Look Ahead: Cassini “Proximal” Mission

First, there was Equinox. And then came Solstice. Ever faithful, the Cassini probe continues to defy even the wildest expectations at its launch in 1997. And now, NASA is asking for public participation in preparing the spacecraft for its final mission:

Starting in late 2016, the Cassini spacecraft will repeatedly climb high above Saturn’s north pole, flying just outside its narrow F ring. Cassini will probe the water-rich plume of the active geysers on the planet’s intriguing moon Enceladus, and then will hop the rings and dive between the planet and innermost ring 22 times.

Because the spacecraft will be very close to Saturn, the team has been calling this phase “the proximal orbits.” But they think someone out there can conjure up a cooler name. Here’s where you come in: you can choose your faves from a list already assembled, or you can submit your own ideas (up to three). The big reveal for the final name will be in May 2014.

This naming contest is part of the 10-year anniversary celebration. The mission will mark a decade of exploring Saturn, its rings and moons on June 30 PDT (July 1 EDT).

The name game is already underway. And they’ve already released an awesome trailer in advance of Cassini’s astounding swan song.

No, really, watch the trailer.

This is going to be so cool.

Cassini’s last mission could well be the inspiration of our next generation of scientists. It really is all that.

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Postcard From Cassini

There is always this. Given the times, and the scale of science fiction, perhaps the idea of a holiday snap featuring four moons does not necessarily strike us as anything special. But then we stop to think about it:

Two pairs of moons make a rare joint appearance. The F ring’s shepherd moons, Prometheus and Pandora, appear just inside and outside of the F ring (the thin faint ring furthest from Saturn). Meanwhile, farther from Saturn the co-orbital moons Janus (near the bottom) and Epimetheus (about a third of the way down from the top) also are captured.

Prometheus (53 miles, or 86 kilometers across) and Pandora (50 miles, or 81 kilometers across) sculpt the F ring through their gravitational influences. Janus (111 miles, or 179 kilometers across) and Epimetheus (70 miles, or 113 kilometers across) are famous for their orbital dance, swapping places about every four years. They are also responsible for gravitationally shaping the outer edge of the A ring into seven scallops.

NASA/JPL-Caltech/SSI)

Just to go clockwise, that’s Epimetheus, Prometheus, Pandora, and Janus.

Seriously, though … anyone have a holiday snap to match? Didn’t think so.

Happy π Day

Happy π Day. Π? π? I go with π, since that’s what this is all about, anyway. right?

Well, you know, to our American friends. Never mind. Dumb joke. Predictable. Happy π Day to each and every one of you around the world and throughout the Universe.

On a related note, NASA proudly recalls the Pi Transfer:

On Jan. 19, 2007, the Cassini spacecraft took this view of Saturn and its rings—the visible documentation of a technique called a “pi transfer” completed with a Titan flyby. A pi transfer uses the gravity of Saturn’s largest moon, Titan, to alter the orbit of the Cassini spacecraft so it can gain different perspectives on Saturn and achieve a wide variety of science objectives. During a pi transfer, Cassini flies by Titan at opposite sides of its orbit about Saturn (i.e., Titan’s orbital position differs by pi radians between the two flybys) and uses Titan’s gravity to change its orbital perspective on the ringed planet.

Taking in the rings in their entirety was the focus of this particular imaging sequence. Therefore, the camera exposure times were just right to capture the dark-side of its rings, but longer than that required to properly expose the globe of sunlit Saturn. Consequently, the sunlit half of the planet is overexposed.

Yeah. They can do this. Happy π Day.

Adjectives Aside ….

The headline might be overwritten, but what are you going to do?

The classic model of Saturn’s atmosphere portrays it as a layered sandwich of sorts, with a deck of water clouds at the bottom, ammonia hydrosulfide clouds in the middle, and ammonia clouds near the top. Those layers are just below an upper tropospheric haze of unknown composition that obscures almost everything.

But this storm appears to have disrupted those neat layers, lofting up water vapor from a lower layer that condensed and froze as it rose. The water ice crystals then appeared to become coated with more volatile materials like ammonium hydrosulfide and ammonia as the temperature decreased with their ascent, the authors said.

“We think this huge thunderstorm is driving these cloud particles upward, sort of like a volcano bringing up material from the depths and making it visible from outside the atmosphere,” said Sromovsky. “The upper haze is so optically thick that it is only in the stormy regions where the haze is penetrated by powerful updrafts that you can see evidence for the ammonia ice and the water ice. Those storm particles have an infrared color signature that is very different from the haze particles in the surrounding atmosphere.”

In understanding the dynamics of this Saturn storm, researchers realized that it worked like the much smaller convective storms on Earth, where air and water vapor are pushed high into the atmosphere, resulting in the towering, billowing clouds of a thunderstorm. The towering clouds in Saturn storms of this type, however, were 10 to 20 times taller and covered a much bigger area. They are also far more violent than an Earth storm, with models predicting vertical winds of more than about 300 mph (500 kilometers per hour) for these rare giant storms.

