Space and astronomy news
If you try to apply simple common sense to how Saturn’s rings really work you’re going to be sorely mistaken: the giant planet’s signature features run circles around average Earthly intuition. This has been the case for centuries and is still true today after recent news from Cassini that the most opaque sections of rings aren’t necessarily the densest; with Saturn looks literally are deceiving.
Continue reading “Saturn’s Rings Continue to Surprise Scientists”
I don’t think I’ll ever tire of seeing pictures of Saturn’s moon Enceladus, with those captivating water jets and plumes at its South Pole. And this new images from the Cassini mission is just stunning – and intriguing. Carolyn Porco, the Cassini imaging team lead described the image on Twitter: “Be moved by crescent Enceladus with its ghostly geysers floating above Saturn’s glowing rings.”
There are over 100 geyser jets of varying sizes near Enceladus’s south pole spraying water vapor, icy particles, and organic compounds out into space. Enticingly, this distant and small moon (313 miles or 504 kilometers across) has a global subsurface ocean of liquid water, as tidal forces from Enceladus’ orbital relationship to Saturn and another moon, Dione heats the interior.
Liquid water and the observation of organic chemicals in the plumes of Enceladus make this moon of high astrobiological interest to scientists. In a 2014 paper by Porco and astrobiologist Chris McKay, the due wrote that Enceladus’ “steady plume derives from a subsurface liquid water reservoir that contains organic carbon, biologically available nitrogen, redox energy sources, and inorganic salts. … No other world has such well-studied indications of habitable conditions.”
While the rings of Saturn are also beautiful, they are they are frozen and geologically dead. “The small ring particles are too tiny to retain internal heat and have no way to get warm,” the Cassini imaging team explained on the CICLOPS website.
This image was taken in July of 2015, and was not part of two close flybys of Enceladus in October of this year. Project scientist Linda Spilker hinted there might be some new discoveries from those flybys (see images here and here), as she said, “Cassini’s stunning images are providing us a quick look at Enceladus from this ultra-close flyby, but some of the most exciting science is yet to come.”
This beautiful view of Enceladus and Saturn’s rings looks toward the unilluminated side of the rings from about 0.3 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 29, 2015.
The view was acquired at a distance of approximately 630,000 miles (1.0 million kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase angle of 155 degrees. Image scale is 4 miles (6 kilometers) per pixel.
See a larger version of this image here from NASA.
Host: Fraser Cain (@fcain)
Special Guest: Yoav Landsman,WSH Crew Member; Principal System Engineer at SpaceIL; member of first GLXP to “hitch a ride.”
Guests:
Pamela Gay (cosmoquest.org / @cosmoquestx / @starstryder)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Paul Sutter (pmsutter.com / @PaulMattSutter)
Dave Dickinson (@astroguyz / www.astroguyz.com)
Alessondra Springmann (@sondy)
Continue reading “Weekly Space Hangout – Oct. 30, 2015: Yoav Landsman and the Enceladus Flyby”
Oh, to hitch a ride aboard NASA’s Cassini spacecraft this week. The Saturn orbiting sentinel recently completed an amazing series of passes near the enigmatic ice-covered moon Enceladus, including a daredevil dive only 49 km (31 miles) above the southern pole of the moon and through an ice geyser. Images of the dramatic flyby were released by the Cassini team earlier this morning, revealing the moon in stunning detail.
“Cassini’s stunning images are providing us a quick look at Enceladus from this ultra-close flyby, but some of the most exciting science is yet to come,” says NASA mission project scientist Linda Spilker in today’s NASA/JPL press release.
Launched in 1997 from Cape Canaveral Florida in a dramatic night shot, Cassini arrived at the Saturnian system in 2004, and has delivered on some amazing planetary science ever since.
Discovered in 1789 by William Herschel, we got our very first views of Enceladus via the Voyager 1 spacecraft at 202,000 kilometers distant in 1980. Cassini has flown by the moon 21 times over the past decade, and ice geysers were seen sprouting from the surface of the moon by Cassini on subsequent flybys. one final flyby of Enceladus is planned for this coming December.
