jpl caltech

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A small, faint star relatively close by is home to seven Earth-size planets with conditions that could be right for liquid water and maybe even life.

The discovery sets a record for both the most Earth-size planets and the most potentially habitable planets ever discovered around a single star.

The strange planetary system is quite compact, with all of these worlds orbiting their star closer than Mercury orbits the sun, according to a newly published report in Nature.

“If you were on the surface of one of these planets, you would see the other ones as we see the moon, or a bit smaller,” says Michaël Gillon, an astronomer at the University of Liège in Belgium. “The view would be very impressive.”

Astronomers Find 7 Earth-Size Planets Around A Nearby Star

Images: NASA/JPL-Caltech

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NASA Saturn Mission Prepares for ‘Ring-Grazing Orbits’

First Phase in Dramatic Endgame for Long-Lived Cassini Spacecraft

A thrilling ride is about to begin for NASA’s Cassini spacecraft.

Engineers have been pumping up the spacecraft’s orbit around Saturn this year to increase its tilt with respect to the planet’s equator and rings.

And on Nov. 30, following a gravitational nudge from Saturn’s moon Titan, Cassini will enter the first phase of the mission’s dramatic endgame.

Launched in 1997, Cassini has been touring the Saturn system since arriving there in 2004 for an up-close study of the planet, its rings and moons. During its journey, Cassini has made numerous dramatic discoveries, including a global ocean within Enceladus and liquid methane seas on Titan.

Between Nov. 30 and April 22, Cassini will circle high over and under the poles of Saturn, diving every seven days – a total of 20 times – through the unexplored region at the outer edge of the main rings.

“We’re calling this phase of the mission Cassini’s Ring-Grazing Orbits, because we’ll be skimming past the outer edge of the rings,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. “In addition, we have two instruments that can sample particles and gases as we cross the ringplane, so in a sense Cassini is also 'grazing’ on the rings.”

On many of these passes, Cassini’s instruments will attempt to directly sample ring particles and molecules of faint gases that are found close to the rings. During the first two orbits, the spacecraft will pass directly through an extremely faint ring produced by tiny meteors striking the two small moons Janus and Epimetheus. Ring crossings in March and April will send the spacecraft through the dusty outer reaches of the F ring.

“Even though we’re flying closer to the F ring than we ever have, we’ll still be more than 4,850 miles (7,800 kilometers) distant. There’s very little concern over dust hazard at that range,” said Earl Maize, Cassini project manager at JPL.

The F ring marks the outer boundary of the main ring system; Saturn has several other, much fainter rings that lie farther from the planet. The F ring is complex and constantly changing: Cassini images have shown structures like bright streamers, wispy filaments and dark channels that appear and develop over mere hours. The ring is also quite narrow – only about 500 miles (800 kilometers) wide. At its core is a denser region about 30 miles (50 kilometers) wide.

So Many Sights to See
Cassini’s ring-grazing orbits offer unprecedented opportunities to observe the menagerie of small moons that orbit in or near the edges of the rings, including best-ever looks at the moons Pandora, Atlas, Pan and Daphnis.

Grazing the edges of the rings also will provide some of the closest-ever studies of the outer portions of Saturn’s main rings (the A, B and F rings). Some of Cassini’s views will have a level of detail not seen since the spacecraft glided just above them during its arrival in 2004. The mission will begin imaging the rings in December along their entire width, resolving details smaller than 0.6 mile (1 kilometer) per pixel and building up Cassini’s highest-quality complete scan of the rings’ intricate structure.

The mission will continue investigating small-scale features in the A ring called “propellers,” which reveal the presence of unseen moonlets. Because of their airplane propeller-like shapes, scientists have given some of the more persistent features informal names inspired by famous aviators, including “Earhart.” Observing propellers at high resolution will likely reveal new details about their origin and structure.

And in March, while coasting through Saturn’s shadow, Cassini will observe the rings backlit by the sun, in the hope of catching clouds of dust ejected by meteor impacts.

Preparing for the Finale
During these orbits, Cassini will pass as close as about 56,000 miles (90,000 kilometers) above Saturn’s cloud tops. But even with all their exciting science, these orbits are merely a prelude to the planet-grazing passes that lie ahead. In April 2017, the spacecraft will begin its Grand Finale phase.

