Looking outward into our Milky Way galaxy, astronomers have discovered over 5,500 confirmed exoplanets, or planets orbiting distant stars. And there are thousands more exoplanet candidates. But possible exomoons orbiting these distant worlds would be much tougher to see. So astronomers have reported only a handful so far. But these discoveries are hard to come by. And some discoveries aren’t certain. For example, giant exomoons supposedly orbited two distant gas giant worlds, known as Kepler-1625b and Kepler-1708b. On December 8, 2023, researchers at the Max Planck Institute for Solar System Research and the Sonnenberg Observatory – both in Germany – said those two giant exomoons might not exist.

The researchers published their peer-reviewed doubts in Nature Astronomy on December 5.

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Giant exomoons around Kepler-1625b and Kepler-1708b?

Kepler-1625b and Kepler-1708b are gas giant planets similar to our solar system’s biggest planet, Jupiter. We know all of the gas and ice giant planets in our solar system – Jupiter, Saturn, Uranus, Neptune – have numerous moons. Saturn holds the record with 146 known moons! So it seems likely that giant worlds in other planetary systems have moons as well.

It was in 2018 that scientists at Columbia University in New York said they’d found evidence of a huge moon orbiting Kepler-1625b. The researchers found it in data from the Kepler Space Telescope. But then things got confusing. When researchers cleaned the data of extraneous noise, evidence for the moon disappeared. But then, still later, when the Hubble Space Telescope subsequently observed Kepler-1625b, the moon was back!

It was in 2022 that astronomers found the second possible giant moon. This one seemed to orbit Kepler-1708b. This moon, if real, was huge, even larger than Earth.

Scientists have debated their existence since their discoveries. The paper stated [emphasis added by EarthSky]:

The best exomoon candidates so far are two nearly Neptune-sized bodies orbiting the Jupiter-sized transiting exoplanets Kepler-1625b and Kepler-1708b. But their existence has been contested.

So the best exomoon candidates found so far are now in doubt.

Giant doubts about the giant exomoons

The tentative discovery of the two giant exomoons was exciting, of course. They were unusual in that both of them were much larger than even the largest moons in our own solar system. But, if they truly existed and truly were so large, that fact would help explain why astronomers were able to detect them in the data.

Which brings us to now. The new study from the Max Planck Institute for Solar System Research and the Sonnenberg Observatory casts serious doubts on the original discoveries. The researchers found scenarios without moons that can explain the observations just as well as ones with moons. As René Heller, first author of the new paper at Max Planck Institute, stated:

We would have liked to confirm the discovery of exomoons around Kepler-1625b and Kepler-1708b. But unfortunately, our analyses show otherwise.

Michael Hippke at Sonnenberg is the second co-author of the new paper. As for Kepler-1708b, he said:

The probability of a moon orbiting Kepler-1708b is clearly lower than previously reported. The data do not suggest the existence of an exomoon around Kepler-1708b.

Stellar limb darkening

So what about Kepler-1625b? Unfortunately, the results are similar. Kepler and Hubble had observed transits of the planet in front of its star. During the transit, the telescopes had seen an instantaneous variation in brightness across the disk of the star. This is called stellar limb darkening, where the outer limb (edge) of the disk looks darker than the center.

This darkening appeared different, however, in Kepler than it did Hubble. Why? The two telescopes are sensitive to different wavelengths of light. The researchers now propose that the modeling of that effect can explain the observations better than an exomoon.

False positives

The results are applicable not only to these two exomoon candidates, but perhaps others as well. The findings suggest that exomoon searches overall are prone to produce false-positive results. For example, a light curve similar to that of Kepler-1625b will have a false positive rate of about 11%. Heller said:

The earlier exomoon claim by our colleagues from New York was the result of a search for moons around dozens of exoplanets. According to our estimates, a false-positive finding is not at all surprising, but almost to be expected.

On the other hand, we should be able to detect some exomoons with current technology. But they would still need to be quite large – twice the size of our solar system’s largest moon Ganymede – and have wide orbits around their planets, the researchers said.

Other exomoon candidates

While the new results are disappointing, it doesn’t mean there are no giant exomoons. As we mentioned above, there are still some other current candidates. Astronomers found the first candidate in 2014. They called that possible exomoon system MOA-2011-BLG-262. The astronomers couldn’t further confirm it, however, since they found it during a gravitational microlensing event, which occurs only once.

In 2019, astronomers said they found another exomoon candidate, orbiting the hot Jupiter gas giant planet WASP-49b. The data suggested that this moon might be hypervolcanic, like Jupiter’s moon Io.

Then, in 2020, scientists at Western University in London, Ontario, Canada, said they may have found six more exomoons! They range from 200 to 3,000 light-years away.

Future observations

To sum up, it’s still difficult to confirm any exomoon candidates. Confirmation might have to wait for observations from even better telescopes, such as the upcoming PLATO mission. The paper said:

Thus, any possible exomoon detection in the archival Kepler data or with upcoming PLATO observations will necessarily be odd when compared to the solar system moons. In this sense, the now refuted claims of Neptune- or super-Earth-sized exomoons around Kepler-1625 b and Kepler-1708 b could nevertheless foreshadow the first genuine exomoon discoveries that may lay ahead.

Bottom line: Astronomers in Germany say that two possible giant exomoons probably don’t actually exist. That’s disappointing, but there are still some other candidates.

Source: Large exomoons unlikely around Kepler-1625 b and Kepler-1708 b

Via Max-Planck-Gesellschaft

Read more: Astronomers may have spotted the first exomoon!

Read more: A new way to search for exomoons

The post The strange case of 2 missing giant exomoons (and maybe others) first appeared on EarthSky.

