans, the flowers started drying out—an issue relayed to the scientists on the ground in 2015 by astronaut Scott Kelly, who took a special interest in the zinnias. Kelly suggested the astronauts water the plants by hand, just like a gardener would on Earth. A little injection of water into the pillows here and there, and the plants perked right up, Massa says.

With the zinnias growing happily, the astronauts began cultivating other flora, including cabbage, lettuce, and microgreens—shoots of salad vegetables—that they used to wrap their burgers and even to make imitation lobster rolls. The gardening helped to boost the astronauts’ diets, and also, anecdotally, brought them joy. “We’re just starting to study the psychological benefits of plants in space,” Massa says, noting that gardening has been shown to relieve stress. “If we’re going to have this opportunity available for longer-term missions, we have to start now.”

The team is currently working to make the greenhouses less dependent on people, as tending to plants during space missions might take astronauts away from more-critical tasks, Massa says. The researchers recently developed Veggie PONDS (Passive Orbital Nutrient Delivery System) with help from Techshot and Tupperware Brands Corporation. This system still uses absorbent mats to wick water to plants’ seeds and roots, but does so more consistently by evenly distributing the moisture. As a result, the crew shouldn’t have to keep such a close eye on the vegetation, and should be able to grow hard-to-cultivate garden plants, such as tomatoes and peppers. Time will tell. NASA sent Veggie PONDS to the ISS this past March, and astronauts are just now starting to compare the new system’s capabilities to those of Veggie.

“What they are doing on the ISS is really neat,” says astronomer Ed Guinan of the University of Pennsylvania. If astronauts are going to venture into deep space and be able to feed themselves, then they need to know how plants grow in environments other than Earth, and which grow best. The projects on the ISS will help answer those questions, he says. Guinan was so inspired by the ISS greenhouses he started his own project in 2017 studying how plants would grow in the soil of Mars—a likely future destination for manned space exploration. He ordered soil with characteristics of Martian dirt and told students in his astrobiology course, “You’re on Mars, there’s a colony there, and it’s your job to feed them.” Most of the students worked to grow nutritious plants, such as kale and other leafy greens, though one tried hops, a key ingredient in beer making. The hops, along with some of the other greens, grew well, Guinan reported at the American Astronomical Society meeting in January.

Yet, if and when astronauts go to Mars, they probably won’t be using the Red Planet’s dirt to grow food, notes Gene Giacomelli, a horticultural engineer at the University of Arizona. There are toxic chemicals called perchlorates to contend with, among other challenges, making it more probable that a Martian greenhouse will operate on hydroponics, similar to the systems being tested on the ISS. “The idea is to simplify things,” says Giacomelli, who has sought to design just such a greenhouse. “If you think about Martian dirt, we know very little about it—so do I trust it is going to be able to feed me, or do I take a system I know will feed me?”

For the past 10 years, Giacomelli has been working with others on a project, conceived by now-deceased business owner Phil Sadler, to build a self-regulating greenhouse that could support a crew of astronauts. This is not a benchtop system like you find on the space station, but a 5.5-meter-long, 2-meter-diameter cylinder that unfurls into an expansive greenhouse with tightly controlled circulation of air and water. The goal of the project, which was suspended in December due to lack of funding, was to show that the lab-size greenhouse could truly sustain astronauts. The greenhouse was only partially successful; the team calculated that a single cylinder would provide plenty of fresh drinking water, but would produce less than half the daily oxygen and calories an astronaut would need to survive a space mission. Though the project is on hold, Giacomelli says he hopes it will one day continue.

This kind of work, both here and on the ISS, is essential to someday sustaining astronauts in deep space, Giacomelli says. And, if researchers can figure out how to make such hydroponic systems efficient and waste-free, he notes, “the heck with Mars and the moon, we could bring that technology back to Earth.”

https://www.the-scientist.com/?articles.view/articleNo/54637/title/Researchers-Grow-Veggies-in-Space/


This view of Pluto’s Sputnik Planitia nitrogen-ice plain was captured by NASA’s New Horizons spacecraft during its flyby of the dwarf planet in July 2015.

At its heart, Pluto may be a gigantic comet.

Researchers have come up with a new theory about the dwarf planet’s origins after taking a close look at Sputnik Planitia, the vast nitrogen-ice glacier that constitutes the left lobe of Pluto’s famous “heart” feature.

“We found an intriguing consistency between the estimated amount of nitrogen inside the glacier and the amount that would be expected if Pluto was formed by the agglomeration of roughly a billion comets or other Kuiper Belt objects similar in chemical composition to 67P, the comet explored by Rosetta,” Chris Glein, a scientist at the Southwest Research Institute (SwRI) in San Antonio, said in a statement.