After nearly 20 years in space, the mission is drawing near its end because the spacecraft is running low on fuel. The Cassini team carefully designed the finale to conduct an extraordinary science investigation before sending the spacecraft into Saturn to protect its potentially habitable moons.

During its grand finale, Cassini will pass as close as 1,012 miles (1,628 kilometers) above the clouds as it dives repeatedly through the narrow gap between Saturn and its rings, before making its mission-ending plunge into the planet’s atmosphere on Sept. 15. But before the spacecraft can leap over the rings to begin its finale, some preparatory work remains.

To begin with, Cassini is scheduled to perform a brief burn of its main engine during the first super-close approach to the rings on Dec. 4. This maneuver is important for fine-tuning the orbit and setting the correct course to enable the remainder of the mission.

“This will be the 183rd and last currently planned firing of our main engine. Although we could still decide to use the engine again, the plan is to complete the remaining maneuvers using thrusters,” said Maize.

To further prepare, Cassini will observe Saturn’s atmosphere during the ring-grazing phase of the mission to more precisely determine how far it extends above the planet. Scientists have observed Saturn’s outermost atmosphere to expand and contract slightly with the seasons since Cassini’s arrival. Given this variability, the forthcoming data will be important for helping mission engineers determine how close they can safely fly the spacecraft.

Some 40 light-years from Earth, a planet called TRAPPIST-1e offers a heart-stopping view: brilliant objects in a red sky, looming like larger and smaller versions of our own moon. But these are no moons. They are other Earth-sized planets in a spectacular planetary system outside our own. These seven rocky worlds huddle around their small, dim, red star, like a family around a campfire. Any of them could harbor liquid water, but the planet shown here, fourth from the TRAPPIST-1 star, is in the habitable zone, the area around the star where liquid water is most likely to be detected. This system was revealed by the TRansiting Planets and PlanetIsmals Small Telescope (TRAPPIST) and NASA’s Spitzer Space Telescope. The planets are also excellent targets for NASA’s James Webb Space Telescope. Take a planet-hopping excursion through the TRAPPIST-1 system.

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Jupiter’s North Pole Unlike Anything Encountered in Solar System


NASA’s Juno spacecraft has sent back the first-ever images of Jupiter’s north pole, taken during the spacecraft’s first flyby of the planet with its instruments switched on. The images show storm systems and weather activity unlike anything previously seen on any of our solar system’s gas-giant planets.

Juno successfully executed the first of 36 orbital flybys on Aug. 27 when the spacecraft came about 2,500 miles (4,200 kilometers) above Jupiter’s swirling clouds. The download of six megabytes of data collected during the six-hour transit, from above Jupiter’s north pole to below its south pole, took one-and-a-half days. While analysis of this first data collection is ongoing, some unique discoveries have already made themselves visible.

“First glimpse of Jupiter’s north pole, and it looks like nothing we have seen or imagined before,” said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio. “It’s bluer in color up there than other parts of the planet, and there are a lot of storms. There is no sign of the latitudinal bands or zone and belts that we are used to – this image is hardly recognizable as Jupiter. We’re seeing signs that the clouds have shadows, possibly indicating that the clouds are at a higher altitude than other features.”

One of the most notable findings of these first-ever pictures of Jupiter’s north and south poles is something that the JunoCam imager did not see.

“Saturn has a hexagon at the north pole,” said Bolton. “There is nothing on Jupiter that anywhere near resembles that. The largest planet in our solar system is truly unique. We have 36 more flybys to study just how unique it really is.”

Along with JunoCam snapping pictures during the flyby, all eight of Juno’s science instruments were energized and collecting data. The Jovian Infrared Auroral Mapper (JI-RAM), supplied by the Italian Space Agency, acquired some remarkable images of Jupiter at its north and south polar regions in infrared wavelengths.

“JIRAM is getting under Jupiter’s skin, giving us our first infrared close-ups of the planet,” said Alberto Adriani, JIRAM co-investigator from Istituto di Astrofisica e Planetologia Spaziali, Rome. “These first infrared views of Jupiter’s north and south poles are revealing warm and hot spots that have never been seen before. And while we knew that the first ever infrared views of Jupiter’s south pole could reveal the planet’s southern aurora, we were amazed to see it for the first time. No other instruments, both from Earth or space, have been able to see the southern aurora. Now, with JIRAM, we see that it appears to be very bright and well structured. The high level of detail in the images will tell us more about the aurora’s morphology and dynamics.”