Could there be life on Saturn’s ocean moon Enceladus? And if there’s microscopic life in the ocean underneath its icy crust, could we detect it? The moon’s subsurface global ocean contains water, heat and organic material. All three are crucial to life, at least the kinds of life we’re familiar with on Earth. The ocean lies beneath an outer crust of ice. However, numerous geyser-like plumes spew ocean water into space. Researchers from the University of California, San Diego, said on December 5, 2023, that amino acids – the building blocks of proteins – could survive a tumultuous journey on the moon’s plumes.

The research team published their peer-reviewed findings in the Proceedings of the National Academy of Sciences (PNAS) on December 4, 2023.

Update: On a related note, just as this article was about to be published, NASA released some news about another intriguing discovery at Enceladus. On December 14, researchers said that an additional study of data sent back by the Cassini spacecraft confirmed the presence of hydrogen cyanide, a molecule that is key to the origin of life, in the plumes. Hydrogen cyanide is one of the most important and versatile molecules needed to form amino acids. There is also new evidence that the ocean itself contains a powerful source of chemical energy, much more than previously calculated. The energy source is in the form of several organic compounds.

Plumes on Enceladus

Enceladus’ plumes erupt like geysers through cracks, called tiger stripes, in the icy crust at the moon’s south pole. In fact, NASA’s Cassini spacecraft sampled them directly by flying through them. While it confirmed the presence of organic molecules, Cassini wasn’t designed to detect life itself. But we do know now that various kinds of organic compounds exist in the plumes. Cassini also found ice grains, salts and concentrations of sodium, potassium, chlorine and carbonate-containing compounds.

Last June, scientists also said that new analyses of Cassini data revealed phosphorus in the plumes, another key ingredient and building block for life.

The paper states:

The search for extraterrestrial life, especially within our solar system, is one of the biggest endeavors of mankind. The icy moons of Saturn and Jupiter, Enceladus and Europa, are particularly promising for hosting life, as they have shown evidence for the three important criteria: water, energy and organic chemicals. Both moons eject their subsurface ocean material as a plume of icy particles, providing the opportunity to study the ocean composition and potential habitability via plume flythrough sampling.

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A matter of speed

But how many kinds of organics can survive being blasted into space? What about those that might be directly associated with life, such as amino acids? It all comes down to speed. The plumes are fast-moving, erupting at about 800 miles per hour (360 m/s). Would organic particles be destroyed at that speed, when they impact with each other? We already know that some can survive, since Cassini found them. But what about amino acids?

The study showed that amino acids in the plumes could survive at speeds up to 9,400 miles per hour (4,200 m/s). And the plumes are erupting significantly slower than that. So, the researchers concluded that amino acids – if they exist – should survive the trip into space. In fact, they could be detected with limited fragmentation up to the top velocities. The paper says, using a mass spectrometer, they could fly through Enceladus’ plumes at speeds of 9,400 miles per hour (15,000 km/h) and successfully detect intact amino acids.

Measuring impacts of single ice grains in the plumes on Enceladus

This is the first time that scientists have measured what happens when a single ice grain hits another surface. Enceladus’ plumes are made up of tiny ice grains, which form after the water vapor erupting from the cracks in the ice crust freeze.

In the experiment, the researchers created ice grains by using electrospray ionization, where water is pushed through a needle held at a high voltage. The electric charge breaks the water down into increasingly smaller droplets. Then, the researchers eject the droplets into a vacuum chamber, where they freeze.

The team was able to measure the mass and charge of the grains. Image charge detectors observed the grains as they passed through the spectrometer. Using a microchannel plate detector, the researchers accurately timed the moment of impact of the ice grains down to the nanosecond. A nanosecond is one-billionth of a second.

The fact that amino acids can withstand the impacts is crucial. It shows that similar intact amino acids could still exist in the plumes of Enceladus, or even the tentative ones of Europa. (Europa’s are not proven to exist yet, but evidence is growing).

Co-author Robert Continetti at the University of California, San Diego, said:

To get an idea of what kind of life may be possible in the solar system, you want to know there hasn’t been a lot of molecular fragmentation in the sampled ice grains, so you can get that fingerprint of whatever it is that makes it a self-contained life form. Our work shows that this is possible with the ice plumes of Enceladus.

Salt and amino acids

The new study also showed how salt can affect the detectability of amino acids in the plumes. The data from Cassini suggests that Enceladus’ ocean is salty, like oceans on Earth. Salt can change the solubility of some molecules. This means that molecules like amino acids could be detected more easily. This is because they might cluster on the surface of the ice grains in the plumes. That would make it easier for a spacecraft sampling the plumes to find those molecules.

This is exciting because it means that evidence for life – traces of molecules associated with living organisms – could be detected directly in the plumes. No need to drill through the ice crust to get to the ocean below. It will require a follow-up mission to Cassini, but it can be done. Continetti said:

The implications this has for detecting life elsewhere in the solar system without missions to the surface of these ocean-world moons is very exciting, but our work goes beyond biosignatures in ice grains. It has implications for fundamental chemistry as well. We are excited by the prospect of following in the footsteps of Harold Urey and Stanley Miller, founding faculty at UC San Diego in looking at the formation of the building blocks of life from chemical reactions activated by ice grain impact.

Return to Enceladus … and Europa

While there aren’t any scheduled missions yet back to Enceladus, scientists are eager to return. In the meantime, the amino acid research results could also useful for the Europa Clipper mission to Europa, scheduled to launch in October 2024. As the paper summarized:

Our results provide a benchmark for this orbital sampling method to successfully detect signs of life and for the interpretation of past and future data. This work has implications not only for a potential Enceladus mission but also for the forthcoming Europa Clipper mission.

So we don’t know yet if the plumes on Enceladus hold signs of life. But we are getting closer to finding out.

Bottom line: Do the plumes on Enceladus contain evidence of life from the moon’s ocean? A new study shows that amino acids could survive and be detectable by spacecraft.