The European Space Agency’s Rosetta mission orbited Comet 67P/Churyumov-Gerasimenko from 2014 through 2016. The orbiting mothership also dropped a lander named Philae onto the icy body, pulling off the first-ever soft touchdown on a comet’s surface. (The Kuiper Belt is the ring of frigid objects beyond Neptune’s orbit; Pluto is the belt’s largest resident.)

Glein and his SwRI colleague Hunter Waite devised the new Pluto-formation scenario after analyzing data from Rosetta and NASA’s New Horizons mission, which flew by Pluto in July 2015.

The scientists also made some inferences about the dwarf planet’s evolution in their new study, which was published online Wednesday (May 23) in the journal Icarus.

“Our research suggests that Pluto’s initial chemical makeup, inherited from cometary building blocks, was chemically modified by liquid water, perhaps even in a subsurface ocean,” Glein said.

Glein and Waite aren’t claiming to have nailed down Pluto’s origin definitively; a “solar model,” in which the dwarf planet coalesced from cold ices with a chemical composition closer to that of the sun, also remains in play, the duo said.

“This research builds upon the fantastic successes of the New Horizons and Rosetta missions to expand our understanding of the origin and evolution of Pluto,” Glein said.

“Using chemistry as a detective’s tool, we are able to trace certain features we see on Pluto today to formation processes from long ago,” he added. “This leads to a new appreciation of the richness of Pluto’s ‘life story,’ which we are only starting to grasp.”

Rosetta’s mission ended in September 2016, when the probe’s handlers steered it to an intentional crash-landing on 67P’s surface. New Horizons’ work, however, is far from done. The NASA spacecraft is speeding toward a flyby of a small Kuiper Belt object known officially as 2014 MU69 (and unofficially as Ultima Thule). This close encounter, which will occur on Jan. 1, 2019, about 1 billion miles (1.6 billion kilometers) beyond Pluto’s orbit, is the centerpiece of New Horizons’ extended mission.

https://www.space.com/40687-pluto-formation-1-billion-comets.html


A NASA artist visualized what Earth would look like if it entered the “snowball state” predicted by new research from the University of Washington

By Chelsea Gohd

Earth-like planets with severe tilts and orbits could enter abrupt “snowball states,” in which entire oceans freeze and surface life cannot survive, according to new research.

Researchers at the University of Washington (UW) have found a new reason why, just because a planet is located in a “habitable zone” — meaning it’s close enough to its host star to sustain liquid water — it isn’t necessarily habitable. The team found that the axial tilt and orbital dynamics of planets in the habitable zone around “G dwarf” stars like our own sun can lead to “snowball states,” which are essentially extreme ice ages.

This new research looked at how a planet’s obliquity, or the angle at which a planet’s rotation axis tilts, and its orbital eccentricity, a parameter that determines the amount that an orbit deviates from a perfect circle, could affect that planet’s potential to be habitable.

Previous research suggested that planets in a habitable zone with a sun-like star that had a severe axial tilt or tilting orbit would be warmer, according to the statement. The team’s research found that the opposite holds true, which was quite a shock, they said.”We found that planets in the habitable zone could abruptly enter ‘snowball’ states if the eccentricity or the semi-major axis variations — changes in the distance between a planet and star over an orbit — were large or if the planet’s obliquity increased beyond 35 degrees,” Russell Deitrick, lead author of the new work and a postdoctoral researcher at the University of Bern who completed this research at UW, said in a statement.

Luckily, Earth’s axial tilt varies ever so slightly, leaving Earth “a relatively calm planet, climate-wise,” co-author Rory Barnes, an astronomer at UW, said in the statement. But, as it pertains to exoplanets, Deitrick “has essentially shown that ice ages on exoplanets can be much more severe than on Earth, that orbital dynamics can be a major driver of habitability and that the habitable zone is insufficient to characterize a planet’s habitability,” Barnes said.

A planet’s position in the habitable zone is typically a major factor in considering whether it may be habitable. However, this new research shows that even if a planet seems Earth-like and is orbiting at the right distance from its star, if “its orbit and obliquity oscillate like crazy, another planet might be better for follow-up with telescopes of the future,” Deitrick said.

With this research in mind, orbital dynamics should be considered an important part of determining a planet’s habitability, Deitrick added.

The work will be published in The Astronomical Journal, according to the statement.

https://www.space.com/40606-exoplanets-sudden-ice-age-snowball-states.html

By Jeanna Bryner

Congress is talking about spending a bunch of money on the search for extraterrestrial intelligence (or SETI) for the first time in 25 years.

