Today’s digital palette cleanser is bought to you courtesy of Cassini and a small icy moon filled with intrigue.
As we constantly check the news sites for updates on the minutia of our daily lives, refresh our social media feeds, and ponder the existential dread that seems to be flooding our immediate future with increasing volume, it’s nice to find little islands of tranquility that appear out of nowhere. Today, I found that island in a beautiful processed image of Saturn’s moon Enceladus by the incredibly talented Kevin Gill, who works at NASA’s Jet Propulsion Laboratory:
[NASA/JPL-Caltech/SSI/CICLOPS/Kevin M. Gill]
In his tweet, Kevin simply describes this view as “solitude” and that’s pretty damn near perfect. In this image, the beautifully back-lit plumes are visible with the tenuous E-ring of Saturn creating an atmospheric backdrop.
Enceladus is a fascinating moon. During the NASA Cassini mission, which ended its glorious 13-year reign in Saturn orbit in 2017, the spacecraft became intimately familiar with the icy moon and its famous geysers. After flying through the plumes of water vapor, it became clear to mission scientists that not only does this 313 mile wide icy marble have an extensive subsurface liquid water ocean, that ocean contains organic molecules that could hint at astrobiological possibilities.
It’s sometimes nice to escape to Saturn orbit every now and again, so be sure to check out Kevin’s awe-inspiring Flickr album for more.
InSight’s recording of Martian winds isn’t what you’d hear if you were on the planet yourself
Artist’s impression of the European Huygens lander that descended through Titan’s atmosphere and landed on the Saturn moon’s surface [ESA]
We live in a world where spacecraft are now routinely landing on other worlds and recording their sounds. Soviet probes aimed at Venus captured the thunder and howling winds on the volcanic world, giving us the first ever audio recording captured beyond Earth. We’ve been able to reconstruct the sound of alien rain on Saturn’s moon Titan. And now, for the first time, we get to hear the low hum of Martian winds sweeping down the planes. Except not exactly. You see, while InSight did in fact record a 10 to 15 mile per hour draft on Martian, the recording’s pitch had to be dialed up and its frequency sped up roughly 100 times for the human ear to make any real sense of it. But why is it so hard to hear them otherwise?
Unlike Venus or Titan, Mars has an extremely thin, barely there atmosphere stripped away by solar winds and with virtually no protection from its weak magnetosphere. It’s so thin and fragile that it might actually make the planet impossible to terraform if we ever wanted to try to make it even a little more like our world. Even hurricane force winds would feel like a gentle breeze because there’s just not enough air to impart any meaningful kinetic energy. So, if you were able to stand on the surface of Mars without a spacesuit, you’d probably hear and feel nothing, hence NASA had to help us out so we could get some appreciation of what they were able to record, which is still exquisitely haunting and beautiful in the end.
What about winds on other planets and moons?
With extremely thick atmospheres, you’d have absolutely no problem hearing and feeling the full force of the wind on worlds like Venus, Jupiter and the other gas giants, and of course, Titan. In the turbulent clouds of gas giants, the winds would never stop and without anything solid to act as a brake, gusts can howl at astonishing speeds. Neptune boasts the fastest winds in the solar system at 1,200 miles per hour, with Saturn not far behind as 1,118 mile per hour gales whip around its equator, making Jupiter seem almost inert by comparison with peak wind speeds of 384 miles per hour around its Great Red Spot.
Exactly how hard that wind would hit you will depend on your altitude in the gas giants’ vast atmospheres but analogies with the impacts of anything between a tornado and a freight train come to mind. At this point, we would consider the kinetic energy of winds on Venus and Titan because they have solid surfaces and very thick atmospheres, but on both worlds, a very odd and interesting thing happens as you descend through the clouds. That atmospheric thickness means that gasses are compressed as you get close and closer to the surface and winds very quickly die down under the mass of the air through which they have to move.
On Titan, winds reach maybe 2 miles per hour at ground level at their strongest. On Venus, they peak at 3 miles per hour. Still, because there’s so much mass in motion, they would feel like a stiff breeze of 20 to 25 miles per hour if we note that the gusts in question are strong enough to scatter small rocks and use the Beaufort scale to translate that into comparable conditions right here on Earth. You would certainly hear it as well, deeper and more ominous than you’d expect, with absolutely no need to increase the pitch or speed up frequency for your ear to know what’s happening.