Mission planners are getting more daring with the spacecraft as its mission nears completion in 2017. The idea of reaching out and ‘tasting’ an icy plume emanating from Enceladus has been an enticing one, though a fast-moving good-sized ice pellet could spell disaster for the spacecraft.
NASA successfully established contact with the spacecraft on Wednesday night October 28th after the closest approach for the flyby at 11:22 AM EDT/ 15:22 UT (Universal Time) earlier in the day. Cassini is reported to be in good health, and we should see further images along with science data returns in the weeks to come.
A second, more distant flyby of Enceladus was completed by Cassini earlier this month as it passed 1,142 miles (1,839 kilometers) from the northern pole of Enceladus on October 14th, 2015 on its E-20 flyby.
But beyond just pretty post-cards from the outer solar system, Cassini’s successive passes by the mysterious moon will characterize just what might be occurring far down below.
Why Enceladus? Well, ever since ice geysers were spotted gushing from the fractured surface of the moon, it’s been on NASA’s short list of possible abodes for life in the solar system. Other contenders include Mars, Jupiter’s moon Europa, and Saturn’s giant moon, Titan. If the story of life on Earth is any indication, you need a place where an abundant level of chemical processes are occurring, and a subsurface ocean under the crust of Enceladus heated by tidal flexing may just fit the bill.
We’ll be adding further images and info to this post as more data comes in over the weekend, plus Cassini mission highlights, a look at the mission and final objectives and the last days of Cassini and more…
Stay tuned!
The end of Cassini in 2017 as it burns up in the atmosphere of Saturn will be a bittersweet affair, as our outer solar system eyes around the ringed planet fall silent. Cassini represents the most distant spacecraft inserted into orbit around a planet, and ESA’s Huygens lander on Titan marked the most remote landing on another world as well. Will we one day see a Titan Blimp or Ocean Explorer, or perhaps a dedicated life-finding mission to Enceladus? Final mission objectives for NASA’s Cassini spacecraft include a final flyby of Saturn’s large moon Titan, which will set the course for its final death plunge into the atmosphere of Saturn on September 15th, 2017.
Want to see Enceladus for yourself? The moon orbits Saturn once every 1.4 days, reaching a maximum elongation of 13″ from the ring tips of Saturn and a maximum brightness of magnitude +11.7. Enceladus is one of six major moons of Saturn visible in a backyard telescope, and one of 62 moons of the ring planet known overall. The other five moons within reach of an amateur telescope are: Titan, Mimas, Dione, Rhea, and Tethys, and the fainter moon Hyperion shining at magnitude +15 might just be within reach of skill observers with large light bucket instruments.
Enjoy the amazing views of Enceladus, courtesy of Cassini!
Exploring the Solar System is like peeling an onion. With every layer removed, one finds fresh mysteries to ponder over, each one more confounding than the last. And this is certainly the case when it comes to Jupiter’s system of moons, particularly its four largest – Io, Europa, Ganymede and Callisto. Known as the Galilean Moons, in honor of their founder, these moons possess enough natural wonders to keep scientists busy for centuries.
As Jupiter’s innermost moon, it is also the fourth-largest moon in the Solar System, has the highest density of any known moon, and is the driest known object in the Solar System. It is also one of only four known bodies that experiences active volcanism and – with over 400 active volcanoes – it is the most geologically active body in the Solar System.
Host: Fraser Cain (@fcain)
Special Guest: Dr. Carolyn Porco is the leader of the Cassini Imaging Science team and the Director of the Cassini Imaging Central Laboratory for Operations (CICLOPS) at the Space Science Institute in Boulder, Colorado.
