The biggest conundrum in cosmology may be closer to being solved, thanks to the James Webb Space Telescope.

Scientists disagree on the expansion rate of the universe, known as the Hubble constant. There are two main methods for measuring it – one based on exploding stars called supernovae and the other on the universe’s oldest light, the cosmic microwave background. The two techniques have been in conflict for a decade, in what is known as the “Hubble tension” (SN: 21.3.14). If this tension is real and not the result of an error in one of the measurements, it would require a drastic change in the way scientists understand the universe.

New papers published by two of the central players are raising hopes that additional observations by the James Webb Space Telescope, or JWST, of several types of stars and supernovae could settle the question of whether the discrepancy is real, once and for all.

The two teams disagree on whether that tension exists at all. One team says there is no strong evidence for Hubble tension from JWST data. But the other group says the JWST data strengthens the case that the two types of measurements are in conflict. “I’m even more intrigued by the Hubble tension,” says cosmologist Adam Riess of Johns Hopkins University, leader of one of the teams.

The different camps are finally seeing eye to eye on one part of their measurements: the distances to nearby galaxies, which are needed to infer the expansion rate of the universe from supernovae. “This is really new—we’re agreeing on distances, and that’s a real breakthrough,” says cosmologist Wendy Freedman of the University of Chicago, who leads the other team.

“If you had told me 10 years ago that this would all be agreed at this level, I would have just jumped up and down,” says cosmologist Daniel Scolnic of Duke University, a member of Riess’s team.

This agreement gives scientists new confidence that the long-standing dispute is close to being resolved. “I’m very optimistic that in the next couple of years, the questions we’re talking about now, we’ll have solved them,” Freedman says.

Reaching consensus on distances

Scientists’ theory of the universe, called the standard cosmological model, is based largely on unknowns. Dark matter, a substance that adds invisible mass to galaxies, has never been directly detected. And dark energy, a phenomenon that causes the universe’s expansion to accelerate, is also a total question mark. But the model has proved remarkably successful in describing the cosmos.

Starting from the ancient light of the cosmic microwave background, scientists can use the standard cosmological model to determine today’s rate of expansion. This technique reveals that space is expanding at 67 kilometers per second per megaparsec. (A megaparsec is about 3 million light years.)

But supernova measurements by Riess and colleagues peg the number at about 73 km/s/Mpc – putting the two results in direct conflict. This may hint that something is wrong with the standard cosmological model.

To determine the rate of expansion through the supernova technique, cosmologists must measure the distances to many distant supernovae. This requires a technique called a distance scale, to translate close distances to farther ones.

Under special scrutiny is the second rung of this scale, in which scientists observe certain types of stars – most commonly, pulsating stars called Cepheids – to determine the distances to the galaxies where they reside, as well as to the supernovae that occurred in them the same galaxies. Observing these stars with JWST, which has better resolution than the Hubble Space Telescope, could highlight flaws in measurements on that scale.

In addition to Cepheids, Freedman and colleagues used two other types of stars for their distance measurements. Using JWST data for all three, Freedman and colleagues find an expansion rate of about 70 km/s/Mpc. Given the uncertainties in the measurements, this is close enough to the cosmic microwave background number that it does not require physicists to rethink the cosmos, the team reports in a paper submitted Aug. 12 to arXiv.org. But it also does not completely rule out the existence of the Hubble tension. “We need more data to answer the question definitively,” says Freedman.

The three distance measurement techniques were generally in agreement, Freedman says. The Cepheid measurements result in a slightly higher value of the Hubble constant than the other two methods, but not enough to indicate anything wrong with the technique. “There’s a trade-off, but the uncertainties are big enough that you can’t say for sure, ‘This is the way it’s going to turn out,'” Freedman says.

Hubble constant

Despite agreeing on the distances, the teams still differ on Hubble’s constant. This may be due to the small number of measurements made with JWST so far, Riess, Scolnic and colleagues report in a paper submitted to arXiv.org on August 21. If Freedman’s team had chosen different galaxies to observe with JWST, they would have obtained a larger value of the Hubble constant, the team argues. (None of the papers have been peer-reviewed, and results may change under further review.)

