astronomy

the-moon-had-volcanic-activity-much-more-recently-than-we-knew

The Moon had volcanic activity much more recently than we knew

astronomy, eruptions, moon, planetary science, Science, volcanism / /

New Moon —

Eruptions seem to have continued long after widespread volcanism had ended.

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Image of the face of the Moon.

Enlarge / The eruptions that produced the dark mare on the lunar surface ended billions of years ago.

Signs of volcanic activity on the Moon can be viewed simply by looking up at the night-time sky: The large, dark plains called “maria” are the product of massive outbursts of volcanic material. But these were put in place relatively early in the Moon’s history, with their formation ending roughly 3 billion years ago. Smaller-scale additions may have continued until roughly 2 billion years ago. Evidence of that activity includes samples obtained by China’s Chang’e-5 lander.

But there are hints that small-scale volcanism continued until much more recent times. Observations from space have identified terrain that seems to be the product of eruptions, but only has a limited number of craters, suggesting a relatively young age. But there’s considerable uncertainty about these deposits.

Now, further data from samples returned to Earth by the Chang’e-5 mission show clear evidence of volcanism that is truly recent in the context of the history of the Solar System. Small beads that formed during an eruption have been dated to just 125 million years ago.

Counting beads

Obviously, some of the samples returned by Chang’e-5 are solid rock. But it also returned a lot of loose material from the lunar regolith. And that includes a decent number of rounded, glassy beads formed from molten material. There are two potential sources of those beads: volcanic activity and impacts.

The Moon is constantly bombarded by particles ranging in size from individual atoms to small rocks, and many of these arrive with enough energy to melt whatever it is they smash into. Some of that molten material will form these beads, which may then be scattered widely by further impacts. The composition of these beads can vary wildly, as they’re composed of either whatever smashed into the Moon or whatever was on the Moon that got smashed. So, the relative concentrations of different materials will be all over the map.

By contrast, any relatively recent volcanism on the Moon will be extremely rare, so is likely to be from a single site and have a single composition. And, conveniently, the Apollo missions already returned samples of volcanic lunar rocks, which provide a model for what that composition might look like. So, the challenge was one of sorting through the beads returned from the Chang’e-5 landing site, and figuring out which ones looked volcanic.

And it really was a challenge, as there were over 3,000 beads returned, and the vast majority of them would have originated in impacts.

As a first cutoff, the team behind the new work got rid of anything that had a mixed composition, such as unmelted material embedded in the bead, or obvious compositional variation. This took the 3,000 beads down to 764. Those remaining beads were then subject to a technique that could determine what chemicals were present. (The team used an electron probe microanalyzer, which bombards the sample with electrons and uses the photons that are emitted to determine what elements are present.) As expected, compositions were all over the map. Some beads were less than 1 percent magnesium oxide; others nearly 30 percent. Silicon dioxide ranged from 16 to 60 percent.

Based on the Apollo samples, the researchers selected for beads that were high in magnesium oxide relative to calcium and aluminum oxides. That got them down to 13 potentially volcanic samples. They also looked for low nickel, as that’s found in many impactors, which got the number down to six. The final step was to look at sulfur isotopes, as impact melting tends to preferentially release the lighter isotope, altering the ratio compared to intact lunar rocks.

After all that, the researchers were left with three of the glassy beads, which is a big step down from the 3,000 they started with.

Erupted

Those three were then used to perform uranium-based radioactive dating, and they all produced numbers that were relatively close to each other. Based on the overlapping uncertainties, the researchers conclude that all were the product of an eruption that took place about 123 million years ago, give or take 15 million years. Considering that the most recent confirmed eruptions were about 2 billion years ago, that’s a major step forward in timing.

And that’s quite a bit of a surprise, as the Moon has had plenty of time to cool, and that cooling would have increased the distance between its surface and any molten material left in the interior. So it’s not obvious what could be creating sufficient heating to generate molten material at present. The researchers note that the Moon has a lot of material called KREEP (potassium, rare earth elements, phosphorus) that is high in radioactive isotopes and might lead to localized heating in some circumstances.

Unfortunately, it will be tough to associate this with any local geology, since there’s no indication of where the eruption occurred. Material this small can travel quite a distance in the Moon’s weak gravitational field and then could be scattered even farther by impacts. So, it’s possible that these belong to features that have been identified as potentially volcanic through orbital images.

In the meantime, the increased exploration of the Moon planned for the next few decades should get us more opportunities to see whether similar materials are widespread on the lunar surface. Eventually, that might potentially allow us to identify an area with higher concentrations of volcanic material than one particle in a thousand.

Science, 2024. DOI: 10.1126/science.adk6635  (About DOIs).

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Astronomers think they’ve found a plausible explanation of the Wow! signal

aliens, astronomy, astrophysics, Physics, Science, WOW! signal / /

“I’m not saying it’s aliens…” —

Magnetars could zap clouds of atomic hydrogen, producing focused microwave beams.

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The Wow! signal represented as

Enlarge / The Wow! signal, represented as “6EQUJ5,” was discovered in 1977 by astronomer Jerry Ehman.

Public domain

An unusually bright burst of radio waves—dubbed the Wow! signal—discovered in the 1970s has baffled astronomers ever since, given the tantalizing possibility that it just might be from an alien civilization trying to communicate with us. A team of astronomers think they might have a better explanation, according to a preprint posted to the physics arXiv: clouds of atomic hydrogen that essentially act like a naturally occurring galactic maser, emitting a beam of intense microwave radiation when zapped by a flare from a passing magnetar.

As previously reported, the Wow! signal was detected on August 18, 1977, by The Ohio State University Radio Observatory, known as “Big Ear.” Astronomy professor Jerry Ehman was analyzing Big Ear data in the form of printouts that, to the untrained eye, looked like someone had simply smashed the number row of a typewriter with a preference for lower digits. Numbers and letters in the Big Ear data indicated, essentially, the intensity of the electromagnetic signal picked up by the telescope over time, starting at ones and moving up to letters in the double digits (A was 10, B was 11, and so on). Most of the page was covered in ones and twos, with a stray six or seven sprinkled in.

But that day, Ehman found an anomaly: 6EQUJ5 (sometimes misinterpreted as a message encoded in the radio signal). This signal had started out at an intensity of six—already an outlier on the page—climbed to E, then Q, peaked at U—the highest power signal Big Ear had ever seen—then decreased again. Ehman circled the sequence in red pen and wrote “Wow!” next to it. The signal appeared to be coming from the direction of the Sagittarius constellation, and the entire signal lasted for about 72 seconds. Alas, SETI researchers have never been able to detect the so-called “Wow! Signal” again, despite many tries with radio telescopes around the world.