Guests:
Pamela Gay (cosmoquest.org / @cosmoquestx / @starstryder)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Kimberly Cartier (@AstroKimCartier )
Dave Dickinson (@astroguyz / www.astroguyz.com)
Nicole Gugliucci (cosmoquest.org / @noisyastronomer)
Alessondra Springmann (@sondy)
Rhys Taylor (G+: Rhys Taylor)
Continue reading “Weekly Space Hangout – Oct. 16, 2015: Dr. Carolyn Porco and Cassini Update; Sexual Harassment in Astronomy and Academia”
If you thought Saturn’s moon Enceladus couldn’t get any more bizzare — with its magnificent plumes, crazy tiger-stripe-like fissures and global subsurface salty ocean — think again. New images of this moon’s northern region just in from the Cassini spacecraft show surprising and perplexing features: a tortured surface where craters look like they are melting, and fractures that cut straight across the landscape.
“We’ve been puzzling over Enceladus’ south pole for so long, time to be puzzled by the north pole!” tweeted NASA engineer Sarah Milkovich, who formerly worked on the Cassini mission.
While the Cassini mission has been at the Saturn system since 2004 and flown by this moon several times, this is the spacecraft’s first close-up look at the north polar region of Enceladus. On October 14, 2015 the spacecraft passed at an altitude of just 1,839 kilometers (1,142 miles) above the moon’s surface.
See more imagery below:
The reason Cassini hasn’t been able to see the northern terrain of Enceladus previously is that it was concealed by the darkness of winter. It’s now summer in the high northern latitudes, and scientists have been anxious to take a look at this previously unseen region. Gauging by the posts of “Wow!” and “Enceladus what are you doing??” by scientists on social media, the Cassini team is as excited and perplexed by these images as the rest of us.
“We’ve been following a trail of clues on Enceladus for 10 years now,” said Bonnie Buratti, a Cassini science team member and icy moons expert at NASA’s Jet Propulsion Laboratory. “The amount of activity on and beneath this moon’s surface has been a huge surprise to us. We’re still trying to figure out what its history has been, and how it came to be this way.”
While these raw images just arrived this morning, already image editing enthusiasts have dived into the data to create composite and color images. Here are two from UT writer Jason Major and image contributor Kevin Gill:
In an email, Cassini imaging team leader Carolyn Porco explained the flyby: “Our cameras were active during most of this encounter, allowing the imaging team and other remote-sensing instrument teams to observe the Saturn-opposing side of Enceladus on the inbound leg of the encounter, and a narrow, sunlit crescent outbound.”
From previous imagery and study of this moon, it has been suggested that the fractured and wrinkled terrain on Enceladus could be the scars of a shift in the moon’s spin rate. The moon has likely undergone multiple episodes of geologic activity spanning a considerable portion of its lifetime.
While these images are incredible, get ready for even more. An even closer flyby of Enceladus is scheduled for Wednesday, Oct. 28, during which Cassini will come dizzyingly close to the icy moon, passing just 49 kilometers (30 miles) above the moon’s south polar region. NASA says that during this encounter, Cassini will make its deepest-ever dive through the moon’s plume of icy spray, collecting images and valuable data about what’s going on beneath the frozen surface. Cassini scientists are hopeful data from that flyby will provide evidence of how much hydrothermal activity is occurring in the moon’s ocean, and how the amount of activity impacts the habitability of Enceladus’ ocean.
Then another flyby — Cassini’s final scheduled close flyby of Enceladus — on Dec. 19 will examine how much heat is coming from the moon’s interior from an altitude of 4,999 kilometers (3,106 miles).
An interesting side note is that the Cassini mission launched 18 years ago today (October 15, 1997).
Again stay tuned for more, and you can see all of Cassini’s raw image here, and find out more details of the upcoming flybys at this CICLOPS page.
Could there be life on Saturn’s large moon Titan? Asking the question forces astrobiologists and chemists to think carefully and creatively about the chemistry of life, and how it might be different on other worlds than it is on Earth. In February, a team of researchers from Cornell University, including chemical engineering graduate student James Stevenson, planetary scientist Jonathan Lunine, and chemical engineer Paulette Clancy, published a pioneering study arguing that cell membranes could form under the exotic chemical conditions present on this remarkable moon.