Scientists are working only with the first data sets from JWST. To solve the puzzle, “the best thing we can do is use much more JWST time to study the distance scale,” says astronomer John Blakeslee of NOIRLab in Tucson, Ariz., who was not involved in the research. .

Freedman wants to continue looking for unidentified issues known as systematic uncertainties that could artificially push estimates of the Hubble constant higher. One concern is clumping—too many stars clumped together in the same place, throwing off Cepheid measurements. Last year, Riess’ team found no evidence of clumping in the JWST data (SN: 28/9/23). But this effect may be more apparent at greater distances than has been studied so far with JWST, Freedman suggests.

If scientists find that different distance measurements disagree, says cosmologist Saul Perlmutter of the University of California, Berkeley, who was not involved in the research, “then it may suggest that we still have to get to the bottom of the systematic uncertainties first.” before we get to a major problem with the cosmological model.”

But many physicists are satisfied with the Hubble tension. First, various other methods have also found higher-than-expected expansion rates, says cosmologist Eleonora Di Valentino of the University of Sheffield in England, who was not involved in the research. “The Hubble tension is still very strong.”

“I see these results as supporting … the fact that we have this difference between what we expect from our standard cosmological model and what we see from these measurements,” says cosmologist Lloyd Knox of the University of California, Davis, who was not involved. in each team.

The standard cosmological model, he notes, relies on mysterious dark energy and dark matter. “Maybe this is a clue to the dark universe, and we just have to figure out how to interpret it.”

For the first time, scientists have measured a long-sought global electric field in Earth’s atmosphere. This field, called the ambipolar electric field, was predicted to exist decades ago but was never discovered until now.

“That’s the big noise,” says atmospheric scientist Glyn Collinson of NASA’s Goddard Space Flight Center in Greenbelt, Md.

The field is weak, just 0.55 volts — about as strong as a watch battery, Collinson says. But it is strong enough to control the shape and evolution of the upper atmosphere, features that may have implications for our planet’s suitability for life.

“It’s essential to the DNA of our planet,” says Collinson, who reported the new measurement in Nature August 28.

The existence of the ambipolar electric field was first predicted in the 1960s, at the dawn of the space age. Early spacecraft flying over Earth’s poles detected a supersonic outflow of charged particles from the atmosphere, called the polar wind.

The most reasonable thing to explain the fast wind would be an electric field in the atmosphere. The idea is that sunlight can strip electrons from atoms in the upper atmosphere. Those negatively charged electrons are light and energetic enough that they want to float around in space. The positively charged oxygen ions left behind are heavier and tend to sink under Earth’s gravity.

But the atmosphere wants to remain electrically neutral, maintaining an even balance between electrons and ions. The electric field is formed to keep the electrons attached to the ions and prevent them from escaping.

Once established, the field can act as a booster for lighter ions such as hydrogen, giving them enough energy to break free from Earth’s gravity and drift away as the polar wind. It can also pull heavier ions higher into the atmosphere than they would otherwise reach, where other forces can also remove them into space.

That was the hypothesis. But until recently, the technology to detect the field did not exist.

“It really was thought impossible to do,” says Collinson. “[The field] so weak, it was just assumed you would never measure up.”

Collinson realized that this measurement had not been obtained after he and his colleagues tried to measure a similar field on Venus. A search for a paper reporting Earth’s field strength for comparison came up empty.

“It turned out, funny story, it’s never been done,” he says. “We were like, ‘Game on!'”

Collinson and colleagues developed a new instrument called a photoelectron spectrometer specifically to detect the electric field. The team mounted the spectrometer on a rocket called the Endurance, after the ship that carried Ernest Shackleton to explore Antarctica in 1914.

Reaching the launch site in Svalbard, Norway was a journey worthy of the rocket’s name. The team traveled by boat for 17 hours to reach the Svalbard archipelago, located just a few hundred kilometers from the North Pole. Several members of the team contracted COVID-19 along the way. And the war between Russia and Ukraine had started only a few months earlier.

“At the time, there was some nervousness about launching missiles,” says Collinson. “Polar bears were the fewest. We had war and pestilence.”

Two more days of storms kept the Endurance grounded. When the rocket finally launched on May 11, 2022, it went straight into the atmosphere at about 770 kilometers, measuring the energies of the electrons every 10 seconds. The entire flight lasted 19 minutes. In the end, the rocket was thrown into the Greenland Sea.

