We await the data! Yesterday Cassini did its 118th flyby of Titan, getting close enough for two of its instruments to directly measure the planet’s upper atmosphere.
More here.
After more than a hundred flybys by Cassini of Titan scientists think they have located most of Titan’s mountains, including what they think will be its highest peak.
Cool image time! Using radar images taken during the past decade by Cassini scientists have discovered changes taking place along the shorelines of Titan’s hydrocarbon seas.
Analysis by Cassini scientists indicates that the bright features, informally known as the “magic island,” are a phenomenon that changes over time. They conclude that the brightening is due to either waves, solids at or beneath the surface or bubbles, with waves thought to be the most likely explanation. They think tides, sea level and seafloor changes are unlikely to be responsible for the brightening.
The images in the column at left show the same region of Ligeia Mare as seen by Cassini’s radar during flybys in (from top to bottom) 2007, 2013, 2014 and 2015.
These shoreline changes are not the only ones spotted by Cassini. However, because these are radar images, not visual, there are many uncertainties about what causes the changes, which is why they list several possibilities. For example, with radar, a simple roughness on the surface (such as waves) could cause a brightening.
The Cassini science team has released new maps of Titan, including new maps of both poles, assembled from images taken during the 100 flybys that the spacecraft has made of the moon since it arrived in orbit around Saturn.
The scale is rough, just less than a mile at best, and there is no topographic information because the thick atmosphere allows for no strong sunlight or shadows. The images show differences in surface brightness, which does tell us where Titan’s dark methane lakes are.
This is likely the best we will get of Titan for decades, until another spacecraft is sent there.
…watch a video of its descent.
The video is posted below the fold. This anniversary also celebrates the tenth anniversary of Cassini orbiting Saturn.
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Thar’s black gold up thar! Data from Cassini has confirmed the presence of ocean waves on Titan’s seas, while also providing suggesting that they are made mostly of liquid methane, not ethane as had been predicted.
The maximum depth of Kraken Mare appears to be 160 meters, and Ligeia Mare could be as much as 200 meters deep, reported Marco Mastrogiuseppe of Sapienza University of Rome. The fact that the radar signals could bounce off the sea bottom suggests that the seas were more transparent than expected and thus must contain mostly methane, not ethane. Hayes says his best estimate is about 90% methane. Essam Marouf, a planetary scientist at San José State University in California, reported on the first results from a separate radar experiment that sent radar reflections to Earth instead of back to the spacecraft. Those tests provide independent evidence that the seas are dominated by methane, Marouf says, and it implies that the lakes are kept filled by precipitating methane.
As the article also notes, this methane is “55 times Earth’s oil reserves.”
Cassini has captured a wonderful image of Titan’s polar lakes glinting from sunlight.
The uncertainty of science: New data from the ground-based telescope ALMA suggest that certain organic molecules in Titan’s atmosphere are not evenly distributed through the atmosphere as expected.
At the highest altitudes, the pockets of organic molecules were shifted away from the poles. These off-pole concentrations are unexpected because the fast-moving, east-west winds in Titan’s middle atmosphere should thoroughly mix the molecules formed there. The researchers do not have an obvious explanation for these findings yet.
I would not take these results too seriously, as the data are very sketchy. With better data many of these questions will vanish, replaced by new questions that are better based on reality.
Data from Cassini has found that the onset of winter in Titan’s southern hemisphere is coming on faster and colder than expected, with toxic clouds to boot.
The toxic cloud at the south pole is made up of hydrogen cyanide, and it could only form if the temperature there was colder than expected.
Cassini images taken in 2007, 2013, and 2014 of one of Titan’s largest hydrocarbon seas find that a mysterious feature there keeps appearing and disappearing.
The mysterious feature, which appears bright in radar images against the dark background of the liquid sea, was first spotted during Cassini’s July 2013 Titan flyby. Previous observations showed no sign of bright features in that part of Ligeia Mare. Scientists were perplexed to find the feature had vanished when they looked again, over several months, with low-resolution radar and Cassini’s infrared imager. This led some team members to suggest it might have been a transient feature. But during Cassini’s flyby on August 21, 2014, the feature was again visible, and its appearance had changed during the 11 months since it was last seen.
Scientists on the radar team are confident that the feature is not an artifact, or flaw, in their data, which would have been one of the simplest explanations. They also do not see evidence that its appearance results from evaporation in the sea, as the overall shoreline of Ligeia Mare has not changed noticeably. The team has suggested the feature could be surface waves, rising bubbles, floating solids, solids suspended just below the surface, or perhaps something more exotic.
That the seasons are slowly changing on Titan is probably contributing to the transient nature of this feature.
New Cassini images of Titan have spotted the appearance of clouds above the planet’s northern seas, suggesting the overdue onset of the summer storms that climate models have predicted.
For several years after Cassini’s 2004 arrival in the Saturn system, scientists frequently observed cloud activity near Titan’s south pole, which was experiencing late summer at the time. Clouds continued to be observed as spring came to Titan’s northern hemisphere. But since a huge storm swept across the icy moon’s low latitudes in late 2010, only a few small clouds have been observed anywhere on the icy moon. The lack of cloud activity has surprised researchers, as computer simulations of Titan’s atmospheric circulation predicted that clouds would increase in the north as summer approached, bringing increasingly warm temperatures to the atmosphere there.
“We’re eager to find out if the clouds’ appearance signals the beginning of summer weather patterns, or if it is an isolated occurrence,” said Elizabeth Turtle, a Cassini imaging team associate at the Johns Hopkins University Applied Physics Lab in Laurel, Maryland. “Also, how are the clouds related to the seas? Did Cassini just happen catch them over the seas, or do they form there preferentially?”
