A survey of small, cool stars is helping to narrow in on the conditions that might set the stage for life beyond our solar system.

A look at about 200 ultracool dwarf stars shows that they lack sufficient ultraviolet light intensity to have the potential to jump-start life, researchers report December 1 in the Monthly Notices of the Royal Astronomical Society. That may initially seem to be bad news for finding signs of alien life on distant planets. But the diminutive stars could instead serve as test beds to determine what other conditions can create the chemical foundations of life.

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Compared with our sun, the dwarf stars in the new study are minuscule, roughly the size of Jupiter and weighing about a tenth as much as the sun. They’re also among the most common types of stars. And because they’re cool and comparatively dim, it’s often easier to spot planets orbiting them than it is in the glare of large bright stars. Astronomers studying the tiny red star TRAPPIST-1, for example, found that it hosts seven Earth-sized planets, including three that may be within the star’s habitable zone, where conditions are amenable to life (SN: 2/22/17).

For life to exist on a habitable planet, though, it must start somehow. One possibility is that UV starlight provides the energy needed to link together the hydrogen, oxygen, carbon, nitrogen, sulfur and other atoms that make up the compounds that are precursors to life.

With that in mind, space scientist Antígona Segura and colleagues used the Transiting Exoplanet Survey Satellite to measure the amount of UV radiation — among other things — emitted from 208 comparatively nearby ultracool dwarfs within 130 light-years from Earth (SN: 4/12/18). The stars they studied do emit UV light, as our sun does, and many produce bursts of UV when they let off flares. But overall, the UV energy the small stars release is too low to forge the chemicals needed to kick-start life, the team found.

The dearth of UV light doesn’t necessarily quash hopes of finding life around such stars. “UV is an energy source for prebiotic chemistry that we can measure, and that is why we focused on it,” says Segura, of the National Autonomous University of Mexico in Mexico City. “But there are many other energy sources, like cosmic and stellar particles, and particles, radiation and heat produced by radioactive decay, to name a few.”

Ultracool stars might be useful to discover whether something other than UV light can get life going. “We should search for life on the planets that have the least [UV] activity, where we can know with confidence that UV-driven prebiotic chemistry cannot happen,” says Paul Rimmer, a University of Cambridge astrophysicist who was not involved in the study. “If we find evidence of life on these [types of] planets, this will show that there are other paths to life.”

Also, Segura notes, sources of energy that could start life can also make planets less habitable for more complex life-forms. “We cannot currently say which [effects] would prevail. The best approach now is to study case by case and wait for more observational constraints, like for the case of the TRAPPIST-1 system.”

If astronomers eventually find life on planets orbiting ultracool dwarfs, it will confirm the potential for UV-free origins of life. But, Rimmer says, if it turns out that there are no signs of habitability on planets around the many small, dim dwarf stars we see, that would lower estimates of the likelihood of finding life outside our solar system. Either way, future surveys of ultracool dwarf stars could give researchers a better handle on the possible prevalence of extraterrestrial life in the universe. More

Like a phoenix, some stars may burst to life covered in “ash,” rising from the remains of stars that had previously passed on.

Two newfound fireballs that burn hundreds of times as bright as the sun and are covered in carbon and oxygen, ashy byproducts of helium fusion, belong to a new class of stars, researchers report in the March Monthly Notices of the Royal Astronomical Society: Letters. Though these blazing orbs are not the first stellar bodies found covered in carbon and oxygen, an analysis of the light emitted by the stars suggests they are the first discovered to also have helium-burning cores.

“That [combination] has never been seen before,” says study coauthor Nicole Reindl, an astrophysicist from the University of Potsdam in Germany. “That tells you the star must have evolved differently.”

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The stars may have formed from the merging of two white dwarfs, the remnant hearts of stars that exhausted their fuel, another team proposes in a companion study. The story goes that one of the two was rich in helium, while the other contained lots of carbon and oxygen.These two white dwarfs had already been orbiting one another, but gradually drew together over time. Eventually the helium-rich white dwarf gobbled its partner, spewing carbon and oxygen all over its surface, just as a messy child might get food all over their face.

Such a merger would have produced a stellar body covered in carbon and oxygen with enough mass to reignite nuclear fusion in its core, causing it to burn hot and glow brilliantly, say Tiara Battich, an astrophysicist from the Max Planck Institute for Astrophysics in Garching, Germany, and her colleagues.

To test this hypothesis, Battich and her colleagues simulated the evolution, death and eventual merging of two stars. The team found that aggregating a carbon-and-oxygen-rich white dwarf onto a more massive helium one could explain the surface compositions of the two stars observed by Reindl and her colleagues.

“But this should happen very rarely,” Battich says.

In most cases the opposite should occur — the carbon-oxygen white dwarf should cover itself with the helium one. That’s because carbon-oxygen white dwarfs are usually the more massive ones. For the rarer scenario to occur, two stars slightly more massive than the sun must have formed at just the right distance apart from each other. What’s more, they needed to have then exchanged material at just the right time before both running out of nuclear fuel in order to leave behind a helium white dwarf of greater mass than a carbon-and-oxygen counterpart.

