Tag: Saturn

Saturn as seen by Cassini in 2004, four months before orbital insertion

12:18 pm

Saturn as first seen up close by Cassini
Click for original.

Cool image time! As most of the new cool images coming down from space seem mostly limited to Mars and deep space astronomy, I decided today to dig into the archive of the probe Cassini, which orbited Saturn from July 1, 2004 until September 15, 2017, when it was sent plunging into the gas giant’s atmosphere.

The picture to the right heralded the start of that mission, in that it was taken on February 19, 2004, a little over four months before the spacecraft fired its engines and entered orbit. I have rotated the image and cropped it to post here.

When Cassini snapped this picture it was just approaching the gas giant. The image itself is relatively small, with the resolution also relatively poor. You can see one of Saturn’s moons above the planet, but I can’t tell you which one. As noted at the webpage, this is a raw image that has not been “validated or calibrated.”

While not up to the amazing standard exhibited by Cassini’s images during its thirteen year stay at Saturn, it gave us a flavor of the wonders to come. Of all the planets, Saturn might be the most beautiful.

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Inexplicable very large patterns found in Saturn’s upper atmosphere

9:40 am

Beads and arms in Saturn's upper atmosphere
Click for original image.

Using the Webb Space Telescope’s infrared capabilities, scientists have detected several different and inexplicable large atmospheric structures linked somehow to the gas giant’s north pole aurora.

The two images to the right, cropped, reduced, and annotated to post here, show both types of newly discovered features.

The international team of researchers, comprising 23 scientists from institutions across the UK, US and France, made the discoveries during a continuous 10-hour observation period on 29 November 2024, as Saturn rotated beneath JWST’s view. The team focused on detecting infrared emissions by a positively charged molecular form of hydrogen, H3+, which plays a key role in reactions in Saturn’s atmosphere and so can provide valuable insights into the chemical and physical processes at work. JWST’s Near Infrared Spectrograph allowed the team to simultaneously observe H₃⁺ ions from the ionosphere, 1,100 kilometres above Saturn’s nominal surface, and methane molecules in the underlying stratosphere, at an altitude of 600 kilometres.

In the electrically-charged plasma of the ionosphere, the team observed a series of dark, bead-like features embedded in bright auroral halos. [top picture] These structures remained stable over hours but appeared to drift slowly over longer periods.

Around 500 kilometres lower, in Saturn’s stratosphere, the team discovered an asymmetric star-shaped feature [bottom picture]. This unusual structure extended out from Saturn’s north pole towards the equator. Only four of the star’s six arms were visible, with two mysteriously missing, creating a lopsided pattern.

A more accurate word for the “beads” I think would be “patches”, as they are not small but major dark regions that appear to rotate with the planet, as do the arms. Both also seem to be related to each other as their rotations match, though one sits about 300 miles lower in the atmosphere. As noted in the press release, “the processes that are driving the patterns may influence a column stretching right through Saturn’s atmosphere.”

All guesses. All we have at this point is a truly intriguing observation.

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NASA inspector general: Dragonfly mission is vastly overbudget and behind schedule

9:24 am

Artist rendering of Dragonfly soaring over Titan's surface
Artist rendering of Dragonfly soaring
over Titan’s surface

According to a new NASA inspector general report issued today, NASA’s Dragonfly mission to Titan is now billions overbudget and is likely not be ready to launch in 2028.

You can download the report here [pdf]. From its executive summary:

Dragonfly was selected under a New Frontiers Announcement of Opportunity with a $850 million cost cap on Principal Investigator-Managed Mission Costs, which primarily includes development costs but excludes launch vehicle and post-launch operations costs. However, by April 2024, those costs had grown to $2.6 billion and the launch delayed by more than 2 years, from April 2026 to July 2028. The cost increase and schedule delay were largely the result of NASA directing APL to conduct four replans between June 2019 and July 2023 early in Dragonfly’s development. Justifications for these replans included the COVID-19 pandemic, supply chain issues, changes to accommodate a heavy-lift launch vehicle, projected funding challenges, and inflation.

The report now estimates the budget will eventually rise above $3 billion, cost that is eating away at NASA’s entire planetary budget, making other missions impossible. The project itself is far from ready, with multiple unfinished issues that make its present launch target of 2028 very unlikely.
» Read more

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Astronomers observe cloud changes above the northern polar lakes of Titan

10:15 am

Changes seen in Titan's atmosphere
Click for full resolution image.

Using data from both ground- and space-based telescopes, astronomers have now observed clouds rising in the thick atmosphere of the Saturn moon Titan.

The team observed Titan in November 2022 and July 2023 using both Keck Observatory and the James Webb Space Telescope. Those observations not only showed clouds in the mid and high northern latitudes on Titan — the hemisphere where it is currently summer — but also showed those clouds apparently rising to higher altitudes over time. While previous studies have observed cloud convection at southern latitudes, this is the first time evidence for such convection has been seen in the north. This is significant because most of Titan’s lakes and seas are located in its northern hemisphere and evaporation from lakes is a major potential methane source. Their total area is similar to that of the Great Lakes in North America.

