According to Colwell

This is probably the most bizarre picture from Mars I’ve ever seen. Identified as one of seven openings to subsurface caves on the flank of the volcano Arsia Mons, the utter blackness of the hole suggests steep walls and an overhang at the surface. It just looks very peculiar. I’d love to get a view inside with the Sun more overhead, but even in this image it was 38 degrees above the horizon. That’s not that low. Notice how even on the shadowed rim (lower left) there is visible surface detail. That means that on the right the surface is either totally unreflective or is hidden far back to the right underneath a large overhang. Weird.

Mike Mellon (LASP, University of Colorado), a HiRISE team member offered this explanation for the peculiar appearance of this image:

It looks black because of the DN cut off in the lookup table. HiRISE is a 14 bit camera, but we usually LUT the data to 8 bits based on what we predict the histogram to look like. An unpredicted dark spot would get cut off.

Image credit: NASA/JPL/University of Arizona

JPL issued a press release today describing the results of our occultation analysis of Saturn’s rings. I’ve written about the basic idea and preliminary results before here and here. Press releases mean conversations with reporters, so I’ve had a few and it made me think of ways to describe what we’ve done that is easy to relate to. Larry Esposito, Principal Investigator of the Cassini Ultraviolet Imaging Spectrograph (the instrument team I work on), was the first to come up with the CAT scan analogy. The only problem with this is that most people (including me when this first came up) don’t know how a CAT scan works either (or even what “CAT” stands for).

CAT stands for Computed Axial Tomography, and these days they are typically known as CT scans, dropping the “axial” part because the same general technique can be done without the requirement of axial symmetry. That’s good, because that’s what we do with the occultations of Saturn’s rings, so in essence we’re doing CT (Computed Tomography) scans of the rings. CT scans take linear x-ray images of the body from multiple vantage points to construct a model of a slice of the body. By doing these scans at multiple “levels” or locations along the length of the body a full three-dimensional model can be constructed. In CT imaging the number of views through the body is large and in regularly-spaced viewing geometries so that an accurate model of the interior of the body can derived. We do not have the full range of viewing geometries available in our stellar occultations of the rings, however, and I only used about a dozen occultations to arrive at the model of clumps in the rings reported today.

So I thought of another analogy for the technique we used to see how ring particles clump together. Imagine that you are looking at a forest from a great distance, too far away to see individual trees. Now imagine that someone on the other side of the forest shines a bright light at you through the forest while you walk by. As you move you’ll see the light flicker as it is blocked by individual trees and occasionally passes through a gap between the trees. This single observation would tell you that there are things in the forest that completely block the light and it would tell you something about how big they are, but not their shape. But if you repeat the experiment with your friend on different sides of the forest you can begin to deduce that trees have cylindrical trunks.

Our paper in the journal Icarus describes our results for clumps known as self-gravity wakes in the B ring of Saturn. These clumps exist throughout the A ring (the outermost main ring) where they have long been known to produce a very visible “azimuthal brightness asymmetry” in images of the rings. The effect in the B ring is far more subtle. Observations from the Hubble Space Telescope also show the presence of self-gravity wakes in the B ring as described in a paper by Richard French and co-authors, also in Icarus. The advantage of the occultations as observed by Cassini is that they are able to probe most of the B ring even where the particles are tightly packed, allowing very little light to pass through. By using a model of self-gravity wakes as, essentially, parallel tree trunks lying flat in the rings, we were able to make the observations fit the model if the wakes are very broad and flat, more than ten times wider than they are thick. We are not yet able to measure the length of the clumps directly. The image this gives of the B ring is not of a sea of particles, but of a sea of broad sheets or clumps of particles, with relatively narrow and mostly empty space between them. Further observations will enable us to use more sophisticated models than the parallel tree trunk model and learn more about what Saturn’s rings would look like if we could get right on top of them.