Among the more unique data sets collected by Juno during its first scientific sweep by Jupiter was that acquired by the mission’s Radio/Plasma Wave Experiment (Waves), which recorded ghostly- sounding transmissions emanating from above the planet. These radio emissions from Jupiter have been known about since the 1950s but had never been analyzed from such a close vantage point.

“Jupiter is talking to us in a way only gas-giant worlds can,” said Bill Kurth, co-investigator for the Waves instrument from the University of Iowa, Iowa City. “Waves detected the signature emissions of the energetic particles that generate the massive auroras which encircle Jupiter’s north pole. These emissions are the strongest in the solar system. Now we are going to try to figure out where the electrons come from that are generating them.”

The Juno spacecraft launched on Aug. 5, 2011, from Cape Canaveral, Florida and arrived at Jupiter on July 4, 2016. JPL manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for NASA’s Science Mission Directorate. Lockheed Martin Space Systems, Denver, built the spacecraft. Caltech in Pasadena, California, manages JPL for NASA.

IMAGE 1….As NASA’s Juno spacecraft closed in on Jupiter for its Aug. 27, 2016 pass, its view grew sharper and fine details in the north polar region became increasingly visible.
The JunoCam instrument obtained this view on August 27, about two hours before closest approach, when the spacecraft was 120,000 miles (195,000 kilometers) away from the giant planet (i.e., for Jupiter’s center).
Unlike the equatorial region’s familiar structure of belts and zones, the poles are mottled with rotating storms of various sizes, similar to giant versions of terrestrial hurricanes. Jupiter’s poles have not been seen from this perspective since the Pioneer 11 spacecraft flew by the planet in 1974.

IMAGE 2….Storm systems and weather activity unlike anything encountered in the solar system are on view in these color images of Jupiter’s north polar region from NASA’s Juno spacecraft.
Two versions of the image have been contrast-enhanced differently to bring out detail near the dark terminator and near the bright limb.
The JunoCam instrument took the images to create this color view on August 27, when the spacecraft was about 48,000 miles (78,000 kilometers) above the polar cloud tops.
A wavy boundary is visible halfway between the grayish region at left (closer to the pole and the nightside shadow) and the lighter-colored area on the right. The wavy appearance of the boundary represents a Rossby wave – a north-south meandering of a predominantly east-west flow in an atmospheric jet. This may be caused by a difference in temperature between air to the north and south of this boundary, as is often the case with such waves in Earth’s atmosphere.
The polar region is filled with a variety of discrete atmospheric features. Some of these are ovals, but the larger and brighter features have a “pinwheel” shape reminiscent of the shape of terrestrial hurricanes. Tracking the motion and evolution of these features across multiple orbits will provide clues about the dynamics of the Jovian atmosphere.
This image also provides the first example of cloud shadowing on Jupiter: near the top of the image, a high cloud feature is seen past the normal boundary between day and night, illuminated above the cloud deck below.
While subtle color differences are visible in the image, some of these are likely the result of scattered light within the JunoCam optics. Work is ongoing to characterize these effects.

IMAGE 3….This image from NASA’s Juno spacecraft provides a never-before-seen perspective on Jupiter’s south pole.
The JunoCam instrument acquired the view on August 27, 2016, when the spacecraft was about 58,700 miles (94,500 kilometers) above the polar region. At this point, the spacecraft was about an hour past its closest approach, and fine detail in the south polar region is clearly resolved.
Unlike the equatorial region’s familiar structure of belts and zones, the poles are mottled by clockwise and counterclockwise rotating storms of various sizes, similar to giant versions of terrestrial hurricanes. The south pole has never been seen from this viewpoint, although the Cassini spacecraft was able to observe most of the polar region at highly oblique angles as it flew past Jupiter on its way to Saturn in 2000

IMAGE 4….This infrared image gives an unprecedented view of the southern aurora of Jupiter, as captured by NASA’s Juno spacecraft on August 27, 2016.
The planet’s southern aurora can hardly be seen from Earth due to our home planet’s position in respect to Jupiter’s south pole. Juno’s unique polar orbit provides the first opportunity to observe this region of the gas-giant planet in detail.
Juno’s Jovian Infrared Auroral Mapper (JIRAM) camera acquired the view at wavelengths ranging from 3.3 to 3.6 microns – the wavelengths of light emitted by excited hydrogen ions in the polar regions. The view is a mosaic of three images taken just minutes apart from each other, about four hours after the perijove pass while the spacecraft was moving away from Jupiter.