The image to the right shows these methane clouds, indicated by the arrows, as seen by Webb on July 11, 2023 and then three days later by Keck. The clouds appear to have shifted downward during these observations.

The data suggests we are seeing one small aspect of Titan’s atmospheric methane cycle, where the liquid methane in the lakes evaporates to form clouds, which later than condense to rain back down. Though superficially similar to the water cycle here on Earth, the details suggest it will be very different on Titan.

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Astronomers discover 128 more moons around Saturn

9:01 am

Using a ground-based telescope, astronomers have now identified 128 new moons circling Saturn, bringing its moon count to 274, more than the total moons around all the other planets in the solar system combined.

Edward Ashton at Academia Sinica in Taipei, Taiwan, and his colleagues found the new moons with the Canada-France-Hawaii Telescope, revealing dozens that have previously evaded astronomers. They took hours of images of Saturn, adjusted them for the planet’s movement through the sky and stacked them on top of each other to reveal objects that would otherwise be too dim to see.

All the new moons are between 2 and 4 kilometres in diameter and are likely to have been formed hundreds of millions or even billions of years ago in collisions between larger moons, says Ashton.

That Saturn has so many moons should surprise no one. Saturn actually has possibly millions, maybe even billions, of moons, if you count every particle in its rings. In fact, the gas giant poses a problem for astronomers in defining what a moon actually is. How small must an object be before you stop calling it a moon?

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New computer simulations suggest Saturn’s rings are not young but formed at the same time as the solar system

9:12 am

A bright spot in Saturn's rings
Click for original source.

The uncertainty of science: Scientists doing computer simulations now posit that Saturn’s rings are not young, between 100 to 400 million years old as has been believed for the last few decades, but formed instead when Saturn formed, 4.6 billion years ago.

You can read their paper here [pdf].

The young age had been based on data from the Cassini orbiter, which showed the ring particles to be very bright and clean. If old those particles would have been darker as they accumulated dust over time on their surface. The new computer simulations suggest a process whereby those particles get “cleaned,” thus making it possible for the rings to be very old, possibly as old as Saturn itself.

Must I point out the uncertainties? The paper itself admits in its abstract “uncertainties in our models that assume no porosity, strength, or ring particle granularity.” Seems these assumptions make the conclusions very uncertain indeed.

Then again, the previous young estimates of the age of the rings had many similar assumptions and uncertainties. Essentially, we don’t have enough information to make any definitive determinations.

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SpaceX wins launch contract for Dragonfly mission to Titan

8:58 am

NASA yesterday announced that it has awarded the launch contract for sending its Dragonfly mission to Titan to SpaceX’s Falcon Heavy rocket.

The firm-fixed-price contract has a value of approximately $256.6 million, which includes launch services and other mission related costs. The Dragonfly mission currently has a targeted launch period from July 5, 2028, to July 25, 2028, on a SpaceX Falcon Heavy rocket from Launch Complex 39A at NASA’s Kennedy Space Center in Florida.

Dragonfly is a truly cutting edge mission. Though we have relatively limited information about Titan’s atmosphere and the environment on its surface, it will attempt to fly there like a helicopter, landing and taking off multiple times.

And though there are certainly additional costs required for such a mission, that quarter-billion dollar contract price probably triples what it normally costs SpaceX for a Falcon Heavy mission. Even if it requires the expending of all three first stages, the company is almost certainly getting a big windfall from this deal.

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NASA approves Dragonfly mission to the Saturn moon Titan

9:50 am

NASA yesterday announced that it has given final approval for the Dragonfly helicopter mission to the Saturn moon Titan.

With the release of the president’s fiscal year 2025 budget request, Dragonfly is confirmed with a total lifecycle cost of $3.35 billion and a launch date of July 2028. This reflects a cost increase of about two times the proposed cost and a delay of more than two years from when the mission was originally selected in 2019. Following that selection, NASA had to direct the project to replan multiple times due to funding constraints in fiscal years 2020 through 2022. The project incurred additional costs due to the COVID-19 pandemic, supply chain increases, and the results of an in-depth design iteration. To compensate for the delayed arrival at Titan, NASA also provided additional funding for a heavy-lift launch vehicle to shorten the mission’s cruise phase.

The rotorcraft, targeted to arrive at Titan in 2034, will fly to dozens of promising locations on the moon, looking for prebiotic chemical processes common on both Titan and the early Earth before life developed. Dragonfly marks the first time NASA will fly a vehicle for science on another planetary body. The rotorcraft has eight rotors and flies like a large drone.

Be prepared for the project to go overbudget, as NASA’s biggests projects almost always do.

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Scientists: We think the Saturn moon Mimas may have a young underground ocean

8:45 am

The uncertainty of science: Using computer modeling based on orbital data obtained from the orbiter Cassini, scientist now believe the Saturn moon Mimas may have a young underground ocean.