Source: Detection of intact amino acids with a hypervelocity ice grain impact mass spectrometer

Via University of California, San Diego

Read more: Building block for life found on Saturn’s moon Enceladus

NASA Study Finds Life-Sparking Energy Source and Molecule at Enceladus

Enceladus’ ocean even more habitable than thought

The post Watery plumes on Enceladus could hold signs of life first appeared on EarthSky.

Chiron is a centaur: a small, rocky body that orbits between the gas giant planets Saturn and Uranus. In 2015, astronomers said that Chiron might have rings. Previously, in 2014, astronomers discovered rings around a similar body, the centaur Chariklo. But scientists have been unsure whether Chiron’s rings are true rings. Some studies suggested a 2-ring system. On November 29, 2023, the Planetary Science Institute in Tucson, Arizona, said that a new study indicates that Chiron doesn’t have true rings. Instead, the study says “evolving material” is orbiting Chiron.

The researchers published their peer-reviewed results in The Planetary Science Journal on November 28, 2023.

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‘Evolving material’ instead of rings?

According to the new study, instead of stable rings, the researchers say the material is likely “evolving” over time. Amanda Sickafoose of the Planetary Science Institute, who led the study, said:

These data were used to rule out any substantial global atmosphere around Chiron. The locations and amounts of material that were detected around Chiron are different enough from previous observations to suggest that there is not a stable ring system but rather surrounding material that is currently evolving.

As Sickafoose explained:

There is material orbiting around Chiron that is evolving on relatively short timescales. Past stellar occultation observations have detected material around Chiron’s nucleus, and it was thought to be due to jets or a shell of surrounding debris. Data from a 2011 occultation were interpreted to be a two-ring system like that discovered at Chariklo. The observation reported here, from 2018, is not consistent with the two-ring interpretation.

The researchers determined the changing nature of the material by comparing observations from 2011, 2018 (the stellar occultation) and 2022. The paper states:

These results suggest that the properties of the surrounding material have evolved between the 2011, 2018 and 2022 observations …

Here’s how they know

The findings are based on a stellar occultation of Chiron in 2018. Astronomers often use stellar occultations to measure the sizes and shapes of small bodies in the outer solar system, like centaurs and other asteroids or comets. They also use them to discover and characterize planetary atmospheres and rings.

The South African Astronomical Observatory (SAAO) observed the stellar occultation on November 28, 2018, using the 74-inch (1.9-meter) telescope in Sutherland, South Africa. Lead author Amanda Sickafoose of the Planetary Science Institute said:

We observed a star passing behind the centaur Chiron from the 1.9-meter [74-inch] telescope in Sutherland, South Africa. We detected dips in the starlight as it was blocked by Chiron’s nucleus as well as by material located between 300 to 400 kilometers [186 to 249 miles] on either side.

Additional observations of Chiron and other bodies

Astronomers will continue to observe Chiron, as well as other centaurs and asteroids that may have rings. So far, Chiron is the only smaller solar system body that has material orbiting it that mimics rings. Some others, like Chariklo, do indeed have actual rings. Most smaller objects like these appear to not have any material surrounding them at all. Therefore, it will be interesting to see if any more of the known small-body ring systems turn out to be false rings as well.

NASA has also previously proposed a Chiron Orbiter Mission, as part of The National Research Council’s Planetary Science Decadal Survey.

Chariklo is the largest known centaur, with a diameter of 188 miles (302 km). Its rings orbit at a distance of about 250 miles (402 km) from the center of the body. Astronomers discovered its rings in 2013. In February 2023, NASA said that the James Webb Space Telescope had observed Chariklo’s rings, also during a stellar occultation.

Centaurs, named after the mythological creatures that were part human and part horse, have characteristics of both asteroids and comets. A NASA study from 2013 suggested that most centaurs have a cometary origin.

Bottom line: A new study suggests that the possible rings around the centaur Chiron in the outer solar system are instead “evolving material” that mimics rings.

Source: Material around the Centaur (2060) Chiron from the 2018 November 28 UT Stellar Occultation

Via Planetary Science Institute

Read more: Possible rings around minor planet Chiron

Read more: Webb observes Chariklo’s rings during occultation

The post Does Chiron have rings? Or ring mimics? first appeared on EarthSky.

There’s growing evidence for water worlds in our galaxy, worlds even richer in water than Earth. Some distant planets might be true water worlds, completely covered in deep oceans. How can we learn more about them? In late November 2023, scientists at Johns Hopkins University in Baltimore, Maryland, said that haze in the planets’ atmospheres might help. These scientists used a computer model to simulate different kinds of haze on water worlds, with the idea of helping other scientists learn how these worlds form and evolve. They said their study might also provide clues about the habitability – the potential to sustain any form of life, even microbial life – of water worlds.

The researchers published their peer-reviewed paper on November 27 in Nature Astronomy. There is a free preprint of the paper available on arXiv as well.

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Water worlds and the search for life

Water is essential for life, at least life as we know it. So water worlds are an intriguing target for astronomers. Lead author Chao He at Johns Hopkins said:

Water is the first thing we look for when we’re trying to see if a planet is habitable, and there are already exciting observations of water in exoplanet atmospheres.

But haze can be a problem. It can hamper telescopic views of distant worlds in space. That’s true both of telescopes on the ground and in space. Hazes cause opacity – an inability to see clearly – that can mask spectral features from water and other gases in an exoplanet’s atmosphere. Chao He added:

… This haze really complicates our observations, as it clouds our view of an exoplanet’s atmospheric chemistry and molecular features.

How haze on water worlds affects habitability

So haze in exoplanet atmospheres – solid particles suspended in gas – can interfere with astronomers’ observations. But it’s worth noting that haze can have an effect on the habitability of a planet. Haze can influence global temperatures and can affect how much light from the planet’s sun is able to reach its surface. Both of those factors can have an impact on biological activity, either positive or negative.

