There are few sights on Mars more satisfying than its oddly familiar — yet weirdly alien — dunes.
On the one hand, the Martian dunes look much like the dunes we have on Earth — aeolian (“wind-driven”) formations undulating across the landscape have similarities regardless of which planet they were blown on.
But there’s something uncanny about Martian dunes. Maybe it’s the “extra” tiny ripples that NASA’s Curiosity itself discovered — a phenomenon that is exclusive to the Martian atmosphere. Or maybe it’s just that I know these dunes are being seen through synthetic eyes on a world millions of miles across the interplanetary void.
But right now, the six-wheeled robot is sampling grains of wind-blown regolith from a linear dunes on the slopes of Mount Sharp to help planetary scientists on Earth build a picture of how this ancient landscape was shaped.
Curiosity scooped samples of linear dune material into the rover’s Sample Analysis at Mars (SAM) so they could be compared with material from other dunes it had visited in 2015 and 2016. Samples are also planned to be delivered to the mission’s Chemistry and Mineralogy (CheMin) instrument. As NASA points out, this is the first ever study of extraterrestrial dunes. (Dune fields also exist on Saturn’s moon Titan, but as recent research indicates, those are very different beasts and haven’t been directly sampled.)
“At these linear dunes, the wind regime is more complicated than at the crescent dunes we studied earlier,” said Mathieu Lapotre, of the California Institute of Technology (Caltech), in Pasadena, Calif., who led the Curiosity dune campaign. “There seems to be more contribution from the wind coming down the slope of the mountain here compared with the crescent dunes farther north.”
All of the dunes Curiosity has sampled are a part of the Bagnold Dunes, a dune field that stretches up the northwestern flank of Mount Sharp. Within the field, depending on the wind conditions, different types of dunes have been found.
“There was another key difference between the first and second phases of our dune campaign, besides the shape of the dunes,” said Lapotre in a NASA statement. “We were at the crescent dunes during the low-wind season of the Martian year and at the linear dunes during the high-wind season. We got to see a lot more movement of grains and ripples at the linear dunes.”
It’s official, there’s a whole lot of nothing in Saturn’s innermost ring gap.
This blunt — and slightly mysterious — conclusion was reached when scientists studied Cassini data after the spacecraft’s first dive through the gas giant’s ring plane. At first blush, this might not sound so surprising; the 1,200-mile-wide gap between Saturn’s upper atmosphere and the innermost edge of its rings does appear like an empty place. But as the NASA spacecraft barreled through the gap on April 26, mission scientists expected Cassini to hit a few stray particles on its way through.
Instead, it hit nothing. Or, at least, far fewer particles than they predicted.
“The region between the rings and Saturn is ‘the big empty,’ apparently,” said Earl Maize, Cassini’s project manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected.”
Using Cassini’s Radio and Plasma Wave Science (RPWS), the scientists expected to detect multiple “cracks and pops” as the spacecraft shot through the gap. Instead, it picked up mainly signals from energetic charged particles buzzing in the planet’s magnetic field. When converted into an audio file, these signals make a whistling noise and this background whistle was expected to be drowned out by the ruckus of dust particles bouncing off the spacecraft’s body. But, as the following audio recording proves, very few pops and cracks of colliding debris were detected — it sounds more like an off-signal radio tuner:
Compare that with the commotion Cassini heard as it passed through the ring plane outside of Saturn’s rings on Dec. 18, 2016:
Now that is what it sounds like to get smacked by a blizzard of tiny particles at high speed.
“It was a bit disorienting — we weren’t hearing what we expected to hear,” said William Kurth, RPWS team lead at the University of Iowa, Iowa City. “I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.”
From this first ring gap dive, NASA says Cassini likely only hit a handful of minute, 1 micron particles — particles no larger than those found in smoke. And that’s a bit weird.
As weird as it may be, the fact that the region of Cassini’s first ring dive is emptier than expected now allows mission scientists to carry out optimized science operations with the spacecraft’s instruments. On the first pass, Cassini’s dish-shaped high-gain antenna was used as a shield to protect the spacecraft as it made the dive. On its next ring dive, which is scheduled for Tuesday at 12:38 p.m. PT (3:38 p.m. ET), this precaution is evidently not needed and the spacecraft will be oriented to better view the rings as it flies through.