So, in case you ever look at the night sky and wonder about how different other planets are from the one on which you’re standing, consider that something seemingly as simple as the sound of moving air can be vastly different from world to world, what you’d consider a gentle breeze could be imperceptible on one planet and blow an umbrella out of your hand on another, and that sometimes, to appreciate what our robotic probes are detecting, we need to specially process the data they’ve gathered so you can even start making sense of it.
The impact crater Stickney (and the smaller crater Limtoc) as imaged by NASA’s Mars Reconnaissance Orbiter in 2008 [NASA/JPL-Caltech]
Earth has them. So does the Moon. As does Mars. And now we know dwarf planet Ceres has them, too. Could a Martian moon also have them? Well, according to new research, they could explain the mystery behind Phobos’ strange lines that are carved into its dusty surface.
What am I talking about? Boulders. Specifically boulders that have been on the move. Boulders that — in the presence of a gravitational field, no matter how weak — roll and bounce, leaving their grooves on some of our most beloved celestial bodies.
“These grooves are a distinctive feature of Phobos, and how they formed has been debated by planetary scientists for 40 years,” said planetary scientist Ken Ramsley (Brown University) who led the work, in a statement. “We think this study is another step toward zeroing in on an explanation.”
Ever since NASA’s Mariner and Viking missions spied Phobos’ lines in the 1970’s, scientists have debated what could have created them. The ancient natural satellite of Mars is only 27 kilometers wide and possesses long, etched lines that, in some cases, loop around the entirety of the moon’s circumference.
A popular hypothesis for these lines focused on the possibility that Phobos is a dying moon; the tidal forces from Mars ultimately pulling the body apart. In this scenario, the lines are a sign that the moon’s interior is crumbling, creating fault lines in the surface that our space robots have been able to image. Another idea is that the lines were created by crater chains; multiple impacts by smaller rocks that etched out long lines around Phobos’ surface.
However, according Ramsley’s study, which is published in the journal Planetary and Space Science, the real mechanism that created Phobos’ stripes is far more elegant, and more familiar to us Earthlings. What’s more, it was one of the original hypotheses that was posited when the lines were discovered over 40 years ago.
In 1998, NASA’s Mars Global Surveyor imaged Phobos’ stripes [NASA/JPL-Caltech/LLNL]
You see, Phobos has a huge, nine-kilometer-wide crater on one side, called Stickney (named after Angeline Stickney who motivated the search for Mars’ natural satellites in the late 19th Century), that was excavated by a massive impact in the moon’s ancient past. Using computer models, the researchers simulated what would happen post-impact and where the excavated material (including some hefty boulders) would have ended up. Although a huge quantity of material would have been lost to space during the Stickney impact, a few large rocks may have been kicked across the moon’s surface — these boulders would have rolled slowly, slow enough to be held in contact with Phobos, but fast enough, in some cases, to make more than one trip around the moon.
But many of these lines intersect one another and don’t appear to be radially blasted from the crater. Also, there are regions on the surface where the lines entirely disappear. Ramsley’s simulation explains these oddities.
The simulations show that because of Phobos’ small size and relatively weak gravity, Stickney stones just keep on rolling, rather than stopping after a kilometer or so like they might on a larger body. In fact, some boulders would have rolled and bounded their way all the way around the tiny moon. That circumnavigation could explain why some grooves aren’t radially aligned to the crater. Boulders that start out rolling across the eastern hemisphere of Phobos produce grooves that appear to be misaligned from the crater when they reach the western hemisphere.
This also helps to explain why many of these lines cross and superimpose themselves on one another: Grooves that were laid down by boulders rolling immediately after the impact were crossed by boulders that completed a complete traverse of the globe of the moon, some ending up where they started, minutes or hours later. This also explains why Stickney itself has grooves inside its crater basin.
The dark surface of Phobos with Mars as the backdrop, as seen by the European Mars Express [ESA]
But there’s a blank area on Phobos that appears to contain no grooves, a phenomenon that the simulation also addresses. This region is located at a comparatively low elevation part of Phobos, surrounded by a higher-elevation lip. “It’s like a ski jump,” said Ramsley. “The boulders keep going but suddenly there’s no ground under them. They end up doing this suborbital flight over this zone.
“We think this makes a pretty strong case that it was this rolling boulder model accounts for most if not all the grooves on Phobos.”