IMAGE 5….This montage of 10 JunoCam images shows Jupiter growing and shrinking in apparent size before and after NASA’s Juno spacecraft made its closest approach on August 27, 2016, at 12:50 UTC.
The images are spaced about 10 hours apart, one Jupiter day, so the Great Red Spot is always in roughly the same place. The small black spots visible on the planet in some of the images are shadows of the large Galilean moons.
The images in the top row were taken during the inbound leg of the orbit, beginning on August 25 at 13:15 UTC when Juno was 1.4 million miles (2.3 million kilometers) away from Jupiter, and continuing to August 27 at 04:45 UTC when the spacecraft was 430,000 miles (700,000 kilometers) away. The images in the bottom row were obtained during the outbound leg of the orbit. They begin on August 28 at 00:45 UTC when Juno was 750,000 miles (920,000 kilometers) away and continue to August 29 at 16:45 UTC when the spacecraft was 1.6 million miles (2.5 million kilometers) away.

IMAGE 6….This image provides a close-up view of Jupiter’s southern hemisphere, as seen by NASA’s Juno spacecraft on August 27, 2016. The JunoCam instrument captured this image with its red spectral filter when the spacecraft was about 23,600 miles (38,000 kilometers) above the cloud tops.
The image covers an area from close to the south pole to 20 degrees south of the equator, centered on a longitude at about 140 degrees west. The transition between the banded structures near the equator and the more chaotic polar region (south of about 65 degrees south latitude) can be clearly seen.
The smaller version at right of this image shows the same view with a latitude/longitude grid overlaid.
This image has been processed to remove shading effects near the terminator – the dividing line between day and night – caused by Juno’s orbit.

Cosmic ‘Winter’ Wonderland

Although there are no seasons in space, this cosmic vista invokes thoughts of a frosty winter landscape. It is, in fact, a region called NGC 6357 where radiation from hot, young stars is energizing the cooler gas in the cloud that surrounds them. 

Located in our galaxy about 5,500 light years from Earth, NGC 6357 is actually a “cluster of clusters,” containing at least three clusters of young stars, including many hot, massive, luminous stars. The X-rays from Chandra and ROSAT reveal hundreds of point sources, which are the young stars in NGC 6357, as well as diffuse X-ray emission from hot gas. There are bubbles, or cavities, that have been created by radiation and material blowing away from the surfaces of massive stars, plus supernova explosions.

Credit: X-ray: NASA/CXC/PSU/L. Townsley et al; Optical: UKIRT; Infrared: NASA/JPL-Caltech

NASA’s Curiosity Rover Sharpens Paradox of Ancient Mars

Fast Facts:
› Curiosity rover findings add to a puzzle about ancient Mars because the same rocks that indicate a lake was present also indicate there was very little carbon dioxide in the air to help keep a lake unfrozen.
› No carbonate has been found definitively in rock samples analyzed by Curiosity.
› A new study calculates how much carbon dioxide could have been in the ancient atmosphere without resulting in carbonate detectable by the rover: not much.

Mars scientists are wrestling with a problem. Ample evidence says ancient Mars was sometimes wet, with water flowing and pooling on the planet’s surface. Yet, the ancient sun was about one-third less warm and climate modelers struggle to produce scenarios that get the surface of Mars warm enough for keeping water unfrozen.

A leading theory is to have a thicker carbon-dioxide atmosphere forming a greenhouse-gas blanket, helping to warm the surface of ancient Mars. However, according to a new analysis of data from NASA’s Mars rover Curiosity, Mars had far too little carbon dioxide about 3.5 billion years ago to provide enough greenhouse-effect warming to thaw water ice.

The same Martian bedrock in which Curiosity found sediments from an ancient lake where microbes could have thrived is the source of the evidence adding to the quandary about how such a lake could have existed. Curiosity detected no carbonate minerals in the samples of the bedrock it analyzed. The new analysis concludes that the dearth of carbonates in that bedrock means Mars’ atmosphere when the lake existed – about 3.5 billion years ago – could not have held much carbon dioxide.