To try to determine if a water world planet might be habitable, computer modeling is needed. Co-author Sarah Hörst, also at Johns Hopkins, said:

The big picture [of what we’re trying to do] is whether there is life outside the solar system. But trying to answer that kind of question requires really detailed modeling of all different types, specifically in planets with lots of water. This has been a huge challenge. We just don’t have the lab work to do that. So we’re trying to use these new lab techniques to get more out of the data that we’re taking in with all these big, fancy telescopes.

Simulating alien atmospheres

So, how did the researchers simulate the possible atmospheres of water worlds? They used two mixtures of gas containing water vapor and other compounds scientists think are common on exoplanets. Then, the researchers used ultraviolet light to simulate the ultraviolet light coming from the planets’ host stars. It is that light that can react with the a planet’s atmosphere to produce haze. Then, in turn, the researchers wanted to know how the haze particles would react with light in a planet’s atmosphere. To do that, they measured how much light the particles absorbed or reflected.

Further, the research team also compared the data from their simulation to an actual known exoplanet called GJ 1214 b. It was a match! Having the model match a real-world planet gives the scientists confidence they’re on the right track.

Further study of haze on water worlds

Hörst explained:

People will be able to use that data when they model those atmospheres to try to understand things like what the temperature is like in the atmosphere and the surface of that planet, whether there are clouds, how high they are and what they are made of, or how fast the winds go. All those kinds of things can help us really focus our attention on specific planets and make our experiments unique instead of just running generalized tests when trying to understand the big picture.

How many water worlds are there in our galaxy? Could any of them support life? The study of atmospheric hazes on these exotic worlds, and more observations, will help to answer such fascinating questions.

Bottom line: Researchers at Johns Hopkins are simulating haze on water worlds. The haze muddles observations but can also help determine if an exoplanet is habitable.

Source: Optical properties of organic haze analogues in water-rich exoplanet atmospheres observable with JWST

Source (preprint): Optical Properties of Organic Haze Analogues in Water-rich Exoplanet Atmospheres Observable with JWST

Via Johns Hopkins University

Read more: Habitable water worlds don’t have to be Earth-like

Read more: Water worlds may be abundant in our galaxy

The post Can haze on water worlds aid in the search for life? first appeared on EarthSky.

Astronomers have found an ever-growing number of rocky exoplanets, including some about the same size and mass as Earth, orbiting distant stars. Scientists have thought that these worlds form in relatively benign regions around their stars, that is, in places where ultraviolet radiation from their stars is relatively mild. Such radiation from stars can destroy the molecules that are the building blocks for rocky planets. But on November 30, 2023, an international team of researchers presented an alternative view. Using the James Webb Space Telescope, they found, for the first time, that rocky planets can form even in extreme radiation environments.

Webb detected a wide variety of planet-building molecules in a radiation-soaked region of a planet-forming disk, or protoplanetary disk, in the Lobster nebula (NGC 6537). It is just one of many disks in the nebula, 5,500 light-years away. These disks of dust and gas around young stars are where new planets are born.

The researchers published their peer-reviewed results in The Astrophysical Journal Letters on November 30, 2023.

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Building blocks of rocky exoplanets

Just like living organisms, planets are made from molecular building blocks. This can include water, carbon and many others. A lot of factors play in to what a planet will be like, including the environment it forms in around its star. If it is too close to the star, ultraviolet light can break apart many of those molecules.

Hence, scientists have thought that the best place for rocky planets to form is where there is less radiation. As in, a more benign region a bit farther out from their stars.

Webb makes surprising discovery

But now, Webb has made an unexpected discovery. It has found building blocks of rocky planets in an extreme and hostile environment in a protoplanetary disk about 5,500 light-years away in the Lobster nebula. Protoplanetary disks are massive flattened rotating disks of dust and gas around young stars. It is in these disks that planets – of all kinds – can form. The young stars in the Lobster nebula are massive, emitting much more ultraviolet radiation than smaller stars.

The Lobster nebula is a massive star-forming complex, and also one of the closest to us. Webb is the only telescope that currently can study planet-forming disks in such complexes. Lead author María Claudia Ramírez-Tannus, at the Max Planck Institute for Astronomy in Germany, stated:

Webb is the only telescope with the spatial resolution and sensitivity to study planet-forming disks in massive star-forming regions.

Webb targeted 15 protoplanetary disks in the Lobster nebula. In one of them, called XUE 1, Webb detected water, carbon monoxide, carbon dioxide, hydrogen cyanide, acetylene and partially crystalline silicate dust. All of those are building blocks for rocky planets.

One of the most extreme environments in our galaxy

What’s exciting is the molecules are in the inner region of the disk, which is highly irradiated by its star. These regions are some of the most extreme known in our galaxy. The fact that Webb has confirmed the existence of the molecules shows that rocky planets can, indeed, form in such hostile environments.

The researchers say that XUE 1 has likely been exposed to intense radiation ever since it first formed. And yet the rocky planet-forming molecules are still there. Co-author Rens Waters at Radboud University in the Netherlands said:

We find that the inner disk around XUE 1 is remarkably similar to those in nearby star-forming regions. We’ve detected water and other molecules like carbon monoxide, carbon dioxide, hydrogen cyanide and acetylene. However, the emission found was weaker than some models predicted. This might imply a small outer disk radius.

Co-author Lars Cuijpers, also at Radboud University, added:

We were surprised and excited because this is the first time that these molecules have been detected under these extreme conditions.

Good news for rocky exoplanets

So, why is this significant? Surprisingly, the results show that the conditions in the inner disk of XUE 1 are similar to those in protoplanetary disks around lower-mass stars. This means that the range of environments where rocky planets can form is much larger than previously thought. If rocky planets can form around both low-mass and high-mass stars, in both benign and extreme environments, then there are probably many more out there than astronomers had previously calculated.

