QUEST Community Science Blog Author: Ben Burress

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Personal Comet

January 29th, 2010 by Ben Burress

Comet Wild 2, as imaged by NASA's Stardust spacecraft.Nothing seems to capture the pure grandeur and extra-Earthly splendor of outer space like a comet: pure white cosmic snow, shining brilliant in the Sun's radiance, a vastly long tail of silky celestial gossamer…unreachable, untouchable, unspoilable….

Well, at Chabot, we like to bring things down to Earth a bit—not to diminish their wonder and awe-inspiring beauty, but rather to give us a chance to connect with pieces of the Universe in a personal way that—we hope—will only enhance their wonder.

Such it is with the Personal Comet. We make them in our classrooms, and our teen volunteers—Galaxy Explorers—sometimes set up a table in our exhibits to make comets for our visitors.

Last week I was teaching a lively group of 3rd graders our class, "Shooting Stars" (I'm not the usual teacher for this class, but love teaching this one especially).

"Let's make a comet," I announced, receiving a classroomful of suddenly puzzled 8-year-old faces. "Follow me." I led the group to the back of the room and had them sit in front of our rolling comet kitchen, tying on an apron and donning the "Comet Chef" hat.

"What's in a comet?" I quizzed. Hands went up, and answers were plucked out. "Water." "Ice." "Very small pebbles."

"Good answers. Let's start cookin'…."

One by one, and two at a time, I called up volunteers (no lack of these at all) to add ingredients into the mixing bowl.

Water first—two cupfuls. What else? The Chef helped out his students a bit: pebbles are fine, but what are they?

Silicon, calcium, to name a couple—so we add a source of these: sand. Then, iron, and magnesium—two more known comet constituents. Source? Dirt! Dirt can contain these, among other things.

For the carbon in our comet, we added—carbon: black charcoal dust; just a dusting.

There is nitrogen mixed up in comets too, so we had to add some to our concoction. Our nitrogen source (other than all the gaseous nitrogen floating about us in the air) is ammonia—NH₃ (what's a little hydrogen in the compound, more or less? In fact, ammonia itself has been detected in comets, so our recipe is true).

Organic compounds—carbon based organic molecules—have also been detected in comets…so we add a couple glugs of corn syrup. Okay, that's cheating a bit, because comet organics aren't known to come from agricultural products….

And lastly, but not leastly, is the two-in-one ingredient: contained in a plastic bag, I had the class use mallets to pulverize a few cupfuls of dry ice pellets into a fine powder. This adds not only the carbon dioxide to the material makeup of the Personal Comet, but that which really makes the difference between a bowlful of slightly sweet mud and the astral nugget of a comet: COLD! Space is cold, and so is dry ice.
In goes the frigid, dry frost, and out erupts clouds of billowing vapor—very exciting stuff. Now the Chef had to work fast, stirring and mixing and shaking the brew, and then squeezing the convulsive mixture in its plastic bag, with gloved hands, into a hard, solid lump. It takes a lot of squeezing, as it turns out….

Is it done yet?

I pulled out of the bag our Personal Comet, holding it out for the kids to marvel at—and they did. The double-fist-sized, dirty whitish, somewhat gritty hard blob is covered with pits and knobs and spouting plumes vapor. And, magically, it looks almost identical to a photograph of the nucleus of comet Wild 2, taken by NASA's Stardust spacecraft some years ago.

Everyone got to touch the comet—quickly, because it was quite cold—and make a personal connection with a tiny piece of the heavens. Now, I think, these kids are armed with an experience that will make their first comet-observing experience (yet to come for many of them!) a bit deeper, as I hope when they do see the vastly awesome sight in the sky, or through the eyepiece of a telescope, they'll also remember what it's like to touch a comet, or smell a comet, or see one spouting vapor right before them, in the palm of their hand….




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Martian Robot Roundup

January 15th, 2010 by Ben Burress

Gullies in wall of Hale Crater. Credit: NASA/MROOut of about 40 robotic missions launched toward Mars since the early 1960's, about 17 of them have been successful (I say "about" to hedge my bets, because the "success" of some of those missions is a bit gray), and of all of those, three orbiters, two rovers, and maybe—MAYbe—one lander are still active.