[I]n 2014, a team that included Lainey and that was led by Radwan Tajeddine, an astronomer then at the Paris Observatory, analysed images taken by NASA’s Cassini spacecraft, which explored Saturn and its moons between 2004 and 2017. By studying how the 400-kilometre-wide Mimas wobbled in its orbit around Saturn, the researchers concluded that it had either a buried ocean or a rugby-ball-shaped core. As more scientists studied how an ocean could have formed and evolved, it became harder to explain the geology of Mimas without invoking an ocean.

In the 2024 study, Lainey and his colleagues seem to have nailed the case. They went further than they had in 2014, by analysing not just the orbit’s wobble but also how Mimas’s rotation around Saturn changed over time. The team combined Cassini observations with simulations of Mimas’s interior and its orbit to conclude that there must be an ocean 20–30 kilometres below Mimas’s surface.

The journal Nature published the paper, and the link above goes to an article in Nature describing the results, with a headline “The Solar System has a new ocean — it’s buried in a small Saturn moon.” This is very poor journalism, but very typical these days from Nature. Nowadays that journal routinely pushes the results it publishes with great certainty, even if the data is quite uncertain.

And these results are quite uncertain. They are based on computer simulations using orbital data only. No data from Mimas itself is involved. While that orbital data and computer models might suggest an underground ocean that is very young, that is the best it does, “suggest.” Without question this conclusion is very intriguing, but it should not be treated as a discovery, only a theory that still needs confirmation with much better data.

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New Hubble image of Saturn

10:04 am

Saturn and its rings, as seen by Hubble

The annotated image above was taken by the Hubble Space Telescope on October 22, 2023, showing Saturn, its glorious rings, and several of its dozens of moons from a distance of about 850 million miles. For the unannotated version, go here. Of all the features, the spokes in the rings are the most intriguing.

Saturn’s spokes are transient features that rotate along with the rings. Their ghostly appearance only persists for two or three rotations around Saturn. During active periods, freshly-formed spokes continuously add to the pattern. In 1981, NASA’s Voyager 2 first photographed the ring spokes. Hubble continues observing Saturn annually as the spokes come and go. This cycle has been captured by Hubble’s Outer Planets Atmospheres Legacy (OPAL) program that began nearly a decade ago to annually monitor weather changes on all four gas-giant outer planets.

Hubble’s crisp images show that the frequency of spoke apparitions is seasonally driven, first appearing in OPAL data in 2021 but only on the morning (left) side of the rings. Long-term monitoring shows that both the number and contrast of the spokes vary with Saturn’s seasons. Saturn is tilted on its axis like Earth and has seasons lasting approximately seven years.

This year, these ephemeral structures appear on both sides of the planet simultaneously as they spin around the giant world. Although they look small compared with Saturn, their length and width can stretch longer than Earth’s diameter!

Though the origin of the spokes remains unsolved, the leading theory proposes they are caused by interactions between Saturn’s magnetic field and the seasonal changes in solar radiation.

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Close-up of Helene, one of Saturn’s many many moons

2:04 pm

Helene, as seen by Cassini in 2011
Helene, as seen by Cassini in 2011

Cool image time! Though the Saturn orbiter Cassini is long gone, having been sent into Saturn’s atmosphere to burn up in 2017, its image archive of magnificent pictures is still available to peruse. To encourage others to do so, NASA today issued a series of press releases, listing the spacecraft’s top ten pictures from 2011, 2012, 2013, 2014, and 2015.

The picture to the right, cropped, reduced, and sharpened to post here, comes from the 2011 collection and was taken on June 18, 2011. It shows a close-up of 21-mile-wide Helene, one of Saturn’s many many moons and only discovered in 1980. Back in 2010 I featured another Cassini image of Helene, but that picture did not reveal the small surface features seen in the photo to the right.

The light and dark streaks probably indicate dust flowing downhill on the surface. Though the gravity of this object is tiny, it will be enough for dust to act like almost like a liquid, flowing down grade and then pooling in the central pond at the lowest point near the center of the picture. That process is so much like liquid flowing that it appears to have even eroded gullies on slopes near the top and bottom of the picture.

Side note: NASA’s “Science Editorial Team” also issued a press release today that falsely and ignorantly claimed these releases were “to celebrate 10 years since arriving at Saurn,” implying that Cassini arrived in 2013 and is still functioning.

The problem is that Cassini arrived in orbit around Saturn in 2004 and as I noted above ended its mission in 2017. It thus appears that the NASA Science Editorial Team is unable to do even one five-second web search to find out what really happened.

Just another data point indicating the dark age we now live in.

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Webb takes an infared look at Saturn

10:36 am

Webb's five images of Saturn
Webb’s five images of Saturn. Click for original.

Using the Webb Space Telescope, scientists have obtained five infrared images of Saturn to get a more detailed look at the gas giant’s atmosphere and the molecules within it.