One reason for the excited reaction is that such a signal had been proposed as a possible communication from extraterrestrial civilizations in a 1959 paper by Cornell University physicists Philip Morrison and Giuseppe Cocconi. Morrison and Cocconi thought that such a civilization might use the 1420 megahertz frequency naturally emitted by hydrogen, the universe’s most abundant element and, therefore, something an alien civilization would be familiar with. In fact, the Big Ear had been reassigned to the SETI project in 1973 specifically to hunt for possible signals. Ehman himself was quite skeptical of the “it could be aliens” hypothesis for several decades, although he admitted in a 2019 interview that “the Wow! signal certainly has the potential of being the first signal from extraterrestrial intelligence.”

Several other alternative hypotheses have been suggested. For instance, Antonio Paris suggested in 2016 that the signal may have come from the hydrogen cloud surrounding a pair of comets, 266P/Christensen and 335P/Gibbs. This was rejected by most astronomers, however, in part because comets don’t emit strongly at the relevant frequencies. Others have suggested the signal was the result of interference from satellites orbiting the Earth, or a signal from Earth reflected off a piece of space debris.

Space maser!

Astrobiologist Abel Mendez of the University of Puerto Rico at Arecibo and his co-authors think they have the strongest astrophysical explanation to date with their cosmic maser hypothesis. The team was actually hunting for habitable exoplanets using signals from red dwarf stars. In some of the last archival data collected at the Arecibo radio telescope (which collapsed in 2020), they noticed several signals that were remarkably similar to the Wow! signal in terms of frequency—just much less intense (bright).

Mendez admitted to Science News that he had always viewed the Wow! signal as just a fluke—he certainly didn’t think it was aliens. But he realized that if the signals they were identifying had blazed brighter, even momentarily, they would be very much like the Wow! signal. As for the mechanism that caused such a brightening, Mendez et al. propose that a magnetar (a highly magnetic neutron star) passing behind a cloud of atomic hydrogen could have flared up with sufficient energy to produce stimulated emission in the form of a tightly focused beam of microwave radiation—a cosmic maser. (Masers are akin to lasers, except they emit microwave radiation rather than visible radiation.)

Proving their working hypothesis will be much more challenging, although there have been rare sightings of such naturally occurring masers from hydrogen molecules in space. But nobody has ever spotted an atomic hydrogen cloud with an associated maser, and that’s what would be needed to explain the intensity of the Wow! signal. That’s why other astronomers are opting for cautious skepticism. “A magnetar is going to produce [short] radio emissions as well. Do you really need this complicated maser stuff happening as well to explain the Wow! signal?” Michael Garrett of the University of Manchester told New Scientist. “Personally, I don’t think so. It just makes a complicated story even more complicated.”

arXiv, 2024. DOI: 10.48550/arXiv.2408.08513  (About DOIs).

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Meteorites give the Moon its extremely thin atmosphere

astronomy, atmosphere, Impacts, meteors, planetary science, Science, the Moon / /

The exosphere gets the vapors —

Impacts that vaporize bits of the lunar surface maintain the Moon’s thin atmosphere.

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Graphic of a spacecraft above a grey planetary body, with a distant sun in the background.

Enlarge / Artist’s rendition of the LADEE mission above the lunar surface.

The Moon may not have much of an atmosphere, mostly because of its weak gravitational field (whether it had a substantial atmosphere billions of years ago is debatable). But it is thought to presently be maintaining its tenuous atmosphere—also known as an exosphere—because of meteorite impacts.

Space rocks have been bombarding the Moon for its 4.5-billion-year existence. Researchers from MIT and the University of Chicago have now found that lunar soil samples collected by astronauts during the Apollo era show evidence that meteorites, from hulking meteors to micrometeoroids no bigger than specks of dust, have launched a steady flow of atoms into the exosphere.

Though some of these atoms escape into space and others fall back to the surface, those that do remain above the Moon create a thin atmosphere that keeps being replenished as more meteorites crash into the surface.

“Over long timescales, micrometeorite impact vaporization is the primary source of atoms in the lunar atmosphere,” the researchers said in a study recently published in Science Advances.

Ready for launch

When NASA sent its orbiter LADEE (Lunar Atmosphere and Dust Environment Explorer) to the Moon in 2013, the mission was intended to find out the origins of the Moon’s atmosphere. LADEE observed more atoms in the atmosphere during meteor showers, which suggested impacts had something to do with the atmosphere. However, it left questions about the mechanism that converts impact energy into a diffuse atmosphere.

To find these answers, a team of MIT and University of Chicago researchers, led by professor Nicole Nie of MIT’s Department of Earth, Atmospheric and Planetary Sciences, needed to analyze the isotopes of elements in lunar soil that are most susceptible to the effects of micrometeoroid impacts. They chose potassium and rubidium.

Potassium and rubidium ions are especially prone to two processes: impact vaporization and ion sputtering.

Impact vaporization results from particles colliding at high speeds and generating extreme amounts of heat that excite atoms enough to vaporize the material they are in and send them flying. Ion sputtering involves high-energy impacts that set atoms free without vaporization. Atoms that are released by ion sputtering tend to have more energy and move faster than those released by impact vaporization.

Either of these can create and maintain the lunar atmosphere in the wake of meteorite impacts.

So, if atoms sent into the atmosphere by ion sputtering have an energy advantage, then why did the researchers find that most atoms in the atmosphere actually come from impact vaporization?

Touching back down

Since the lunar soil samples provided by NASA had previously had their lighter and heavier isotopes of potassium and rubidium quantified, Lie’s team used calculations to determine which collision process is more likely to keep different isotopes from fleeing the atmosphere.

The researchers found that atoms transferred to the atmosphere by ion sputtering are sent zooming at such high energies that they often reach escape velocity—the minimum velocity needed to escape the Moon’s already feeble gravity—and continue to travel out into space. Atoms that end up in the atmosphere can also be lost from the atmosphere, after all.

The fraction of atoms that reach escape velocity after impact vaporization depends on the temperature of those atoms. Lower energy levels associated with impact vaporization result in lower temperatures, which give atoms a lower chance of escape.

“Impact vaporization is the dominant long-term source of the lunar atmosphere, likely contributing more than 65 percent of atmospheric [potassium] atoms, with ion sputtering accounting for the rest,” Lie and her team said in the same study.

There are other ways atoms are lost from the lunar atmosphere. It is mostly lighter ions that tend to stick around in the exosphere, with ions falling back to the surface if they’re too heavy. Others are photoionized by electromagnetic radiation from the solar wind and often carried off into space by solar wind particles.

What we’ve learned about the lunar atmosphere through lunar soil could influence studies of other bodies. Impact vaporization has already been found to launch atoms into the exosphere of Mercury, which is thinner than the Moon’s. Studying Martian soil, which may land on Earth with sample return missions in the future, could also give more insight into how meteorite impacts affect its atmosphere.

