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.

The Geminid meteor shower is peaking on the nights of December 13 and 14. Read more about 2023’s Geminid meteor shower.

Weirdly comet-like 3200 Phaethon

Most meteors in annual showers have comets as their sources. But not December’s Geminid meteors, whose source, known as 3200 Phaethon, is a strange hybrid of an asteroid and a comet. This “rock-comet” isn’t icy, like a comet is. But it brightens as it nears the sun, as comets do. And it’s been observed to have a tail when nearest the sun. Plus, it spawns the Geminid meteor shower. And so scientists have long puzzled over 3200 Phaethon. How can a rocky asteroid leave behind debris that sparks a meteor shower? Where does its tail come from?

In 2023, a couple of new studies provide insights on 3200 Phaethon, parent object of one of the year’s best meteor showers.

Available now! 2024 EarthSky lunar calendar. A unique and beautiful poster-sized calendar showing phases of the moon every night of the year. Makes a great gift!

New research from Lowell Observatory

The Planetary Science Journal published a new study about 3200 Phaethon in April 2023.

On December 13, 2023, Spaceweather.com quoted astronomer Karl Battams of the U.S. Naval Observatory – a co-author of the April study – as saying:

Our work has upended years of belief about 3200 Phaethon, the source of the Geminids. It’s not what we thought it was.

In other words, since its discovery in 1983, 3200 Phaethon has appeared to be a rocky asteroid. NASA’s STEREO spacecraft first observed its tail – which appears when 3200 Phaethon passes near the sun in its 524-day orbit – in 2009 and 2012.

But, according to the story in Spaceweather.com today (December 13), Qicheng Zhang at Lowell Observatory in Flagstaff was “never convinced.” Spaceweather.com explained:

For one thing, the Geminid debris stream is massive (1,013 kg or 2,233 pounds), while the tail of 3200 Phaethon is puny, providing less than 1% of the mass required to explain the Geminids.

‘The tail we see today could never supply enough dust to supply the Geminid meteor shower,’ says Zhang.

Zhang, Battams, and colleagues decided to take a closer look. Using coronagraphs on the Solar and Heliospheric Observatory (SOHO), they monitored Phaethon as it passed by the sun in 2022. Color filters on the spacecraft revealed no dust or rock. Instead, Phaethon’s tail is made of sodium gas.

And therein lies the twist. Meteor showers are made of meteoroids, not gas. Suddenly, the Geminids are a mystery again.

‘We’re back to square one,’ says Zhang. ‘Where do the Geminids come from?’

Source: Sodium Brightening of (3200) Phaethon near Perihelion

More new research on 3200 Phaethon

Could the answer come from more new research, published on November 2, 2023, by a team at the University of Helsinki? This new study appears in the journal Nature Astronomy.

This team compared an infrared spectrum of 3200 Phaethon – from NASA’s Spitzer space telescope – to infrared spectra of known meteorites. They found Phaethon’s spectrum showed olivine, carbonates, iron sulfides and oxide minerals. Those substances are also found in the composition of CY carbonaceous chondrite meteorites (a rare type of meteorites with only six samples available for study).

When CY meteorites are exposed to high temperatures, the carbonates in the meteorites produce carbon dioxide. That releases water vapor, and the sulfides release sulfur gas. Could that be what’s happening in 3200 Phaethon also? Is that why this object has a tail when nearest the sun?

Source: Thermal decomposition as the activity driver of near-Earth asteroid (3200) Phaethon

NASA also found sodium coming off 3200 Phaethon’s surface

Scientists with NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, first announced sodium fizzing from the asteroid’s surface in 2021. Their statement explained that this asteroid:

… brightens as it gets close to the sun. Comets typically behave like this: When they heat up, their icy surfaces vaporize, causing them to become more active and brighten as the venting gases and dust scatter more sunlight. But what is causing Phaethon to brighten if not vaporizing ices?

So it’s been thought for a few years that sodium could play a role in the formation of 3200 Phaethon’s tail.