So there we have it, the first mysterious result of Cassini’s awesome Grand Finale! 21 ring dives to go…
UPDATE (1:30 a.m. PT): A firehose of Cassini data has opened up and raw images of the spacecraft’s approach to the ring plane are coming in at a rapid pace. You can see the raw images appear online at the same time Cassini’s science team sees them here. At time of writing (and without any scientific analysis) the images have been of Saturn’s polar vortex and various views of the planet’s upper atmosphere. It’s going to take some time for more detailed views to become available, but, wow, it’s exhilarating to see Cassini images arrive at such a rate. Here are a few:
Original: As NASA planned, just before midnight on Wednesday (April 26), the veteran Cassini spacecraft made radio contact with the Goldstone 70-meter antenna in California, part of the Deep Space Network (DSN), which communicates with missions in space. Within minutes, Goldstone was receiving data, meaning the spacecraft had not only survived its first ring dive of the “Grand Finale” phase of its mission, but that it was also transmitting science data from a region of space that we’ve never explored before.
“We did it! Cassini is in contact with Earth and sending back data after a successful dive through the gap between Saturn and its rings,” tweeted the official NASA Cassini account just after the DSN confirmed it was receiving telemetry.
“The gap between Saturn and its rings is no longer unexplored space – and we’re going back 21 times,” they added.
Around 22 hours prior to Cassini’s signal, the spacecraft made its daring transit through the gap between Saturn’s upper atmosphere and innermost ring after using the gravity of Titan on Friday (April 21) to send it on a ballistic trajectory through the ring plane. But during that time the spacecraft went silent, instead devoting resources to carrying out science observations during the dive.
Of course there was much anticipation for Cassini to “phone home” tonight and it did just that right on schedule and now we can look forward to another 21 dives through Saturn’s rings before Cassini burns up in the gas giant’s upper atmosphere on Sept. 15, ending its epic 13 year mission at the solar system’s ringed planet.
“No spacecraft has ever been this close to Saturn before. We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” said Earl Maize, Cassini Project Manager at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., in a statement. “I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape.”
So now we wait until images of this never-before-explored region of Saturn are released.
NASA’s Cassini mission sure has a knack for putting stuff into perspective — and this most recent view from Saturn orbit is no different. That dot in the center of the image isn’t a dud pixel in Cassini’s camera CCD. That’s us. All of us. Everyone.
To quote Carl Sagan:
“Look again at that dot. That’s here. That’s home. That’s us. On it everyone you love, everyone you know, everyone you ever heard of, every human being who ever was, lived out their lives…”
Sagan wrote that passage in his book “Pale Blue Dot: A Vision of the Human Future in Space” when reflecting on the famous “Pale Blue Dot” image that was beamed back to Earth by NASA’s Voyager 1 spacecraft in 1990. That’s when the mission returned a profound view of our planet from a distance of 3.7 billion miles (or 40.5AU) as it was traveling through the solar system’s hinterlands, on its way to interstellar space. Since then, there’s been many versions of pale blue dots snapped by the armada of robotic missions around the solar system and Cassini has looked back at us on several occasions from its orbital perch.
Now, just before Cassini begins the final leg of its Saturnian odyssey, it has again spied Earth through a gap between the gas giant’s A ring (top) and F ring (bottom). In a cropped and enhanced version, our moon is even visible! The image is composed of many observations captured on April 12, stitched together as a mosaic when Saturn was 870 million miles (roughly 9.4AU) from Earth.
On April 20 (Friday), Cassini will make its final flyby of Titan, Saturn’s largest moon, using its gravity to fling itself through Saturn’s ring plane (on April 26) between the innermost ring and the planet’s cloudy upper atmosphere, revealing a view that we’ve never before seen. For 22 orbits, Cassini will dive into this uncharted region, possibly revealing new things about Saturn’s evolution, what material its rings contain and incredibly intimate views of its atmosphere.
This daring maneuver will signal the beginning of the end for this historic mission, however. On Sept. 15, Cassini will be intentionally steered into Saturn’s atmosphere to burn up as a human-made meteor. It is low in fuel, so NASA wants to avoid the spacecraft from crashing into and contaminating one of Saturn’s potentially life-giving moons — Titan or Enceladus.
So, appreciate every image that is captured by Cassini over the coming weeks. The pictures will be like nothing we’ve seen before of the ringed gas giant, creating a very bittersweet phase of the spacecraft’s profound mission to Saturn.
Imagine speeding down the highway and plowing into an unfortunate swarm of mosquitoes. Now imagine that you had the ability to precisely measure the mass of each mosquito, the speed at which it was traveling and the direction it was going before it exploded over your windscreen.
Granted, the technology to accomplish that probably isn’t feasible in such an uncontrolled environment. Factors such as vibration from the car’s motor and tires on the road, plus wind and air turbulence will completely drown out any “splat” from a minuscule insect’s body, rendering any signal difficult to decipher from noise.