In many ways, Titan is Earth’s twin. It’s the second largest moon in the solar system and bigger than the planet Mercury. Like Earth, it has a substantial atmosphere, with a surface atmospheric pressure a bit higher than Earth’s. Besides Earth, Titan is the only object in our solar system known to have accumulations of liquid on its surface. NASA’s Cassini space probe discovered abundant lakes and even rivers in Titan’s polar regions. The largest lake, or sea, called Kraken Mare, is larger than Earth’s Caspian Sea. Researchers know from both spacecraft observations and laboratory experiments that Titan’s atmosphere is rich in complex organic molecules, which are the building blocks of life.
All these features might make it seem as though Titan is tantalizingly suitable for life. The name ‘Kraken’, which refers to a legendary sea monster, fancifully reflects the eager hopes of astrobiologists. But, Titan is Earth’s alien twin. Being almost ten times further from the sun than Earth is, its surface temperature is a frigid -180 degrees Celsius. Liquid water is vital to life as we know it, but on Titan’s surface all water is frozen solid. Water ice takes on the role that silicon-containing rock does on Earth, making up the outer layers of the crust.
The liquid that fills Titan’s lakes and rivers is not water, but liquid methane, probably mixed with other substances like liquid ethane, all of which are gases here on Earth. If there is life in Titan’s seas, it is not life as we know it. It must be an alien form of life, with organic molecules dissolved in liquid methane instead of liquid water. Is such a thing even possible?
The Cornell team took up one key part of this challenging question by investigating whether cell membranes can exist in liquid methane. Every living cell is, essentially, a self-sustaining network of chemical reactions, contained within bounding membranes. Scientists think that cell membranes emerged very early in the history of life on Earth, and their formation might even have been the first step in the origin of life.
Here on Earth, cell membranes are as familiar as high school biology class. They are made of large molecules called phospholipids. Each phospholipid molecule has a ‘head’ and a ‘tail’. The head contains a phosphate group, with a phosphorus atom linked to several oxygen atoms. The tail consists of one or more strings of carbon atoms, typically 15 to 20 atoms long, with hydrogen atoms linked on each side. The head, due to the negative charge of its phosphate group, has an unequal distribution of electrical charge, and we say that it is polar. The tail, on the other hand, is electrically neutral.
These electrical properties determine how phospholipid molecules will behave when they are dissolved in water. Electrically speaking, water is a polar molecule. The electrons in the water molecule are more strongly attracted to its oxygen atom than to its two hydrogen atoms. So, the side of the molecule where the two hydrogen atoms are has a slight positive charge, and the oxygen side has a small negative charge. These polar properties of water cause it to attract the polar head of the phospholipid molecule, which is said to be hydrophilic, and repel its nonpolar tail, which is said to be hydrophobic.
When phospholipid molecules are dissolved in water, the electrical properties of the two substances work together to cause the phospholipid molecules to organize themselves into a membrane. The membrane closes onto itself into a little sphere called a liposome. The phospholipid molecules form a bilayer two molecules thick. The polar hydrophilic heads face outward towards the water on both the inner and outer surface of the membrane. The hydrophobic tails are sandwiched between, facing each other. While the phospholipid molecules remain fixed in their layer, with their heads facing out and their tails facing in, they can still move around with respect to each other, giving the membrane the fluid flexibility needed for life.
Phospholipid bilayer membranes are the basis of all terrestrial cell membranes. Even on its own, a liposome can grow, reproduce and aid certain chemical reactions important to life, which is why some biochemists think that the formation of liposomes might have been the first step towards life. At any rate, the formation of cell membranes must surely been an early step in life’s emergence on Earth.
If some form of life exists on Titan, whether sea monster or (more likely) microbe, it would almost certainly need to have a cell membrane, just like every living thing on Earth does. Could phospholipid bilayer membranes form in liquid methane on Titan? The answer is no. Unlike water, the methane molecule has an even distribution of electrical charges. It lacks water’s polar qualities, and so couldn’t attract the polar heads of phospholipid molecule. This attraction is needed for the phospholipids to form an Earth-style cell membrane.