“We’ve been particularly struck with the absence of carbonate minerals in sedimentary rock the rover has examined,” said Thomas Bristow of NASA’s Ames Research Center, Moffett Field, California. “It would be really hard to get liquid water even if there were a hundred times more carbon dioxide in the atmosphere than what the mineral evidence in the rock tells us.” Bristow is the principal investigator for the Chemistry and Mineralogy (CheMin) instrument on Curiosity and lead author of the study being published this week in the Proceedings of the National Academy of Sciences.

Curiosity has made no definitive detection of carbonates in any lakebed rocks sampled since it landed in Gale Crater in 2012. CheMin can identify carbonate if it makes up just a few percent of the rock. The new analysis by Bristow and 13 co-authors calculates the maximum amount of carbon dioxide that could have been present, consistent with that dearth of carbonate.

In water, carbon dioxide combines with positively charged ions such as magnesium and ferrous iron to form carbonate minerals. Other minerals in the same rocks indicate those ions were readily available. The other minerals, such as magnetite and clay minerals, also provide evidence that subsequent conditions never became so acidic that carbonates would have dissolved away, as they can in acidic groundwater.

The dilemma has been building for years: Evidence about factors that affect surface temperatures – mainly the energy received from the young sun and the blanketing provided by the planet’s atmosphere – adds up to a mismatch with widespread evidence for river networks and lakes on ancient Mars. Clues such as isotope ratios in today’s Martian atmosphere indicate the planet once held a much denser atmosphere than it does now. Yet theoretical models of the ancient Martian climate struggle to produce conditions that would allow liquid water on the Martian surface for many millions of years. One successful model proposes a thick carbon-dioxide atmosphere that also contains molecular hydrogen. How such an atmosphere would be generated and sustained, however, is controversial.

The new study pins the puzzle to a particular place and time, with an on-the-ground check for carbonates in exactly the same sediments that hold the record of a lake about a billion years after the planet formed.

For the past two decades, researchers have used spectrometers on Mars orbiters to search for carbonate that could have resulted from an early era of more abundant carbon dioxide. They have found far less than anticipated.

“It’s been a mystery why there hasn’t been much carbonate seen from orbit,” Bristow said. “You could get out of the quandary by saying the carbonates may still be there, but we just can’t see them from orbit because they’re covered by dust, or buried, or we’re not looking in the right place. The Curiosity results bring the paradox to a focus. This is the first time we’ve checked for carbonates on the ground in a rock we know formed from sediments deposited under water.”

The new analysis concludes that no more than a few tens of millibars of carbon dioxide could have been present when the lake existed, or it would have produced enough carbonate for Curiosity’s CheMin to detect it. A millibar is one one-thousandth of sea-level air pressure on Earth. The current atmosphere of Mars is less than 10 millibars and about 95 percent carbon dioxide.

“This analysis fits with many theoretical studies that the surface of Mars, even that long ago, was not warm enough for water to be liquid,” said Robert Haberle, a Mars-climate scientist at NASA Ames and a co-author of the paper. “It’s really a puzzle to me.”

Researchers are evaluating multiple ideas for how to reconcile the dilemma.

“Some think perhaps the lake wasn’t an open body of liquid water. Maybe it was liquid covered with ice,” Haberle said. “You could still get some sediments through to accumulate in the lakebed if the ice weren’t too thick.”

A drawback to that explanation is that the rover team has sought and not found in Gale Crater evidence that would be expected from ice-covered lakes, such as large and deep cracks called ice wedges, or “dropstones,” which become embedded in soft lakebed sediments when they penetrate thinning ice.

If the lakes were not frozen, the puzzle is made more challenging by the new analysis of what the lack of a carbonate detection by Curiosity implies about the ancient Martian atmosphere.

“Curiosity’s traverse through streambeds, deltas, and hundreds of vertical feet of mud deposited in ancient lakes calls out for a vigorous hydrological system supplying the water and sediment to create the rocks we’re finding,” said Curiosity Project Scientist Ashwin Vasavada of NASA’s Jet Propulsion Laboratory, Pasadena, California.

“Carbon dioxide, mixed with other gases like hydrogen, has been the leading candidate for the warming influence needed for such a system. This surprising result would seem to take it out of the running.”