The European LISA Pathfinder spacecraft is a proof of concept mission that’s currently in space, orbiting a region of gravitational stability between the Earth and the sun — called the L1 point located a million miles away. The spacecraft was launched there in late 2015 to carry out precision tests of instruments that will eventually be used in the space-based gravitational wave detector eLISA. Inside the payload is a miniaturized laser interferometer system that measures the distance between two test masses.
When launched in 2034, eLISA (which stands for Evolved Laser Interferometer Space Antenna) will see three spacecraft, orbiting the sun at the L1 point, firing ultra-precise lasers at one another as part of a space-based gravitational wave detector. Now we actually know gravitational waves exist — after the US-based Laser Interferometer Gravitational-wave Observatory (or LIGO) detected the space-time ripples created after the collisions of black holes — excitement is building that we might, one day, be able to measure other phenomena, such as the ultra-low frequency gravitational waves that were created during the Big Bang.
But the only way we can do this is to send stunningly precise interferometers into space, away from our vibration-filled atmosphere to stand a chance of detecting some of the faintest space-time rumbles in our cosmos that would otherwise be drowned out by a passing delivery truck or windy day. And LISA Pathfinder is currently out there, testing a tiny laser interferometer in a near-perfect gravitational free-fall, making the slightest of slight adjustments with its “ultra-precise micro-propulsion system.”
Although LISA Pathfinder is a test (albeit a history-making test of incredible engineering ingenuity), NASA thinks that it could actually be used as an observatory in its own right; not for hunting gravitational waves, but for detecting comet dust.
Like our mosquito-windscreen analogy, spacecraft get hit by tiny particles all the time, and LISA Pathfinder is no exception. These micrometeoroides come from eons of evaporating comets and colliding asteroids. Although measuring less than the size of a grain of sand, these tiny particles zip around interplanetary space at astonishing speeds — well over 22,000 miles per hour (that’s 22 times faster than a hyper-velocity rifle round) — and can damage spacecraft over time, slowly eroding unprotected hardware.
Therefore, it would be nice if we could create a map of regions in the solar system that contain lots of these particles so we can be better prepared to face the risk. Although models of solar system evolution help and we can estimate the distribution of these particles, they’ve only ever been measured near Earth, so it would be advantageous to find the “ground truth” and measure them directly from another, unexplored region of the solar system.
This is where LISA Pathfinder comes in.
As the spacecraft gets hit by these minuscule particles, although they are tiny, their high speed ensures they pack a measurable punch. As scientists want the test weights inside the spacecraft to be completely shielded from any external force — whether that’s radiation pressure from the sun or marauding micro-space rocks — the spacecraft has been engineered to be an ultra-precise container that carefully adjusts its orientation an exact amount to directly counter these external forces (hence the “ultra-precise micro-propulsion system”).
This bit is pretty awesome: Whenever these tiny space particles hit the spacecraft, it compensates for the impact and that compensation is registered as a “blip” in the telemetry being beamed back to Earth. After careful analysis of the various data streams, researchers are learning a surprising amount of information about these micrometeoroides — such as their mass, speed, direction of travel and even their possible origin! — all for the ultimate goal of getting to know the tiny pieces of junk that whiz around space.
“Every time microscopic dust strikes LISA Pathfinder, its thrusters null out the small amount of momentum transferred to the spacecraft,” said Diego Janches, of NASA’s Goddard Space Flight Center in Greenbelt, Md. “We can turn that around and use the thruster firings to learn more about the impacting particles. One team’s noise becomes another team’s data.”
So, it turns out that you can precisely measure a mosquito impact on your car’s windshield — so long as that “mosquito” is a particle of space dust and your “car” is a spacecraft a million miles from Earth.
NASA put together a great video, watch it:
Aside: So it turned out that I inadvertently tested the “car-mosquito” hypothesis when driving home from Las Vegas — though some of these were a lot bigger than mosquitoes…
The NASA robot continues to rove the unforgiving slopes of Mount Sharp, but dramatic signs of damage are appearing on its aluminum wheels.
In 2013, earlier than expected signs of damage to Curiosity’s wheels were causing concern. Four years on and, unsurprisingly, the damage has gotten worse. The visible signs of damage have now gone beyond superficial scratches, holes and splits — on Curiosity’s middle-left wheel (pictured above), there are two breaks in the raised zigzag tread, known as “grousers.” Although this was to be expected, it’s not great news.
The damage, which mission managers think occurred some time after the last wheel check on Jan. 27, “is the first sign that the left middle wheel is nearing a wheel-wear milestone,” said Curiosity Project Manager Jim Erickson, at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., in a statement.