Experiments have been conducted where phospholipids are dissolved in non-polar liquids at Earthly room temperature. Under these conditions, the phospholipids form an ‘inside-out’ two layer membrane. The polar heads of the phospholipid molecules are at the center, attracted to one another by their electrical charges. The non-polar tails face outward on each side of the inside-out membrane, facing the non-polar solvent.
Could Titanian life have an inside out phospholipid membrane? The Cornell team concluded that this wouldn’t work, for two reasons. The first is that at the cryogenic temperatures of liquid methane, the tails of phospholipids become rigid, depriving any inside-out membrane that might form of the fluid flexibility needed for life. The second is that two key ingredients of phospholipids; phosphorus and oxygen, are probably unavailable in the methane lakes of Titan. In their search for Titanian cell membranes, the Cornell team needed to probe beyond the familiar realm of high school biology.
Although not composed of phospholipids, the scientists reasoned that any Titanian cell membrane would nevertheless be like the inside-out phospholipid membranes created in the lab. It would consist of polar molecules clinging together electrically in a solution of non-polar liquid methane. What molecules might those be? For answers the researchers looked to data from the Cassini spacecraft and from laboratory experiments that reproduced the chemistry of Titan’s atmosphere.
Titan’s atmosphere is known to have a very complex chemistry. It is made mostly of nitrogen and methane gas. When the Cassini spacecraft analyzed its composition using spectroscopy it found traces of a variety of compounds of carbon, nitrogen, and hydrogen, called nitriles and amines. Researchers have simulated the chemistry of Titan’s atmosphere in the lab by exposing mixtures of nitrogen and methane to sources of energy simulating sunlight on Titan. A stew of organic molecules called ‘tholins’ is formed. It consists of compounds of hydrogen and carbon, called hydrocarbons, as well as nitriles and amines.
The Cornell investigators saw nitriles and amines as potential candidates for their Titanian cell membranes. Both are polar molecules that might stick together to form a membrane in non-polar liquid methane due to the polarity of nitrogen containing groups found in both of them. They reasoned that candidate molecules must be much smaller than phospholipids, so that they could form fluid membranes at liquid methane temperatures. They considered nitriles and amines containing strings of between three and six carbon atoms. Nitrogen containing groups are called ‘azoto’ –groups, so the team named their hypothetical Titanian counterpart to the liposome the ‘azotosome’.
Synthesizing azotosomes for experimental study would have been difficult and expensive, because the experiments would need to be conducted at the cryogenic temperatures of liquid methane. But since the candidate molecules have been studied extensively for other reasons, the Cornell researchers felt justified in turning to the tools of computational chemistry to determine whether their candidate molecules could cohere as a flexible membrane in liquid methane. Computational models have been used successfully to study conventional phospholipid cell membranes.
The group’s computational simulations showed that some candidate substances could be ruled out because they would not cohere as a membrane, would be too rigid, or would form a solid. Nevertheless, the simulations also showed that a number of substances would form membranes with suitable properties. One suitable substance is acrylonitrile, which Cassini showed is present in Titan’s atmosphere at 10 parts per million concentration. Despite the huge difference in temperature between cryogenic azotozomes and room temperature liposomes, the simulations showed them to exhibit strikingly similar properties of stability and response to mechanical stress. Cell membranes, then, are possible for life in liquid methane.
The scientists from Cornell view their findings as nothing more than a first step towards showing that life in liquid methane is possible, and towards developing the methods that future spacecraft will need to search for it on Titan. If life is possible in liquid methane, the implications ultimately extend far beyond Titan.
When seeking conditions suitable for life in the galaxy, astronomers typically search for exoplanets within a star’s habitable zone, defined as the narrow range of distances over which a planet with an Earth-like atmosphere would have a surface temperature suitable for liquid water. If methane life is possible, then stars would also have a methane habitable zone, a region where methane could exist as a liquid on a planet or moon, making methane life possible. The number of habitable worlds in the galaxy would be greatly increased. Perhaps, on some worlds, methane life evolves into complex forms that we can scarcely imagine. Maybe some of them are even a bit like sea monsters.