When two lines of scientific evidence appear irreconcilable, the scene may be set for an advance in understanding why they are not. The Curiosity mission is continuing to investigate ancient environmental conditions on Mars.

It is managed by JPL, a division of Caltech in Pasadena, for NASA’s Science Mission Directorate, Washington. Curiosity and other Mars science missions are a key part of NASA’s Journey to Mars, building on decades of robotic exploration to send humans to the Red Planet in the 2030s

IMAGE….View of Yellowknife Bay Formation, with Drilling Sites This mosaic of images from Curiosity’s Mast Camera (Mastcam) shows geological members of the Yellowknife Bay formation, and the sites where Curiosity drilled into the lowest-lying member, called Sheepbed, at targets “John Klein” and “Cumberland.” The scene has the Sheepbed mudstone in the foreground and rises up through Gillespie Lake member to the Point Lake outcrop. These rocks record superimposed ancient lake and stream deposits that offered past environmental conditions favorable for microbial life. Rocks here were exposed about 70 million years ago by removal of overlying layers due to erosion by the wind.
The 50-centimeter scale bars at different locations in the image are about 20 inches long. The lower scale bar is about 26 feet (8 meters) away from where Curiosity was positioned when the view was recorded. The upper scale bar is about 98 feet (30 meters) from the rover’s location. The scene is a portion of a 111-image mosaic acquired during the 137th Martian day, or sol, of Curiosity’s work on Mars (Dec. 24, 2012). The foothills of Mount Sharp are visible in the distance, upper left, southwest of camera position.

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GOING OUT IN A BLAZE OF GLORY: CASSINI’S GRAND FINALE

With the conclusion of the international Cassini mission set for September 15, 2017, the spacecraft is poised to soon begin a thrilling two-part endgame.

Cassini will enter the first part of this denouement on November 30, 2016, when the spacecraft begins a series of 20 passes just beyond the outer edge of the main rings. These weekly loops around Saturn are called the F ring orbits, and they send the spacecraft high above and below the planet’s poles. During these orbits, Cassini will approach to within 4,850 miles (7,800 kilometers) of the center of the narrow F ring, with its wispy and ever-changing structure.

“During the F ring orbits we expect incredible views of the rings, along with the small moons and other structures embedded in them, as we’ve never seen them before,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. “The last time we got this close to the rings was during arrival at Saturn in 2004, and we saw only their backlit side. Now we have dozens of opportunities to examine their structure at extremely high resolution on both sides.”

Cassini’s final phase – called the Grand Finale – begins in earnest in April 2017. A close flyby of Saturn’s giant moon Titan will reshape the spacecraft’s orbit so that, instead of passing outside the rings, it passes through the gap between the rings and the planet. The spacecraft is expected to make 22 plunges through this gap – an unexplored space only about 1,500 miles (2,400 kilometers) wide – beginning with its first dive on April 27.

During the Grand Finale, Cassini will make the closest-ever observations of Saturn, mapping the planet’s magnetic and gravity fields with exquisite precision and returning ultra-close views of the atmosphere. Scientists also hope to gain new insights into Saturn’s interior structure, the precise length of a Saturn day, and the total mass of the rings – which may finally help settle the question of their age. The spacecraft will also directly analyze dust-sized particles in the main rings and sample the outer reaches of Saturn’s atmosphere – both first-time measurements for the mission.

The mission will come to a dramatic end on Sept. 15, 2017, after more than 13 years studying Saturn, its rings and moons – and nearly 20 years since launch. On that day, Cassini will dive into Saturn, returning data about the chemical composition of the planet’s upper atmosphere until its signal is lost, after which the spacecraft to burn up like a meteor.

“While it will be sad to say goodbye, Cassini’s final act is like getting a whole new mission in its own right,” said Spilker today at the joint 48th meeting of the American Astronomical Society’s Division for Planetary Sciences and 11th European Planetary Science Congress in Pasadena, California. “The scientific value of the F ring and Grand Finale orbits is so compelling that you could imagine an entire mission to Saturn designed around what we’re about to do.”

This view from NASA’s Cassini spacecraft showcases some of the amazingly detailed structure of Saturn’s rings.

The rings are made up of many smaller ringlets that blur together when seen from a distance. But when imaged up close, the rings’ structures display quite a bit of variation. Ring scientists are debating the nature of these features — whether they have always appeared this way or if their appearance has evolved over time.