The image to the right is Figure 1 from the paper, showing the location of those five images on Saturn, placed over a much higher resolution Hubble Space Telescope optical image. The graph on the bottom shows the molecules revealed from spectroscopic data obtained by Webb’s infrared view. From the abstract:

We show evidence that a stratospheric circulation pattern detected by Cassini during northern winter has now fully reversed in northern summer, with the low-latitude stratosphere being cool and depleted in aerosols due to summertime upwelling. MIRI [Webb’s mid-infrared instrument] provides access to spectral regions that were not possible with the Cassini spacecraft, particularly in the 5–7 μm region where reflected sunlight and thermal emission blend together. Ammonia and phosphine are enriched at Saturn’s equator, suggesting strong mixing from the deeper troposphere. MIRI’s high sensitivity enables the first identification of previously unseen emission propane bands, along with the first measurements of the distribution of several gaseous species: tropospheric water, and stratospheric ethylene, benzene, methyl, and carbon dioxide.

The paper notes that this work still has uncertainty because when the infrared images were taken engineers were still working out the kinks for using Webb. Nonetheless, the results illustrate the large potential for future planetary discoveries from Webb.

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Scientists: Saturn has rainstorms of ammonia lasting hundreds of years

11:31 am

Using radio telescope data of Saturn scientists now believe that the big storm first detected in 2011 produced rainstorms of ammonia which are expected to last hundreds of years.

As reported in the new study, de Pater, Li and UC Berkeley graduate student Chris Moeckel found something surprising in the radio emissions from the planet: anomalies in the concentration of ammonia gas in the atmosphere, which they connected to the past occurrences of megastorms in the planet’s northern hemisphere.

According to the team, the concentration of ammonia is lower at midaltitudes, just below the uppermost ammonia-ice cloud layer, but has become enriched at lower altitudes, 100 to 200 kilometers deeper in the atmosphere. They believe that the ammonia is being transported from the upper to the lower atmosphere via the processes of precipitation and reevaporation. What’s more, that effect can last for hundreds of years. [emphasis mine]

In other words, Saturn has an ammonia cycle similar to the water cycle on Earth.

Need I add that this study carries great uncertainties, and that the amount of data about Saturn’s interior and atmosphere is sparse, at best?

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Webb takes infrared (heat) image of Saturn

8:41 am

Saturn in infrared
Click for original image.

Using the Webb Space Telescope, scientists on June 25, 2023 took the wonderful false color infrared (heat) image of Saturn above, cropped to post here, as part of a research project [pdf] to take a number of long exposures of the ringed planet in order to test Webb’s ability to see its small moons. From the press release:

Saturn itself appears extremely dark at this infrared wavelength observed by the telescope, as methane gas absorbs almost all of the sunlight falling on the atmosphere. However, the icy rings stay relatively bright, leading to the unusual appearance of Saturn in the Webb image.

…This new image of Saturn clearly shows details within the planet’s ring system, along with several of the planet’s moons – Dione, Enceladus, and Tethys. Additional deeper exposures (not shown here) will allow the team to probe some of the planet’s fainter rings, not visible in this image, including the thin G ring and the diffuse E ring. Saturn’s rings are made up of an array of rocky and icy fragments – the particles range in size from smaller than a grain of sand to a few as large as mountains on Earth.

The picture also shows differences between Saturn’s northern and southern hemispheres, caused by the seasonal differences between the two.

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Scientists detect evidence of phosphorus coming from the interior of Enceladus

9:13 am

Using archival data from the Cassini orbiter, scientists have now detected the first evidence of phosphorus – a key element in the development of life on Earth – coming from the interior of the Saturn moon Enceladus.

The small moon is known to possess a subsurface ocean, and water from that ocean erupts through cracks in Enceladus’ icy crust as geysers at its south pole, creating a plume. The plume then feeds Saturn’s E ring (a faint ring outside of the brighter main rings) with icy particles.

During its mission at the gas giant from 2004 to 2017, Cassini flew through the plume and E ring numerous times. Scientists found that Enceladus’ ice grains contain a rich array of minerals and organic compounds – including the ingredients for amino acids – associated with life as we know it.

Phosphorus, the least abundant of the essential elements necessary for biological processes, hadn’t been detected until now. The element is a building block for DNA, which forms chromosomes and carries genetic information, and is present in the bones of mammals, cell membranes, and ocean-dwelling plankton. Phosphorus is also a fundamental part of energy-carrying molecules present in all life on Earth. Life wouldn’t be possible without it.

“We previously found that Enceladus’ ocean is rich in a variety of organic compounds,” said Frank Postberg, a planetary scientist at Freie Universität Berlin, Germany, who led the new study, published on Wednesday, June 14, in the journal Nature. “But now, this new result reveals the clear chemical signature of substantial amounts of phosphorus salts inside icy particles ejected into space by the small moon’s plume. It’s the first time this essential element has been discovered in an ocean beyond Earth.”

You can read the paper here. It is very important to emphasize that though phosphorus is essential for life, life in the underground ocean of Enceladus has not been discovered. The scientists have merely found evidence of this specific ingredient needed for life, suggesting that these ingredients are common in our solar system. Going from a list of ingredients to a finished dish one can eat is something else entirely.

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Webb detects large water plume released from Saturn’s moon Enceladus

9:10 am

Water vapor plume seen by Webb
Click for original image.