After the 2013 realization that Curiosity’s aluminum wheels were accumulating wear and tear faster than hoped, tests on Earth were carried out to understand when the wheels would start to fail. To limit the damage, new driving strategies were developed, including using observations from orbiting spacecraft to help rover drivers chart smoother routes.
It was determined that once a wheel suffers three grouser breaks, the wheel would have reached 60 percent of its useful life. Evidently, the middle left wheel is almost there. According to NASA, Curiosity is still on course for fulfilling its science goals regardless of the current levels of wheel damage.
“This is an expected part of the life cycle of the wheels and at this point does not change our current science plans or diminish our chances of studying key transitions in mineralogy higher on Mount Sharp,” added Ashwin Vasavada, Curiosity’s Project Scientist also at JPL.
While this may be the case, it’s a bit of a downer if you were hoping to see Curiosity continue to explore Mars many years beyond its primary mission objectives. Previous rover missions, after all, have set the bar very high — NASA’s Mars Exploration Rover Opportunity continues to explore Meridiani Planum over 13 years since landing in January 2004! But Curiosity is a very different mission; it’s bigger, more complex and exploring a harsher terrain, all presenting very different engineering challenges.
Currently, the six-wheeled rover is studying dunes at the Murray formation and will continue to drive up Mount Sharp to its next science destination — the hematite-containing “Vera Rubin Ridge.” After that, it will explore a “clay-containing geological unit above that ridge, and a sulfate-containing unit above the clay unit,” writes NASA.
Since landing on Mars in August 2012, the rover has accomplished an incredible array of science, adding amazing depth to our understanding of the Red Planet’s habitable potential. To do this, it has driven 9.9 miles (16 kilometers) — and she’s not done yet, not by a long shot.
Never before has a space probe come so close to the pint-sized moon embedded in Saturn’s rings — and when NASA’s Cassini buzzed Pan, the spacecraft revealed what a strange moon it really is.
This is Pan, a 22 mile-wide moon that scoots through Saturn’s rings, orbiting the gas giant once every 13.8 hours. And it’s weird.
Resembling a giant ravioli or some kind of “flying saucer” from a classic alien invasion sci-fi comic, Pan is known as a “shepherd moon” occupying the so-called Encke Gap inside Saturn’s A Ring. This gap is largely free of particles and it has become Pan’s job to hoover up any stray material — the moon’s slight gravity pulls particles onto its surface and scatters others back out into the ring system. This gravitational disturbance creates waves that ripple through the ring material, propagating for hundreds of miles.
On March 7, NASA’s Cassini mission came within 15,268 miles of Pan, revealing incredible detail in the moon’s strange surface. It’s thought that its characteristic equatorial ridge (a trait it shares with another Saturn moon Atlas) is caused by the gradual accumulation of ring material throughout the moon’s formation and with these new observations, scientists will be able to better understand how Pan came to be.
As Cassini rapidly approaches the end of its mission, eventually orbiting through Saturn’s ring plane as a part of its “Grand Finale,” we can expect more of these striking views from orbit before the veteran probe is steered into Saturn’s atmosphere in September, bringing its historic mission to an end.
Evidence is mounting around the cryovolcanic history of the solar system’s innermost dwarf planet — and its most recent eruptions may have happened within the last four million years.
Since NASA’s Dawn mission arrived at dwarf planet Ceres in 2015, we’ve been treated to some wonderfully detailed images of the small world’s pockmarked terrain. Understanding the underlying processes of what is believed to be an ice-filled celestial body, however, is taking some time to decipher. But with more observations comes more understanding and planetary scientists are getting close to realizing what lies beneath those craters and, possibly, unlocking the secrets behind a very icy and very alien phenomenon we have no experience of in our terrestrial lives.
That phenomenon is cryovolcanoes. And Ceres seems to have them.
The most startling feature on Ceres is Occator Crater. This 57 mile-wide feature is the result of a massive impact tens of millions of years ago. Large craters on small worlds isn’t necessarily a strange thing in our battered solar system, but what is strange about Occator is the very bright feature (and small bright patches surrounding it) in the crater’s center. Even before Dawn arrived in orbit and only fuzzy images of Ceres were available, hopes were high that this bright anomaly in the otherwise gray Cererian landscape could be indicative of ices or some mineral compound that was formed by the presence of water.
Cryovolcanoes — or, simply, ice volcanoes — are hypothetical features that are believed to be common throughout the outer solar system. These ice volcanoes are thought to erupt in a similar fashion to the volcanoes we have on Earth, but instead of molten rock, these volcanoes erupt ice-cold volatiles — like water, methane or ammonia. Dwarf planet Pluto, for example, has features that look like cryovolcanoes, as does Saturn’s moon Titan and Jupiter’s moon Ganymede. These locations are extremely cold and known to contain large quantities of methane and water, so internal heating (caused by radioactive decay or tidal processes) melt the ices and force them to the surface. When they vent through the crust, gases are released and the liquids quickly freeze and sublimate.