As we approach a new era of manned lunar missions, the Moon may have more to tell us about where its atmosphere comes from—and where it goes.

Science Advances, 2024.  DOI: 10.1126/sciadv.adm7074

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How Kepler’s 400-year-old sunspot sketches helped solve a modern mystery

astronomy, astrophysics, Johannes Kepler, Physics, Science, solar physics, sun spots / /
A naked-eye sunspot group on 11 May 2024

Enlarge / A naked-eye sunspot group on May 11, 2024. There are typically 40,000 to 50,000 sunspots observed in ~11-year solar cycles.

E. T. H. Teague

A team of Japanese and Belgian astronomers has re-examined the sunspot drawings made by 17th century astronomer Johannes Kepler with modern analytical techniques. By doing so, they resolved a long-standing mystery about solar cycles during that period, according to a recent paper published in The Astrophysical Journal Letters.

Precisely who first observed sunspots was a matter of heated debate in the early 17th century. We now know that ancient Chinese astronomers between 364 and 28 BCE observed these features and included them in their official records. A Benedictine monk in 807 thought he’d observed Mercury passing in front of the Sun when, in reality, he had witnessed a sunspot; similar mistaken interpretations were also common in the 12th century. (An English monk made the first known drawings of sunspots in December 1128.)

English astronomer Thomas Harriot made the first telescope observations of sunspots in late 1610 and recorded them in his notebooks, as did Galileo around the same time, although the latter did not publish a scientific paper on sunspots (accompanied by sketches) until 1613. Galileo also argued that the spots were not, as some believed, solar satellites but more like clouds in the atmosphere or the surface of the Sun. But he was not the first to suggest this; that credit belongs to Dutch astronomer Johannes Fabricus, who published his scientific treatise on sunspots in 1611.

Kepler read that particular treatise and admired it, having made his sunspot observations using a camera obscura in 1607 (published in a 1609 treatise), which he initially thought was a transit of Mercury. He retracted that report in 1618, concluding that he had actually seen a group of sunspots. Kepler made his solar drawings based on observations conducted both in his own house and in the workshop of court mechanic Justus Burgi in Prague.  In the first case, he reported “a small spot in the size of a small fly”; in the second, “a small spot of deep darkness toward the center… in size and appearance like a thin flea.”

The earliest datable sunspot drawings based on Kepler's solar observations with camera obscura in May 1607.

Enlarge / The earliest datable sunspot drawings based on Kepler’s solar observations with camera obscura in May 1607.

Public domain

The long-standing debate that is the subject of this latest paper concerns the period from around 1645 to 1715, during which there were very few recorded observations of sunspots despite the best efforts of astronomers. This was a unique event in astronomical history. Despite only observing some 59 sunspots during this time—compared to between 40,000 to 50,000 sunspots over a similar time span in our current age—astronomers were nonetheless able to determine that sunspots seemed to occur in 11-year cycles.

German astronomer Gustav Spörer noted the steep decline in 1887 and 1889 papers, and his British colleagues, Edward and Annie Maunder, expanded on that work to study how the latitudes of sunspots changed over time. That period became known as the “Maunder Minimum.” Spörer also came up with “Spörer’s law,” which holds that spots at the start of a cycle appear at higher latitudes in the Sun’s northern hemisphere, moving to successively lower latitudes in the southern hemisphere as the cycle runs its course until a new cycle of sunspots begins in the higher latitudes.

But precisely how the solar cycle transitioned to the Maunder Minimum has been far from clear. Reconstructions based on tree rings have produced conflicting data. For instance, one such reconstruction concluded that the gradual transition was preceded either by an extremely short solar cycle of about five years or an extremely long solar cycle of about 16 years. Another tree ring reconstruction concluded the solar cycle would have been of normal 11-year duration.

Independent observational records can help resolve the discrepancy. That’s why Hisashi Hayakawa of Nagoya University in Japan and co-authors turned to Kepler’s drawings of sunspots for additional insight, which predate existing telescopic observations by several years.

How Kepler’s 400-year-old sunspot sketches helped solve a modern mystery Read More »

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Webb confirms: Big, bright galaxies formed shortly after the Big Bang

astronomy, cosmology, galaxies, galaxy formation, Science, Webb telescope / /

They grow up so fast —

Structure of galaxy rules out early, bright objects were supermassive black holes.

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Image of a field of stars and galaxies.

Enlarge / Some of the galaxies in the JADES images.

One of the things that the James Webb Space Telescope was designed to do was look at some of the earliest objects in the Universe. And it has already succeeded spectacularly, imaging galaxies as they existed just 250 million years after the Big Bang. But these galaxies were small, compact, and similar in scope to what we’d consider a dwarf galaxy today, which made it difficult to determine what was producing their light: stars or an actively feeding supermassive black hole at their core.

This week, Nature is publishing confirmation that some additional galaxies we’ve imaged also date back to just 300 million years after the Big Bang. Critically, one of them is bright and relatively large, allowing us to infer that most of its light was coming from a halo of stars surrounding its core, rather than originating in the same area as the central black hole. The finding implies that it formed through a continuing burst of star formation that started just 200 million years after the Big Bang.

Age checks

The galaxies at issue here were first imaged during the JADES (JWST Advanced Deep Extragalactic Survey) imaging program, which includes part of the area imaged for the Hubble Ultra Deep Field. Initially, old galaxies were identified by using a combination of filters on one of Webb’s infrared imaging cameras.

Most of the Universe is made of hydrogen, and figuring out the age of early galaxies involves looking for the most energetic transitions of hydrogen’s electron, called the Lyman series. These transitions produce photons that are in the UV area of the spectrum. But the redshift of light that’s traveled for billions of years will shift these photons into the infrared area of the spectrum, which is what Webb was designed to detect.

What this looks like in practice is that hydrogen-dominated material will emit a broad range of light right up to the highest energy Lyman transition. Above that energy, photons will be sparse (they may still be produced by things like processes that accelerate particles). This point in the energy spectrum is called the “Lyman break,” and its location on the spectrum will change based on how distant the source is—the greater the distance to the source, the deeper into the infrared the break will appear.

Initial surveys checked for the Lyman break using filters on Webb’s cameras that cut off different areas of the IR spectrum. Researchers looked for objects that showed up at low energies but disappeared when a filter that selected for higher-energy infrared photons was swapped in. The difference in energies between the photons allowed through by the two filters can provide a rough estimate of where the Lyman break must be.

Locating the Lyman break requires imaging with a spectrograph, which can sample the full spectrum of near-infrared light. Fortunately, Webb has one of those, too. The newly published study involved turning the NIRSpec onto three early galaxies found in the JADES images.