Using the infrared cameras on the Webb Space Telescope, astronomers have detected a surprisingly long and large plume of water vapor erupting from the tiger stripe fractures on Saturn’s moon Enceladus that scientists for years have detected vapor plumes.

The false color image to the right shows that plume.

A water vapor plume from Saturn’s moon Enceladus spanning more than 6,000 miles – nearly the distance from Los Angeles, California to Buenos Aires, Argentina – has been detected by researchers using NASA’s James Webb Space Telescope. Not only is this the first time such a water emission has been seen over such an expansive distance, but Webb is also giving scientists a direct look, for the first time, at how this emission feeds the water supply for the entire system of Saturn and its rings.

…The length of the plume was not the only characteristic that intrigued researchers. The rate at which the water vapor is gushing out, about 79 gallons per second, is also particularly impressive. At this rate, you could fill an Olympic-sized swimming pool in just a couple of hours. In comparison, doing so with a garden hose on Earth would take more than 2 weeks.

Though that rate of release sounds large, we must remember it is being released from a moon 313 miles across. From that perspective the rate of flow is quite reasonable.

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Another study suggests Saturn’s rings are young, much younger than the planet

5:59 pm

Scientists using data from Cassini, which orbited Saturn from 2004 to 2017, have confirmed earlier research that said Saturn’s rings are much younger than the planet, only about 400 million years old.

From 2004 to 2017, the team used an instrument called the Cosmic Dust Analyzer aboard NASA’s late Cassini spacecraft to analyze specks of dust flying around Saturn. Over those 13 years, the researchers collected just 163 grains that had originated from beyond the planet’s close neighborhood. But it was enough. Based on their calculations, Saturn’s rings have likely been gathering dust for only a few hundred million years.

Though I cannot cite the earlier research, I distinctly remember a study from about a decade ago that posited the rings being young, only a few hundred million years old. This research confirms this conclusion, and likely firms up the theory considerably.

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Saturn now has 145 known moons

3:41 pm

Using ground-based images analyzed in a new way, astronomers have discovered an additional 62 small moons orbiting Saturn, giving the ringed gas giant a total of 145 known moons.

The data used by the team was collected between 2019 and 2021 in three-hour spans by the Canada-France-Hawaii Telescope (CFHT) on top of Maunakea in Hawaii. It allowed the astronomers to detect moons around Saturn as small as 1.6 miles (2.5 kilometers) in diameter. That’s about two-thirds the length of Hollywood’s Walk of Fame.

Though some of the moons had been spotted as early as 2019, it takes more than sighting an object close to a planet to confirm it is a moon and not an asteroid making a brief close passage to that planet. To change these objects from “suspected moons” to “confirmed moons” of Saturn, the astronomers had to track them for several years to ensure each is actually orbiting the gas giant.

Performing a painstaking process of matching objects detected on different nights over the course of 24 months, the team tracked 63 objects that they ended up confirming as moons. One of these satellites was revealed back in 2021, with the remaining 62 moons gradually announced over the past few weeks.

To a certain extent, this declared number of moons around Saturn is utterly irrelevant. Think about it. Every single object in its rings should be defined as a moon, totaling hundreds of thousands. At some point the question of what defines a moon becomes the relevant question.

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Webb and Keck telescopes track clouds on Titan

11:08 am

Clouds on Titan
Click for original image.

Astronomers have used the Webb Space Telescope and the Keck Observatory in Hawaii to take infrared images days apart of the evolving clouds on the Saturn moon Titan.

The false-color infrared images to the right are those observations. From the press release:

As part of their investigation of Titan’s atmosphere and climate, Nixon’s team used JWST’s Near-Infrared Camera (NIRCam) to observe the moon during the first week of November. After seeing the clouds near Kraken Mare, the largest known liquid sea of methane on the surface of Titan, they immediately contacted the Keck Titan Observing Team to request follow-up observations.

“We were concerned that the clouds would be gone when we looked at Titan a day later with Keck, but to our delight there were clouds at the same positions on subsequent observing nights, looking like they had changed in shape,” said Imke de Pater, emeritus professor of astronomy at the University of California, Berkeley, who leads the Keck Titan Observing Team.

Using Keck Observatory’s second generation Near-Infrared Camera (NIRC2) in combination with the Keck II Telescope’s adaptive optics system, de Pater and her team observed one of Titan’s clouds rotating into and another cloud either dissipating or moving out of Earth’s field of view due to Titan’s rotation.

These images only increase my mourning for a Saturn orbiter. Since the end of Cassini’s mission in 2017, we have essentially been blind to the ringed planet and its many moons. These images, while producing excellent data, also illustrate well what we have lost.

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New theory: Saturn’s rings came from a lost and destroyed moon

9:24 am

The uncertainty of science: According to a new computer simulation, scientists have proposed that the reason Saturn’s rings are tilted 27 degrees is because they were created by the destruction of a moon 160 million years ago, an event that was also linked to the way the orbits of Saturn and Neptune interact, combined with the on-going slow evolutionary changes in Titan’s orbit around Saturn.