As a fan of rolling boulders on other worlds, I particularly enjoy imagining the lumbering slow roll of these massive rocks that circumnavigated Phobos. They had to keep their roll slow so not to achieve escape velocity, but fast enough to leave their indelible marks for humans to ponder their origins.
Artist’s impression of Titan’s surface and atmosphere (credit: Benjamin de Bivort, debivort.org / CC BY-SA 3.0)
Titan is a very strange moon.
Orbiting the ringed gas giant Saturn, Titan is the only moon in the solar system that sports a thick atmosphere. Although the moon is extremely cold, its atmosphere is very dynamic; exhibiting seasons, precipitation and even creating vast seas.
Although this may sound very much like Earth’s atmosphere — where water evaporates from the oceans, condenses as clouds and precipitates as rain, forming rivers that flow back into the oceans — Titan’s atmosphere is dominated by a methane cycle, not a water cycle.
This may sound like the antithesis of Earth’s life-giving chemistry, but astrobiologists have been gradually finding clues to Titan’s habitable potential and today (July 28) scientists have announced the confirmation of a key molecule that could be the proverbial backbone to a weird kind of “alternative” alien life on Titan — based not on liquid water, but on liquid methane.
“The presence of vinyl cyanide in an environment with liquid methane suggests the intriguing possibility of chemical processes that are analogous to those important for life on Earth,” said astrochemistry researcher Maureen Palmer, of NASA’s Goddard Space Flight Center in Greenbelt, Md.
Palmer is lead author of a study published in Science Advances describing the detection of vinyl cyanide (also known as acrylonitrile) at Titan using the awesome power of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.
B. Saxton (NRAO/AUI/NSF); NASA
Previous observations of Titan’s atmosphere by NASA’s Cassini mission and chemical modeling of the moon’s surface have hinted that it is the ideal environment for vinyl cyanide to form. But it was only when analysis of archived data collected by ALMA between February to May 2014 was carried out that its presence was confirmed. And there appears to be a lot of the stuff.
So what is vinyl cyanide and why is it so important?
The molecule (C2H3CN) has the ability to form membranes and, if found in liquid pools of hydrocarbons on Titan’s surface, it could form a kind of lipid-based cell membrane analog of living organisms on Earth. In other words, this molecule could stew in primordial pools of hydrocarbons and arrange itself in such a way to create a “protocell” that is “stable and flexible in liquid methane,” said Jonathan Lunine (Cornell University) who, in 2015, was a member of the team who modeled vinyl cyanide and found that it might form cell membranes.
“This is a step forward in understanding whether Titan’s methane seas might host an exotic form of life,” Lunine, who wasn’t a member part of the team that announced today’s results, said in a statement.
Life As We Don’t Know It
When studying Titan’s nitrogen-rich atmosphere, ALMA detected three unambiguous millimeter-wavelength signals produced by vinyl cyanide that originated from 200 kilometers above Titan’s surface. It is well known that the moon’s atmosphere is a vast chemical factory; the energy of the sun and particles from space convert simple organic molecules into more complex chemistry. These chemicals then cycle down to Titans rich hydrocarbon surface.
But speculating about life on Titan is a hard task. The moon’s atmosphere is often compared with that of early Earth’s, but there are some huge differences. Titan is crazy-cold, averaging around 95 Kelvin (that’s an incredible -178 degrees Celsius or -288 degrees Fahrenheit); at no time in history has Earth’s atmosphere been that cold. Also, it’s thought that early Earth had large quantities of carbon dioxide in its atmosphere, Titan does not. As for water? Frozen. Oxygen? Forget about it.
So this research underpins our quest to find the chemistry of life as we DON’T know it, using the building blocks that follow the pattern of life that we do know, but swapping out key components (like water) to see if an analog of life’s chemistry can under very alien conditions.
“Saturn’s moon, Enceladus is the place to search for life like us, life that depends on — and exists in — liquid water,” said Lunine. “Titan, on the other hand, is the place to go to seek the outer limits of life — can some exotic type of life begin and evolve in a truly alien environment, that of liquid methane?”
Perhaps it’s time for a return mission to Titan’s extreme surface.
The structure of a planet, a planet with a disk and a synestia, all of the same mass (Simon Lock and Sarah Stewart)
Pluto is going to be pissed.
After studying computer simulations of planetary collisions, scientists have discovered a possible phase of planetary formation that has, so far, been overlooked by astronomy. And they think this phase is so significant that it deserves its own planetary definition.