Too many, too soon

The researchers involved in the analysis only ended up with data from two of these galaxies. NIRSpec doesn’t gather as much light as one of Webb’s cameras can, and so the faintest of the three just didn’t produce enough data to enable analysis. The other two, however, produced very clear data that placed the galaxies at a redshift measure roughly z = 14, which means we’re seeing them as they looked 300 million years after the Big Bang. Both show sharp Lyman breaks, with the amount of light dropping gradually as you move further into the lower-energy part of the spectrum.

There’s a slight hint of emissions from heavily ionized carbon atoms in one of the galaxies, but no sign of any other specific elements beyond hydrogen.

One of the two galaxies was quite compact, so similar to the other galaxies of this age that we’d confirmed previously. But the other, JADES-GS-ZZ14-0, was quite distinct. For starters, it’s extremely bright, being the third most luminous distant galaxy out of hundreds we’ve imaged so far. And it’s big enough that it’s not possible for all its light to be originating from the core. That rules out the possibility that what we’re looking at is a blurred view of an active galactic nucleus powered by a supermassive black hole feeding on material.

Instead, much of the light we’re looking at seems to have originated in the stars of JADES-GS-ZZ14-0. Most of those stars are young, and there seems to be very little of the dust that characterizes modern galaxies. The researchers estimate that star formation started at least 100 million years earlier (meaning just 200 million years after the Big Bang) and continued at a rapid pace in the intervening time.

Combined with earlier data, the researchers write that this confirms that “bright and massive galaxies existed already only 300 [million years] after the Big Bang, and their number density is more than ten times higher than extrapolations based on pre-JWST observations.” In other words, there were a lot more galaxies around in the early Universe than we thought, which could pose some problems for our understanding of the Universe’s contents and their evolution.

Meanwhile, the early discovery of the extremely bright galaxy implies that there are a number of similar ones out there awaiting our discovery. This means there’s going to be a lot of demand for time on NIRSpec in the coming years.

Nature, 2024. DOI: 10.1038/s41586-024-07860-9  (About DOIs).

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Astronomers find first emission spectra in brightest GRB of all time

astronomy, astrophysics, B.O.A.T., Fermi space telescope, Gamma ray bursts, Physics, Science / /

shine on, you beautiful BOAT —

Chance that first detected emission line is a noise fluctuation is one in half a billion.

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A jet of particles moving at nearly light speed emerges from a massive star in this artist’s concept.

Enlarge / A jet of particles moving at nearly light-speed emerges from a massive star in this artist’s concept of the BOAT.

NASA’s Goddard Space Flight Center Conceptual Image Lab

Scientists have been all aflutter since several space-based detectors picked up a powerful gamma-ray burst (GRB) in October 2022—a burst so energetic that astronomers nicknamed it the BOAT (Brightest Of All Time). Now an international team of astronomers has analyzed an unusual energy peak detected by NASA’s Fermi Gamma-ray Space Telescope and concluded that it was an emission spectra, according to a new paper published in the journal Science. Per the authors, it’s the first high-confidence emission line ever seen in 50 years of studying GRBs.

As reported previously, gamma-ray bursts are extremely high-energy explosions in distant galaxies lasting between mere milliseconds to several hours. There are two classes of gamma-ray bursts. Most (70 percent) are long bursts lasting more than two seconds, often with a bright afterglow. These are usually linked to galaxies with rapid star formation. Astronomers think that long bursts are tied to the deaths of massive stars collapsing to form a neutron star or black hole (or, alternatively, a newly formed magnetar). The baby black hole would produce jets of highly energetic particles moving near the speed of light, powerful enough to pierce through the remains of the progenitor star, emitting X-rays and gamma rays.

Those gamma-ray bursts lasting less than two seconds (about 30 percent) are deemed short bursts, usually emitting from regions with very little star formation. Astronomers think these gamma-ray bursts are the result of mergers between two neutron stars, or a neutron star merging with a black hole, comprising a “kilonova.” That hypothesis was confirmed in 2017 when the LIGO collaboration picked up the gravitational wave signal of two neutron stars merging, accompanied by the powerful gamma-ray bursts associated with a kilonova.

Several papers were published last year reporting on the analytical results of all the observational data. Those findings confirmed that GRB 221009A was indeed the BOAT, appearing especially bright because its narrow jet was pointing directly at Earth. But the various analyses also yielded several surprising results that puzzled astronomers. Most notably, a supernova should have occurred a few weeks after the initial burst, but astronomers didn’t detect one, perhaps because it was very faint, and thick dust clouds in that part of the sky were dimming any incoming light.

Earlier this year, astronomers confirmed that the BOAT came from a supernova, thanks to the telltale signatures of key elements like calcium and oxygen that one would expect to find with a supernova. However, they did not find evidence of the expected heavy elements like platinum and gold, which bears on the longstanding question of the origin of such elements in the universe. The BOAT might just be special in that regard; further data will tell us more.

“It gave me goosebumps”

A few minutes after the BOAT erupted, Fermi’s Gamma-ray Burst Monitor recorded an unusual energy peak. Scientists now say this feature is the first high-confidence emission line ever seen in 50 years of studying GRBs.

The newly detected spectral emission line was likely caused by the collision of matter and anti-matter, according to the authors, producing a pair of gamma rays that are blue-shifted toward higher energies because we are looking into the jet. Having a spectral emission associated with a GRB is important because it can shed light on the specific chemicals involved in the interactions. There have been prior studies reporting possible evidence for absorption or emission lines in other GRBs, but they have usually turned out likely to be statistical noise.

That’s not the case with this latest detection, according to co-author Om Sharan Salafia at INAF-Brera Observatory in Milan, Italy, who added that the odds of this turning out to be a statistical fluctuation “are less than one chance in half a billion.” His INAF colleague and co-author, Maria Edvige Ravasio, said that when she first saw the signal, “it gave me goosebumps.”

Why did astronomers take so long to detect it? When the BOAT first erupted in 2022, it saturated most of the space-based gamma-ray detectors, including the Fermi Space Telescope, making them unable to measure the most intense part of that blast. The emission line didn’t appear until a good five minutes after the burst when it had sufficiently dimmed for Fermi to make a measurement. The spectral emission lasted for about 40 seconds and reached a peak energy of about 12 MeV, compared to 2 or 3 MeB for visible light, per the authors.

Science, 2024. DOI: 10.1126/science.adj3638  (About DOIs).

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Webb directly images giant exoplanet that isn’t where it should be

astronomy, exoplanets, planetary science, Science, Webb telescope / /

How do you misplace that? —

Six times bigger than Jupiter, the planet is the oldest and coldest yet imaged.

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A dark background with read and blue images embedded in it, both showing a single object near an area marked with an asterisk.