Read more: Fizzing Sodium Could Explain Asteroid Phaethon’s Cometlike Activity

All that, and blue, too

By the way, the comet-like behavior of this asteroid isn’t the only unusual thing about it. For one thing, 3200 Phaethon has an odd color for an asteroid. Most asteroids are dull grey to red, depending on the type of material on their surface. 3200 Phaethon is blue. It’s not the only blue asteroid, but blue asteroids make up only a fraction of all known asteroids. And Phaethon isn’t just blue. It’s one of the bluest of similarly colored asteroids (or comets) in the solar system.

Here’s another odd feature of 3200 Phaethon. While comets tend to have more elliptical orbits, asteroid orbits are more circular. 3200 Phaethon’s orbit – which is now exceedingly well known – is highly elongated, reminiscent of some comets. Its orbit crosses the orbits of Mars, Earth, Venus and Mercury.

Plus, its orbit brings 3200 Phaethon closer to the sun than any other named asteroid (though some smaller, unnamed asteroids come even closer). At its closest point, Phaethon is only 13 million miles (20.9 million km) from the sun. That’s less than half of Mercury’s closest distance.

The name of this object – 3200 Phaethon – honors its relationship to the sun. In Greek mythology, Phaethon was the son of the sun god Helios.

A potentially hazardous asteroid

3200 Phaethon is classified as a potentially hazardous asteroid. But that doesn’t mean it’s a threat to Earth. It just means two things. First, 3200 Phaethon is big. The latest estimates (2021) suggest it’s 3.6 miles (5.8 km) wide. It’s big enough to cause significant regional damage if it were to strike Earth. Second, it makes periodic close approaches to Earth. But astronomers know of no upcoming strike by this object in the foreseeable future.

In 2017, 3200 Phaethon came closer to Earth than it will again until 2093. At its closest in 2017, it was still about 26 times the moon’s distance away.

Videos of 3200 Phaethon

Both amateur and professional astronomers watched 3200 Phaethon as carefully as they could in 2017. For example, Northolt Branch Observatories in London, England, created the animation below from images it captured in 2017.

Steven Bellavia also produced a video (below) of 3200 Phaethon in 2017. He commented then that he’d endured cloudy weather and subfreezing temperatures in order to capture the images.

The history of 3200 Phaethon

3200 Phaethon was the first asteroid discovered via spacecraft, on October 11, 1983. Astronomers Simon F. Green and John K. Davies noticed it while searching Infrared Astronomical Satellite data for moving objects. Charles T. Kowal confirmed it optically and said it was asteroid-like in appearance. The object received the provisional designation 1983 TB. Two years later, in 1985, using the convention for naming asteroids, astronomers assigned it its asteroid number and name: 3200 Phaethon.

Before 3200 Phaethon, scientists linked all known meteor showers to comets and not asteroids.

Thus, 3200 Phaethon surprised them from the beginning, because – while it looked like an asteroid – it appeared to be the source of the annual Geminid meteor shower. Astronomers began calling 3200 Phaethon a comet-asteroid hybrid, an asteroid that behaves like a comet. Later, they began using the term rock-comet.

What else will we learn about this object, as the years pass?

Bottom line: The Geminid meteor shower has a unique source – 3200 Phaethon – sometimes called a comet-asteroid hybrid, or a rock-comet. In November 2023, scientists found the composition of 3200 Phaethon matches a rare type of meteorite that releases gas when heated to temperatures like 3200 Phaethon experiences when it nears the sun. And in 2021, scientists suggested that some of this object’s comet-like behavior might stem from sodium fizzing from its surface.

Source: Thermal decomposition as the activity driver of near-Earth asteroid (3200) Phaethon

Via University of Helsinki, JPL and U.S. Naval Research Lab

The post Mysterious 3200 Phaethon – parent to the Geminids – revealed? first appeared on EarthSky.