Liquid water gets astronomers excited these days as the search for life elsewhere in the universe has become something of a unifying underlying theme of planetary science. No life on Earth exists without water. Of course, finding water elsewhere says little about the possibility for life except that, given our experience with terrestrial life, it probably can’t be ruled out. Hence the excitement over the recent discovery of the so-called “Earth-like” extra-solar planet, which in all likelihood is probably less Earth-like than Mars. Gliese 581c, five times more massive than Earth, orbits its star (Gliese 581) in only 13 days and is more than 10 times closer to it than we are to the Sun. It manages to keep an average surface temperature amenable to liquid water because Gliese 581 is a stellar wimp. Gliese 581 is an M-type star, which is a spectral type whose technical definition is “cold”. The spectral types of normal stars in order of decreasing temperature are OBAFGKM (”Oh, be a fine girl/guy: kiss me!” is the classic mnemonic). Gliese 581 is at the cold end of the distribution (the Sun is a G-type star; I make a living looking at hot O and B stars with the Cassini UVIS instrument). Its close proximity to the star means that the planet may be tidally locked to the star, keeping one side in perpetural daylight and the other in constant darkness. If the planet has a global ocean, sub-surface currents could lead to a layer in the ocean that is amenable to life. A planet this size likely has the raw materials (in the form of heavier elements) for life. Its high temperature means it has both energy available, and possibly liquid water. These are three key ingredients astrobiologists look for.

Closer to home, new work is exploring the water vapor geysers on Saturn’s moon Enceladus. Previous studies posited a near-surface reservoir of liquid water as the source of these geysers. A new paper by Francis Nimmo and Bob Pappalardo suggests that liquid water is many km below the icy surface and that the proximate source of the geyser material is heating produced by friction in the moon’s so-called “tiger stripes”. These roughly parallel grooves centered on the south-polar region are the apparent source of Enceladus’ geysers. Tidal flexing of the moon could cause blocks of ice to rub against each other, heating them enough to allow sublimation of ice (the direct evaporation of water from ice to gas). The tidal flexing is due to Enceladus’ slightly eccentric (non-circular) orbit around Saturn: when it is closer to Saturn the moon gets stretched slightly more than when it is a little further away. This leads to flexing or distortion of the moon as it orbits Saturn. Nimmo and Pappalardo calculate a half-meter slide of ice in the tiger stripes, and that much flexing requires that there is liquid water in the interior (if it were solid all the way through, the amount of flexing would be smaller and would not generate enough heat to produce the geysers). The JPL press release can be found here.

While Enceladus may have liquid water below its icy crust, unlike Gliese 581c it is poor in the energy and raw materials department. Future mission planning for the Saturn system is still focused on Titan, and Jupiter’s moon Europa which possibly harbors a sub-surface ocean, tops the list of icy worlds for future missions.

Next is based on the Philip K. Dick story The Golden Man about a man who sees his own future, but only the next two minutes. Produced by, and starring Nicolas Cage as Cris Johnson, Next features a terrorist nuclear bomb threat as the thriller backdrop. Julianne Moore plays FBI agent Callie Ferris who has somehow glommed onto the idea that Johnson, who “hides his ability in plain sight” as a second-tier Las Vegas magician, actually has the ability to see into the future. She figures this is the best way to track down the terrorists and their bomb. Exactly how this might work is not clear, though, as even Ferris knows that Cris can only see a couple of minutes into the future. I think two minutes warning that a nuclear bomb is going to go off in downtown L.A. is not going to do much good.

Unbeknownst to Ferris, though, Cris has discovered his foresight muse: Jessica Biel plays Liz who is linked somehow to Cris and enables him to see much further into his future - days at least. The threat of the nuclear bomb, and the terrorists who are chasing Cris because the FBI is chasing him, moves the plot along and provides some urgency. But there is enough in Dick’s idea of the character to make for a fascinating character study without the bombs and snipers. The gimmick presents an interesting storytelling challenge that director Lee Tamahori handles beautifully. Cris sees what will happen in his future, but once he sees that he can change his actions which changes what will happen next. Tamahori shows us these possible futures as Cris cycles through various possible plans of action. It is skillfully done and works well.

This video is an amazing graphical and educational treat about the complex machinery of organic chemistry within individual cells.

It’s been a big year for Alan Stern. He has been named one of the 100 most influential people by Time magazine, his New Horizons mission to Pluto is well on its way, having completed a very successful flyby of Jupiter, and he has been named Associate Administrator for Science of NASA. This is following the establishment of the Boulder office of the Southwest Research Institute, now a leading center for planetary science.