Endurance measured a difference in electrical potential of 0.55 volts between altitudes of 248 kilometers and 768 kilometers—just enough to explain the polar wind on its own, without any other atmospheric effects.

The measurement is solid and exciting, says planetary scientist David Brain of the University of Colorado Boulder, who was not involved in the new work. But it’s just one data point from a rocket. “I think this result is a really big result that argues that there should be more measurements like this,” he says.

Collinson agrees. He and his colleagues recently won NASA approval for a follow-up rocket—this time called Resolute, for an Arctic exploration ship that launched in 1850.

Because the ambipolar electric field helps control how quickly a planet’s atmosphere escapes into space, it probably plays a role in making a planet hospitable to life, Collinson says. Scientists think Mars was once more like Earth, but lost much of its atmosphere to space over time (SN: 11/27/15). Venus may once have been much wetter than it is today (SN: 8/1/17).

Both of these planets also have ambipolar electric fields, but they may have been better off without them.

“If this process didn’t exist on Venus and Mars, then I think it’s possible that Venus and Mars would have lost less oxygen, and therefore less water,” says Brain.

Earth’s ambipolar electric field helps push its oxygen into space, too. But Earth has one major advantage over Mars and Venus: a global magnetic field to direct charged particles around the planet. “The electric field is the engine that makes the particles move,” says Brain. “The magnetic field is a kind of path along which particles move.” The Earth’s magnetic field means that oxygen can only escape near the poles, and not from every part of the atmosphere. This may help explain why Earth has retained its habitable atmosphere for much longer than Venus or Mars.

“Basically, what makes a planet habitable is going to be a lot of things,” Collinson says. “But I think comparing these different energy fields across different planets is one way to answer the question, why is Earth habitable? Why are we here?”

NASA’s Europa Clipper spacecraft is on its way to help solve a quarter-century-old mystery: Could anything live in the ocean lurking beneath the icy shell of Jupiter’s moon Europa?

“This is a mission we’ve dreamed about for 25 years now, since I was in graduate school,” says planetary geologist Cynthia Phillips of NASA’s Jet Propulsion Laboratory in Pasadena, California. “It’s a generational mission.”

An Oct. 10 launch from the Kennedy Space Center in Florida was canceled because of Hurricane Milton, but on Oct. 14, the spacecraft lifted off just after noon ET and began its five-and-a-half-year journey to Jupiter.

Once there, Clipper will be placed into orbit around the giant planet in April 2030, repeatedly passing the icy moon to take pictures of its frozen terrain, measure the surface’s chemistry and deduce internal structure of the moon.

“We think ocean worlds may actually be a common type of world outside our solar system,” NASA’s planetary science chief Gina DiBraccio said at a Sept. 17 press conference. “Clipper will be the first in-depth mission that will allow us to characterize habitability on what may be the most common type of habitable world in our universe.”

Planetary scientists have become increasingly confident that Europa hosts a subsurface ocean since NASA’s Galileo spacecraft visited Jupiter in the 1990s.SN: 18.2.02).

“During the Galileo mission, it was like a detective story,” says Phillips. Constructed data. The lack of craters suggests that the surface is always moving and changing. Lines, cracks and pits, suggesting uplift from below. Regions known as “chaos terrain”, which look like tilted icebergs in a sloping sea (SN: 16/11/11).

And finally, the measurement of an internal magnetic field caused by Jupiter’s external one. This was the “coup d’état,” says Phillips. The only geologically plausible material that can sustain this magnetic field is salt water.

On Earth, water means life. But the findings in Europa were not enough to declare it a habitable world (SN: 19.4.24). Many mysteries remained: How deep is the ocean? How thick is the ice shell? And more importantly, how do they interact? Could material from the surface sink into the salty depths to provide food for the microbes that wait?

The Europa Clipper, named for the fast clipper ships of the 19th century, is poised to pick up where Galileo left off. The spacecraft is tasked with investigating the habitability of Europa by searching for three main ingredients: water, energy and organic compounds.