Betelgeuse nearly disappeared

The bright star Betelgeuse did become fainter – and, for experienced observers using the right equipment, nearly disappeared – last night (December 11, 2023). The event occurred as asteroid Leona passed in front of the star. But the event was quick! And it was subtle: a momentary dimming of the star.

El asteroide 319 Leona pasó esta noche frente a la estrella Betelgeuse y parece ser que solo disminuyó su brillantez un par de segundos y no la ocultó totalmente, al menos desde la perspectiva de Italia. "Spikes" o líneas de brillo desaparecen brevemente.

(Video: Antonio Piras) pic.twitter.com/NVV7n5q8gv

— SocAstronomíaCaribe (@Soc_AstroCaribe) December 12, 2023

Translation: Asteroid 319 Leona passed in front of the star Betelgeuse tonight and it seems that it only decreased its brightness for a couple of seconds and did not completely hide it, at least from the perspective of Italy. “Spikes” or glow lines disappear briefly. Video: Antonio Piras.

The post above – from Italy – shows what the eye would have seen: a dimming, but not a total disappearance.

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Report from cyberspace

We also heard from experienced observer and EarthSky community member Eliot Herman in Tucson, Arizona, who said he watched the event online at several different channels. He said:

I watched first in Sardina. It looked maybe 50% decrease for 2 seconds there. Then I flipped to Portugal and saw nothing. Betelguese must either be larger than thought in apparent diameter or the asteroid smaller.

And here’s a light curve

Preliminary light curve of a recording of the stellar occultation of #Betelgeuse by asteroid (319) Leona by M. O'Connell and A. Pratt, located south of Alicante, Spain. Camera Watec 910 HX/RC and 40mm f/4.5 apo with Bessel V filter.? pic.twitter.com/iEeFXSTwOm

— IOTA / European Section (@IOTAEuropeanSec) December 12, 2023

From Córdoba, Andalusia

The video above is from Sebastian Voltmer (@SeVoSpace on Twitter, @spacemovie on YouTube). He was observing at Almodóvar del Río, a Spanish municipality in the province of Córdoba, Andalusia.

Betelgeuse eclipse on December 11 or 12

Betelgeuse is a famous red supergiant star in the constellation Orion the Hunter. Prior to the event, Betelgeuse’s light was predicted to look dimmed or extinguished for up to 7 seconds. But we didn’t see any reports of its dimming for that long (some might still come in).

The event took place at 1:24:54 UTC on December 12, 2023.

Betelgeuse is a temperamental star

Betelgeuse is already famous for how it varies in brightness. And, since 2019, there’s been a noticeable uptick in the brightening and dimming of Betelgeuse. It’s the nearest red supergiant star to Earth, lying some 1,000 light-years away. It will explode someday, though that might be today or thousands of years from now. A paper in 2023 said that it might explode within “tens of years.” That would be amazing to see!

If it were to explode, we would see it as an incredibly bright star, even visible in daylight for roughly a year until it faded away completely, leaving a darkness where Orion’s shoulder was. Fortunately, Earth is too far away for this explosion to harm, much less destroy, life on Earth.

Bottom line: On December 11 and 12, 2023, the star Betelgeuse dimmed, and nearly disappeared, for several seconds as asteroid Leona passed in front of it.

The post Betelgeuse nearly disappeared – for some – in rare eclipse first appeared on EarthSky.

When the sun dies

What does death mean for the sun? It means our sun will run out of fuel in its interior. It’ll cease the internal thermonuclear reactions that enable stars to shine. It’ll swell into a red giant, whose outer layers will engulf Mercury and Venus and likely reach the Earth. Life on Earth will end.

If the sun were more massive – estimates vary, but at least several times more massive – it would explode as a supernova. So … no supernova. But what? What happens next? An international team of astronomers used a stellar data-model that predicts the life cycle of stars to answer this question.

Their research was published in the peer-reviewed journal Nature Astronomy and is available to read at arXiv.org. It suggested that the sun is almost exactly the lowest mass star that – at the end of its life – produces a visible, though faint, planetary nebula.

