Tag: Cassini

Mapping Titan, the Most Earth-Like Body in Our Solar System

In an image created by NASA’s Cassini spacecraft, sunlight reflects off lakes of liquid methane around Titan’s north pole.  Cassini radar and visible-light images allowed researchers to put together the first global geological map of Saturn’s largest moon.  (NASA/JPL-Caltech/University of Arizona/University of Idaho)

Saturn’s moon Titan has lakes and rivers of liquid hydrocarbons, temperatures that hover around -300 degrees Fahrenheit, and a thick haze that surrounds it and has cloaked it in mystery.   An unusual place for sure, but perhaps what’s most unusual is that Titan more closely resembles Earth of all the planets and moons in our solar system.

This is because like only Earth it has that flowing liquid on its surface, it has a climate featuring wind and rain that form dunes, rivers, lakes, deltas and seas (probably of filled with liquid methane and ethane), it has a thick atmosphere and it has weather patterns that change with the seasons.  The moon’s methane cycle is quite similar to our water cycle.

And now astronomers have used data from NASA’s Cassini-Huygens mission to map the entire surface of Titan for the first time.  Their work has found a global terrain of mountains, plains, valleys, craters and lakes .  Again, this makes Titan unlike anywhere else in the solar system other than Earth.

“Titan has an atmosphere like Earth. It has wind, it has rain, it has mountains,” said Rosaly Lopes, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena.  She and her colleagues wove together images and radar measurements taken by the spacecraft to produce the first global map of the moon.

“Titan has an active methane-based hydrologic cycle that has shaped a complex geologic landscape, making its surface one of most geologically diverse in the solar system,” she said.  “It’s a really very interesting world, and one of the best places in the solar system to look for life,”

Cassini orbited Saturn from 2004 to 2017 and collected vast amounts of information about the ringed gas giant and its moons. The mission included more than 100 fly-bys of Titan,  which allowed researchers to study the moon’s surface through its thick atmosphere and survey its terrain in unprecedented detail.

The first global geologic map of Titan is based on radar and visible-light images from NASA’s Cassini mission.

Their work, which now adds the surface of Titan to the kind of geological mapping done of the surfaces of Mars, Mercury and our moon, was published in Nature Astronomy.Read more

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

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.… Read more

Cassini Nearing the End, Still Working Hard

 

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).… Read more

Cassini Inside the Rings of Saturn

 

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.… Read more

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

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.… Read more

Some Spectacular Images (And Science) From The Year Past

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:

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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.

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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. … Read more

Waiting on Enceladus

NASA's Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. Credits: NASA/JPL-Caltech

NASA’s Cassini spacecraft completed its deepest-ever dive through the icy plume of Enceladus on Oct. 28, 2015. (NASA/JPL-Caltech)

Of all the possible life-beyond-Earth questions hanging fire, few are quite so intriguing as those surrounding the now famous plumes of the moon Enceladus:  what telltale molecules are in the constantly escaping jets of water vapor, and what dynamics inside the moon are pushing them out?

Seldom, if ever before, have scientists been given such an opportunity to investigate the insides of a potentially habitable celestial body from the outside.

The Cassini mission to Saturn made its closest to the surface (and last) plume fly-through a year ago, taking measurements that the team initially said they would report on within a few weeks.

That was later updated by NASA to include this guidance:  Given the important astrobiology implications of these observations, the scientists caution that it will be several months before they are ready to present their detailed findings.

The reference to “important astrobiology implications” certainly could cover some incremental advance, but it does seem to at least hint of something more.

I recently contacted the Jet Propulsion Lab for an update on the fly-through results and learned that a paper has been submitted to the journal Nature and that it will hopefully be accepted and made public in the not-too-distant future.

All this sounds most interesting but not because of any secret finding of life — as some might infer from that official language.  Cassini does not have the capacity to make such a detection, and there is no indication at this point that identifiable byproducts of life are present in the plumes.

What is intriguing is that the fly-through was only 30 miles above the moon’s surface — the closest pass through a plume ever by Cassini — and so presumably its instruments produced some new and significant findings.

The scientists writing the paper could not, of course, discuss their findings before publication.  But Jonathan Lunine, a Cornell University planetary scientist and physicist on the Cassini mission with a longtime and deep interest in Enceladus, was comfortable discussing what is known about the moon and what Cassini (and future missions) still have to explain.

And thanks to that briefing, it became apparent that whatever new findings are coming, they will not make or break the case for the moon as a habitable place. Rather, they will essentially add to a strong case that has already been made.… Read more

Enceladus and Water Worlds

Ice geysers erupt on Enceladus, the bright and shiny inner moon of Saturn. Shown in this false-color image, a backlit view of the moon’s southern limb, the icy plumes were first discovered by instruments on the Cassini Spacecraft during close encounters with Enceladus in 2005. Eight source locations for these geysers have now been identified along substantial surface fractures in the moon’s south polar region. Researchers suspect the geysers arise from near-surface pockets of liquid water with temperatures near 273 kelvins (0 degrees C). (NASA/ESA/ SSI/JPL/Cassini Imagining Team)

 

As if the prospect of billions of potentially habitable exoplanets wasn’t enough to get people excited, what about all those watery exo-moons too?

The question arises as the Cassini mission makes its final pass near the now famous geysers at the south pole of the moon Enceladus.  The plumes are currently in darkness and so it’s a perfect time to tease out a particularly compelling aspect of the Enceladus story:  how hot is the inside of the mini-moon.  Earlier measurements of the water ice spray took place when the sun was on that southern pole, so this will be the first time Cassini can measure precisely how much of the already detected heat comes from the moon’s interior.

The expectation is that much of the heat does indeed come from inside, warmed substantially by tidal forces and perhaps hydrothermal vents that together serve to keep liquid a subsurface ocean all around the moon.  As a result, the evolving scientific view is that tiny Enceladus, one of 63 moons of Saturn, just may have the ingredients and characteristics that put it into an improbable habitable zone.

“Step by step, we’re learning about an environment that seemed impossible not long ago,” said Cassini Mission Scientist Linda Spilker.  “We know that Enceladus has some rocky core, and that it touches the liquid water.  We also know that some of the compounds identified in the geysers can only be formed when rock is in contact with hot water, and that must be happening at the bottom of the moon’s ocean.  All the pieces are coming together to tell us that the moon has an ocean that might be able to support life.”

 

NASA's Cassini spacecraft captured this view as it neared icy Enceladus for its closest-ever dive past the moon's active south polar region. The view shows heavily cratered northern latitudes at top, transitioning to fractured, wrinkled terrain in the middle and southern latitudes. The wavy boundary of the moon's active south polar region -- Cassini's destination for this flyby -- is visible at bottom, where it disappears into wintry darkness. This view looks towards the Saturn-facing side of Enceladus. North on Enceladus is up and rotated 23 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 28, 2015. The view was acquired at a distance of approximately 60,000 miles (96,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 45 degrees. Image scale is 1,896 feet (578 meters) per pixel.

The Cassini spacecraft, sponsored by NASA, the European Space Agency and the Italian space Agency,  captured this view on Oct. 28 as it neared Enceladus. The wavy boundary of the moon’s active south polar region — Cassini’s destination for this flyby — is visible at bottom.

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