The spacecraft will not directly orbit Europa. The moon is located within Jupiter’s punishing radiation environment, where high-energy charged particles accelerated by the planet’s magnetic field can fry spacecraft components (SN: 11/9/20). Instead, Clipper will dip in and out of that radiation zone to fly past Europa at least 49 times — aiming all nine of its instruments at the Moon at once — each time retreating to quieter territory to process the data and send it back to Earth. .

One of the first things Clipper will do when it arrives is confirm — or perhaps disprove — the presence of the subsurface ocean. The way the moon gravitationally pulls the spacecraft will immediately reveal the details of its interior, JPL’s deputy project scientist Bonnie Buratti said at the press conference.

The pictures will come next. Galileo’s antenna was never positioned properly, so its images weren’t as sharp as they could have been, Phillips says. Galileo’s spectrometer wasn’t designed to work on Europa either, so scientists tried to find out the composition of anything that wasn’t ice on the surface. Clipper’s images and spectra will reveal clues about surface and possibly subsurface chemistry that Galileo never could.

Finally, Clipper will delve into details like the thickness of the crust, the depth of the ocean, and how they interact.

There are some limitations. Clipper’s gaze will not reach the bottom of the ocean, where rock and water meet. This may be the most likely place for microbial ecosystems to harbor, similar to sea vents on Earth. But Clipper won’t be able to sense them directly.

However, there is strong circumstantial evidence that water sometimes rises to the surface, either in plumes of steam or in slower-flowing streams or lakes, and may deposit any other material it carries in the ice.SN: 14.5.18). Clipper will search for chemicals on the surface and find out what might be brewing in the dark depths.

“The holy grail would be if we could see something like an amino acid on the surface,” says Buratti. “But only by looking at many organic molecules will there be good evidence that we have all the conditions for life.”

What Clipper won’t do is search directly for life. “We don’t have a tricorder that we can point from Europa and say, ‘It’s life, Jim!'” like in Star Trek, Phillips says. “It will again be multiple lines of indirect evidence.”

“To do a life detection mission,” she says, “you’re going to have to touch that surface.” Or maybe it falls under it (SN: 5/2/14).

As long as he’s had to wait to get to Europe, Phillips doesn’t expect to see that mission for himself. But she hopes scientists won’t have to wait another 25 years.

“I hope this momentum will grow,” she says. “I accept that I probably won’t see that Europa submarine, but I hope my children or maybe my grandchildren will.”

Dozens of runaway stars were caught escaping from a dense star cluster in a satellite galaxy of the Milky Way. The cluster of fast-moving stars may mean that such runaways had a greater influence on cosmic evolution than previously thought, astronomers report Oct. 9 in Nature.

Massive stars are born in new clusters, packed so close together that they can shake each other out of place. Sometimes, encounters between pairs of massive stars or neighboring supernova explosions can send a star crawling out of the cluster altogether, to seek its fate in the wider galaxy and beyond.

Astronomer Mitchel Stoop of the University of Amsterdam and his colleagues searched for runaway stars around a large cluster of massive stars called Radcliffe 136 using data from the Gaia spacecraft on the velocities and positions of billions of stars. (SN: 6/13/22). R136 is located about 170,000 light-years from Earth in the Large Magellanic Cloud, a dwarf galaxy orbiting the Milky Way.

The cluster “is an iconic object,” says astrophysicist Sally Oey of the University of Michigan in Ann Arbor, who was not involved in the new work. The view from Earth’s neighborhood is so clear, “we can see things up close and personal.”

Previous studies had found some stars escaping the cluster (SN: 5/7/10). But in a broader search, Stoop found that an astonishing 55 stars had fled at speeds greater than roughly 100,000 kilometers per hour in the past 3 million years.

“That’s an incredible number to think about,” says Stoop. The observation suggests that a third of the brightest and most massive stars born in the cluster have left home.

This means that runaway stars may be an underestimated force in the universe. These massive stars, about five to 140 times the mass of the Sun, emit ultraviolet radiation and supersonic stellar winds that can sculpt the gas and dust around them. (SN: 7/11/22). At the end of their lives, heavy stars explode as supernovae, spreading heavy elements around the galaxy. (SN: 7/7/21).