After two planetary objects collide, researchers from the University of California Davis and Harvard University in Cambridge, Mass., realized that a bloated, spinning mass of molten rock can form. It looks a bit like a ring doughnut with the hole filled in. What’s more, it is thought that Earth (and other planets in the solar system) probably went through this violent period before becoming the solid spinning globes we know and love today.
They call this partly vaporized rock “synestia” — “syn-” for “together” and “Estia” after the Greek goddess of architecture and structures.
Over a range of masses and collision speeds, planetary scientist Sarah Stewart (Davis) and graduate student Simon Lock (Harvard) simulated planetary collisions and focused on how the angular momentum of colliding bodies might influence the system. Their study has been published in the Journal of Geophysical Research: Planets. Basically, when two bodies — with their own angular momentum — collide and merge, the sum of their momenta must be conserved and this can have a dramatic effect on the size and structure of the merged mass.
“We looked at the statistics of giant impacts, and we found that they can form a completely new structure,” said Stewart.
After colliding, the energetic event causes both planets to melt and partially vaporize, expanding with a connected ring-like structure. And this structure — a synestia — would eventually cool, contract and solidify. It could also form moons; post-collision molten debris in the synestia doughnut ring may emerge in a stable orbit around the planet.
The synestia phase would be a fleeting event in any planet’s life, however. For an Earth-sized mass, the post-collision synestia would likely last only 100 years or so. But the larger the mass, the longer the phase, the researchers theorize.
So, giving this theoretical “planetary object” a classification might be a little generous — a move that would raise recently “demoted” Pluto’s eyebrow — but as telescopes become more advanced, we might one day be lucky enough to spy a synestia in a young star system where dynamic instabilities are causing planets to careen into one another.
Mars’ moons were likely formed by a ring of debris blasted into space after the Red Planet was hit by a massive impact and, when the moon Phobos disintegrates in 70 million years, another ring may form.
Sunrise over Gale Crater as seen by NASA’s Mars rover Curiosity and how it might look if the Red Planet had a ring system (NASA/JPL-Caltech-MSSS, edit by Ian O’Neill)
Mars is currently known as the “Red Planet” of the solar system; its unmistakable ruddy hue is created by dust rich in iron oxide covering its landscape. But in Mars’ ancient past, it might have also been called the “Ringed Planet” of the inner solar system and, in the distant future, it may sport rings once more.
The thing is, we live in a highly dynamic solar system, where the planets may appear static over human (or even civilization) timescales, but over millions to billions of years, massive changes to planetary bodies occur frequently. And should there be a massive impact on a small rocky world — on Mars, say — these changes can be nothing short of monumental.
In new NASA-funded research published in the journal Nature Geoscience, planetary scientists have developed a new model of Mars when it was hit by a massive impact over 4 billion years ago. This catastrophic impact created a vast basin called the Borealis Basin in the planet’s northern hemisphere and the event could be part of the reason why Mars lacks a global magnetic field — it’s hypothesized that a powerful impact (or series of impacts) caused massive disruption to the Martian inner dynamo.
But the impact also blasted a huge amount of rocky debris from Mars’ crust into space, ultimately settling into a ring system, like a miniaturized rocky version of Saturn. Over time, as the debris drifted away from Mars and settled, rocky chunks would have formed under gravity and these “moonlets” would have clumped together to form larger and larger moons. So far, so good; this is how we’d expect moons to form. But there’s a catch.
Phobos as imaged by Europe’s Mars Express mission (ESA)
After forming in Mars orbit, any moon would have slowly lost orbital altitude, creeping toward the planet’s so-called Roche Limit — a region surrounding any planetary body that is a bad place for any moon to hang out. The Roche Limit is the point at which a planet’s tidal forces become too great for the structural integrity of an orbiting body. When approaching this limit, the closest edge of the moon to the planet will experience a greater tidal pull than the far side, overcoming the body’s gravity. At some point, something has to give and the moon will start to break apart.
And this is what’s going to happen to Phobos in about 70 million years. Its orbit is currently degrading and when it reaches this invisible boundary, tidal stresses will pull it apart, trailing pieces of moon around the planet, some debris falling onto the Martian surface as a series of meteorite impacts, while others remain in orbit.