The paper stated:

Our findings imply that the inner regions of highly irradiated disks can retain similar physical and chemical conditions to disks in low-mass star-forming regions, thus broadening the range of environments with similar conditions for inner disk rocky planet formation to the most extreme star-forming regions in our galaxy.

And if such worlds are abundant, then potentially more of them could be habitable.

How common are rocky exoplanets?

But just how common are rocky planets, overall? As Ramírez-Tannus noted:

XUE 1 shows us that the conditions to form rocky planets are there, so the next step is to check how common that is. We will observe other disks in the same region to determine the frequency with which these conditions can be observed.

Researchers will need to conduct additional observations, however, to determine the rate of rocky planet formation in extreme environments. As the paper said:

XUE 1 shows that the conditions for terrestrial planet formation can also happen in extreme environments. Nevertheless, the remaining observations from the XUE program are crucial to establish the frequency with which this occurs.

Also at the end of November, researchers from the U.K., Germany and the U.S. said they discovered the first known protoplanetary disk in another galaxy! This one is in the Large Magellanic Cloud, 160,000 light-years away.

Bottom line: NASA’s James Webb Space Telescope has found molecular building blocks of rocky exoplanets in a region previously thought to be too extreme and hostile.

Source: XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Protoplanetary Disk

Via Webb Space Telescope

Read more: Weird rocky exoplanets unlike any seen before

Read more: 1st planet-forming disk found in another galaxy

The post Rocky exoplanets can form in the most extreme environments first appeared on EarthSky.

Our Earth and the other planets in our solar system were born from a giant disk of dust and gas around our sun. And astronomers have found many such disks in our Milky Way galaxy. They call them circumstellar disks, or protoplanetary disks. It’s in these disks that planets are being born. On November 29, 2023, scientists said that – for the first time – they’ve found a circumstellar disk around a massive young star in another galaxy.

The disk resides in the Large Magellanic Cloud, a neighboring galaxy to our Milky Way, 160,000 light-years away.

The discovery shows that such planet-forming disks are likely common around stars in other galaxies besides our own.

Researchers from the U.K., Germany and the U.S. used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to make the discovery.

The research team published their peer-reviewed results in Nature on November 29, 2023.

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1st extragalactic accretion disk

The circumstellar disk is a type of accretion disk. In accretion disks, things are both orbiting a central body – a sun, or, for example, a black hole – and small bodies are also accreting, or sticking together, to make larger bodies. Thus planets are born. The disk that ALMA discovered is the first accretion disk ever detected in a galaxy outside of our own Milky Way. As Anna McLeod, lead author at Durham University in the U.K., stated:

When I first saw evidence for a rotating structure in the ALMA data I could not believe that we had detected the first extragalactic accretion disk. It was a special moment. We know disks are vital to forming stars and planets in our galaxy, and here, for the first time, we’re seeing direct evidence for this in another galaxy.

This video summarizes the discovery of the 1st planet-forming disk in another galaxy. Video via ESO/ YouTube.

Previous hints of a planet-forming disk

The ALMA observations are the first to confirm the circumstellar disk, but there were previous hints as to its existence. In 2019, the European Southern Observatory (ESO) released an image from its Multi Unit Spectroscopic Explorer (MUSE) instrument on the Very Large Telescope (VLT) of a jet of material being emitted by a young star. That star, HH 1177, is deep inside a gas cloud in the Large Magellanic Cloud. This is the same star ALMA observed the circumstellar disk around. McLeod said:

We discovered a jet being launched from this young massive star, and its presence is a signpost for ongoing disc accretion.

Now, ALMA has confirmed that the astronomers’ suspicions were correct; there really is a planet-forming disk around this star.

Detecting accretion disks

So, how do astronomers detect accretion disks? A major clue has to do with speed. The material – gas and dust – around a young star is pulled in toward the star. But it doesn’t hit the star. Instead, it forms a broad, flattened, spinning disk. Not all the material is moving at the same speed, however. The closer the material in the disk is to the star, the faster it rotates. Astronomers can measure that difference in speed and deduce that there’s an accretion disk around the star. This also affects the frequency of light coming from the disk. Co-author Jonathan Henshaw at Liverpool John Moores University in the U.K. explained:

The frequency of light changes depending on how fast the gas emitting the light is moving towards or away from us. This is precisely the same phenomenon that occurs when the pitch of an ambulance siren changes as it passes you and the frequency of the sound goes from higher to lower.

The discovery will help astronomers learn more about how planets form, both in our galaxy and well beyond. As McLeod said:

We are in an era of rapid technological advancement when it comes to astronomical facilities. Being able to study how stars form at such incredible distances and in a different galaxy is very exciting.

Bottom line: For the first time, astronomers have discovered a planet-forming disk around a young star in another galaxy outside our own Milky Way galaxy.

Source: A likely Keplerian disk feeding an optically revealed massive young star

Via ESO

Read more: Bubbles of brand new stars

Read more: Stars and planets grow rapidly together

The post 1st planet-forming disk found in another galaxy first appeared on EarthSky.

China’s Zhurong rover mission to Mars is over. But the data it sent back to Earth are still providing insights. The rover explored its landing site in Utopia Planitia, the largest impact basin on Mars, beginning in May 2021 and for 357 days (347 Mars sols) afterward. In a new paper published on November 23, 2023, Chinese researchers said that Zhurong found irregular polygon-shaped wedges – apparent clumps made of sandy Martian soil and ice, with three or more straight sides – beneath Mars’ surface. The rover used its radar to detect the geometrically shaped clumps, which are thought to be caused by freeze-thaw cycles on Mars.

Utopia Planitia, by the way, is a historic site on Mars for us earthlings. It’s where one of the first two Mars landers – NASA’s Viking 2 – set down in 1976.

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Polygons beneath Mars’ surface

Polygons beneath the surface are common on Mars. And they’re found on Earth, too. But they hadn’t been found at Utopia Planitia, until now. Space journalist Leonard David wrote about the discovery in his blog Leonard David’s INSIDE OUTER SPACE on November 24, 2023.