Any conclusions drawn at this time about the seasonal weather patterns of Titan must be considered highly uncertain, since we only have been observing the planet for a period that only covers one very short portion of its very long 30 year-long year.
The mysteries of science: Radar images of Titan taken in 2013 by Cassini show a twelve-mile patch appear in one of the moon’s methane lakes, then disappear.
They really don’t know what this patch is.
Prior to the July 2013 observation, that region of Ligeia Mare had been completely devoid of features, including waves. Titan’s seasons change on a longer time scale than Earth’s. The moon’s northern hemisphere is transitioning from spring to summer. The astronomers think the strange feature may result from changing seasons.
In light of the changes, Hofgartner and the other authors speculate on four reasons for this phenomenon:
- Northern hemisphere winds may be kicking up and forming waves on Ligeia Mare. The radar imaging system might see the waves as a kind of “ghost” island.
- Gases may push out from the sea floor of Ligeia Mare, rising to the surface as bubbles.
- Sunken solids formed by a wintry freeze could become buoyant with the onset of warmer temperatures during the late Titan spring.
- Ligeia Mare has suspended solids, which are neither sunken nor floating, but act like silt in a terrestrial delta.
“Likely, several different processes – such as wind, rain and tides – might affect the methane and ethane lakes on Titan,” [says Hofgarnter]
It is very important to remember that Titan is a very alien planet to the Earth. While some features, its methane lakes, have a superficial resemblance to lakes on Earth, the materials and environment are completely different. For example, on Earth the only thing that generally floats on water is ice, so that when winter arrives the surface freezes while the water below remains liquid. On Titan, if the methane freezes the ice will sink.
Using images from Cassini scientists think they have made their first detection of waves on a lake on Titan.
Using Cassini data scientists theorize that the lack of craters in the lowlands of Titan is because those lowlands were swamps that quickly erased the evidence.
A new image of Titan’s northern lakes.
Spring is moving to summer on Titan, and as the season changes scientists are expecting the number of storms in the northern latitudes to increase, thereby filling these lakes.
Why has Cassini detected no waves on the lakes of Titan?
Scientists have released the first topo map of Titan.
Whereas Earth’s tallest mountain towers nearly 9 kilometers above sea level, Titan’s topographic variations are mild: Its highest point is just half a kilometer above the mean and its lowest just 1.7 kilometers below.
Overall the detail here is not very great. None of the instruments on Cassini can see anything smaller than a half kilometer, about 1,500 feet, so the data doesn’t really show us the rough details. Moreover, the best data is spotty, as it has been accumulated by about a hundred Cassini fly-bys, rather than systematically by an orbiting spacecraft.
The seasons change on Titan as winter clouds begin to form over its south pole.
Scientists now think it is possible for there to be floating methane ice on the lakes of Titan.
Up to this point, Cassini scientists assumed that Titan lakes would not have floating ice, because solid methane is denser than liquid methane and would sink. But the new model considers the interaction between the lakes and the atmosphere, resulting in different mixtures of compositions, pockets of nitrogen gas, and changes in temperature. The result, scientists found, is that winter ice will float in Titan’s methane-and-ethane-rich lakes and seas if the temperature is below the freezing point of methane — minus 297 degrees Fahrenheit (90.4 kelvins). The scientists realized all the varieties of ice they considered would float if they were composed of at least 5 percent “air,” which is an average composition for young sea ice on Earth. (“Air” on Titan has significantly more nitrogen than Earth air and almost no oxygen.)
New data suggests that the icy crust of Titan is twice as thick as previously estimated.
“The picture of Titan that we get has an icy, rocky core with a radius of a little over 2,000 kilometers, an ocean somewhere in the range of 225 to 300 kilometers thick and an ice layer that is 200 kilometers thick,” [said Howard Zebker of Stanford University]. Previous models of Titan’s structure estimated the icy crust to be approximately 100 kilometers thick.
This means that the methane lakes and rivers of Titan are flowing across a bedrock of ice, which at the cold temperatures there would be as solid as rock is here on Earth.
How Huygens bounced on Titan. With animation.
Scientists are proposing that Europe send a probe to Titan and sail it on that planet’s methane lakes.
This concept had been proposed to NASA last year but it was rejected when the Obama administration shut down the planetary program.
Turn, turn, turn: Cassini has now seen the beginnings of a vortex over Titan’s south pole, the first sign that winter is coming to the planet’s southern hemisphere.
Data of the tidal fluxes on Titan by the Cassini spacecraft now suggest that there is a liquid ocean below Titan’s icy crust.
The team’s analyses suggest that the surface of the moon can rise and fall by up to 10 metres during each orbit, says Iess. That degree of warpage suggests that Titan’s interior is relatively deformable, the team reports today in Science1. Several models of the moon’s internal structure suggest such flexibility — including a model in which the moon is solid but soft and squishy throughout. But the researchers contend that the most likely model of Titan is one in which an icy shell dozens of kilometres thick floats atop a global ocean. The team’s findings, together with the results of previous studies, hint that Titan’s ocean may lie no more than 100 km below the moon’s surface.
Scientists have found that the structure of Titan’s atmosphere appears to change daily and seasonally, much like the Earth’s.
“The most interesting point is that their model shows the presence of two different boundaries, the lower one caused by the daily heating and cooling of the surface – and varying in height during the day – and the higher one caused by the seasonal change in global air circulation,” commented Paulo Penteado from the Institute of Astronomy, Geophysics and Atmospheric Science at the University of São Paulo in Brazil. According to [Benjamin Charnay from the French National Centre for Scientific Research (CNRS) in Paris], this link between the lower atmosphere’s layers and the moon’s daily and seasonal cycle has never been seen on another moon or planet besides the Earth.
One caveat: the results are based upon a computer climate model. Though this model was tweaked based on actual data, that data remains slim and incomplete.
