Two Tempting Reprise Missions: Explore Titan or Bring Back a Piece of A Comet

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Dragonfly is a quadcopter lander that would take advantage of the environment on Titan to fly to multiple locations, some hundreds of miles apart, to sample materials and determine the composition of the surface.  A central goal would be to analyze Titan’s organic chemistry and assess its habitability. (NASA)

Unmanned missions to planets and moons and asteroids in our solar system have been some of NASA’s most successful efforts in recent years, with completed or on-going ventures to Mars, Saturn, Jupiter, the asteroid Bennu, our moon, Pluto, Mercury and bodies around them all.   On deck are a funded mission to Europa, another to Mars and one to the unique metal asteroid 16 Psyche orbiting the sun between Mars and Jupiter.

We are now closer to adding another New Frontiers class destination to that list, and NASA announced this week that it will be to either Saturn’s moon Titan or to the comet 67P/Churyumov-Gerasimenko.

After assessing 12 possible New Frontiers proposals, these two made the cut and will receive $4 million each to further advance their proposed science and technology. One of them will be selected in spring of 2019 for launch in the mid 2020s.

With the announcement, associate administrator for NASA’s Science Mission Directorate Thomas Zurbuchen described the upcoming choice as between two “tantalizing investigations that seek to answer some of the biggest questions in our solar system today.”

Those questions would be:  How did water and other compounds essential for life arrive on Earth?  Comets carry ancient samples of both, and so can potentially provide answers.

And with its large inventories of nitrogen, methane and other organic compounds, is Titan potentially habitable?  Then there’s the added and very intriguing prospect of visiting the methane lakes of that frigid moon.

The CAESAR mission would return to the nucleus of  comet explored by the European Space Agency’s Rosetta mission, and its lander Philae.  (NASA)

Both destinations selected have actually been visited before.

The European Space Agency’s Rosetta mission orbited the comet 67P/Churyumov-Gerasimenko comet for two years and deployed a lander, which did touch down but sent back data for only intermittently for several days.

And the NASA’s Cassini-Huygens mission to Saturn passed by Titan regularly during its decade exploring that system, and the ESA’s Huygens probe did land on Titan and sent back information for a short time.

So both Rosetta and Cassini-Huygens began the process of understanding these distant and potentially revelatory destinations, and now NASA is looking to take it further.

The Titan “Dragonfly” mission, for instance, would feature a “quadcopter” or “rotorcraft” — a vehicle that is part helicopter and part drone.  It’s designed to hop hundreds of miles around the moon to sample what has already been determined to be a surface with many organic compounds and liquid methane lakes.

Those already identified hydrocarbon seas may contain amino acids and other interesting molecules, making Titan a test bed of sorts on how life arose on Earth. With spectrometers, drills, and cameras, Dragonfly would split its mission between science in the air and on the ground.

Although frigid, Titan is otherwise now known to be a relatively benign place, and the rotorcraft could potentially survive for several years. That could give the team time to “evaluate how far prebiotic chemistry has progressed in an environment where we know we have the ingredients for life,” said lead investigator Elizabeth Turtle from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland.

“Titan is a unique ocean world, with lakes and rivers of liquid methane flowing across its surface,” she said.  But it is also very cold. Average surface temperatures are -290 degrees Fahrenheit,  so any potential lifeforms would face some major challenges.

A methane lake near the northern pole of Saturn’s moon, Titan. The image was taken using radar on the Cassini spacecraft. NASA/JPL-Caltech

The comet mission CAESAR (Comet Astrobiology Exploration SAmple Return) will take a very different route than Rosetta did and will use different propulsion that will get the spacecraft to the comet in four years.  The plan is to then perform a “touch and go” maneuver with an extended arm to pick up 100 grams of precious Rosetta material from the nucleus.

And then unlike with Rosetta, the plan is to cache the sample and bring it back to Earth for intensive study.

By returning to 67P/Churyumov-Gerasimenko, a body mapped in detail by Rosetta, the mission is “able to design our spacecraft specifically for the conditions we know,” said Steven Squyres of Cornell University, principal investigator for the mission.

During a news conference, Squyres said that “comets are among the most scientifically important objects in the solar system, but they’re also among the most poorly understood.

“They’re the most primitive building blocks of planets; they contain materials that date from the very earliest moments of solar system formation and even before. Comets were a source of water for the Earth’s oceans, and critically they were a source of organic molecules that contributed to the origin of life.”

Squyres told me after the announcement that the CAESAR instruments will allow for more precise measurements than from Rosetta, and that a successful sample return could potentially change our understanding of the Earth’s history substantially.  He said the sample collection would also importantly include gases.

NASA has already succeeded with comet sample return — the Stardust mission to fly through the plume of comet Wild-2.  It did gather some dust, but it didn’t land on the nucleus like Rosetta did and CAESAR would.

Sample return is clearly a high priority for NASA and other space agencies.  The NASA 2020 mission to Mars is designed to collect and cache rock samples for later return, and two other sample return missions are underway.  Both are to asteroids, with one launched last year by NASA and the other by the Japanese space agency JAXA in 2014.