The origins story Battich and her colleagues propose demands a very specific and unusual set of circumstances, says Simon Blouin, an astrophysicist from the University of Victoria in Canada, who was not involved with either study. “But in the end, it makes sense.” Stellar mergers are dynamic and complicated events that can unfold in many ways, he says (SN: 12/1/20). “This is just another.” More

Small worlds around other stars may come in more than two varieties. Using exoplanet densities, astronomers have largely sorted planets that are bigger than Earth but smaller than Neptune into two categories: denser, rocky super-Earths and larger, puffy mini-Neptunes (SN: 6/19/17). Mini-Neptunes are generally thought to be padded in thick layers of hydrogen and helium […] More

Bright, artificial lights are drowning out the night sky’s natural glow. Now, an exhibition is highlighting some of the consequences of a fading starry night — and how people can help restore it.

“Lights Out,” open through 2025 at the Smithsonian National Museum of Natural History in Washington, D.C., illuminates how light pollution is affecting astronomy, natural ecosystems and human cultures around the world. “We want people to understand that it’s a global problem, and it’s having broad impact,” says Jill Johnson, an exhibit developer at the museum.

Upon entering the exhibition, the dimly lit space resets the mood for nighttime exploration. The exhibition spans a long hallway that can be entered from either end. One entrance quickly draws in visitors with a personal connection. An interactive display invites you to experience your own night sky, whether in a city, suburb or remote location. Three tactile panels feature raised elements, including dots representing light pollution and crosses indicating visible stars. The more populated a place, the more dots are smattered across the panel.

Visitors can also listen to the artificial light and starlight in each sky through data that have been translated into sound. The multisensory experience is especially engaging for visitors who may not be able to experience the exhibition visually.

The other entrance offers a more didactic introduction to the exhibition. A timeline presents a brief history of human-made light, from fire-lit torches to today’s LEDs, and then segues to astronomy (SN: 1/19/23). Space scientists rely on light, both visible and not, to understand celestial bodies. And their views of the universe have become increasingly obstructed by artificial light.

“Astronomers were some of the first folks to sound the alarm on light pollution,” says Ryan Lavery, a public affairs specialist at the museum.

Astronomers aren’t the only scientists who have noticed the repercussions. Biologists have observed light pollution’s toll on plants and animals, whether harming corals’ moonlight-triggered reproduction or bats’ ability to pollinate flowers. Here, much of the evidence on display is visual. Photographs and specimens demonstrate the variety of critters that are active at night, while a glass case of preserved birds presents the grim consequences of light pollution. All of these birds died from striking buildings in Washington, D.C., or Baltimore after being disoriented by the bright cityscapes.

Losing dark, starry nights also affects human cultures. Another area of the exhibition presents people’s ancient and modern-day connections to the night sky through photographs, stories and cultural items. A glistening beadwork depicting the Milky Way was crafted specially for “Lights Out” by Gwich’in artist Margaret Nazon, who grew up staring at the stars in Canada’s Northwest Territories.

Our connections under a shared sky are emphasized in the exhibition’s small central theater. It replicates a starry night over Coudersport, Pa., through speckled lighting and walls bearing illustrations of trees and hills. A short film describes the star cluster Messier 45, also known as the Pleiades, and explains the stars’ origins according to tales from three cultures — the ancient Greeks, the Ainu in Japan and the Māori in New Zealand.

“Cultures all over the world have a deep relationship to the night sky,” says Stephen Loring, cocurator of the exhibition and an archaeologist at the museum. “If we lose the night sky, we lose an avenue to our understanding of what it is to be a human being.”

But the exhibition isn’t all bleak. Sprinkled throughout it are success stories of how people are reducing light pollution, from France’s outdoor lighting curfews to beach communities that have altered their lighting systems to avoid drawing hatchling sea turtles away from the ocean. And visitors may be heartened to learn about simple but meaningful actions that they can take, such as aiming outdoor lights downward and using the dimmest settings.

Overall, “Lights Out” instills a sense of hope and a desire to reconnect with the night sky. “This is an optimistic exhibition,” Loring says. “We can solve this problem.” More

The lander was listening. On February 18, NASA’s InSight lander on Mars turned its attention to the landing site for another mission, Perseverance, hoping to detect its arrival on the planet.

But InSight heard nothing.

Tungsten blocks ejected by Perseverance during entry landed hard enough to create craters on the Martian surface. Collisions like these — whether from space missions or meteor strikes — send shock waves through the ground. Yet in the first experiment of its kind on another world, InSight failed to pick up any seismic waves from the blocks’ impacts, researchers report October 28 in Nature Communications.

As a result, researchers think that less than 3 percent of the energy from the impacts made its way into the Martian surface. The intensity of impact-generated rumblings varies from planet to planet and is “really important for understanding how the ground will change from a big impact event,” says Ben Fernando, a geophysicist at the University of Oxford.

Perseverance left behind several craters (one indicated with the arrow) after pieces of the mission disengaged as planned during entry, creating a rare opportunity to see how Mars absorbs energy from impacts. Univ. of Arizona, JPL-Caltech/NASA

But getting these measurements is tricky. Scientists need sensitive instruments placed relatively near an impact site. Knowing when and where a meteor will strike is nearly impossible, especially on another world.

Enter Perseverance: a hurtling space object set to hit Mars at an exact time and place (SN: 2/17/21). To help with its entry, Perseverance dropped about 78 kilograms of tungsten as the rover landed about 3,450 kilometers from InSight. The timing and weight of the drop provided a “once-in-a-mission opportunity” to study the immediate seismic effects of an impact from space, Fernando says.

The team had no idea whether InSight would be able to detect the blocks’ impacts or not, but the quiet arrival speaks volumes. “It lets us put an upper limit on how much energy from the tungsten blocks turned into seismic energy,” Fernando says. “We’ve never been able to get that number for Mars before.”

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