Wisdom and his colleagues believe Saturn acquired its tilt because of a peculiar synchronicity: the precession of Saturn’s spin axis—the way it wobbles like a top with a particular rhythm—is suspiciously in tune with a precession in Neptune’s orbit. If Saturn and Neptune were trapped in this resonance, Saturn’s tilt would be “kind of vulnerable to other forces that could cause it to change,” says Rola Dbouk, an MIT graduate student in planetary science. In 2020, Cassini scientists discovered what the study team thinks is that external stimulus: Titan, Saturn’s largest moon, is migrating away from Saturn by 11 centimeters a year. In a study published today in Science, Dbouk, Wisdom, and colleagues show how Titan’s migration, in combination with the Saturn-Neptune resonance, could have ratcheted up Saturn’s tilt over the course of 1 billion years.

The work also yielded a potential explanation for the origin of Saturn’s rings. Using Cassini’s measurements of Saturn’s gravitational fields to model the planet’s interior structure, the researchers refined calculations for the wobble of Saturn’s spin axis and found it is no longer in sync with Neptune. “Something kicked it out of the resonance,” Dbouk says. They first ruled out the possibility that chaotic changes in the orbits of some of the largest of Saturn’s dozens of moons could be responsible. But when they added another moon to the mix, things got interesting.

In simulations, the researchers included an object about the size of Iapetus, Saturn’s third largest moon, orbiting about 43 Saturn radii out—between the orbits of Titan and Iapetus. They found this moon could have provided the necessary nudge to the resonance if it were suddenly knocked from its orbit because of chaotic interactions with its neighbors about 160 million years ago.

To say that this theory is uncertain is no different that saying the sky is blue. It is so uncertain that it is difficult to take it seriously. It could be right, but as one scientist quoted at the article noted, there is no way to test it.

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Hubble’s 2021 survey of the outer solar system

2:18 pm

Jupiter in 2021 by Hubble
Click for full Jupiter image.

Saturn in 2021 by Hubble
Click for full Saturn image.

Uranus in 2021 by Hubble
Click for full Uranus image.

Neptune in 2021 by Hubble
Click for full Neptune image.

NASA today released the annual survey of images taken each year by the Hubble Space Telescope of the large planets that comprise the outer solar system, Jupiter, Saturn, Uranus, and Neptune.

These Hubble images are part of yearly maps of each planet taken as part of the Outer Planets Atmospheres Legacy program, or OPAL. The program provides annual, global views of the outer planets to look for changes in their storms, winds, and clouds. Hubble’s longevity, and unique vantage point, has given astronomers a unique chance to check in on the outer planets on a yearly basis. Knowledge from the OPAL program can also be extended far beyond our own solar system in the study of atmospheres of planets that orbit stars other than our Sun.

The four photos, all either cropped or reduced slightly to post here, are to the right. Each shows some changes in these planets since the previous survey images the year before.

On Jupiter for example the equatorial region shows several new storms, with that band remaining a deep orange color longer than expected.

On Saturn the various bands have continued to show the frequent and extreme color changes that the telescope has detected since it began these survey images back in the 1990s.

The photo of Uranus meanwhile looks at the gas giant’s northern polar regions, where it is presently spring. The increased sunlight and ultraviolet radiation has thus caused the upper atmosphere at the pole to brighten. The photo also confirms that the size of this bright “polar hood” continues to remain the same, never extending beyond the 43 degree latitude where scientists suspect a jet streams acts to constrain it.

The image of Neptune, the farthest and thus hardest planet for Hubble to see, found that the dark spot in the planet’s northern hemisphere appears to have stopped moving south and now appears to be heading north. Also,

In 2021, there are few bright clouds on Neptune, and its distinct blue with a singular large dark spot is very reminiscent of what Voyager 2 saw in 1989.

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Saturn’s core is a slushy mix of rocks and liquid

9:31 am

Saturn's rings
Click for more information.

Using archival data from the Cassini orbiter that mapped ripples in the rings of Saturn, scientists have produced a model of Saturn’s core that suggests it is a slushy soup that as it sloshes about shifts the gas giant’s gravitational field.

By using the famous rings like a seismograph, scientists studied processes in the planet’s interior and determined that its core must be “fuzzy.” Instead of a solid sphere like Earth’s, the core of Saturn appears to consist of a ‘soup’ of rocks, ice and metallic fluids that slosh around and affect the planet’s gravity.

…Not only does the planet’s core seem sludgy, it also appears to extend across 60% of the planet’s diameter, making it much larger than previously estimated. The analysis showed that Saturn’s core might be about 55 times as massive as the entire planet Earth. Of the total mass of the core, 17 Earth masses are made of ice and rock, with the rest consisting of a hydrogen and helium-based fluid, the study suggests.

The image above was taken in 2017, and shows both a density wave in the rings (the parallel lines in the center) caused by a Saturn moon, and numerous “propellers”, small distortions in the rings caused by slightly larger objects.