The nucleus of the 67P/Churyumov-Gerasimenko comet, where the CAESAR mission hopes to be headed in the 2020s. (ESA)

What “Dragonfly” would return is data about a moon shrouded in haze and unlike any other body in our solar system.

When the Huygen’s probe descended to the moon in early 2005, planetary scientists weren’t sure if the moon’s surface was covered in oceans methane and ethane.  So Huygens was designed to float if solid ground wasn’t to be found.

As the lander sailed through the haze it took hundreds of aerial images that showed an alien but strikingly Earth-like landscape of mountains, dry floodplains and what appeared to be river deltas. Huygens did land on something solid, though liquid methane flowed nearby and the Huygens cameras could see intricate channels cutting into the surface.

When Huygens touched down, it did so with a soft thud and a short slide across the frozen surface. Later analysis of the lander’s telemetry showed that Huygens sank around 4.7 inches into the surface on first contact, bounced and slid before coming to a stop.

This knowledge made possible a Titan project with a lander that can jump from one spot to another quite far away.  Those methane lakes, it is now understood, are largely found near the northern pole, and so floatation equipment is no longer necessary.

The Huygens descent to the surface of Titan, as recorded in 2005.  (ESA/NASA)

Squyres, a professor of physical science at Cornell University, is also principal investigator for the long-lasting Mars exploration rovers, one of which operated successfully for 8 years and the other –Opportunity — is still exploring Mars 13 years after landing.

He told me that his long years heading the Mars rover mission had convinced him that his greatest satisfaction in science comes from identifying a plausible space project, putting together a team of scientists, engineers and managers who can plausibly pull it off, and then work nonstop for years putting together a proposal to get it selected and funded. His team now numbers about 150 people and will soon grow much larger.

It was that sense of “shared struggle,” he said, that gave him enormous satisfaction. That came, of course, with a happy ending in several competitions, but he said he also knows the disappointment of not being selected for others.

Two other missions were selected for additional, though limited, funding under the New Frontiers program.  One is headed by NASA Ames Research Center astrobiologist Chris McKay and will be funded to develop “cost-effective techniques that limit spacecraft contamination and thereby enable life detection measurements on cost-capped missions.”

The larger mission his team proposed would go to the water vapor plume spurting out of Saturn’s moon Enceladus, with the goal of searching for signs of life.

The two projects selected were no doubt something of a disappointment to researchers who have longed for NASA to return to Venus.  As the study of exoplanets progresses, one of the key questions facing scientists is why Earth and Venus evolved so differently.  Both are within our sun’s habitable zone, but Venus experienced a runaway greenhouse effect that parched the surface and pushed surface temperatures to a led-melting 870 degrees F.

Three of the proposed New Frontiers missions were to Venus but, as in other recent competitions, none were selected by NASA.  One of the Venus proposals, led by Goddard’s Lori Glaze, was selected for further technology development.

Venus hasn’t been visited by a NASA spacecraft in decades, leading to hopes that one of the New Frontiers finalists would be a mission there. But it was not to be. ESA operated the Venus Express mission orbiting the planet from 2006 to 2014 and the Japanese Space Agency has a probe (Akatsuki) here now. (NASA)

Also noticeably absent among the finalists was any pr0ject going to the moon, especially since the Trump administration has made a lunar colony a priority.  Apparently a New Frontiers mission is not what the administration has in mind.

New Frontiers initiative is the largest NASA planetary exploration program open to outside competition and leadership.  But NASA does set the priorities, as put forward by the planetary science and astrobiology communities.

Previous spacecraft launched under New Frontiers include New Horizons, which surveyed Pluto and is now due to visit MU69, an icy object in the farthest reaches of the solar system; Juno, now in orbit around Jupiter; and OSIRIS-REx, launched last year, which will collect samples from an asteroid and return them to Earth.

Since the New Frontiers program began at the beginning of the century, NASA has selected two missions for each decade, making them the most frequent of the major agency missions.  Costs are capped at $1 billion — with $850 million for the mission and $150 million for the launch.  So far, the money has been demonstrably well spent.

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Cassini Nearing the End, Still Working Hard

Facebooktwittergoogle_plusredditpinterestlinkedinmail

 

Spiral density wave on Saturn’s moon Janus. (NASA/JPL-Caltech)

As the Cassini mission embarks on its final dive this Friday into Saturn, it will continue taking photos all the way down (or as far as it remains operations.)

We’ve grown accustomed to seeing remarkable images for the mission and the planet, but clearly the show is not over, and perhaps far from it.

This is what NASA wrote describing the image above:

This view  shows a wave structure in Saturn’s rings known as the Janus 2:1 spiral density wave. Resulting from the same process that creates spiral galaxies, spiral density waves in Saturn’s rings are much more tightly wound. In this case, every second wave crest is actually the same spiral arm which has encircled the entire planet multiple times.