Here's a quick status on the active ones:

Mars Reconnaissance Orbiter: The most recent arrival at Mars (2006), MRO's 5-year mission (hmmm—sound vaguely familiar?) is to study the history of water and climate on Mars, as well as to serve as a telecommunications relay for other spacecraft. Armed with a suite of powerful instruments to study the atmosphere, surface, and subsurface of Mars—including a camera, HiRISE, that can almost read the license plates on Martian automobiles—MRO has to date sent back more data than all other Mars missions combined. It's not been a glitchless flight, however: in 2009, MRO's computer reset itself four times for unknown reasons; the last reset, in August, was followed by a 4-month operational hiatus as Earth-side controllers performed some careful programming updates to help guard against effects of any future resets. MRO resumed operation in December.

Mars Odyssey 2001: NASA's 2001 Odyssey is still going fine after nine years—although the computer glitchiness out around Mars seems to be catching: Odyssey's computer put itself into a safe mode last November 2009 in response to a memory error. This was corrected and Odyssey has resumed doing science. Among Odyssey's major discoveries was the detection of huge expanses of water ice just under the surface of polar lowlands, and the surveying of deposits of water-related minerals in various locations around the planet.

Mars Express: Arriving at Mars in 2004, Mars Express became the European Space Agency's first mission to another planet, which was recently extended to 2012. Though the Beagle 2 lander component of the mission fell to Mars and was never heard from again, the Mars Express orbiter has sent back years of captivating images and important data, including the confirmation of methane in Mars' atmosphere (whose source is in all likelihood subsurface, and the origin of which—organic or inorganic processes—is being debated).

Mars Exploration Rover Opportunity: After six years of crawling around Meridiani Planum discovering chemical and geological evidence for past water on Mars, Opportunity is now on a long march to a large impact crater, which it will reach (if it can keep on running) in about two years. Currently, the rover has stopped to RAT out chemical and geological information from a rock called Marquette Island—the RAT is its rock abrasion tool, or rock grinder. Still going….

Mars Exploration Rover Spirit: Also still alive after six years—almost 25 times longer than it was planned to run—Spirit has been stuck in a sand bog for the last six months. With a couple of wheels on the fritz, Earth-side operators have been confounded in trying to free the robot—but Spirit has continued to make scientific measurements anyway…and in fact made a significant discovery in the course of trying to get unstuck.

Phoenix lander: Although it's been in the deep dark freeze of a Martian winter since November 2008, the Phoenix lander has an outside chance of survival. Now that light is returning to Phoenix's landing site, NASA is listening for the robot's radio signal, in case the return of solar power means that Phoenix will rise from the frost and live again! So far, no such signal….

Next up: The Mars Science Laboratory rover, "Curiosity."




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Flash! Lakes Confirmed in Titan's Northern Hemisphere!

January 1st, 2010 by Ben Burress

NASA's Cassini spacecraft captured this image of sunlight
reflecting off of a lake on the surface of Saturn's moon Titan.
Credit: NASA/CassiniIn a literal flash of insight—well, "infrared sight," really–NASA's Cassini spacecraft has confirmed the existence of lakes of liquid in the Northern Hemisphere of Saturn's moon, Titan. That's really big news for scientists, and for those like me who absolutely love to envision the sweep of the landscape on alien worlds, be they science fiction or, as in this case, fact….

The evidence for the existence of lakes on Titan has been building since 2004, when the Cassini spacecraft, and its Titan-landing probe Huygens, arrived in the Saturn system and began collecting data.

First it was imagery from the Huygens camera as it descended through Titan's thick, hazy atmosphere: what looked like dark, flat, featureless regions defining apparent coastlines along solid terrain, as well as dentritic patterns like river channels draining into them.

Then it was imagery from Cassini's smog-penetrating infrared cameras showing numerous systems that looked for all the moon like giant lakes—on the order of size of Earth's Great Lakes. Cassini radar bouncing off the surfaces suggested that they were exceptionally flat, as one expects a watery surface to be.

Then there was confirmation of surface liquid in Titan's Southern Hemisphere—but not in the north, where the lake-like shapes were by far more numerous…an apparent land o' lakes.

Finally, what scientists hoped to see appeared, in a flash: sunlight, reflecting off of a Titanian lake called Kraken Mare, came shining through the moon's haze and was captured by Cassini's infrared camera. It's the same kind of reflection you see when sunlight blazes off the surface of the ocean before sunset. Astronauts see the same thing from Earth orbit, looking down at the ocean-lined limb of the Earth when the Sun is at the right position over it.

It required the right conditions; the Sun had to be in just the right position relative to the lake for the reflection to be seen. Ever seen the light of the setting Sun reflecting off the window of a distant house, though only for a moment when the geometry is just right? And only recently did the Sun rise over Kraken Mare's extreme northern latitude, after the 15-year dark of a Titanian arctic winter.