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The changing seasons of Saturn

1:58 pm

Saturn changing
Click for full image.

Images of Saturn taken by the Hubble Space Telescope since 2018 now reveal the slow seasonal changes to the gas giant’s atmosphere during its lengthy year, twenty-nine Earth years long.

The Hubble data show that from 2018 to 2020 the equator got 5 to 10 percent brighter, and the winds changed slightly. In 2018, winds measured near the equator were about 1,000 miles per hour (roughly 1,600 kilometers per hour), higher than those measured by NASA’s Cassini spacecraft during 2004-2009, when they were about 800 miles per hour (roughly 1,300 kilometers per hour). In 2019 and 2020 they decreased back to the Cassini speeds. Saturn’s winds also vary with altitude, so the change in measured speeds could possibly mean the clouds in 2018 were around 37 miles (about 60 kilometers) deeper than those measured during the Cassini mission. Further observations are needed to tell which is happening.

The photo above shows Saturn’s northern hemisphere in 2018, 2019, and 2020. Note how the darker region at the pole grows with time.

This data supplements the data obtained by Cassini when it was in orbit around Saturn, and is presently the best information we can get since the Cassini mission ended.

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Hydrazine on the surface of Saturn’s moon Rhea?

12:27 pm

The uncertainty of science: Scientists using data from several Cassini flyby’s of the Saturn moon Rhea now think that hydrazine, a very toxic chemical routinely used by spacecraft as fuel, might exist on its surface.

Their effort was an attempt to identify an unknown spectroscopy absorption feature at a specific wavelength.

In comparison to chloromethane, the production of hydrazine monohydrate was easier to explain due to chemical reactions involving water-ice and ammonia or delivery from Titan’s nitrogen rich atmosphere. Elowitz et al. considered the possibility of contamination of the UVIS data by a hydrazine propellant from the Cassini spacecraft, although it was highly unlikely since the hydrazine thrusters were not used during icy satellite flybys.

The team confirmed the specific signature of a 184-nm feature on Rhea’s surface using the UV spectrometer observations made by the Cassini spacecraft. In addition to that, the irradiation of ammonia by charged particles from Saturn’s magnetosphere induced the dissociation of ammonia molecules to form diazene and hydrazine. The source of ammonia on Rhea could be primordial, incorporated into its interior during formation and brought to the surface within a period of endogenic activity, as evident in Cassini ISS imagery, although ammonia was unlikely to survive indefinitely on the surface. The team suggest further analysis to understand the potential for satellite-to-satellite transfer of materials across Titan’s atmosphere to explain the presence of hydrazine monohydrate on Rhea.

Though useful as a fuel, its poisonous nature will make any exploration of these moons very hazardous, and will also likely make its usefulness difficult initially in that exploration

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The seas of Titan, deep and alien

11:29 am

Radar track through the estuaries of Titan's large sea, Kraken Mare

The uncertainty of science: In a new paper scientists have taken the radar data from the more than 120 fly-bys by Cassini of Titan to map out the estimated depths for several of Titan’s seas, using that data to also better constrain the make-up of those seas. From their abstract:

Our analysis reveals that the seafloor at the center of Moray Sinus—an estuary located at the northern end of Kraken Mare, is up to 85 m deep. The radar waves are absorbed to an extent such that the liquid composition is compatible with 70% methane, 16% nitrogen, and 14% ethane (assuming ideal mixing). The analysis of the altimetry data in the main body of Kraken Mare showed no evidence for signal returns from the sea floor, suggesting the liquid is either too deep or too absorptive for Cassini’s radio waves to penetrate. However, if the liquid in the main body of Kraken Mare is similar in composition to Moray Sinus, as one would expect, then its depth exceeds 100 m.

The image above, cropped and reduced to post here, is figure two from the paper. » Read more

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The conjunction of Jupiter and Saturn, as seen from the Moon

9:21 am

Jupiter and Saturn as seen by LRO
Click for full image.

With Jupiter and Saturn closer to each other in the sky than they have been in about 800 years, the science team for Lunar Reconnaissance Orbiter (LRO) decided to aim that lunar orbiter at the two gas giants to get a picture.

The photo to the right, cropped and expanded to post here, was also enhanced by the science team to brighten Saturn so that it would match Jupiter. As they note at the link,

[LRO] captured this view just a few hours after the point of closest separation (0.1°) between the two giant planets. With the sharp focus of the NAC [camera], you can see that the two planets are actually separated by about 10 Jupiter diameters

Both planets however look fuzzy in the image, probably because the camera was not designed to obtain sharp images from this distance. Nonetheless, this is a very cool photo.

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The liquids in Titan’s lakes stratify into different density layers

9:50 am

Using the data archive from the Cassini mission to Saturn, scientists now think that the liquids in Titan’s lakes can stratify into different density layers.

Lakes on Saturn’s moon Titan, composed of methane, ethane, and nitrogen rather than water, experience density driven stratification, forming layers similar to lakes on Earth. However, whereas lakes on Earth stratify in response to temperature, Titan’s lakes stratify solely due to the strange chemical interactions between its surface liquids and atmosphere, says a paper by Planetary Science Institute Research Scientist Jordan Steckloff.