This view looks toward the sunlit side of the rings from about 4 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Sept. 24, 2016.

The view was acquired at a distance of approximately 283,000 miles (456,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 32 degrees. Image scale is 17 miles (27 kilometers) per pixel.

Image Credit: NASA/JPL-Caltech/Space Science Institute/ Cassini

Time And Space

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Mars Rover Views Spectacular Layered Rock Formations

The layered geologic past of Mars is revealed in stunning detail in new color images returned by NASA’s Curiosity Mars rover, which is currently exploring the “Murray Buttes” region of lower Mount Sharp.

The new images arguably rival photos taken in U.S. National Parks.
Curiosity took the images with its Mast Camera (Mastcam) on Sept. 8.

The rover team plans to assemble several large, color mosaics from the multitude of images taken at this location in the near future.

“Curiosity’s science team has been just thrilled to go on this road trip through a bit of the American desert Southwest on Mars,” said Curiosity Project Scientist Ashwin Vasavada, of NASA’s Jet Propulsion Laboratory, Pasadena, California.

The Martian buttes and mesas rising above the surface are eroded remnants of ancient sandstone that originated when winds deposited sand after lower Mount Sharp had formed.

“Studying these buttes up close has given us a better understanding of ancient sand dunes that formed and were buried, chemically changed by groundwater, exhumed and eroded to form the landscape that we see today,” Vasavada said.

The new images represent Curiosity’s last stop in the Murray Buttes, where the rover has been driving for just over one month. As of this week, Curiosity has exited these buttes toward the south, driving up to the base of the final butte on its way out. In this location, the rover began its latest drilling campaign (on Sept. 9). After this drilling is completed, Curiosity will continue farther south and higher up Mount Sharp, leaving behind these spectacular formations.

Curiosity landed near Mount Sharp in 2012. It reached the base of the mountain in 2014 after successfully finding evidence on the surrounding plains that ancient Martian lakes offered conditions that would have been favorable for microbes if Mars has ever hosted life. Rock layers forming the base of Mount Sharp accumulated as sediment within ancient lakes billions of years ago.

On Mount Sharp, Curiosity is investigating how and when the habitable ancient conditions known from the mission’s earlier findings evolved into conditions drier and less favorable for life.

IMAGE 1….This view from the Mast Camera (Mastcam) in NASA’s Curiosity Mars rover shows an outcrop with finely layered rocks within the “Murray Buttes” region on lower Mount Sharp.
The buttes and mesas rising above the surface in this area are eroded remnants of ancient sandstone that originated when winds deposited sand after lower Mount Sharp had formed. Curiosity closely examined that layer – called the “Stimson formation” – during the first half of 2016, while crossing a feature called “Naukluft Plateau” between two exposures of the Murray formation. The layering within the sandstone is called “cross-bedding” and indicates that the sandstone was deposited by wind as migrating sand dunes.
The image was taken on Sept. 8, 2016, during the 1454th Martian day, or sol, of Curiosity’s work on Mars.


IMAGE 2….This view from the Mast Camera (Mastcam) in NASA’s Curiosity Mars rover shows a sloping hillside within the “Murray Buttes” region on lower Mount Sharp. The rim of Gale Crater, where the rover has been active since landing in 2012, is visible in the distance, through the dusty haze.
The image was taken on Sept. 8, 2016, during the 1454th Martian day, or sol, of Curiosity’s work on Mars.


IMAGE 3….This view from the Mast Camera (Mastcam) in NASA’s Curiosity Mars rover shows sloping buttes and layered outcrops within the “Murray Buttes” region on lower Mount Sharp.
The buttes and mesas rising above the surface are eroded remnants of ancient sandstone that originated when winds deposited sand after lower Mount Sharp had formed. Curiosity closely examined that layer – called the “Stimson formation” – during the first half of 2016, while crossing a feature called “Naukluft Plateau” between two exposures of the Murray formation. The layering within the sandstone is called “cross-bedding” and indicates that the sandstone was deposited by wind as migrating sand dunes.
The image was taken on Sept. 8, 2016, during the 1454th Martian day, or sol, of Curiosity’s work on Mars.