Around these vents, cryovolcanoes will grow, and if Ceres really does have its own ice volcanoes, this will be the closest planetary body to the sun (and Earth) known to have them.
Now, in research headed by the Max Planck Institute for Solar System Research (MPS) in Göttingen, Germany, scientists using Dawn data have, for the first time, taken a stab at dating the age of the bright material in the center of Occator Crater and realized that the location has likely been the site of many cryovolcanic eruptions in the recent past.
In the center of Occator, a pit measuring around 7 miles wide can be found, likely formed during the massive impact approximately 30 million years ago. But around the edges of that pit are mountains, some 750 meters high, and in the center is a cracked dome measuring 400 meters high and nearly 2 miles wide. This bright dome is called Cerealia Facula and surrounding it appears to be material that was spewed from a cryovolcanic vent. Analysis has shown that this material contains salts that were formed in the presence of water from Ceres’ interior and then deposited onto the surface. The minerals around Cerealia Facula has been dated to only four million years, meaning that there has been cryovolcanic eruptions long after the Occator impact punctured Ceres’ crust.
“The age and appearance of the material surrounding the bright dome indicate that Cerealia Facula was formed by a recurring, eruptive process, which also hurled material into more outward regions of the central pit,” said Andreas Nathues, lead investigator of Dawn’s Framing Camera. “A single eruptive event is rather unlikely.” As noted in an MPS news release, Jupiter moons Callisto and Ganymede have similar features that are also believed to be related to cryovolcanic eruptions.
“The large impact that tore the giant Occator crater into the surface of the dwarf planet must have originally started everything and triggered the later cryovolcanic activity,” added Nathues.
Previous imagery of haze inside Occator Crater has led to the suspicion that ices remain on the surface today; the haze could be vapor from sublimating water ice exposed on the surface having been forced to the surface from Ceres’ interior. Evidence for this haze has been supported by other studies and appears to vary throughout the day as one would expect — increased sunlight would accelerate sublimation (ice turning from a solid to a vapor without passing through the liquid phase).
If volatiles are still being extruded through this vent today, this would seem to indicate that, in addition to the cryovolcanic eruptions in the last four million years, some form of activity continues to this day. Add this to the recent discovery of organic material on Ceres’ surface, this small world has become a very big asset for planetary science.
For more on Ceres’ icy eruptions, check out one of my last DNews videos:
Last week’s Juno flyby of Earth was an exciting event. NASA’s Jupiter-bound mission buzzed our planet on Wednesday (Oct. 9) only 350 miles from the surface, providing amateur astronomers with an opportunity to snapshot Juno as she flew past, stealing a little momentum from Earth and sling-shotting toward the largest planet in the Solar System. Alas, the flyby event wasn’t without incident.
The spacecraft dropped into “safe mode” shortly after its terrestrial encounter. Safe mode is a fail safe on spacecraft that protects onboard instruments from an unexpected condition. This can come in the form of a power spike or some other instrumental error. It is not known at this time what triggered this particular event, but the upshot is that Juno is back in its nominal state.
“Onboard Juno, the safe mode turned off instruments and a few non-critical spacecraft components, and pointed the spacecraft toward the Sun to ensure the solar arrays received power. The spacecraft acted as expected during the transition into and while in safe mode.”
Juno’s planned trajectory was not impacted during the flyby and it is expected to make orbital insertion around Jupiter in July 2016.
The mission was launched from Cape Canaveral, Fla., in 2011 and, through a wonderful bit of orbital mechanics, was commanded to do one 2-year orbit around the Sun. Then, last week, it ended up where it started to use our planet as a speed booster, flinging it further out into the Solar System toward Jupiter’s orbit. This acceleration “freebie” was needed as the launch vehicle, an Atlas V rocket, didn’t have the oomph to propel the spacecraft deeper into space.
Once Juno arrives at Jupiter, it will give the gas giant a thorough full-body examination, investigating what lies beneath its clouds, how it generates its powerful magnetic field and how it evolved. The repercussions of Juno’s one-year primary mission will hopefully expose not only how Jupiter is formed, but how Earth evolved into its current state.
As Juno sped past on Wednesday, I allowed myself an early celebration of some fine flying by NASA scientists with a Gin & Tonic (or a Juno & Tonic) in my special JPL-bought Juno glasses.
Good luck Juno, will look forward to seeing you at Jupiter in a little under three years time!