Lei Zhang at the CAS Engineering Laboratory for Deep Resources Equipment and Technology, Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing, China, led the research team. The researchers published their peer-reviewed findings in Nature Astronomy on November 23.

Zhurong traveled about 0.7 miles (1.2 km) during its mission. Along the route, the rover used its radar to study the subsurface. It found the polygons about 115 feet (35 meters) below the surface. David wrote:

In the just-published work, the country’s Zhurong Mars rover made use of onboard radar and detected irregular wedges (polygons) underneath its exploration zone.

The paper explained:

As the largest basin on Mars, Utopia Planitia has both experienced and recorded variations of the Martian paleoclimate. Layered subsurface structures have been identified by ground-penetrating radar in southern Utopia Planitia but lateral variations of the subsurface, potentially linked to the Martian paleoclimatic evolution, have not been investigated. Here we report the lateral frequency-variation patterns of Zhurong radar reflections and interpret them as buried polygonal terrain below a depth of 35 meters.

Altogether, Zhurong detected 16 polygons within the distance it had traveled. This suggests that the polygons are likely widespread throughout Utopia Planitia.

Freeze-thaw cycles

So, how did they form?

Zhang and his colleagues tested various possibilities through a process of elimination. Their conclusion? The researchers think that repeated cycles of freezing and thawing produced the polygons. This process has created similar features elsewhere on the planet as well. David said:

The Chinese researchers are proposing that the polygons were potentially generated by freeze-thaw cycles. That interpretation implies that there was a strong paleoclimatic variability at low-to-mid latitudes (roughly 25 degrees north), possibly due to the high obliquity of ancient Mars.

The freeze-thaw cycles may have involved water and ice and would have required an overall cold climate to occur in, the researchers said. They also would have happened when the planet was still young. The paper said that the polygons:

… might be related to water/ice freeze–thaw processes in southern Utopia Planitia on early Mars.

The water and ice may have had various possible sources, as the paper stated:

The possible presence of water and ice required for the freeze–thaw process in the wedges may have come from cryogenic suction-induced moisture migration from an underground aquifer on Mars, snowfall from the air or vapor diffusion for pore ice deposition.

The Zhurong rover mission

The Zhurong rover, part of the Tianwen-1 mission, landed in the southern part of Utopia Planitia on May 15, 2021. It had a nominal expected lifetime of 90 sols (Martian days, just slightly longer than days on Earth). The solar-powered rover had been hibernating through the harsh Martian winter, starting in May 2022. The mission team expected the rover to wake up again after that, but it never did.

China is also now looking to launch its own sample-return mission to Mars in 2028. Utopia Planitia may be the target for that mission as well, but that has not been confirmed yet.

Bottom line: China’s Zhurong rover has found polygonal wedges below the surface in Utopia Planitia on Mars. Freeze-thaw cycles of water and ice likely created the polygons.

Source: Buried palaeo-polygonal terrain detected underneath Utopia Planitia on Mars by the Zhurong radar

Via Leonard David’s INSIDE OUTER SPACE

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Have you heard of STARCOM? It’s also known as the Space Training and Readiness Command, headquartered at Peterson Space Force Base, Colorado. STARCOM works in education and training, and in doctrine, for the U.S. Space Force. And on November 16, 2023, STARCOM released a publication titled SDP 3-100: Space Domain Awareness.

Space domain awareness is routine stuff. It’s the detection, tracking and cataloging of objects orbiting Earth (active or inactive and foreign or domestic satellites, for example).

But there’s one part of the new document that has caught people’s attention. It has become part of the continued discussion of what the U.S. government calls Unidentified Anomalous Phenomena, or UAP … known to most of us as UFOs.

In short, the Space Force wants to track “abnormal observables and patterns of life” with “unknown origins.”

Sounds intriguing, but what does it mean?

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What is space domain awareness?

Brett Tingley wrote about the new STARCOM publication for Space.com on November 22, 2023. As Tingley noted:

Most of the document describes the need to maintain a safe environment by monitoring and tracking such objects as pieces of space debris, the ever-growing number of commercial satellites, spacecraft operated by adversaries, and ‘the hazards posed by the space environment and natural debris’ such as meteoroids or solar flares.

The Space Domain Awareness document itself said:

Operating safely in the space domain requires the ability to detect, track, characterize, discriminate between and maintain custody of increasingly smaller spacecraft and debris with increased accuracy. It requires the ability to detect, track, characterize, discriminate, and maintain custody of objects that are dimmer, more distant or otherwise difficult to observe despite the increased proliferation of objects that are nearer and brighter.

Tracking ‘abnormal observables with unknown origins’

The document continued:

It requires the ability to rapidly identify and respond to threats and hazards, including objects that exhibit abnormal observables and patterns of life and cannot be correlated to any owner or point of origin.

So what are “objects that exhibit abnormal observables and patterns of life?” Usually rockets, as Tingley pointed out:

Most of the time, these are objects launched by other nations. The STARCOM document points out that it is ‘imperative for the safety of space operations that the United States not only knows where objects and spacecraft are at any given time, but also how they got there, who owns them, their potential capabilities and their operator’s intent.’

Space Force connection to UAP?

But could some objects be UAP? That’s what the UFO-interested community wants to know. Perhaps you’ve followed the talk in the U.S. Congress in recent years on the subject of UAP? In July 2022, the U.S. Department of Defense created an All-domain Anomaly Resolution Office, whose job is to investigate:

… Unidentified Flying Objects (UFOs) and other phenomena in the air, sea, and/or space and/or on land: sometimes referred to as ‘Unidentified Aerial Phenomena’ or ‘Unidentified Anomalous Phenomena’ (UAP).