References and Further Reading:
N. Atkinson (2010) Alien Life on Titan? Hang on Just a Minute, Universe Today.
N. Atkinson (2010) Life on Titan Could be Smelly and Explosive, Universe Today.
M. L. Cable, S. M. Horst, R. Hodyss, P. M. Beauchamp, M. A. Smith, P. A. Willis, (2012) Titan tholins: Simulating Titan organic chemistry in the Cassini-Huygens era, Chemical Reviews, 112:1882-1909.
E. Howell (2014) Titan’s Majestic Mirror-Like Lakes Will Come Under Cassini’s Scrutiny This Week, Universe Today.
J. Major (2013) Titan’s North Pole is Loaded With Lakes, Universe Today.
C. P. McKay, H. D. Smith, (2005) Possibilities for methanogenic life in liquid methane on the surface of Titan, Icarus 178: 274-276.
J. Stevenson, J. Lunine, P. Clancy, (2015) Membrane alternatives in worlds without oxygen: Creation of an azotosome, Science Advances 1(1):e1400067.
S. Oleson (2014) Titan submarine: Exploring the depths of Kraken, NASA Glenn Research Center, Press release.
Cassini Solstice Mission, NASA Jet Propulsion Laboratory
NASA and ESA celebrate 10 years since Titan landing, NASA 2015
Host: Fraser Cain (@fcain)
Special Guests:
Dr. Sara Seager, whose research focuses on computer models of exoplanet atmospheres, interiors, and biosignatures. Her favorite projects involve the search for planets like Earth with signs of life
on them.
Guests:
Paul Sutter (pmsutter.com / @PaulMattSutter)
Morgan Rehnberg (cosmicchatter.org / @MorganRehnberg )
Pamela Gay (cosmoquest.org / @cosmoquestx / @starstryder)
Continue reading “Weekly Space Hangout – Sept 18, 2015: Planet Hunter Prof. Sara Seager”
Resembling what the skin on my arms looks like after giving my cat a bath, the surface of Saturn’s moon Tethys is seen above in an extended-color composite from NASA’s Cassini spacecraft showing strange long red streaks. They stretch for long distances across the moon’s surface following the rugged terrain, continuing unbroken over hills and down into craters… and their cause isn’t yet known.
According to a NASA news release, “The origin of the features and their reddish color is currently a mystery to Cassini scientists. Possibilities being studied include ideas that the reddish material is exposed ice with chemical impurities, or the result of outgassing from inside Tethys. The streaks could also be associated with features like fractures that are below the resolution of the available images.”
The images were taken by Cassini during a flyby of the 660-mile-wide (1,062 km) Tethys on April 11, 2015 at a resolution of about 2,300 feet (700 meters) per pixel. They were acquired in visible green, infrared, and ultraviolet light wavelengths and so the composite image reveals colors our eyes can’t directly perceive. The combination of this and the solar illumination needed to image this particular area as the spacecraft passed by are why these features haven’t been seen so well until now.
“The red arcs really popped out when we saw the new images,” said Cassini participating scientist Paul Schenk of the Lunar and Planetary Institute in Houston. “It’s surprising how extensive these features are.”
While the nature of Tethys’ streaks isn’t understood, the observations do indicate a relatively young age compared to the surrounding surface.
“The red arcs must be geologically young because they cut across older features like impact craters, but we don’t know their age in years.” said Paul Helfenstein, a Cassini imaging scientist at Cornell University in Ithaca. “If the stain is only a thin, colored veneer on the icy soil, exposure to the space environment at Tethys’ surface might erase them on relatively short time scales.”
Could these arcs be signs of an underground ocean or reservoir of briny liquid, like Enceladus’ tiger stripes (aka sulcae) or the streaks that crisscross Europa’s ice? Or are they the results of infalling material from one of Saturn’s other moons? More observations with Cassini, now in its eleventh year in orbit at Saturn, are being planned to “study the streaks.”
“We are planning an even closer look at one of the Tethys red arcs in November to see if we can tease out the source and composition of these unusual markings,” said Linda Spilker, Cassini project scientist at JPL.
Source: NASA JPL