The research, carried out by David Minton and Andrew Hesselbrock of Purdue University, Lafayette in Indiana, theorizes that mysterious deposits of material around Mars’ equator might have come from the breakup of ancient moons that came before Phobos and Deimos.
“You could have had kilometer-thick piles of moon sediment raining down on Mars in the early parts of the planet’s history, and there are enigmatic sedimentary deposits on Mars with no explanation as to how they got there,” said Minton. “And now it’s possible to study that material.”
According to their model, each time a moon broke apart to create a ring, the next moon would be five times smaller than its predecessor.
In short, Mars and its moon may appear to be pretty much unchanged for billions of years, but the researchers think that up to seven moon-ring cycles have occurred over the last 4.3 billion years and Mars is on the verge (on geological timescales) of acquiring rings once more. Fascinating.
Venus is a hellish world. Although the planet is nearly the same size of Earth, that’s where the similarities end. Having said that, it does have an atmosphere, but it’s not the kind of atmosphere you would ever want to spend time breathing in. Composed of a dense carbon dioxide/nitrogen mix where clouds are made from sulphuric acid, you can forget about Venus as a tropical holiday destination. Even if you found a way to ‘breathe’ on Venus, you’d need to prepare yourself for the scorching 470°C surface temperatures and bone crushing pressures 100 times the pressure we are used to on Earth.
Doesn’t sound like a very nice place does it? Certainly an interesting world, providing us with invaluable science (after all, the reason for the extreme temperatures on Venus is due to a run-away greenhouse effect, it could help us understand the growing problems we are facing with our comparatively mild global warming woes), but an unlikely candidate for human colonization (unless we lived in the clouds).
Venus might not be a popular world for mankind to live on, but it doesn’t seem to be a popular world for natural satellites to orbit around either. It doesn’t have any moons, and astronomers are a little confused as to why this is the case. The only other planet without moons is the innermost terrestrial planet, Mercury. Every other planet in the Solar System has at least one natural satellite.
For hundreds of years, astronomers have been on the lookout for anything orbiting Venus but they’ve had little luck. However, some of the earliest observations of Venus appeared to indicate the presence satellites (in 1645, F. Fontana mentioned the possibility of a satellite discovery, followed by further observations in the late 1600’s and 1700’s). Since 1768, there have been no further reports of any satellite sightings. 1956 was the last published survey for Venusian satellites, using photographic plates, and that survey (published by Gerard Kuiper in 1961) drew up blanks for any satellites measuring over 2.5 km wide.
The lack of Venusian moons is puzzling, as a Venus-moon interacting mechanism has often been invoked as the reason why Venus has a retrograde spin (i.e. viewed from the ‘top’ of the Solar System plane, Venus has a clockwise rotation, whereas the rest of the planets, apart from Uranus — that spins on its side, bizarrely — have an anti-clockwise, or prograde, spin). Perhaps Venus once had a moon, but it has since been lost due to gravitational interactions with other Solar System bodies, or due to tidal instabilities, the innermost terrestrial planets collided with their large satellites a long time ago.
This is where Scott Sheppard from the Carnegie Institution of Washington and Chadwick Trujillo from the Gemini Observatory (Hawaii) step in. In a recent publication titled, “A Survey for Satellites of Venus,” Sheppard and Trujillo pick up where Kuiper left off, and carry out a systematic survey searching for any natural satellites around Venus. Only this time, by using the cutting-edge 6.5 meter telescope and IMACS wide-field CCD imager at Las Campanas observatory in Chile, they looked for objects only a few hundred meters in diameter.
The researchers scanned the interior of the Venusian ‘Hill Sphere’ to see if any undiscovered tiny moons were lurking. The Hill sphere is the volume of space surrounding a planetary body where natural satellites can orbit without being destabilized by the gravitational effects of the Sun. If there are any unforeseen moons, they should be found in stable orbits within the Hill sphere.
Sheppard and Trujillo have drawn blanks. Although a few errant asteroids were detected, no natural satellites down to a diameter of 600 meters were discovered. They surveyed 90% of the Venusian Hill sphere, and 99% of the inner Hill sphere (0.7rH) — the volume of space predicted to contain the stable orbits of natural satellites.
This new survey improves the non-detection of satellites down to a factor of 50 on previous studies, thereby proving Venus either, a) never possessed any satellites over 1km in diameter, or b) the orbits of past large satellites have become unstable and crashed into Venus or flung into space.
astroengine.com 