This office’s annual report – released in October 2023 – mentions near-Earth space as one of the domains regarding UAP reports. The Glossary of Terms said:

Unidentified Anomalous Phenomenon (UAP): Sources of anomalous detections in one or more domain (i.e., airborne, seaborne, spaceborne and/or transmedium) that are not yet attributable to known actors and that demonstrate behaviors that are not readily understood by sensors or observers. ‘Anomalous detections’ include but are not limited to phenomena that demonstrate apparent capabilities or material that exceed known performance envelopes. A UAP may consist of one or more unidentified anomalous objects and may persist over an extended period of time.

More specifically, it listed UAP in space as:

Spaceborne UAP: Sources of anomalous detections above the Kármán Line [The proposed boundary between Earth’s atmosphere and outer space, located some 6 miles or 10 kilometers above Earth’s mean sea level].

NDAA Science Plan and UAP

As in the previous couple years, the National Defense Authorization Act (NDAA) for 2023 contained UAP-related mandates as well. The Science Plan portion stated:

SCIENCE PLAN – The Director of the Office, on behalf of the Secretary and the Director of National Intelligence, shall supervise the development and execution of a science plan to develop and test, as practicable, scientific theories to:

(1) account for characteristics and performance of unidentified aerospace-undersea phenomena that exceed the known state of the art in science or technology, including in the areas of propulsion, aerodynamic control, signatures, structures, materials, sensors, countermeasures, weapons, electronics and power generation; and

(2) provide the foundation for potential future investments to replicate or otherwise better understand any such advanced characteristics and performance.

So, it sounds like the Space Force could be tracking some objects – among all the “regular” ones – that the Department of Defense might consider to be UAP (and NASA has similar descriptions for UAP).

But, for now at least, most of the information related to any possible tracking of UAP is classified. So we probably won’t hear much about whatever they might find … if indeed there is anything to be found.

Bottom line: The U.S. Space Force is now charged with tracking objects near Earth that exhibit ‘abnormal observables’ and are of ‘unknown origin.’

Source: STARCOM Releases Space Domain Awareness Doctrine Publication

Via Space.com

Read more: Launches: U.S. Space Force takes command

Read more: Will the proposed UAP Disclosure Act reveal UFO secrets?

The post Space Force to track ‘abnormal objects of unknown origin’ first appeared on EarthSky.

Astronomers have been discovering an ever-growing number of rocky exoplanets orbiting distant stars. Some are similar in size to Earth. And some might even be habitable. Unfortunately, that doesn’t seem to be the case with LTT 1445Ac, only 22 light-years away. The Hubble Space Telescope has now obtained the most accurate measurement yet of its diameter. And a team of researchers said last on November 16, 2023, it’s almost an exact twin to Earth in size.

But size is where the similarity ends.

Exoplanet LTT 1445Ac’s closeness to its red dwarf star means its surface is boiling! Surface temperatures hover around 500 degrees Fahrenheit (260 degrees Celsius).

The researchers first published their peer-reviewed results in The Astronomical Journal on September 25, 2023.

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Meet exoplanet LTT 1445Ac

NASA’s Transiting Exoplanet Survey Satellite (TESS) first discovered LTT 1445Ac in 2022. The red dwarf star it orbits is the most common type of star in our galaxy. And, as stated above, it lies only 22 light-years away, in the direction of our constellation Eridanus the River.

This star, LTT 1445A, is one member of a three-star system. The other two stars are closer together and lie about three billion miles (five billion km) away from LTT 1445A. There are also two other known planets in the system, both larger than LTT 1445Ac.

A transiting world

The exoplanet – LTT 1445Ac – transits or passes in front of its star, as seen from Earth. Transiting helps telescopes like Hubble to be able to measure the planet’s size and look for evidence of an atmosphere.

But there’s a rub. As seen from our world, if a distant planet transits across only a small part of a star’s disk, astronomers say it’s a grazing transit. And, in that case, it’s harder to get accurate measurements on the planet. For example, a grazing transit can result in an inaccurate measurement of the lower limit of a planet’s diameter.

And that’s what has made measurements of the size of exoplanet LTT 1445Ac so difficult. Astronomers knew this distant world transited its star, as seen from Earth. But TESS didn’t have quite enough optical resolution – it couldn’t see clearly enough – to determine if the transit was a full one or a grazing one. The paper on this subject, published in September 2023, said:

Previous studies of the exoplanet LTT 1445Ac concluded that the light curve from the Transiting Exoplanet Survey Satellite (TESS) was consistent with both grazing and nongrazing geometries. As a result, the radius and hence density of the planet remained unknown.

Although TESS couldn’t measure the planet’s diameter, Hubble could. First, the observations showed that the planet does indeed make a full transit in front of its star, not just a grazing transit. This helped Hubble obtain an accurate measurement of the planet’s size. And that’s how we know the planet is 1.07 times Earth’s diameter. Lead author Emily Pass of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, said:

There was a chance that this system has an unlucky geometry. And, if that’s the case, we wouldn’t measure the right size. But with Hubble’s capabilities we nailed its diameter.

Not very Earth-like exoplanet

So LTT 1445Ac is almost the same size as Earth. That means it also has similar surface gravity to Earth. But LTT 1445Ac isn’t very Earth-like, otherwise. Even though its star is smaller and dimmer than our sun, the planet orbits closely enough that its surface temperature is much hotter than on Earth. Its surface temperature is a sizzling 500 degrees F (260 degrees C). That’s the same temperature as inside a pizza oven.

So LTT 1445Ac is unlikely to be habitable.

Transiting exoplanets and further observations

Astronomers like transiting exoplanets, since it allows telescopes like TESS and Hubble to detect their atmospheres, if they have them. As Pass noted:

Transiting planets are exciting since we can characterize their atmospheres with spectroscopy, not only with Hubble but also with the James Webb Space Telescope. Our measurement is important because it tells us that this is likely a very nearby terrestrial planet. We are looking forward to follow-on observations that will allow us to better understand the diversity of planets around other stars.