This is the only major density wave visible in Saturn’s B ring. Most of the B ring is characterized by structures that dominate the areas where density waves might otherwise occur, but this innermost portion of the B ring is different.

For reasons researchers do not entirely understand, damping of waves by larger ring structures is very weak at this location, so this wave is seen ringing for hundreds of bright wave crests, unlike density waves in Saturn’s A ring.

The image gives the illusion that the ring plane is tilted away from the camera toward upper-left, but this is not the case. Because of the mechanics of how this kind of wave propagates, the wavelength decreases with distance from the resonance. Thus, the upper-left of the image is just as close to the camera as the lower-right, while the wavelength of the density wave is simply shorter.

This wave is remarkable because Janus, the moon that generates it, is in a strange orbital configuration. Janus and Epimetheus (see PIA12602) share practically the same orbit and trade places every four years. Every time one of those orbit swaps takes place, the ring at this location responds, spawning a new crest in the wave.

The distance between any pair of crests corresponds to four years’ worth of the wave propagating downstream from the resonance, which means the wave seen here encodes many decades’ worth of the orbital history of Janus and Epimetheus.

According to this interpretation, the part of the wave at the very upper-left of this image corresponds to the positions of Janus and Epimetheus around the time of the Voyager flybys in 1980 and 1981, which is the time at which Janus and Epimetheus were first proven to be two distinct objects (they were first observed in 1966).

Epimetheus also generates waves at this location, but they are swamped by the waves from Janus, since Janus is the larger of the two moons.

 

The clouds covering the planet itself consist of ammonia ice.  Further down is also some water ice, some ammonium hydrosulfide ice, and further still is ammonia in a gas phase. Some cloud layers are more than 1000 miles thick. (NASA/JPL-Caltech.

This image is from a few months ago, but it certainly puts you there above the deep, deep clouds of Saturn.  False color was used to make the patterns more discernible.

Saturn has some remarkable features in its atmosphere. When the Voyager missions traveled to the planet in the early 1980s, it imaged a hexagon-shaped cloud formation near the north pole. Twenty-five years later, infrared images taken by Cassini revealed the storm was still spinning, powered by jet streams that push it to speeds of about 220 mph (100 meters per second). At 15,000 miles  across, the long-lasting storm could easily contain an Earth or two.

Cassini is now on its last full orbit, to be following by its partial finale.  The final 22 orbits leading to the plunge into the clouds looked like this:

Cassini’s final orbits, in blue, have taken the spacecraft closer to the planet than ever before, and into the space between the rings and the top of the cloud layers. (NASA/JPL-Caltech)

 

And here is a Jet Propulsion Lab video recapping the Cassini mission and describing its Friday rendezvous:

 

(NASA/JPL-Caltech)

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Cassini Inside the Rings of Saturn

Facebooktwittergoogle_plusredditpinterestlinkedinmail

 

Movie produced from images taken while Cassini flew inside the rings of Saturn – a first. (NASA/JPL-Caltech/Space Science Institute)

The triumphant Cassini mission to Saturn will be coming to an end on September 15, when the spacecraft dives into the planet.  Running out of fuel, NASA chose to end the mission that way rather than run the risk of having the vehicle wander and ultimately land on Europa or Enceladus, potentially contaminating two moons very high on the list of possible habitable locales in our solar system.

Both the science and the images coming back from this descent are (and will be) pioneering, as they bring to an end one of the most successful and revelatory missions in NASA history.

As NASA promised, the 22-dive descent has already produced some of the most compelling images of Saturn and its rings.  Most especially, Cassini has delivered the remarkable 21-image video above.  The images were taken over a four minutes period on August 20 using a wide-angle camera.

The spacecraft captured the images from within the gap between the planet and its rings, looking outward as the spacecraft made one of its final dives through the ring-planet gap as part of the finale.

The entirety of the main rings can be seen here, but due to the low viewing angle, the rings appear extremely foreshortened. The perspective shifts from the sunlit side of the rings to the unlit side, where sunlight filters through.

On the sunlit side, the grayish C ring looks larger in the foreground because it is closer; beyond it is the bright B ring and slightly less-bright A ring, with the Cassini Division between them. The F ring is also fairly easy to make out.

 

NASA’s Cassini spacecraft will make 22 orbits of Saturn during its Grand Finale, exploring a totally new region between the planet and its rings. NASA/JPL-Caltech

While the Cassini team has to keep clear of the rings, the spacecraft is expected to get close enough to most likely answer one of the most long-debated questions about Saturn: how old are those grand features, unique in our solar system?

One school of thought says they date from the earliest formation of the planet, some 4.6 billion years ago. In other words, they’ve been there as long as the planet has been there.

But another school says they are a potentially much newer addition. They could potentially be the result of the break-up of a moon (of which Saturn has 53-plus) or a comet, or perhaps of several moons at different times. In this scenario, Saturn may have been ring-less for eons.