The U.S. House of Representatives has proposed a bill that includes $10 million in NASA funding for the next two years “to search for technosignatures, such as radio transmissions, in order to meet the NASA objective to search for life’s origin, evolution, distribution, and future in the universe.” Such technosignatures would come in the form of radio waves that have the telltale features of being produced by TV- or radio-type technologies. An intelligent civilization could also produce those signals intentionally to communicate with other civilizations like ours.

“If it passes, it would definitely be a sea-change in Congressional attitude since Sen. [Richard] Bryan terminated NASA’s SETI program, the High Resolution Microwave Survey, in 1993,” renowned astronomer Jill Tarter, former diretor of the SETI Institute, told Live Science in an email.

Here’s what Tarter is referring to: In 1992, a huge NASA SETI initiative was launched in order to build instrumentation so that observatories could comb the cosmos for signals from alien civilizations. For instance, the high resolution microwave survey was hooked up to the Arecibo telescope in Puerto Rico for just that. A year later, however, Nevada Sen. Bryan shut it down, and “SETI” became an unmentionable.

“[Bryan] made it clear to the administration that if they came back with SETI in their budget again, it wouldn’t be good for the NASA budget,” Tarter told Marina Koren of The Atlantic. “So, we instantly became the four-letter S-word that you couldn’t say at headquarters anymore, and that has stuck for quite a while.”

She added that the funding proposal seems to be an extension of the efforts of Rep. Lamar Smith, R–Texas, to bring attention to the search for life beyond Earth when he was the chairman of the House Science Committee. (Smith, who announced that he will retire at the end of his term this year, is a known denier of human-caused climate change.)

If the legislation clears the House and passes the Senate, the result would be huge. “It allows for new instrumentation to be built, and data collected and analyzed at scale, by a global community,” Tarter said of the $10 million.

Of course, the hunt for intelligence beyond Earth has not stopped, as private companies and other organizations have funded it, but a buy-in from the federal government is a big deal. [7 Huge Misconceptions about Aliens]

“You need to remember that this is an authorization bill, not an appropriations bill. Even if it passes, the appropriators may not provide any SETI funding in their bill. But if they do, that would be a very big deal,” said Tarter, who was the basis for the heroine Ellie Arroway in Carl Sagan’s novel “Contact” and in the adapted movie by the same name.

Tarter is admittedly ecstatic about the possibility of such a federal focus on SETI. But you don’t become the director of the SETI Institute by keeping your feet on the ground.

“Bring it on! But don’t stop there,” Tarter said about the potential funding. “Earthlings everywhere are fascinated with this search and care about the answer. So, we should create an international endowment for searching for intelligent life beyond Earth. The backers should be private individuals, enlightened corporations, U.S. federal agencies and agencies from other governments around the world.”

She added, “By smoothing out the funding roller coaster that has characterized this research field from the beginning, it will be possible to attract the best and brightest minds with the best ideas from everywhere, and commit to the long-term search efforts that might be required for success.”

Are alien greetings just around the corner? Tarter said we have the technology now to search for more distant and fainter signals in ways we haven’t tried before. “But that doesn’t guarantee success in the ‘near future.’ The cosmos is vast, and we may not yet be looking in the right way, although we are doing the best job possible with what we now know.”

The “correct perspective on timing,” Tarter said, is summed up in a line from a paper published in 1959 in the journal Nature by Giuseppe Cocconi and Philip Morrison: “‘The probability of success is difficult to estimate; but if we never search, the chance of success is zero,'” Tarter said.

https://www.livescience.com/62529-congress-search-for-intelligent-aliens.html?utm_source=notification

Nineteen-year-old Amber Yang has her head in the clouds. Actually, it’s beyond the clouds and well into the Earth’s atmosphere. While some teens are focused on cleaning up the land and water on our planet, Yang has made it her mission to clean up the litter clogging space. And she may just save lives and billions of dollars while she’s at it.

Yang was 15 when she first heard about the escalating issue of space debris that is polluting the Earth’s lower atmosphere. After watching the 2013 movie, “Gravity,” Yang imagined a world in which colliding space debris could set off a series of catastrophic events that threaten lives and technology. While the plot of “Gravity” broke some of the major rules of physics, the underlying premise — that a collision of space debris could lead to disaster — rang true and stuck in Yang’s mind.

That year, over her winter break in Florida, she brushed up on astrophysics, computer coding, and the ins and outs of space junk and developed a program called Seer Tracking to provide an accurate location for each piece of junk orbiting the Earth. Currently, there are millions of pieces of space debris, ranging in size from defunct satellites to tiny specks of paint. Traveling at a rate of around 17,500 miles per hour, each item has the potential to cause a catastrophic collision.