Indeed, astronomers will also be studying LTT 1445Ac further, to analyze its atmosphere, if it has one. The paper says:

As the nearest terrestrial exoplanet to transit an M [red] dwarf (alongside LTT 1445 Ab), this planet is an exciting target for atmospheric characterization, particularly now that it is known to be nongrazing and its radius is therefore appropriately constrained.

Bottom line: Astronomers using the Hubble Space Telescope measured the exact diameter of a nearby Earth-sized exoplanet. The sizzling world is too hot for life, however.

Source: HST/WFC3 Light Curve Supports a Terrestrial Composition for the Closest Exoplanet to Transit an M Dwarf

Via Hubblesite

Read more: Are the TRAPPIST-1 exoplanets habitable, or not?

Read more: 2 possibly Earth-like worlds, just 16 light-years away

The post Nearby exoplanet is Earth twin, but hot as a pizza oven first appeared on EarthSky.

Like the planets in our solar system, exoplanets come in various sizes and types. But some apparently don’t stay the same size. In fact, some exoplanets appear to be able to shrink. How is that possible? Scientists at NASA, Caltech and other institutions said on November 15, 2023, that they might have an answer. They said some sub-Neptune exoplanets – gaseous worlds with smaller radii than our solar system’s planet Neptune, but larger than Neptune in mass and so more dense – have cores that are pushing away their atmospheres from the inside out. So these gaseous planets are losing their atmospheres. And thus they’re shrinking in size.

The existence of shrinking sub-Neptunes might explain the unusual size gap between them and super-Earths, which are more massive than Earth, but less massive than Neptune.

That is, some sub-Neptunes simply become super-Earths.

The researchers published their peer-reviewed findings in The Astronomical Journal on November 15, 2023.

A size gap in exoplanets

After discovering more and more exoplanets over the past few decades, astronomers have noticed something odd. Both rocky super-Earths and larger gaseous sub-Neptunes are fairly common. But there is a distinct lack of exoplanets between those two sizes. This size gap – of planets 1.5 to two times the size of Earth – has puzzled astronomers. What is causing it?

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As lead author Jessie Christiansen at Caltech in Pasadena, California, explained:

Scientists have now confirmed the detection of over 5,000 exoplanets, but there are fewer planets than expected with a diameter between 1.5 and two times that of Earth. Exoplanet scientists have enough data now to say that this gap is not a fluke. There’s something going on that impedes planets from reaching and/or staying at this size.

Shrinking exoplanets

The new findings suggest that shrinking exoplanets can explain the mysterious size gap. Some larger sub-Neptune planets shrink to become super-Earths, leaving no intermediate sized planets. Hence the gap in sizes. But how is that happening?

The researchers said that if a sub-Neptune doesn’t have enough mass, it could start to lose some of its atmosphere. This is due to not enough gravitational force to hold onto all of the atmosphere. By losing some or much of their outer atmospheres, these planets would “shrink” in overall size.

That can explain the size differences, but exactly how are these planets’ atmospheres being decimated? There have been two main theories posited to date: core-powered mass loss and photoevaporation.

In core-powered mass loss, the planet’s hot core releases radiation. That radiation “pushes out” the atmosphere from underneath over time. Photoevaporation is kind of the opposite. Radiation from the planet’s host star blows away the outer atmosphere. Christiansen said that:

… the high-energy radiation from the star is acting like a hair dryer on an ice cube.

There’s another difference between the two scenarios. Scientists think that photoevaporation occurs early in the planet’s history, within the first 100 million years. Core-powered mass loss, however, doesn’t happen until about a billion years later. Both can lead to a loss of atmosphere. Christiansen said:

If you don’t have enough mass, you can’t hold on, and you lose your atmosphere and shrink down.

Star clusters provide clues to shrinking exoplanets

Either process could explain a lost atmosphere. So, how did the researchers determine which of the two possibilities is more likely? They used data from the Kepler Space Telescope‘s extended mission, called K2. They focused on two star clusters specifically, Praesepe (also known as the Beehive cluster or M44) and the Hyades. Both are known to contain many sub-Neptunes.

The ages of the stars in these clusters is of particular importance. The stars are between 600 million and 800 million years old. While still relatively young, their sub-Neptunes – about the same age – are old enough that photoevaporation would have already occurred several hundred million years ago. But they are not old enough yet for core-powered mass loss.

With this in mind, the researchers reasoned that if there were still many full-sized sub-Neptunes in these clusters, then they couldn’t have experienced photo evaporation. And indeed, they found that nearly all the stars in the clusters have a sub-Neptune or at least a candidate. They are still full-sized, meaning they have held onto their atmospheres.

Core-powered mass loss most likely explanation

Meanwhile, in some older star clusters, only about 25% of those stars have sub-Neptunes. This fits with the scenario that core-powered mass loss would have occurred by that point. That would result in fewer sub-Neptunes and more super-Earths. If photo evaporation had happened in Praesepe and the Hyades, then those planets should have lost much of their atmospheres. But they didn’t.

The results leave core-powered mass loss as the most likely explanation for the shrinking planets. But, as the press release said, the research is far from complete, so:

… it is possible that the current understanding of photoevaporation and/or core-powered mass loss could evolve. The findings will likely be put to the test by future studies before anyone can declare the mystery of this planetary gap solved once and for all.

Bottom line: Scientists say they may have solved the mystery of shrinking exoplanets. Radiation from the cores of less massive sub-Neptunes pushes away their atmospheres.

Read more about the differences between super-Earths, mini-Neptunes and sub-Neptunes.

Source: Scaling K2. VII. Evidence For a High Occurrence Rate of Hot Sub-Neptunes at Intermediate Ages

Via NASA

Read more: How shrinking planets might explain missing planets

Read more: Super-Earth and mini-Neptune in synchronized dance

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