As Curt Niebur, lead program scientist at NASA headquarters for the Cassini mission, explained it, the key to dating the rings is a close view of, essentially, how dirty they are. Because small meteorites and dust are a ubiquitous feature of space, the rings would have significantly more mass if they have been there 4.6 billion years. But if they are determined to be relatively clean, then the age is likely younger, and perhaps much younger.

“Space is a very dirty place, with dust and micro-meteorites hitting everything. Over significant time scales this stuff coats things. So if the rings the rings are old, we should find very dirty ice. If there is little covering of the ice, then the rings must be young. We may well be coming to the end of a great debate.”

 

Cassini gazes across the icy rings of Saturn toward the icy moon Tethys, whose night side is illuminated by Saturnshine, or sunlight reflected by the planet. Tethys was on the far side of Saturn with respect to Cassini here; an observer looking upward from the moon’s surface toward Cassini would see Saturn’s illuminated disk filling the sky. Tethys was brightened by a factor of two in this image to increase its visibility. A sliver of the moon’s sunlit northern hemisphere is seen at top. A bright wedge of Saturn’s sunlit side is seen at lower left. (NASA/JPL-Caltech/Space Science Institute)

A corollary of the question of the age of Saturn’s rings is, naturally, how stable they are.

If they turn out to be as old as the planet, then they are certainly very stable.  But if they are not old then it is entirely plausible that they could be a passing phenomenon and will some day disappear — to perhaps re-appear after another moon is shattered or comet arrives.

Another way of looking at the rings is that they may well have been formed at different times.

As project scientist Linda Spilker explained in an email, Cassini’s measurements of the mass of the rings will be key.  “More massive rings could be as old as Saturn itself while less massive rings must be young.  Perhaps a moon or comet got too close and was torn apart by Saturn’s gravity.”

The voyage between the rings will also potentially provide some new insights into the workings of the disks present at the formation of all solar systems.

“The rings can teach us about the physics of disks, which are huge rings floating majestically and with synchronicity  around the new sun,” Niebur said.  “That said, the rings of Saturn have a very active regime, with particles and meteorites and micrometeorites smacking into each other.  It’s an amazing environment and has direct relevance to the nebular model of planetary formation.”

The view above was acquired at a distance of approximately 750,000 miles (1.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 140 degrees. . The distance to Tethys was about 930,000 miles (1.5 million kilometers).

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA and the imaging operations center is based at the Space Science Institute in Boulder, Colorado.

 

Polar region of Saturn, with tumultuous cloud pattern. A bizarre six-sided feature encircling the north pole of Saturn was identified earlier using the visual and infrared mapping spectrometer on NASA’s Cassini spacecraft.(NASA/JPL-Caltech/Space Science Institute)

Among the areas of greatest interest during the final descent are the turbulent clouds on the North Pole of Saturn.  Cassini captured this view of the pole on April 26, 2017 – the day it began its grand finale — as it approached the planet for its first dive through the gap between the planet and its rings.

Although the pole is still bathed in sunlight at present, northern summer solstice on Saturn occurred on May 24, 2017, bringing the maximum solar illumination to the north polar region. Now the Sun begins its slow descent in the northern sky, which eventually will plunge the north pole into Earth-years of darkness. Cassini’s long mission at Saturn enabled the spacecraft to see the Sun rise over the north, revealing that region in great detail for the first time.

This view looks toward the sunlit side of the rings from about 44 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

Saturn boasts some unique features in its atmosphere. When the Voyager missions traveled to the planet in the early 1980s, it imaged a hexagon-shaped cloud formation near the north pole.

Twenty-five years later, infrared images taken by Cassini revealed the storm was still spinning, powered by jet streams that push it to speeds of about 220 mph (100 meters per second). At 15,000 miles (25,000 km) across, the long-lasting storm could easily contain an Earth or two.

The recent view was obtained at a distance of approximately 166,000 miles (267,000 kilometers) from Saturn.

But because Saturn is a gas giant and has no defined surface per se, it’s difficult to describe exactly how far from the planet Cassini might be traveling at any given time.

On the final orbit, Cassini will plunge into Saturn’s atmosphere, sending back new and unique science to the very end. After losing contact with Earth, the spacecraft will burn up like a meteor, becoming part of the planet itself.

Facebooktwittergoogle_plusredditpinterestlinkedinmail

What Scientists Expect to Learn From Cassini’s Upcoming Plunge Into Saturn

Facebooktwittergoogle_plusredditpinterestlinkedinmail
Saturn as imaged from above by Cassini last year. Over the next five months, the spacecraft will orbit closer and closer to the planet and will finally plunge into its atmosphere. (NASA)

Seldom has the planned end of a NASA mission brought so much expectation and scientific high drama.

The Cassini mission to Saturn has already been a huge success, sending back iconic images and breakthrough science of the planet and its system.  Included in the haul have been the discovery of plumes of water vapor spurting from the moon Encedalus and the detection of liquid methane seas on Titan.  But as members of the Cassini science team tell it, the end of the 13-year mission at Saturn may well be its most scientifically productive time.

Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory (JPL) put it this way: “Cassini will make some of its most extraordinary observations at the end of its long life.”

This news was first announced last week, but I thought it would be useful to go back to the story to learn more about what “extraordinary” science might be coming our way, with the help of Spilker and NASA headquarters Cassini program scientist Curt Niebur.

And the very up close encounters with Saturn’s rings and its upper atmosphere — where Cassini is expected to ultimately lose contact with Earth — certainly do offer a trove of scientific riches about the basic composition and workings of the planet, as well as the long-debated age and origin of the rings.  What’s more, everything we learn about Saturn will have implications for, and offer insights into, the vast menagerie of  gas giant exoplanets out there.

“The science potential here is just huge,” Niebur told me.  “I could easily conceive of a billion dollar mission for the science we’ll get from the grand finale alone.”

 

The Cassini spacecraft will make 22 increasingly tight orbits of Saturn before it disappears into the planet’s atmosphere in mid-September, as shown in this artist rendering.  (NASA/JPL-Caltech)

 

The 20-year, $3.26 billion Cassini mission, a collaboration of NASA, the European Space Agency and the Italian Space Agency,  is coming to an end because the spacecraft will soon run out of fuel.  The agency could have just waited for that moment and let the spacecraft drift off into space, but decided instead on the taking the big plunge.

This was considered a better choice not only because of those expected scientific returns, but also because letting the dead spacecraft drift meant that theoretically it could be pulled towards Titan or Enceladus — moons that researchers now believe just might support life.

Because the spacecraft wasn’t sterilized before launch, scientists didn’t want to take the chance that it might carry some earthly bacteria that could possibly contaminate the moons with our life.

So instead Cassini will be sent on 22 closer and closer passes around Saturn, into the region between the innermost ring and the atmosphere where no spacecraft has ever gone.  On April 26, Cassini will make the first of those dives through a 1,500-mile-wide  gap between Saturn and its rings as part of the mission’s grand finale.

As it makes those terminal orbits, the spacecraft will have to be maneuvered with precision so it doesn’t actually fly into one of the rings.  They consist of water ice, small meteorites and dust, and are sufficiently dense to fatally damage Cassini.

“Based on our best models, we expect the gap to be clear of particles large enough to damage the spacecraft. But we’re also being cautious by using our large antenna as a shield on the first pass, as we determine whether it’s safe to expose the science instruments to that environment on future passes,” said Earl Maize, Cassini project manager at the NASA Jet Propulsion Lab. “Certainly there are some unknowns, but that’s one of the reasons we’re doing this kind of daring exploration at the end of the mission.”

Then in mid-September, following a distant encounter with Titan and its gravity, the spacecraft’s path will be bent so that it dives into the planet itself.  The final descent will occur in mid September, when Cassini enters the atmosphere where it will soon begin to spin and tumble, lose radio contact with Earth, and then ultimately explode due to pressures created by the enormous planet.

All the while it will be taking pioneering measurements, and sending back images predicted to be spectacular.

 

The age and origin of the rings of Saturn remains a subject of a great debate that may soon come to an end. Ring particle sizes range from tiny, dust-sized icy grains to a few particles as large as mountains. Two tiny moons orbit in gaps (Encke and Keeler gaps) in the rings and keep the gaps open. (NASA)

 

While the Cassini team has to keep clear of the rings, the spacecraft is expected to get close enough to most likely answer one of the most long-debated questions about Saturn:  how old are those grand features, unique in our solar system?

One school of thought says they date from the earliest formation of the planet, some 4.6 billion years ago.  In other words, they’ve been there as long as the planet has been there.

But another school says they are a potentially much newer addition.  They could potentially be the result of the break-up of a moon (of which Saturn has 53-plus) or a comet, or perhaps of several moons at different times.  In this scenario, Saturn may have been ring-less for eons.

As Niebur explained it, the key to dating the rings is a close view of, essentially, how dirty they are.  Because small meteorites and dust are a ubiquitous feature of space, the rings would have significantly more mass if they have been there 4.6 billion years.  But if they are determined to be relatively clean, then the age is likely younger, and perhaps much younger.

“Space is a very dirty place, with dust and micro-meteorites hitting everything.  Over significant time scales this stuff coats things.  So if the rings the rings are old, we should find very dirty ice.  If there is little covering of the ice, then the rings must be young.  We may well be coming to the end of a great debate.”

A corollary of the question of the age of Saturn’s rings is, naturally, how stable they are.

Curt Neibur, lead program scientist at NASA headquarters for the Cassini mission. (NASA)

If they turn out to be as old as the planet, then they are certainly very stable.  But if they are not old, then it is entirely plausible that they could be a passing phenomenon and will some day disappear — to perhaps re-appear after another moon is shattered or comet arrives.

Another way of looking at the rings is that they may well have been formed at different times.