Enlarge / Image of Epsilon Indi A at two wavelengths, with the position of its host star indicated by an asterisk.

T. Müller (MPIA/HdA), E. Matthews (MPIA)

We have a couple of techniques that allow us to infer the presence of an exoplanet based on its effects on the light coming from its host star. But there’s an alternative approach that sometimes works: image them directly. It’s much more limited, since the planet has to be pretty big and orbiting far away enough from its star to avoid having light coming from the planet swamped by the far more intense starlight.

Still, it has been done. Massive exoplanets have been captured relatively shortly after their formation, when the heat generated by the collapse of material into the planet causes them to glow in the infrared. But the Webb telescope is far more sensitive than any infrared observatory we’ve ever built, and it has managed to image a relatively nearby exoplanet that’s roughly as old as the ones in our Solar System.

Looking directly at a planet

What do you need to directly image a planet that’s orbiting a star light-years away? The first thing is a bit of hardware called a coronagraph attached to your telescope. This is responsible for blocking the light from the star the planet is orbiting; without it, that light will swamp any other sources in the exosolar system. Even with a good coronagraph, you need the planets to be orbiting at a significant distance from the star so that they’re cleanly separated from the signal being blocked by the coronagraph.

Then, you need the planet to emit a fair bit of light. While the right surface composition might allow the planet to be highly reflective, that’s not going to be a great option considering the distances we’d need the planet to be orbiting to be visible at all. Instead, the planets we’ve spotted so far have been young and still heated by the processes that brought material together to form a planet in the first place. Being really big doesn’t hurt matters either.

Put that all together, and what you expect to be able to spot is a very young, very distant planet that’s massive enough to fall into the super-Jupiter category.

But the launch of the Webb Space Telescope has given us new capabilities in the infrared range, and a large international team of researchers pointed it at a star called Epsilon Indi A. It’s a bit less than a dozen light years away (which is extremely close in astronomical terms), and the star is both similar in size and age to the Sun, making it an interesting target for observations. Perhaps most significantly previous data had suggested a large exoplanet would be found, based on indications that the star was apparently shifting as the exoplanet tugged on it during its orbit.

And there was in fact an indication of a planet there. It just didn’t look much like the expected planet. “It’s about twice as massive, a little farther from its star, and has a different orbit than we expected,” said Elisabeth Matthews, one of the researchers involved.

At the moment, there’s no explanation for the discrepancy. The odds of it being an unrelated background object are extremely small. And a reanalysis of data on the motion of Epsilon Indi A suggests that this is likely to be the only large planet in the system—there could be additional planets, but they’d be much smaller. So, the researchers named the planet Epsilon Indi Ab, even though that was the same name given to the planet that doesn’t seem to match this one’s properties.

Big, cold, and a bit enigmatic

The revised Epsilon Indi Ab is a large planet, estimated at roughly six times the mass of Jupiter. It’s also orbiting at roughly the same distance as Neptune. It’s generally bright across the mid-infrared, consistent with a planet that’s roughly 275 Kelvin—not too far off from room temperature. That’s also close to what we would estimate for its temperature simply based on the age of the planet. That makes it the coolest exoplanet ever directly imaged.

While the signal from the planet was quite bright at a number of wavelengths, the planet couldn’t even be detected in one area of the spectrum (3.5 to 5 micrometers, for the curious). That’s considered an indication that the planet has high levels of elements heavier than helium, and a high ratio of carbon to oxygen. The gap in the spectrum may influence estimates of the planet’s age, so further observations will probably need to be conducted to clarify why there are no emissions at these wavelengths.

The researchers also suggest that imaging more of these cool exoplanets should be a priority, given that we should be cautious about extrapolating anything from a single example. So, in that sense, this first exoplanet imaging provides an important confirmation that, with Webb and its coronagraph, we’ve now got the tools we need to do so, and they work very well.

Nature, 2024. DOI: 10.1038/s41586-024-07837-8  (About DOIs).

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Mini-Neptune turned out to be a frozen super-Earth

astronomy, exoplanets, planetary science, Science / /

Like Earth, but super —

The density makes it look like a water world, but its dim host star keeps it cool.

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Image of three planets on a black background, with the two on the left being mostly white, indicating an icy composition. The one on the right is much smaller, and represents Earth.

Enlarge / Renditions of a possible composition of LHS 1140 b, with a patch of ocean on the side facing its host star. Earth is included at right for scale.

Of all the potential super-Earths—terrestrial exoplanets more massive than Earth—out there, an exoplanet orbiting a star only 40 light-years away from us in the constellation Cetus might be the most similar to have been found so far.

Exoplanet LHS 1140 b was assumed to be a mini-Neptune when it was first discovered by NASA’s James Webb Space Telescope toward the end of 2023. After analyzing data from those observations, a team of researchers, led by astronomer Charles Cadieux, of Université de Montréal, suggest that LHS 1140 b is more likely to be a super-Earth.

If this planet is an alternate version of our own, its relative proximity to its cool red dwarf star means it would most likely be a gargantuan snowball or a mostly frozen body with a substellar (region closest to its star) ocean that makes it look like a cosmic eyeball. It is now thought to be the exoplanet with the best chance for liquid water on its surface, and so might even be habitable.

Cadieux and his team say they have found “tantalizing evidence for a [nitrogen]-dominated atmosphere on a habitable zone super-Earth” in a study recently published in The Astrophysical Journal Letters.

Sorry, Neptune…

In December 2023, two transits of LHS 1140 b were observed with the NIRISS (Near-Infrared Imager and Slitless Spectrograph) instrument aboard Webb. NIRISS specializes in detecting exoplanets and revealing more about them through transit spectroscopy, which picks up the light of an orbiting planet’s host star as it passes through the atmosphere of that planet and travels toward Earth. Analysis of the different spectral bands in that light can then tell scientists about the specific atoms and molecules that exist in the planet’s atmosphere.

To test the previous hypothesis that LHS 1140 b is a mini-Neptune, the researchers created a 3D global climate model, or GCM. This used complex math to explore different combinations of factors that make up the climate system of a planet, such as land, oceans, ice, and atmosphere. Several different GCMs of a mini-Neptune were compared with the light spectrum observed via transit spectroscopy. The model for a mini-Neptune typically involves a gas giant with a thick, cloudless or nearly cloudless atmosphere dominated by hydrogen, but the spectral bands of this model did not match NIRISS observations.

With the possibility of a mini-Neptune being mostly ruled out (though further observations and analysis will be needed to confirm this), Cadieux’s team turned to another possibility: a super-Earth.

An Earth away from Earth?

The spectra observed with NIRISS were more in line with GCMs of a super-Earth. This type of planet would typically have a thick nitrogen or CO2-rich atmosphere enveloping a rocky surface on which there was some form of water, whether in frozen or liquid form.