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About planetary nebulae

The name planetary nebula has nothing to do with planets. It describes a massive sphere of luminous gas and dust, material sloughed off an aging star. In the 1780s, William Herschel called these spherical clouds planetary nebulae because, through his early telescope, planetary nebulae looked round, like the planets in our solar system.

Astronomers already knew that 90% of all stars end their active lives as planetary nebulae. They were reasonably sure our sun would meet this fate. The key word here is visible. For years, scientists thought the sun has too low mass to create a visible planetary nebula.

Albert Zijlstra of the University of Manchester in England is a co-author of the study. He said in a statement:

When a star dies it ejects a mass of gas and dust – known as its envelope – into space. The envelope can be as much as half the star’s mass. This reveals the star’s core, which by this point in the star’s life is running out of fuel, eventually turning off and before finally dying.

It is only then the hot core makes the ejected envelope shine brightly for around 10,000 years – a brief period in astronomy. This is what makes the planetary nebula visible. Some are so bright that they can be seen from extremely large distances measuring tens of millions of light-years, where the star itself would have been much too faint to see.

The fate of our sun

Will that be the fate of our sun? Will it – at the end of its life – become briefly visible to alien astronomers on planets millions of light-years away? These astronomers say no. They say their models predict that our sun – though forming a planetary nebula at the end of its life – will remain faint.

Read more about this study from the University of Manchester

By the way … what happens next? Eventually, the planetary nebula will disperse and fade. With its thermonuclear fuel gone, the sun will no longer be able to shine. The immensely high pressures and temperatures in its interior will slacken. The sun will shrink down to become a dying ember of a star, known as a white dwarf, only a little larger than Earth.

Bottom line: A study suggests our sun is about the lowest mass star that – at the end of its life – produces a visible, though faint, planetary nebula. What that is … and more on the fate of our sun, here.

Source: The mysterious cut-off of the Planetary Nebula Luminosity Function

Via University of Manchester

The post When our sun dies, what will happen to Earth? 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.

Comet Halley farthest from the sun on Saturday

Comet Halley – the most famous of all comets – is coming to the end of the invisible tether binding it to our sun. This comet has been heading away from the sun since its last closest approach in 1986. Now it’s reaching the end of its outward journey, due to arrive at its farthest point from our sun on December 9, 2023. Afterwards, it’ll start making the trip back toward the sun, due to arrive in our vicinity by 2061.

Why is Comet Halley so famous? It was the first comet ever predicted to return. After observing a “hairy star” in 1682, English astronomer Edmond Halley looked at the historic record of such objects. He noted similarities in visits from objects in 1531, 1607 and 1682 and believed they were appearances of the same object. Then, he predicted that this “hairy star” would return in 1758.

And so it did, although Halley himself didn’t live to see it. But the comet now bears his name. Perhaps some of you have seen Comet Halley. The comet’s most recent close approach to the sun – called perihelion – was on February 9, 1986. Its next closest approach to the sun will be on July 28, 2061.

And that means means Comet Halley is now nearing its farthest from the sun – or aphelion – on December 9, 2023.

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Halley’s orbit

The relatively predictable and short orbit is what made Comet Halley famous. But – as with all things in nature – the orbit of Comet Halley isn’t precisely predictable. It varies slightly from 75 to 79 years. Still, it has a short-enough orbital period that it’s possible for someone to see it twice in their lifetime. Edmond Halley’s prediction of its return made this idea testable. It became a key to understanding what comets were.

Comet Halley is what we now call a short-period comet, or one that takes less than 200 years to orbit the sun. Long-period comets can take from 200 years up to millions of years to orbit the sun. In fact, it can take comets in the Oort Cloud as long as 30 million years to orbit the sun once.

The comet and 2 meteor showers

Clearly, aphelion – marking an object’s farthest point from the sun – isn’t a good time to observe Comet Halley. But if you don’t want to wait another 38 years to see at least bits of Comet Halley, I’ve got good news for you. We get to see parts of this comet every year in the form of meteors.