Cassini Dances With Crystals

Cassini, ever faithful, brings out the geek in Matt Hedman. And it is to our great benefit:

Since July 19, when Cassini positioned itself in Saturn’s shadow and began gathering data from this rare vantage point, ring scientists such as myself have been poring over the streams of data coming back. We’re waiting—as you all are—to see the full mosaic of the Saturn system stitched together by the imaging team, but in the mean time, we’ve been looking at individual images and near-infrared data to see what we can learn about Saturn’s rings.

Images of Saturn and its rings backlit by the sun are not only exceptionally beautiful, they also provide us with unique information about Saturn’s rings. Earlier backlit images of Saturn’s rings obtained by Cassini back in 2006 and 2012 revealed previously unseen dusty rings as well as unexpected structures in already known rings. The new mosaic will allow us to look again at some of the hardest-to-see rings, to track changes in the distribution of tiny ice grains near Enceladus’ orbit, and to investigate differences in the particle sizes among different dusty rings.

When Cassini looks back towards the sun during opportunities like these, the rings that are most easily seen from Earth appear fairly dark to Cassini. The reason is that the rings we Earthlings can see through telescopes are mostly formed from pebble-to boulder-sized particles, and they are getting the full blast of illumination from the sun. Cassini, however, is looking at the unlit sides of these objects. By contrast, other rings like the D, E and G rings appear exceptionally bright from Cassini’s vantage point. This occurs because the tiny dust-sized grains in these so-called “dusty rings” are very good at scattering light when the sun is behind them. (Just think of how dust motes floating around in a room become visible when we look towards bright windows.)

Since dusty rings are so much easier to see in backlit images, extremely tenuous rings that are otherwise very difficult to detect become clearly visible. In the images Cassini took of the Saturn system in 2006, we can see faint ringlets lying along the orbits of Saturn’s small moons Pallene and Janus. These rings are likely composed of material knocked off the surface of their respective moons by micrometeoroids. We are keen to get another clear look at these features to see if they have changed over the last seven years – which is about the length of a Saturn season. In particular, we are interested in seeing if changes in Janus’ orbit over the last few years due to its interactions with Epimetheus have influenced the structure of its ring.

Enceladus Unveiled

Inertia.

Never mind.

Let us start, then, with something a little more recent, since there is much to see.

Enceladus, perhaps our favorite celestial body in the solar system.

And, ah, Cassini!

The intensity of the jets of water ice and organic particles that shoot out from Saturn’s moon Enceladus depends on the moon’s proximity to the ringed planet, according to data obtained by NASA’s Cassini spacecraft.

The finding adds to evidence that a liquid water reservoir or ocean lurks under the icy surface of the moon. This is the first clear observation the bright plume emanating from Enceladus’ south pole varies predictably. The findings are detailed in a scientific paper in this week’s edition of Nature.

“The jets of Enceladus apparently work like adjustable garden hose nozzles,” said Matt Hedman, the paper’s lead author and a Cassini team scientist based at Cornell University in Ithaca, N.Y. “The nozzles are almost closed when Enceladus is closer to Saturn and are most open when the moon is farthest away. We think this has to do with how Saturn squeezes and releases the moon with its gravity.”

Cassini, which has been orbiting Saturn since 2004, discovered the jets that form the plume in 2005. The water ice and organic particles spray out from several narrow fissures nicknamed “tiger stripes.”

“The way the jets react so responsively to changing stresses on Enceladus suggests they have their origins in a large body of liquid water,” said Christophe Sotin, a co-author and Cassini team member at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Liquid water was key to the development of life on Earth, so these discoveries whet the appetite to know whether life exists everywhere water is present.”

Just a reminder: NASA is an example of a government agency doing its job; that’s why congresses and presidents alike prefer to cut its budget^†.
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^† No, really, click that link; it’s important.

Updates

The upside of being lazy is that you’re not doing anything unpleasant. The downside is that the unpleasantness stacks up at the far end. No, wait, that’s not right. But, you know, sometimes the art of playing catch-up … er … right. Enough about me.

There is plenty going on around the solar system.

First up, Yellowknife Bay, Mars, where our friendly neighborhood robotic space laboratory is still recovering from a memory glitch that forced Curiosity to switch over to its redundant B-side computer:

NASA’s Mars rover Curiosity continues to move forward with assessment and recovery from a memory glitch that affected the rover’s A-side computer. Curiosity has two computers that are redundant of one another. The rover is currently operating using the B-side computer, which is operating as expected.

Over the weekend, Curiosity’s mission operations team continued testing and assessing the A-side computer’s memory.

“These tests have provided us with a great deal of information about the rover’s A-side memory,” said Jim Erickson, deputy project manager for the Mars Science Laboratory/Curiosity mission at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We have been able to store new data in many of the memory locations previously affected and believe more runs will demonstrate more memory is available.”

Two software patches, targeting onboard memory allocation and vehicle safing procedures, are likely to be uplinked later this week. After the software patches are installed, the mission team will reassess when to resume full mission operations.