The models also suggested a secondary atmosphere, which is an atmosphere formed after the original atmosphere of light elements, (hydrogen and helium) escaped during early phases of a planet’s formation. Secondary atmospheres are formed from heavier elements released from the crust, such as water vapor, carbon dioxide, and methane. They’re usually found on warm, terrestrial planets (Earth has a secondary atmosphere).

The most significant Webb/NIRISS data that did not match the GCMs was that the planet has a lower density (based on measurements of its size and mass) than expected for a rocky world. This is consistent with a water world with a mass that’s about 10 to 20 percent water. Based on this estimate, the researchers think that LHS 1140 b might even be a hycean planet—an ocean planet that has most of the attributes of a super-Earth, but an atmosphere dominated by hydrogen instead of nitrogen.

Since it orbits a dim star closely enough to be tidally locked, some models suggest a mostly icy planet with a substellar liquid ocean on its dayside.

While LHS 1140 b may be a super-Earth, the hycean planet hypothesis might end up being ruled out. Hycean planets are prone to the runaway greenhouse effect, which occurs when enough greenhouse gases accumulate in a planet’s atmosphere and prevent heat from escaping. Liquid water will eventually evaporate on a planet that cannot cool itself off.

Though we are getting closer to finding out what kind of planet LHS 1140 b is, and whether it could be habitable, further observations are needed. Cadieux wants to continue this research by comparing NIRISS data with data on other super-Earths that had previously been collected by Webb’s Near-Infrared Spectrograph, or NIRSpec, instrument. At least three transit observations of the planet with Webb’s MIRI, or Mid-Infrared instrument, are also needed to make sure stellar radiation is not interfering with observations of the planet itself.

“Given the limited visibility of LHS 1140b, several years’ worth of observations may be required to detect its potential secondary atmosphere,” the researchers said in the same study.

So could this planet really be a frozen exo-earth? The suspense is going to last a few years.

The Astrophysical Journal Letters, 2024.  DOI:  10.3847/2041-8213/ad5afa

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Seismic data shows Mars is often pummeled by planet-shaking meteorites

astronomy, Impacts, Mars, meteorites, planetary science, Science, seismology / /

Brace for impact —

Seismic information now allows us to make a planet-wide estimate of impact rates.

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One of the craters identified seismically, then confirmed through orbital images.

Enlarge / One of the craters identified seismically, then confirmed through orbital images.

Mars trembles with marsquakes, but not all of them are driven by phenomena that occur beneath the surface—many are the aftermath of meteorite strikes.

Meteorites crash down to Mars every day. After analyzing data from NASA’s InSight lander, an international team of researchers noticed that its seismometer, SEIS, detected six nearby seismic events. These were linked to the same acoustic atmospheric signal that meteorites generate when whizzing through the atmosphere of Mars. Further investigation identified all six as part of an entirely new class of quakes known as VF (very high frequency) events.

The collisions that generate VF marsquakes occur in fractions of a second, much less time than the few seconds it takes tectonic processes to cause quakes similar in size. This is some of the key seismological data that has helped us understand the occurrence of earthquakes caused by meteoric impacts on Mars. This is also the first time seismic data was used to determine how frequently impact craters are formed.

“Although a non-impact origin cannot be definitively excluded for each VF event, we show that the VF class as a whole is plausibly caused by meteorite impacts,” the researchers said in a study recently published in Nature.

Seismic shift

Scientists had typically determined the approximate meteorite impact rate on Mars by comparing the frequency of craters on its surface to the expected rate of impacts calculated using counts of lunar craters that were left behind by meteorites. Models of the lunar cratering rate were then adjusted to fit Martian conditions.

Looking to the Moon as a basis for comparison was not ideal, as Mars is especially prone to being hit by meteorites. The red planet is not only a more massive body that has greater gravitational pull, but it is located near the asteroid belt.

Another issue is that lunar craters are often better preserved than Martian craters because there is no place in the Solar System dustier than Mars. Craters in orbital images are often partly obscured by dust, which makes them difficult to identify. Sandstorms can complicate matters by covering craters in more dust and debris (something that cannot occur on the Moon due to the absence of wind).

InSight deployed its SEIS instrument after it landed in the Elysium Planitia region of Mars. In addition to detecting tectonic activity, the seismometer can potentially determine the impact rate through seismic data. When meteorites strike Mars, they produce seismic waves just like tectonic marsquakes do, and the waves can be detected by seismometers when they travel through the mantle and crust. An immense quake picked up by SEIS was linked to a crater 150 meters (492 feet) wide. SEIS would later detect five more marsquakes that were all associated with an acoustic signal (detected by a different sensor on InSight) that is a telltale sign of a falling meteorite.

A huge impact

Something else stood out about the six impact-driven marsquakes detected with seismic data. Because of the velocity of meteorites (over 3,000 meters or 9,842 feet per second), these events happened faster than any other type of marsquake, even faster than quakes in the high frequency (HF) class. That’s how they earned their own classification: very high frequency, or VF, quakes. When the InSight team used the Mars Reconnaissance Orbiter’s (MRO) Context Camera (CTX) to image the locations of the events picked up by SEIS, there were new craters present in the images.

There are additional seismic events that haven’t been assigned to craters yet. They are thought to be small craters formed by meteorites about the size of basketballs, which are extremely difficult to see in orbital images from MRO.

The researchers were able to use SEIS data to estimate the diameters of craters based on distance from InSight (according to how long it took seismic waves to reach the spacecraft) and the magnitude of the VF marsquakes associated with them. They were also able to derive the frequency of quakes picked up by SEIS. Once a frequency estimate based on the data was applied to the entire surface area of Mars, they estimated that around 280 to 360 VF quakes occur each year.

“The case is strong that the unique VF marsquake class is consistent with impacts,” they said in the same study. “It is, therefore, worthwhile considering the implications of attributing all VF events to meteoroid impacts.”

Their detection has added to the estimated number of impact craters on Mars since many could not be seen from space before. What can VF impacts tell us? The impact rate on a planet or moon is important for determining the age of that object’s surface. Using impacts has helped us determine that the surface of Venus is constantly being renewed by volcanic activity, while most of the surface of Mars has not been covered in lava for billions of years.

Figuring out the rate of meteorite impacts can also help protect spacecraft and, someday, maybe Martian astronauts, from potential hazards. The study suggests that there are periods where impacts are more or less frequent, so it might be possible to predict when the sky is a bit more likely to be clear of falling space rocks—and when it isn’t. Meteorites are not much of a danger to Earth since most of them burn up in the atmosphere. Mars has a much thinner atmosphere that more can make it through, and there is no umbrella for a meteor shower.