Stratification occurs when different parts of a lake have different densities, with the less dense layer floating atop the denser layer. On Earth, lakes in temperate climates often stratify into layers in the summer as the Sun heats the surface of the lake, causing this water to expand and become less dense, forming a layer of warm water that literally floats upon the cooler water below. This density-driven stratification can occur on Titan as well; however it happens due to the amount of atmospheric nitrogen that Titan’s surface liquids can dissolve, rather than the liquids warming up and expanding.

…Because liquid methane is less dense than liquid ethane, it has been long assumed that Titan’s methane would generally float atop its liquid ethane. However, when methane’s affinity for atmospheric nitrogen is accounted for, methane can dissolve sufficient nitrogen at low temperatures to become denser than ethane.

This result has a great deal of uncertainty, mostly because of the relatively small dataset available of Titan. What it really shows is the possibility of this phenomenon. To confirm it will require some in situ measurements.

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A hint of unexpected fresh ice on Enceladus

11:53 am

Two views of Enceladus
Click for full image.

Using data collected by Cassini while it orbited Saturn for thirteen years, scientists have found that there might be more relatively fresh ice on the surface of the moon Enceladus than previously believed.

Cassini scientists discovered in 2005 that Enceladus – which looks like a highly reflective, bright white snowball to the naked eye – shoots out enormous plumes of ice grains and vapor from an ocean that lies under the icy crust. The new spectral map shows that infrared signals clearly correlate with that geologic activity, which is easily seen at the south pole. That’s where the so-called “tiger stripe” gashes blast ice and vapor from the interior ocean.

But some of the same infrared features also appear in the northern hemisphere. That tells scientists not only that the northern area is covered with fresh ice but that the same kind of geologic activity – a resurfacing of the landscape – has occurred in both hemispheres. The resurfacing in the north may be due either to icy jets or to a more gradual movement of ice through fractures in the crust, from the subsurface ocean to the surface.

The image above, cropped, reduced, and rearranged to post here, shows two views of Enceladus. On the left we are looking at one hemisphere, with the south pole at the bottom. On the right we are looking straight down at the south pole. The red areas are where scientists think there is relatively fresh ice. While the new ice is very pronounced at the south pole, where the tiger-striped vents have been found, the northern ice is much less evident, though clearly there.

That northern fresh ice however might not come from the planet’s interior, as suggested by the press release. It might also be new ice deposited from space that came from those very active tiger stripes. At the present time the data doesn’t allow for any solid conclusions.

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A July 4th Hubble image of Saturn

10:27 am

Saturn as seen by Hubble on July 4, 2020
Click for full image, annotated.

Cool image time! The photo to the right, cropped and reduced to post here, was taken by the Hubble Space Telescope on July 4, 2020, and shows Saturn, its rings, plus several moons, in all their glory.

The dot near the bottom center is Enceladus. The dot at center right is Mimas. If you click on the annotated full image it will show the locations of several other smaller moons much harder to see.

This new Saturn image was taken during summer in the planet’s northern hemisphere.

Hubble found a number of small atmospheric storms. These are transient features that appear to come and go with each yearly Hubble observation. The banding in the northern hemisphere remains pronounced as seen in Hubble’s 2019 observations, with several bands slightly changing color from year to year. The ringed planet’s atmosphere is mostly hydrogen and helium with traces of ammonia, methane, water vapor, and hydrocarbons that give it a yellowish-brown color.

Hubble photographed a slight reddish haze over the northern hemisphere in this color composite. This may be due to heating from increased sunlight, which could either change the atmospheric circulation or perhaps remove ices from aerosols in the atmosphere. Another theory is that the increased sunlight in the summer months is changing the amounts of photochemical haze produced.

The distance across from one end of the rings to the other is about 150,000 miles, about two thirds the distance from the Earth to the Moon.

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First global geologic map of Titan

11:43 am

Global geologic map of Titan
Click for full image.

Planetary scientists today released the first global geologic map of the Saturn moon Titan. The image on the right is a reduced version of the full image.

In the annotated figure, the map is labeled with several of the named surface features. Also located is the landing site of the European Space Agency’s (ESA) Huygens Probe, part of NASA’s Cassini mission.

The map legend colors represent the broad types of geologic units found on Titan: plains (broad, relatively flat regions), labyrinth (tectonically disrupted regions often containing fluvial channels), hummocky (hilly, with some mountains), dunes (mostly linear dunes, produced by winds in Titan’s atmosphere), craters (formed by impacts) and lakes (regions now or previously filled with liquid methane or ethane).

To put it mildly, there is a lot of uncertainty here. Nonetheless, this is a first attempt, and it shows us that the distribution of these features is not homogeneous. The dunes favor the equatorial regions, the lakes the polar regions. Also, the small number of craters could be a feature of erosion processes from the planet’s active atmosphere, or simply be because Cassini’s radar data did not have the resolution to see smaller craters. I suspect the former.

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