As Cassini Project Scientist Linda Spilker explained in an email, Cassini’s measurements of the mass of the rings will be key.  “More massive rings could be as old as Saturn itself while less massive rings must be young.  Perhaps a moon or comet got too close and was torn apart by Saturn’s gravity.”

The voyage between the rings will also potentially provide some new insights into the workings of the disks present at the formation of all solar systems.

“The rings can teach us about the physics of disks, which are huge rings floating majestically and with synchronicity  around the new sun,” Niebur said.  “That said, the rings of Saturn have a very active regime, with particles and meteorites and micrometeorites smacking into each other.  It’s an amazing environment and has direct relevance to the nebular model of planetary formation.”

 

This recently released Cassini image show’s moon Daphnis, which is embedded within a ring.  The moon
kicks up waves as it orbits within what is called the Keeler gap. This mosaic combines several previous images to show more waves in the gap edges. (NASA/JPL-Caltech)

 

Another open question that scientists hope will be answered during the plunge is how long, precisely, is a day on Saturn.

The saturnine day is often given as between 10.5 and 11 hours, but that lack of precision is unique in our solar system.

The usual way to determine a planet’s rotation is to look for a distinctive point and watch to see how long it takes to reappear.   But Saturn has thousands of miles of thick clouds between the rings and the core, and so no distinctive points have been found.

The planet’s inner rocky core and outer core of metallic hydrogen create magnetic fields that potentially could be traced to measure a full rotation. But competing magnetic fields in the complex Saturn ring and moon system make that also difficult.

“The truth is that we don’t know how long a day is on Saturn,” Niebur said.  “But after the finale, we will finally know.”

The answer will hopefully come by measuring the expected “wobble” of the magnetic field inside the rings. Since Cassini will pass beyond the magnetic interference of those rings, the probe should get the most precise magnetic readings ever taken.

Project scientist Spilker is optimistic.  “With the magnetic field we’ll be able to get, for the first time, the length of day for the interior of Saturn. If there’s just a slight tilt to the magnetic field, then it will wobble around and give us the length of a day.”

Artist rendering of Cassini over Saturn’s north pole, with it huge hexagon-shaped storm. (NASA/JPL-Caltech)

Perhaps the most consequential findings to come out of the Cassini finale are expected to involve the planet’s internal structure and composition.

The atmosphere is known to contain hydrogen, helium, ammonia and methane, but Niebur said that other important trace elements are expected to be present.  The probe will use its mass spectrometer to “taste” the chemistry of the gases on the outermost edge of Saturn’s atmosphere and return the most detailed information ever about Saturn’s high-altitude clouds, as well as about the ring material.

Instruments will also measure Saturn’s powerful winds (which blow up to 1,000 miles an hour), and determine how deep they go in the atmosphere.  Like much about Saturn, that basic fact falls in the “unknown” category.

For both Spilker and Niebur, the biggest prize is probably determining the size and mass of Saturn’s rocky core, made up largely of iron and nickel.  That core is estimated to be 9 to 22 times the mass of the Earth, and to have a diameter of perhaps 18,000 miles. 

Cassini project scientist Linda Spilker of JPL was on the Voyager team in the 1970s. She has a long-standing research interest in Saturn’s rings. (Bill Youngblood, Caltech)

But these are broad estimates, and neither the size nor mass is really known.  Those thousands of miles of thick clouds atop the atmosphere and the planet’s chaotic magnetic fields have made the necessary readings impossible.

The Cassini instruments, however, are expected to make those measurements during its final months.  As Cassini makes its close-in passes and then enters the atmosphere for the final plunge, it will send back the data needed to make detailed maps of Saturn’s inner magnetic and gravitational fields.  These are what scientists need to understand the core and other structures that lay beneath the planet’s atmosphere.

This work will compliment the parallel efforts underway at Jupiter, where the Juno mission is collecting data on that planet’s core as well.  If scientists can measure the sizes and masses of both cores, they will be able to use that new information to answer many other questions about our solar system and beyond.

“A better understanding Saturn’s interior, coupled with what Juno mission learns about the interior of Jupiter, will lead to (new insights into) how the planets in our solar system formed, and how our solar system itself formed,”  Spilker said in an email.

“This is then related to how exoplanets form around other stars.  Studying our own giant planets will help us understand giant planets around other stars.”

In other words, Saturn and Jupiter are planetary types expected to be found across the galaxies.  And it’s our good fortune to be able to touch and learn from them, and to use that information to analyze distant planets that we can only indirectly detect or just barely see.

 

An animated video about Cassini’s final chapter is available here.

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail

Some Spectacular Images (And Science) From The Year Past

Facebooktwittergoogle_plusredditpinterestlinkedinmail

A rose made of galaxies

This is a golden era for space and planetary science, a time when discoveries, new understandings, and newly-found mysteries are flooding in.  There are so many reasons to find the drama intriguing:  a desire to understand the physical forces at play, to learn how those forces led to the formation of Earth and ultimately us, to explore whether parallel scenarios unfolded on planets far away, and to see how our burgeoning knowledge might set the stage for exploration.