Nature Astronomy, 2024. DOI: 10.1038/s41550-024-02301-z

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Nearby star cluster houses unusually large black hole

astronomy, astrophysics, black hole, globular cluster, Science / /

Big, but not that big —

Fast-moving stars imply that there’s an intermediate-mass black hole there.

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Three panel image, with zoom increasing from left to right. Left most panel is a wide view of the globular cluster; right is a zoom in to the area where its central black hole must reside.

Enlarge / From left to right, zooming in from the globular cluster to the site of its black hole.

ESA/Hubble & NASA, M. Häberle

Supermassive black holes appear to reside at the center of every galaxy and to have done so since galaxies formed early in the history of the Universe. Currently, however, we can’t entirely explain their existence, since it’s difficult to understand how they could grow quickly enough to reach the cutoff for supermassive as quickly as they did.

A possible bit of evidence was recently found by using about 20 years of data from the Hubble Space Telescope. The data comes from a globular cluster of stars that’s thought to be the remains of a dwarf galaxy and shows that a group of stars near the cluster’s core are moving so fast that they should have been ejected from it entirely. That implies that something massive is keeping them there, which the researchers argue is a rare intermediate-mass black hole, weighing in at over 8,000 times the mass of the Sun.

Moving fast

The fast-moving stars reside in Omega Centauri, the largest globular cluster in the Milky Way. With an estimated 10 million stars, it’s a crowded environment, but observations are aided by its relative proximity, at “only” 17,000 light-years away. Those observations have been hinting that there might be a central black hole within the globular cluster, but the evidence has not been decisive.

The new work, done by a large international team, used over 500 images of Omega Centauri, taken by the Hubble Space Telescope over the course of 20 years. This allowed them to track the motion of stars within the cluster, allowing an estimate of their speed relative to the cluster’s center of mass. While this has been done previously, the most recent data allowed an update that reduced the uncertainty in the stars’ velocity.

Within the update data, a number of stars near the cluster’s center stood out for their extreme velocities: seven of them were moving fast enough that the gravitational pull of the cluster isn’t enough to keep them there. All seven should have been lost from the cluster within 1,000 years, although the uncertainties remained large for two of them. Based on the size of the cluster, there shouldn’t even be a single foreground star between the Hubble and the Omega Cluster, so these really seem to be within the cluster despite their velocity.

The simplest explanation for that is that there’s an additional mass holding them in place. That could potentially be several massive objects, but the close proximity of all these stars to the center of the cluster favor a single, compact object. Which means a black hole.

Based on the velocities, the researchers estimate that the object has a mass of at least 8,200 times that of the Sun. A couple of stars appear to be accelerating; if that holds up based on further observations, it would indicate that the black hole is over 20,000 solar masses. That places it firmly within black hole territory, though smaller than supermassive black holes, which are viewed as those with roughly a million solar masses or more. And it’s considerably larger than you’d expect from black holes formed through the death of a star, which aren’t expected to be much larger than 100 times the Sun’s mass.

This places it in the category of intermediate-mass black holes, of which there are only a handful of potential sightings, none of them universally accepted. So, this is a significant finding if for no other reason than it may be the least controversial spotting of an intermediate-mass black hole yet.

What’s this telling us?

For now, there are still considerable uncertainties in some of the details here—but prospects for improving the situation exist. Observations with the Webb Space Telescope could potentially pick up the faint emissions from gas that’s falling into the black hole. And it can track the seven stars identified here. Its spectrographs could also potentially pick up the red and blue shifts in light caused by the star’s motion. Its location at a considerable distance from Hubble could also provide a more detailed three-dimensional picture of Omega Centauri’s central structure.

Figuring this out could potentially tell us more about how black holes grow to supermassive scales. Earlier potential sightings of intermediate-mass black holes have also come in globular clusters, which may suggest that they’re a general feature of large gatherings of stars.

But Omega Centauri differs from many other globular clusters, which often contain large populations of stars that all formed at roughly the same time, suggesting the clusters formed from a single giant cloud of materials. Omega Centauri has stars with a broad range of ages, which is one of the reasons why people think it’s the remains of a dwarf galaxy that was sucked into the Milky Way.

If that’s the case, then its central black hole is an analog of the supermassive black holes found in actual dwarf galaxies—which raises the question of why it’s only intermediate-mass. Did something about its interactions with the Milky Way interfere with the black hole’s growth?

And, in the end, none of this sheds light on how any black hole grows to be so much more massive than any star it could conceivably have formed from. Getting a better sense of this black hole’s history could provide more perspective on some questions that are currently vexing astronomers.

Nature, 2024. DOI: 10.1038/s41586-024-07511-z  (About DOIs).

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Swarm of dusty young stars found around our galaxy’s central black hole

astronomy, astrophysics, black holes, milky way, Science, Star formation / /

Hot young stars —

Stars shouldn’t form that close to the black hole, so these would need explaining.

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Image with a black background, large purple streaks, and a handful of bright blue objects.

Enlarge / The Milky Way’s central black hole is in a very crowded neighborhood.

Supermassive black holes are ravenous. Clumps of dust and gas are prone to being disrupted by the turbulence and radiation when they are pulled too close. So why are some of them orbiting on the edge of the Milky Way’s own supermassive monster, Sgr A*? Maybe these mystery blobs are hiding something.

After analyzing observations of the dusty objects, an international team of researchers, led by astrophysicist Florian Peißker of the University of Cologne, have identified these clumps as potentially harboring young stellar objects (YSOs) shrouded by a haze of gas and dust. Even stranger is that these infant stars are younger than an unusually young and bright cluster of stars that are already known to orbit Sgr A*, known as the S-stars.

Finding both of these groups orbiting so close is unusual because stars that orbit supermassive black holes are expected to be dim and much more ancient. Peißker and his colleagues “discard the en vogue idea to classify [these] objects as coreless clouds in the high energetic radiation field of the supermassive black hole Sgr A*,” as they said in a study recently published in Astronomy & Astrophysics.

More than just space dust

To figure out what the objects near Sgr Amight be the, researchers needed to rule out things they weren’t. Embedded in envelopes of gas and dust, they maintain especially high temperatures, do not evaporate easily, and each orbits the supermassive black hole alone.

The researchers determined their chemical properties from the photons they emitted, and their mid- and near-infrared emissions were consistent with those of stars. They used one of them, object G2/DSO, as a case study to test their ideas about what the objects might be. The high brightness and especially strong emissions of this object make it the easiest to study. Its mass is also similar to the masses of known low-mass stars.

YSOs are low-mass stars that have outgrown the protostar phase but have not yet developed into main sequence stars, with cores that fuse hydrogen into helium. These objects like YSO candidates because they couldn’t possibly be clumps of gas and space dust. Gaseous clouds without any objects inside to hold them together via gravity could not survive so close to a supermassive black hole for long. Its intense heat causes the gas and dust to evaporate rather quickly, with heat-excited particles crashing into each other and flying off into space.