Meanwhile, somewhere near Saturn, faithful Cassini continues to dazzle as the data returns from the fourth and final Rhea flyby of the Solstice mission:

Cassini flew by Rhea at an altitude of 620 miles (997 kilometers) on March 9, 2013. This flyby was designed primarily for the radio science sub-system to measure Rhea’s gravity field. During closest approach and while the radio science sub-system was measuring the icy satellite’s gravity field, the imaging team rode along and captured 12 images of Rhea’s rough and icy surface. Outbound from Rhea, Cassini’s cameras captured a set of global images from a distance of about 167,000 miles (269,000 kilometers).

Data from Cassini’s cosmic dust analyzer were also collected to try to detect any dusty debris flying off the surface from tiny meteoroid bombardments. These data will help scientists understand the rate at which “foreign” objects are raining into the Saturn system.

Cassini will visit Titan (T-90) at a range of 870 miles (1,400 km) on April 5, 2013.

In more earthly realms, Matt McGrath continues his coverage for BBC of the CITES meeting in Bangkok, Thailand:

Three types of critically endangered but commercially valuable shark have been given added protection at the Cites meeting in Bangkok.

The body, which regulates trade in flora and fauna, voted by a two-thirds majority to upgrade the sharks’ status ….

…. The decisions can still be overturned by a vote on the final day of this meeting later this week.

The oceanic whitetip, three varieties of hammerheads and the porbeagle are all said to be seriously threatened by overfishing.

And maybe a bonus Cassini note, because I so adore the photo:

The ghostly spokes in Saturn’s B ring continue to put on a show for the Cassini spacecraft cameras in this recent image. The spokes, believed to be a seasonal phenomenon, are expected to disappear as Saturn nears its northern hemisphere summer. Scientists continue to monitor the spokes to better understand their origin and evolution.

The small moon Atlas also appears here barely visible in between the A ring and the F ring, which is the thin ring located furthest from Saturn, as the fainter dot close to the A ring. Atlas is closer to the bottom of the image. A bright star also appears in the gap between the two rings, and there are six other stars visible (one through the C ring, near the planet).

Rhea (R-4) Flyby

It seems a long way to go for a simple answer, but the Cassini R-4 Rhea Flyby slated for Saturday morning (shortly after ten, Pacific Time) is just one of the many simple answers sought by scientists studying the Saturnian system. And that simplicity, in a way, is a striking reminder of what humanity can achieve.

This gravity flyby is designed to understand the internal structure of Saturn’s second largest moon. Is Rhea a homogeneous body or did it differentiate into a core, mantle, and crust like the Earth? The radio science subsystem will use radio waves beamed to Earth to perform precise measurements designed to answer this question.

That’s No Moon, It’s … Oh, Wait, It’s a Moon

So the Death Star joke has been done to death, and Cassini’s 2010 photo of Mimas has become pretty much the standard picture for the second smallest of the planemo (planetary-mass object) moons around Saturn, which has enough moons that astronomers haven’t finished naming them all^†.

JPL explains the famous Death Star picture:

Herschel Crater is 130 kilometers, or 80 miles, wide and covers most of the right of this image. Scientists continue to study this impact basin and its surrounding terrain (see PIA12569 and PIA12571).

Cassini came within about 9,500 kilometers (5,900 miles) of Mimas on Feb. 13, 2010.This mosaic was created from six images taken that day in visible light with Cassini’s narrow-angle camera on Feb. 13, 2010. The images were re-projected into an orthographic map projection. This view looks toward the area between the region that leads on Mimas’ orbit around Saturn and the region of the moon facing away from Saturn. Mimas is 396 kilometers (246 miles) across. This view is centered on terrain at 11 degrees south latitude, 158 degrees west longitude. North is up. This view was obtained at a distance of approximately 50,000 kilometers (31,000 miles) from Mimas and at a sun-Mimas-spacecraft, or phase, angle of 17 degrees. Image scale is 240 meters (790 feet) per pixel.

Tomorrow, Titan

The countdown is on for the Cassini probe’s latest close encounter with Saturn’s largest moon, Titan. Slated for 5:57 pm PST, February 16 (1:57 AM, February 17, UTC), Cassini will approach within 1,229 miles (1,978 km) from the surface of Titan at a blazing speed of 13,000 mph (5.8 km/s).

NASA’s Jet Propulsion Laboratory explains:

During the Solstice mission, a main science objective is to measure Titan’s gravitational field in order to confirm or deny the presence of an underground ocean. Additional radio science (RSS) gravity observations are needed both to answer this question and to help determine if Titan’s crust is thick and rigid, or thin.

The spacecraft is slated for only four encounters with Titan during the Solstice mission, and scientists hope to get the most out of each pass.

Raw images usually post fairly quickly, so we can expect new glimpses of Titan in the coming days.

Meanwhile, a trivial bit: Did you know that the International Astronomical Union names Titan’s mountains after Middle Earth, from J.R.R. Tolkein’s novels?