Comet Halley is the parent of two meteor showers. When comets orbit the sun, they leave bits of cometary dust behind. And for this comet, Earth’s orbit intersects two of these paths in one calendar year. The first is in May with the Eta Aquariid meteor shower. Then, in October, we intersect with another part of Halley’s path when we see the Orionid meteors.

Bottom line: Comet Halley reaches its farthest point in its orbit from the sun – called aphelion – on December 9, 2023. Afterwards, it’ll begin its return trip to the inner solar system, reaching its closest point to the sun on July 28, 2061.

The post Comet Halley to reach farthest point from sun on December 9 first appeared on EarthSky.

Toward the center of our Milky Way galaxy sits a dark cloud of gas and dust that astronomers say is behaving oddly. Astronomers call this region the Brick, because it’s a big block of dark material. Generally, great clouds of gas and dust like this one are actively forming stars from its raw materials. But the Brick has a surprisingly low rate of star formation. On December 4, 2023, the University of Florida said that the Brick’s inaction may be due to the large amount of frozen carbon monoxide they found there.

The international team of scientists published their peer-reviewed study in The Astrophysical Journal on December 4, 2023.

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More about the Brick

NASA describes the Brick like this:

One of the darkest infrared-dark clouds in our galaxy, this roughly brick-shaped cloud resides near the galaxy’s center, about 26,000 light-years from Earth. More than 100,000 times the mass of the sun, the Brick doesn’t seem to be forming any massive stars … yet. But it has so much mass in such a small area that if it does form stars, as scientists think that it should, it would be one of the most massive star clusters in our galaxy.

So, scientists have been puzzling over this cloud full of dense gas. It should be actively forming stars, but it’s not. Using the James Webb Space Telescope, a team of researchers, led by Adam Ginsburg of the University of Florida, peered into the Brick to find a large amount of carbon monoxide ice. While the researchers knew there was carbon monoxide ice in the cloud, they were surprised to see how much. Ginsburg said:

Our observations compellingly demonstrate that ice is very prevalent there, to the point that every observation in the future must take it into account.

Cold, but not cold enough

When you think of star formation, you probably think of heat, like a furnace turning on. And while that’s true, star formation begins in very cold conditions. Molecular clouds are extremely cold clumps of gas and dust just a bit above absolute zero. So, you’d think a large presence of frozen carbon monoxide would be a good thing to get star formation rolling in the Brick.

However, even with all the carbon monoxide ice, the Brick is still a bit warmer in temperature than other nearby nebulae. This result challenges what scientists know about gas clouds near the galactic center.

Previous observations were limited to seeing carbon monoxide as a gas, but the Webb telescope can see it in its solid, ice form. With a combination of the special filters on Webb and a little Photoshop to remove stars in the way, the researchers were able to get a better look at the Brick. As Ginsburg said:

We’re opening new paths to measure molecules in the solid phase (ice), while previously we were limited to looking at gas. This new view gives us a more complete look at where molecules exist and how they are transported.

More observations of the Milky Way’s center

Ginsburg and team are hoping to use Webb to take more observations of ices near the galactic center. They have more questions that will help them finally unravel the mystery of the Brick. Ginsburg said:

We don’t know, for example, the relative amounts of carbon monoxide, water, carbon dioxide and complex molecules. With spectroscopy, we can measure those and get some sense of how chemistry progresses over time in these clouds.

You can explore the Brick on your own with the visualization tool here.

Bottom line: There’s a dark region near the Milky Way’s center known as the Brick. This cold cloud of gas and dust should be forming stars, but, strangely, it’s not. The answer may lie in the abundance of carbon monoxide ice spotted there.

Source: JWST Reveals Widespread CO Ice and Gas Absorption in the Galactic Center Cloud G0.253+0.016

Via University of Florida

The post Dark cloud near Milky Way’s center is strangely quiet 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.