The team figured out that a cloud comparable in size to G2/DSO would evaporate in about seven years. A star orbiting at the same distance from the supermassive black hole would not be destroyed nearly as fast because of its much higher density and mass.

Another class of object that the dusty blobs could hypothetically be—but are not—is a compact planetary nebula or CPN. These nebulae are the expanding outer gas envelopes of small to medium stars in their final death throes. While CPNs have some features in common with stars, the strength of a supermassive black hole’s gravity would easily detach their gas envelopes and tear them apart.

It is also unlikely that the YSOs are binary stars, even though most stars form in binary systems. The scorching temperatures and turbulence of SGR Awould likely cause stars that were once part of binaries to migrate.

Seeing stars

Further observations determined that some of the dust-obscured objects are nascent stars, and while others are thought to be stars of some kind, but haven’t been definitively identified.

The properties that made G2/DSO an exceptional case study are also the reason it has been identified as a YSO. D2 is another high-luminosity object about as massive as a low-mass star, which is easy to observe in the near- and mid-infrared. D3 and D23 also have similar properties. These are the blobs near the black hole that the researchers think are most likely to be YSOs.

There are other candidates that need further analysis. These include additional objects that may or may not be YSOs, but still show stellar characteristics: D3.1 and D5, which are difficult to observe. The mid-infrared emissions of D9 are especially low when compared to the other candidates, but it is still thought to be some type of star, though possibly not a YSO. Objects X7 and X8 both exhibit bow shock—the shockwave that results from a star’s stellar wind pushing against other stellar winds. Whether either of these objects is actually a YSO remains unknown.

Where these dusty objects came from and how they formed is unknown for now. The researchers suggest that the objects formed together in molecular clouds that were falling toward the center of the galaxy. They also think that, no matter where they were born, they migrated towards Sgr A*, and any that were in binary systems were separated by the black hole’s immense gravity.

While it is unlikely that the YSOs and potential YSOs originated in the same cluster as the slightly older S-stars, they still might be related in some way. They might have experienced similar formation and migration journeys, and the younger stars might ultimately reach the same stage.

“Speculatively, the dusty sources will evolve into low-mass S stars,” Peißker’s team said in the same study.

Even black holes look better with a necklace of twinkling diamonds.

Astronomy and Astrophysics, 2024.  DOI: 10.1051/0004-6361/202449729

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Saturn’s moon Titan has shorelines that appear to be shaped by waves

astronomy, Cassini, geology, planetary science, Saturn, Science, Titan / /

Surf the moon —

The liquid hydrocarbon waves would likely reach a height of a meter.

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Ligeia Mare, the second-largest body of liquid hydrocarbons on Titan.

Enlarge / Ligeia Mare, the second-largest body of liquid hydrocarbons on Titan.

During its T85 Titan flyby on July 24, 2012, the Cassini spacecraft registered an unexpectedly bright reflection on the surface of the lake Kivu Lacus. Its Visual and Infrared Mapping Spectrometer (VIMS) data was interpreted as a roughness on the methane-ethane lake, which could have been a sign of mudflats, surfacing bubbles, or waves.

“Our landscape evolution models show that the shorelines on Titan are most consistent with Earth lakes that have been eroded by waves,” says Rose Palermo, a coastal geomorphologist at St. Petersburg Coastal and Marine Science Center, who led the study investigating signatures of wave erosion on Titan. The evidence of waves is still inconclusive, but future crewed missions to Titan should probably pack some surfboards just in case.

Troubled seas

While waves have been considered the most plausible explanation for reflections visible in Cassini’s VIMS imagery for quite some time, other studies aimed to confirm their presence found no wave activity at all. “Other observations show that the liquid surfaces have been very still in the past, very flat,” Palermo says. “A possible explanation for this is at the time we were observing Titan, the winds were pretty low, so there weren’t many waves at that time. To confirm waves, we would need to have better resolution data,” she adds.

The problem is that this higher-resolution data isn’t coming our way anytime soon. Dragonfly, the next mission to Titan, isn’t supposed to arrive until 2034, even if everything goes as planned.

To get a better idea about possible waves on Titan a bit sooner, Palermo’s team went for inferring their presence from indirect cues. The researchers assumed shorelines on Titan could have been shaped by one of three candidate scenarios. They first assumed there was no erosion at all; the second modeled uniform erosion caused by the dissolution of the bedrock by the ethane-methane liquid; and the third assumed erosion by wave activity. “We took a random topography with rivers, filled up the basin-flooding river valleys all around the lake. Then, we then used landscape evolution computer model to erode the coast to 50 percent of its original size,” Palermo explains.

Sizing the waves

Palermo’s simulations showed that wave erosion resulted in coastline shapes closely matching those actually observed on Titan.

The team validated its model using data from closer to home. “We compared using the same statistical analysis to lakes on Earth, where we know what the erosion processes are. With certainty greater than 77.5 percent, we were able to predict those known processes with our modeling,” Palermo says.

But even the study that claimed there were waves visible in the Cassini’s VIMS imagery concluded they were roughly 2 centimeters high at best. So even if there are waves on Titan, the question is how high and strong are they?

According to Palermo, wave-generation mechanisms on Titan should work just like they do on Earth, with some notable differences. “There is a difference in viscosity between water on Earth and methane-ethane liquid on Titan compared to the atmosphere,” says Palermo. The gravity is also a lot weaker, standing at only one-seventh of the gravity on Earth. “The gravity, along with the differences in material properties, contributes to the waves being taller and steeper than those on Earth for the same wind speed,” says Palermo.

But even with those boosts to size and strength, could waves on Titan actually be any good for surfing?

Surf’s up

“There are definitely a lot of open questions our work leads to. What is the direction of the dominant waves? Knowing that can tell us about the winds and, therefore, about the climate on Titan. How large do the waves get? In the future, maybe we could tell that with modeling how much erosion occurs in one part of the lake versus another in estimated timescales. There is a lot more we could learn,” Palermo says. As far as surfing is concerned, she said that, assuming a minimum height for a surfable wave of around 15 centimeters, surfing on Titan should most likely be doable.

The key limit on the size and strength of any waves on Titan is that most of its seas are roughly the size of the Great Lakes in the US. The largest of them, the Kraken Mare, is roughly as large as the Caspian Sea on Earth. There is no such thing as a global ocean on Titan, and this means the fetch, the distance over which the wind can blow and grow the waves, is limited to tens of kilometers instead of over 1,500 kilometers on Earth. “Still, some models show that the waves on Titan be as high as one meter. I’d say that’s a surfable wave,” Palermo concluded.

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