But always there is also the beauty; the gaudy, the stimulating, the overpowering spectacle of it all.

Here is a small sample of what came in during 2016:

stsci-h-p1642a-m2000x2000

The Small Magellanic Cloud, a dwarf galaxy that is a satellite of our Milky Way galaxy, can be seen only in the southern hemisphere.  Here, the Hubble Space Telescope captured two nebulas in the cloud. Intense radiation from the brilliant central stars is heating hydrogen in each of the nebulas, causing them to glow red.

Together, the nebulas are called NGC 248 and are 60 light-years long and 20 light-years wide. It is among a number of glowing hydrogen nebulas in the dwarf satellite galaxy, which is found approximately 200,000 light-years away.

The image is part of a study called Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE). Astronomers are using Hubble to probe the Milky Way satellite to understand how dust is different in galaxies that have a far lower supply of heavy elements needed to create that dust.  {NASA.ESA, STSci/K. Sandstrom (University of California, San Diego), and the SMIDGE team}

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope.

Probably the biggest exoplanet news of the year, and one of the major science stories, involved the discovery of an exoplanet orbiting Proxima Centauri, the star closest to our own.

This picture combines a view of the southern skies over the European Space Observatory’s 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left).

The planet Proxima Centauri b is thought to lie within the habitable zone of its star.  Learning more about the planet, the parent star and the two other stars in the Centauri system has become a focus of the exoplanet community.

large_web

We all know about auroras that light up our far northern skies, but there’s no reason why they wouldn’t exist on other planets shielded by a magnetic field — such as Jupiter.  Astronomers using the Hubble Space Telescope have found them on the poles of our solar system’s  largest planet, and produced far ultraviolet light images taken as the Juno spacecraft approached the planet.

Auroras are formed when charged particles in the space surrounding the planet are accelerated to high energies along the planet’s magnetic field. When the particles hit the atmosphere near the magnetic poles, they cause it to glow like gases in a fluorescent light fixture. Jupiter’s magnetosphere is 20,000 times stronger than that of Earth.

The full-color disk of Jupiter in this image was separately photographed at a different time by Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble project that annually captures global maps of the outer planets.

Inside the Crab Nebula

Peering deep into the core of the Crab Nebula, this close-up image reveals the heart of one of the most historic and intensively studied remnants of a supernova, an exploding star. The inner region sends out clock-like pulses of radiation and tsunamis of charged particles embedded in magnetic fields.

The neutron star at the very center of the Crab Nebula has about the same mass as the sun but compressed into an incredibly dense sphere that is only a few miles across. Spinning 30 times a second, the neutron star shoots out detectable beams of energy that make it look like it’s pulsating.

The NASA Hubble Space Telescope image is centered on the region around the neutron star (the rightmost of the two bright stars near the center of this image) and the expanding debris surrounding it. Intricate details of glowing gas are shown in red and the blue glow is radiation given off by electrons spiraling at nearly the speed of light in the powerful magnetic field around the crushed stellar core.

Observations of the Crab supernova were recorded by Chinese astronomers in 1054 A.D. The nebula, bright enough to be visible in amateur telescopes, is located 6,500 light-years away in the constellation Taurus.  (NASA, ESA)

hd106906_kalas-1

The Gemini Planet Imager provides some of the earliest high-resolution, high-contrast direct imaging of exoplanets.  Using a coronagraph inside the telescope to block out the light of the star, the GPI can then allow researchers to see the region surrounding that star — in other words, where exoplanets might be.

This image includes a wide-angle view of the star HD 106906 taken by the Hubble Space Telescope and a close-up view from the Planet Imager, which operates on the Gemini South telescope in Chile’s Atacama Desert.  The image reveals a disturbed system of comets near the star, which may be responsible for the orbit of the the unusually distant giant planet (upper right).

The GPI Exoplanet Survey is operated by a team of astronomers from the University of California at  Berkeley and 23 other institutions, and is targeting 600 young stars to understand how planetary systems evolve over time.

Paul Kalas of UC Berkeley is responsible for the image and led the team that wrote about it. That paper actually came out in the Astrophysical Journal in late 2015 but, hey, that’s almost 2016.

Astronomers have regularly found a galaxy or star that is the furthest from us ever to be detected.  But the record is there to be broken, and in 2016 it was astronomers from the Great Observatories Origins Deep Survey (GOODS) who made the discovery.

Galaxy GN-z11, shown in the inset, was imaged as it was 13.4 billion years in the past, just 400 million years after the big bang.  That means the universe was only three percent of its current age when the light left that galaxy.

The galaxy has many blue stars that are bright and young, but it looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe.

(NASA, ESA, P. Oesch (Yale University), G. Brammer ( STScI)), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)

Biggest announce of discovred exoplanets by Kepler. (No, those are not real images, but still...)

No, these are not images of actual exoplanets, but they represent the continuing work of one of NASA’s most pioneering and productive missions, the Kepler Space Telescope. In May the Kepler team announced the detection of 1284 more planets or planet candidates as part of its newest catalog, the largest number announced at once in the mission.