But few people realize that his biggest honor was getting his Ph.D. in the same class as me, back in December 1989 from the Department of Astrophysical, Planetary, and Atmospheric Sciences (now just Astrophysical and Planetary Sciences) at the University of Colorado, Boulder. Getting his Ph.D. at the same time as me was such an incentive to Alan that he managed to finish grad school in just three years and one semester, having started a full year after me (that’s fast: only one other person in my class of a dozen graduated as early as I did, a full year longer than Alan). Since then he’s published roughly three papers for every one of mine (and had three children for every one of mine). Yes, our careers have followed slightly different trajectories since 1989, but oddly enough we’re both leaving the comfortable climes of Boulder this year for the muggy air of the East: Alan to D.C. and me to Orlando. In the brief time he’s been AA for Science at NASA there have already been some positive changes in communication between headquarters and the science community. I’m excited to see what comes next.

Saw this movie built around the World Series of Poker. If you want to know my opinion, you’ll have to call my bet.
Okay, no takers. Well, this is a skillfully made movie with high production value and good acting, but it suffers in my opinion from its subject matter. This looks like a movie made by people who love poker. Not sharing that love, or even an interest in the game, most of the story held little interest for me. If you like poker, though, this movie should entertain.

Hot Fuzz is an odd combination of spoof and light comedy, of gory decapitations and quaint English humor. The first 3/4 of the movie is a mostly lightweight story of an overzealous police officer, Sergeant Nicolas Angel, who has been assigned to a sleepy English village so that he’ll stop driving his London colleagues insane with his perfectionism. The sleepy English village turns out to have more in common with Stepford than with, well, a normal village. Angel, played by Simon Pegg, who co-wrote the movie with director Edgar Wright, is confronted with a series of suspicious fatal accidents and a police force that is disdainful of any attempts at criminal investigation. Pegg and Wright are the team behind the zombie spoof, Shaun of the Dead.

Angel’s partner, the rotund and good-natured Danny (Nick Frost), seems willing to play along with Angel for the sake of having someone to talk to. Meanwhile, Timothy Dalton keeps appearing at the site of the latest fatality complete with sinister leer and none-too-subtle commentary on what really happened. Jim Broadbent plays Danny’s father, the police chief who tries to persuade Angel to leave things alone, and Cate Blanchett makes an uncredited cameo as Nicolas’s ex, though we only see her eyes so it might as well have been anyone. (For that matter, according to IMDB, Peter Jackson of Lord of the Rings fame also has an unrecognizable and uncredited cameo.)

This part of the movie is entertaining enough, but it really serves as a setup for the most improbable movie police shoot-out I’ve seen. The finale is an over-the-top parody of Lethal Weapon and all of its cinematic descendants, complete with a cop armed to Terminator levels, slow-motion bullet-dodging, bad guys who can’t hit the broad side of a barn, and gore galore. It’s quite funny. The movie just takes a little too much time to set it up.

Black Book is not a Hollywood Paul Verhoeven film. The director of Basic Instinct, Total Recall, Robocop, and Starship Troopers has returned to his native Holland and crafted a powerful and intriguing story of love, honor, and betrayal in the waning months of World War 2. Carice Van Houten plays Rachel Stein, a young Jewish woman whose hiding place in the Netherlands is destroyed. Narrowing escaping a massacre at the hands of the Nazis, she joins a cell of the Dutch resistance as Ellis de Vries. As Ellis, she befriends a Nazi officer and gets a job working with the German occupiers. While she works to gather information for the resistance, she runs the risk not only of discovery by the Nazis, but also the risk of being seen as a collaborator by her countrymen after the war.

In a movie packed with plot, the best-laid plans of both the resistance and the Nazis always seem to be foiled. The spies on the resistance side are known, but it is clear that there are also spies for the Nazis. The web of betrayal amid the brutality of the war and the struggle of Ellis and her fellow countrymen to maintain a sense of humanity is at the heart of the movie. The brutal stress of the war exposes ugly fractures between people, as some betray their beliefs for personal gains while subtle prejudices in others flare up into brutal violence. The story of Ellis’s journey through the last months of the war is gripping as a thriller, and is told against a compelling historical backdrop.