The Department of Defense’s Space Surveillance Network currently analyzes Earth’s space debris using tracking and data that could detect a potential collision as far as 10 days in advance, But according to Yang, her Seer Tracking program is able to predict issues weeks ahead. And the scientific community concurs. Her work has earned her the top award at the Intel International Science and Engineering Fair as well as a spot on Forbes 30 under 30 list. Yang has presented her research at the European Organization for Nuclear Research (CERN) in Geneva, Switzerland and was asked to speak at a TEDx Conference about the issues that women face in STEM careers.

Seer Tracking uses artificial neural networks to track space debris. In other words, Yang has developed an algorithim that allows the program to learn from its mistakes, so that its predictions become more accurate over time. As the data accumulates, Seer Tracking increases in its ability to pinpoint debris locations and predict collisions well in advance.

Yang is now finishing up her sophomore year at Stanford University, pursuing a degree in physics while operating Seer Tracking on the side. She’s still working on improving her software and exploring other avenues of “deep learning” in which computers learn from their mistakes.

https://www.mnn.com/family/family-activities/blogs/meet-teen-whos-cleaning-space-junk

By Nola Taylor Redd

Alien civilizations with technology on a par with humanity’s could be detectable using today’s instruments. A new study suggests that if geostationary satellites are thick enough around an alien world, they could be spotted with telescopes already hunting for undiscovered planets.

Both governments and private corporations on our own world use geostationary satellites — which orbit such that they hover over the same spot on Earth — for science, communications, espionage and military applications.

If advanced alien civilizations loft enough satellites into their own geostationary belts, these spacecraft could create a dense, ring-like structure visible from Earth, according to the study.

“It’s … a small chance, but the point is that it’s free,” study lead author Hector Socas-Navarro, of Astrophysics Institute of the Canary Islands, told Space.com by email.

Socas-Navarro simulated the presence of belts of geostationary satellites around exoplanets, to see whether they could be detected by instruments like NASA’s Kepler space telescope and the agency’s recently launched Transiting Exoplanet Survey Satellite (TESS). He found that the belt would need to be about 0.01 percent full for such spacecraft to detect it, whether populated by many small satellites or a handful of large, city-size objects.

“We just need to look for the right signature in the data,” he said.

Socas-Navarro calls this hypothetical structure the Clarke exobelt (CEB), after famed sci-fi author Arthur C. Clarke.

Hunting alien satellites
Both Kepler and TESS detect planets using what’s known as the transit method. The spacecraft watch a field of stars for an extended amount of time. If a planet has the right orbit, and the timing is right, that world will pass in front of its host star from the telescope’s perspective, causing a small, potentially detectable dip in brightness.

In addition to working as an astrophysicist, Socas-Navarro hosts a weekly radio show and podcast. That work helped him come up with the Clarke exobelt idea, he said. One day, a listener asked about a geostationary satellite for the sun.

“As I was doing the calculations to answer this question, I had this mental image of a satellite transiting across the solar disk,” Socas-Navarro said. “That led me to ask myself the question of whether satellites around distant exoplanets would be observable during transit.”

Sufficient material orbiting an exoplanet causes a small dip in starlight before and after the body of the world makes its transit. Scientists have used this method to discover rings around planets outside the solar system and even around distant solar system bodies.

Socas-Navarro said the putative alien-satellite signal would have a signature similar to that of rings — both an exobelt and rings are made up of a swarm of objects orbiting a planet — but there are subtle technical differences in how that signature would look. The signal would also reveal the altitude of the orbiting objects, which could provide a significant clue as to whether the objects were natural or alien-made.

A ring system can occur at any number of distances from the surface of the planet. But if the objects orbited at a planet’s geostationary height — about 22,200 miles (35,700 kilometers) — they are “almost certainly artificial,” Socas-Navarro said.

Similarly, a massive space city or a large station close to a space elevator could look like an exomoon. Again, Socas-Navarro said, altitude is key. If the object hovers at geostationary height, it’s likely to be artificial. [10 Exoplanets That Could Host Alien Life]

“It doesn’t seem to matter too much if they are many small or [a] few large [objects],” he said. “As long as they are spread out all over the orbit, they will basically produce the same signature.”

He also found that the ideal conditions to spot such a satellite belt would be around dim red dwarf stars located within 100 light-years of Earth.

The new study was published last month in The Astrophysical Journal. You can read it for free at the online preprint server arXiv.org.

https://www.space.com/40436-search-alien-life-et-satellites.html