To date, Kepler has identified unconfirmed 4,696 planet candidates, 2,331 confirmed planets, and 21 confirmed small planets in a habitable zone. In addition, the follow-on K2 mission has identified 458 candidate planets and 173 confirmed.

The Kepler spacecraft stared fixedly at a small portion of the sky for four years, looking to identify miniscule dimmings in the brightness of stars that would indicate that a planet was passing between the telescope and the star. In this way, Kepler has established a census of exoplanets that has been extrapolated to show the presence of billions and billions of planets around other stars.

620500322-ed-1

The 21-foot array that will collect photons for the James Webb Space Telescope was finished and put on display in November at the Goddard Space Flight Center. It will be the largest mirror to go into space, and will likely make the JWST into the most powerful and far-seeing observatory ever.

It will observe in the infrared portion of the spectrum because its goals include peering deep into the past of the universe, which is now most visible in the infrared. This means the JWST will have to be cooled to -364 degrees F, just 50 degrees above absolute zero.  To achieve that temperature, it’s insulated from the sun by five membrane layers, each no thicker than a human hair. Placing those membranes was finished in November, marking an end to construction of the telescope “mirror.”

The project has been enormously ambitious, and with that has come long delays and budget overruns that almost resulted in it being scrapped. Just this month, some early vibrating tests – designed to simulate launch conditions – experienced an anomaly that NASA engineers are working on now.  The JWST is scheduled to launch in late 2018.

europa02-photoa-plumes1042x1042-160919-1

This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position of Jupiter’s moon Europa. The plumes, photographed by NASA’s Hubble’s Space Telescope Imaging Spectrograph, were seen in silhouette as the moon passed in front of Jupiter.

While the plumes spitting out of Saturn’s moon Enceladus are much better known now — the Cassini spacecraft flew through them in 2015, after all — the growing scientific consensus that Europa also has some plumes may be of even greater importance.  That moon is much larger, its ice-covered oceans have been determined to hold more water than all the oceans of Earth, and those oceans have clearly been around for a long time.

Hubble’s ultraviolet sensitivity allowed for the detection of the plumes, which rise more than 100 miles above Europa’s icy surface. The image of Europa, superimposed on the Hubble data, is assembled from data from the Galileo and Voyager missions. (NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center.)

compounds being created in the xxx nebula

How the fundamentals needed for life are created in space has been a longstanding mystery.  The cosmos, after all, began with hydrogen and helium, and that was about it.  But life needs carbon atoms connected to hydrogen, oxygen, nitrogen and other elements

Astronomers and astrochemists have been making progress in recent years and now understand the basics of how the heavier elements are formed in space.  New data from the European Space Agency’s Herschel Space Observatory has gone further and has established that ultraviolet light from stars plays a key role in creating these molecules.  Previously, scientists thought that turbulence created by “shock” events was the driving force.

This image is of the Orion nebula, where scientists studied carbon chemistry of a major star-forming region. Herschel probed an area of the electromagnetic spectrum — the far infrared, associated with cold objects — that no other space telescope has reached before so it could take into account the entire Orion Nebula instead of individual stars.

The result was a better understanding of how carbon and hydrogen reach the states necessary to bond and form the basic carbon chemistry of the cosmos (and of life.)

Within the inset image, the emission from ionized carbon atoms (C+), overlaid in yellow, was isolated and mapped out from spectrographic data.

pia17205_hires-1

Following a successful close flyby of Enceladus, the NASA-ESA Cassini spacecraft captured this image of the moon with Saturn’s rings beyond.

The image was taken in visible light with the Cassini spacecraft wide-angle camera when it was about 106,000 miles away from Enceladus. That flyby turned into a fly-through as well, when Cassini entered the plumes of water vapor and dust that shoot out of the bottom of the moon.

Scientists already know that an array of organic and other chemicals are in the plumes, but the field is awaiting word about the presence (or absence) of molecular hydrogen, which is formed when water comes into contact with rocks in hydrothermal vents.  Many think that Enceledus is habitable and should be tested for signs of life because biosignatures could potentially exist in the relatively easy-to-access geysers.

moon-halo-5-13-2016-yuri-beletsky-chile-pano

While Yuri Beletsky is a staff astronomer at the Las Campanas Observatory in Chile, he is also a noted astrophotographer who specializes in capturing the beauty of nighttime scenes — usually connecting the celestial with the terrestrial.

In this 2016 photo, the moon is surrounded by a halo caused by the presence of millions of ice crystals in the upper atmosphere.  Great conditions for an astrophotographer, but pretty much useless for an astronomer.

The star within the halo is Regulus, brightest object in the constellation Leo the Lion. On the left outside the halo is Procyon from Canis Minor and on the right is the planet Jupiter.

As is so often the case in this line of endeavor, it’s quite a sight to see.

 

Facebooktwittergoogle_plusredditpinterestlinkedinmail