“Before, we would expect that there would probably be some escapees,” says Stoop. But because of their presumed low numbers, he says, they would be left out of studies and simulations. If each cluster loses about a third of its stars to the surrounding galaxy, or even the space between galaxies, “they could probably make a big contribution to dumping all these ultraviolet photons into the intergalactic medium.”

Such escapees may also have had a profound impact on the evolution of the early universe. Within a few hundred million years of the Big Bang, more than 13 billion years ago, a source of ultraviolet radiation stripped electrons from a diffuse cloud of hydrogen atoms, a phenomenon called reionization (SN: 11/7/19).

Astronomers think that most of the photons, or particles of light, that cleared the cosmic haze came from dwarf galaxies. (SN: 2/6/17). But simulations have revealed that only a fraction of the necessary photons can escape the environments of those galaxies. Runaway stars can help account for the change, Stoop says.

“Maybe this happened in [early universe] galaxies too, during the reionization epoch,” he says.

Oey says, “There’s no doubt that runaway stars are really important and underrated.” But, she says, there are other ways to remove ionizing radiation from galaxies, and it’s not clear how much of a difference including runaway stars would make.

The timing of the runaway stars from R136 may also throw a wrench into the broader connection of runaway stars to reionization.

Surprisingly, the stars did not all migrate in one wave. Scientists know this because they have the velocities and distances of the stars and can calculate when they began their escape. Most escapees left R136 in all directions about 1.8 million years ago, when the cluster was forming. That’s what you’d expect if they were pulled from dating other massive stars.

But 16 of the escapees left the group more recently, just 200,000 or so years ago. And everyone was running in the same direction. Stoop and his colleagues think that the escape of these stars may have been caused by a merger with another cluster.

“This seems like a pretty unique phenomenon,” says astrophysicist Kaitlin Kratter of the University of Arizona in Tucson. If the double ejection of R136 is unusual, then it may be difficult to extrapolate how many stars other groups lose to their cosmic environment. Finding evidence of similar waves in other clusters would help resolve the question.

Astronomers have finally found an asteroid that keeps pace with Saturn in its orbit around the sun. Such objects, called Trojan asteroids, are already known for the other three giant planets.

“Saturn was kind of the odd man out, if I can call it that, because even though it’s the second most massive planet in the solar system, it didn’t have any Trojans,” says Paul Wiegert, an astronomer at the University of Western Ontario in London, Canada. Like Saturn, the new asteroid takes about 30 years to orbit, but lies 60 degrees ahead of the planet in its orbit, Wiegert and colleagues report in work submitted Sept. 29 to arXiv.org.

Most of the asteroids in the solar system orbit the sun between the paths of Mars and Jupiter. However, in 1906, German astronomer Max Wolf discovered the first Trojan, which he named Achilles, orbiting the sun 60 degrees ahead of Jupiter. Since then, astronomers have found thousands of additional Trojan asteroids – some are 60 degrees ahead of Jupiter, others are 60 degrees behind. NASA’s Lucy spacecraft will visit eight of them between 2027 and 2033 (SN: 15/10/21).

Trojan asteroids also exist for Uranus and Neptune and even for Earth and Mars (SN: 2/1/22).

After a telescope image in Hawaii captured the new asteroid in 2019, an amateur astronomer in Australia, Andrew Walker, suggested the object could be a Saturnian Trojan – if it had the right orbit around the sun.

“The key to getting a good orbit for something in our solar system is to have many observations of it through different telescopes over a long period of time,” says Wiegert. So astronomer Man-To Hui at the Macau University of Science and Technology in China looked for previous images of the asteroid and also planned new observations. Measurements of the asteroid’s position – from 2015 to 2024 – confirmed its Trojan nature. Named 2019 UO₁₄the asteroid is only about 13 kilometers across, the same size as Deimos, the smaller of Mars’ two moons.

Scientists have long predicted Saturnian Trojans, says astronomer Carlos de la Fuente Marcos of the Complutense University of Madrid, who was not involved in the discovery. But all Saturnian Trojans must have unstable orbits because Saturn has giant planets on either side of it.

“Jupiter seems to be the culprit,” says de la Fuente Marcos. Jupiter’s great gravity gradually pulls a Saturnian Trojan, making its orbit around the sun increasingly elliptical. The asteroid then wanders so close to Jupiter or Uranus that one of those giant planets knocks the tiny body out of its Trojan orbit.