IMAGE 4….This view from the Mast Camera (Mastcam) in NASA’s Curiosity Mars rover shows finely layered rocks within the “Murray Buttes” region on lower Mount Sharp.
The buttes and mesas rising above the surface in this area are eroded remnants of ancient sandstone that originated when winds deposited sand after lower Mount Sharp had formed. Curiosity closely examined that layer – called the “Stimson formation” – during the first half of 2016, while crossing a feature called “Naukluft Plateau” between two exposures of the Murray formation. The layering within the sandstone is called “cross-bedding” and indicates that the sandstone was deposited by wind as migrating sand dunes.
The image was taken on Sept. 8, 2016, during the 1454th Martian day, or sol, of Curiosity’s work on Mars.


IMAGE 5….This view from the Mast Camera (Mastcam) in NASA’s Curiosity Mars rover shows a hillside outcrop with layered rocks within the “Murray Buttes” region on lower Mount Sharp.
The buttes and mesas rising above the surface in this area are eroded remnants of ancient sandstone that originated when winds deposited sand after lower Mount Sharp had formed. Curiosity closely examined that layer – called the “Stimson formation” – during the first half of 2016, while crossing a feature called “Naukluft Plateau” between two exposures of the Murray formation. The layering within the sandstone is called “cross-bedding” and indicates that the sandstone was deposited by wind as migrating sand dunes.
The image was taken on Sept. 8, 2016, during the 1454th Martian day, or sol, of Curiosity’s work on Mars.
Malin Space Science Systems, San Diego, built and operates the rover’s Mastcam. NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the Mars Science Laboratory Project for NASA’s Science Mission Directorate, Washington. JPL designed and built the project’s Curiosity rover.

AN OCEAN LIES A FEW KILOMETERS BENEATH ENCELADUS’S ICY SURFACE

With eruptions of ice and water vapor, and an ocean covered by an ice shell, Saturn’s moon Enceladus is one of the most fascinating in the solar system, especially as interpretations of data provided by the Cassini spacecraft have been contradictory until now. An international team including researchers from the Laboratoire de Planétologie Géodynamique de Nantes (CNRS/Université de Nantes/Université d’Angers), Charles University in Prague, and the Royal Observatory of Belgium (and the Instituut voor Sterrenkunde) recently proposed a new model that reconciles different data sets and shows that the ice shell at Enceladus’s south pole may be only a few kilometers thick. This suggests that there is a strong heat source in the interior of Enceladus, an additional factor supporting the possible emergence of life in its ocean. The study has just been published online on the website of Geophysical Research Letters.

Initial interpretations of data from Cassini flybys of Enceladus estimated that the thickness of its ice shell ranged from 30 to 40 km at the south pole to 60 km at the equator. These models were unable to settle the question of whether or not its ocean extended beneath the entire ice shell. However, the discovery in 2015 of an oscillation in Enceladus’s rotation known as a libration, which is linked to tidal effects, suggests that it has a global ocean and a much thinner ice shell than predicted, with a mean thickness of around 20 km. Nonetheless, this thickness appeared to be inconsistent with other gravity and topography data.

In order to reconcile the different constraints, the researchers propose a new model in which the top two hundred meters of the ice shell acts like an elastic shell. According to this study, Enceladus is made up successively of a rocky core with a radius of 185 km, and an internal ocean approximately 45 km deep, isolated from the surface by an ice shell with a mean thickness of around 20 km, except at the south pole where it is thought to be less than 5 km thick. In this model, the ocean beneath the ice makes up 40% of the total volume of the moon, while its salt content is estimated to be similar to that of Earth’s oceans.

All this implies a new energy budget for Enceladus. Since a thinner ice shell retains less heat, the tidal effects caused by Saturn on the large fractures in the ice at the south pole are no longer enough to explain the strong heat flow affecting this region. The model therefore reinforces the idea that there is strong heat production in Enceladus’s deep interior that may power the hydrothermal vents on the ocean floor. Since complex organic molecules, whose precise composition remains unknown, have been detected in Enceladus’s jets, these conditions appear to be favorable to the emergence of life. The relative thinness of the ice shell at the south pole could also allow a future space exploration mission to gather data, in particular using radar, which would be far more reliable and easy to obtain than with the 40 km thick ice shell initially calculated. It looks as if Enceladus still has many secrets in store!


Image showing the thickness of Enceladus’s ice shell, which reaches 35 kilometers in the cratered equatorial regions (shown in yellow) and less than 5 kilometers in the active south polar region (shown in blue).