In fact, researchers estimate that the asteroid has been a Trojan for only about 2,000 years and will remain so for only another 1,000 years. Before its connection with the ringed planet, the asteroid was probably a centaur, an asteroid that moved around the sun between the orbits of the giant planets (SN: 11/12/77).

The asteroid may not be Saturn’s only Trojan. “I’m pretty sure there are more — maybe just a few, but this can’t be the only one,” Wiegert says.

Most of Earth’s meteorites can be traced back to just a few collisions within the asteroid belt between Mars and Jupiter, two new studies report, including a particularly cataclysmic event about 470 million years ago.

The positive side of this discovery, published on October 16 in Natureis that it provides researchers with vital context: By knowing the return address of meteorites, scientists can more easily understand how and where the building blocks of the planets came together to create the solar system we see today. The downside is that it can mean researchers have an extremely biased collection of meteorites that can only tell a sliver of the story.

Meteorites record the tumultuous history of the solar system’s formative years, but the origin of these ancient space rocks is often unknown (SN: 18.4.18). “It’s absolutely like a pot of gold at the end of a rainbow for a meteorologist to know where the sample asteroid is from,” says Sara Russell, a planetary scientist at London’s Natural History Museum, who was not involved in either study. . Without this information, a meteorite is like a piece of a puzzle without a picture of the complete puzzle to accompany it.

Most meteorites on Earth are rocks called ordinary chondrites. Two classes of these chondrites, known as H and L, account for 70 percent of all meteorite falls.

Scientists had suspected that L chondrites originated from an asteroid with a single parent. Many have mineralogical features that indicate they were severely shocked, burned and degassed before gradually cooling, implying that they were released from a giant asteroid – at least 100 kilometers long – through a supersonic collision.

Using radioactive decay elements to determine the age of meteorites has revealed that they first emerged from an impact that occurred 470 million years ago. To search for the site of that destruction derby in the asteroid belt, researchers used NASA’s Infrared Telescope Facility in Hawaii to scan many prominent rocky-type asteroids, comparing the mineral signatures of each to those of L chondrites.

The best fit was a group of asteroids called the Massalia family. Their scattered presence and current orbits could effectively be traced back by scientists – and it looked like the asteroids all formed about 500 million years ago after breaking up from an older, larger asteroid. This timing suggested that the impact that created the L chondrites also created the Massalia family. One of the asteroids in that family is about 140 kilometers long, a perfect fit for the estimated size range of the L chondrite parent body.

Other independent lines of data also point to the Massalia family, including the fact that near-Earth asteroids with L-chondrite-like signatures have orbits that come from the family, as do the orbits of L-chondrite meteors that burn across Earth’s skies. before leaving behind telltale meteorites.

“They all point to the same thing. There is no doubt,” says Michaël Marsset, an astronomer at the European Southern Observatory in Santiago, Chile, and author of both studies.

That ancient impact also set the stage for a more recent bombardment, sending streams of L-chondrite material crashing back into the larger asteroid remnant. Another impact no more than 40 million years ago sent that wreckage to Earth.

Is H going against it? Many are 5 million to 8 million years old, so they came from a different impact event—or two events, it seems. Reconstructing past orbits of mineralogically compatible Koronis₂ family of asteroids, the team found that many of those asteroids existed unified as a single asteroid 7.6 million years ago.

Previous research had already applied the same time-rewinding technique to another group of asteroids, known as the Karin family, and found that many of them had also coalesced as a single asteroid 5.8 million years ago, shortly before an asteroid another hit him. Since both families cover each end of the date range for H chondrites, the team concluded that they are the source of this class of meteorite.

The fact that Earth’s meteorite collection could be so biased toward just a few asteroids is troubling, Russell says. The asteroid belt is home to a variety of rocks, stones and even dwarf planets, each revealing something unique about the solar system (SN: 8/3/16). “Maybe we’re only seeing a small fraction of them” through our meteorites, she says.

There is a solution, albeit a more costly one than scouring the Earth for more meteors. “We have to have space missions to go out there,” she says, and hunt down these ancient rock archives ourselves (SN: 15.2.24).