Titan is the only Solar System object known to have surface liquid, other than Earth. Jupiter's moon Europa is thought to harbor a vast ocean of liquid water, but under its outer crust of ice. Another of Saturn's moon's, Enceladus, also appears to hold liquid water inside, but its surface is as dry as the Earth's Moon. And yes, the Moon was recently confirmed to have surface water—but it's all frozen and mixed in with the lunar soil in a sort of dry cryo-mud.

The difference with Titan, however, is that its surface liquid is not water at all, but methane. It's too cold on Titan's surface for liquid water to exist there—but Titan's atmospheric pressure and temperature are right for methane to exist in its liquid state. So while on Earth we know methane as a greenhouse gas emitted by decomposing plants and the guts of cows—to name a couple of sources—on Titan it is the stuff of cloud, of rain, of river, and of lake.

What a wild world!




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Posted in Astronomy, KQED, Partners | 2 Comments

Spirit Digs a Little Deeper into Martian Geology

December 18th, 2009 by Ben Burress

NASA's rover Spirit has churned up sulfate minerals in the
attempt to free itself from loose soil.
(Credit: NASA/JPL/Cornell)Some robots are born to greatness, and some have greatness forced upon them by circumstance. NASA's Mars rover Spirit has recently fallen into the latter category by making an accidental discovery in the course of trying to free itself from a sand trap….

Has it been six years since the twin rovers, Spirit and Opportunity, landed on Mars to begin their careers? Just about—next month is their landing anniversary.

Both rovers have shown signs of wear and tear, but Spirit, in its exploration range in Gusev Crater, has had the harder knocks. In fact, Spirit has driven backward for a couple of years now, due to a wheel that stopped working and which it was forced to drag through the Martian soil—a robot's form of limping.

About six months ago, Spirit became bogged down in loose soil, spinning its wheels but unable to break free of the trap—not unlike what happened to my car in Death Valley one time…and Spirit can't call upon the assistance of a National Park Ranger with an SUV and winch to help….

Over the months of entrapment, Spirit's handlers on Earth have continued to make measurements with the rover's instruments while trying to free it from its soil trap by manipulating its wheels in different ways (probably not unlike some of the strategies I tried to get my car out of the sand). But to no avail (either for Spirit or my car). Alas, is Spirit destined to remain a stationary explorer until its lifetime finally comes to an end?

Perhaps—but as it turns out, this doesn't mean Spirit can't still make significant discoveries–like a recent one it in fact made. All that wheel spinning and grinding and rocking back and forth have chewed up the soil in which Spirit sits—and has broken through a layer of soil to expose a surprise hiding beneath: a crust of sulfate minerals.

Sulfates—compounds containing sulfur—can be formed in the presence of water, like boiling water or steam escaping from a hydrothermal vent. It may be that these sulfates formed in the distant past when the area was active with volcanism and hydrothermal steam vents. That was then.

This is now: the layer of sulfate (calcium sulfate) Spirit's churning wheels broke through is crusty—a property that may point to more recent water activity than the original sulfate-forming steam vents. Scientists think that the crust may have been formed by the seasonal shifting of water from the Martian polar regions when it warms up in its summer, sending the water toward the equator–where it can even fall out as snow. Then, soil beneath the layer of snow warms the bottom layer of ice and causes it to melt. In turn, the melt water seeps down into the soil, dissolving and carrying away water soluble iron sulfate and leaving behind the crust of calcium sulfate.

In one fell swoop trying to escape sure peril, Spirit appears to have uncovered clues about the nature of Martian water action in the distant past as well as more recent times.

As serendipitous as Spirit's entrapment is to this accidental discovery, it's even better: the rover is stuck square on the edge of a small meteorite crater, allowing it to compare the sulfate concentrations in the sulfate-rich crust and the more typical soil medium, side by side.

Way to go! That's the spirit!




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New Evidence of Martian Life Found in Antarctica?

December 4th, 2009 by Ben Burress

Scene from the 1951 film The Thing From Another WorldFor decades, if not longer, we Earthlings have been collectively waiting for that definitive day when we make First Contact with life from somewhere else in the universe, whether it's a Closer Encounter of the Third Kind kind of advent or the detection of a microbe on another world. Are we there yet? Well, no, not yet–but we may be a healthy step closer to that day now.

On Monday, November 30th, 2009, NASA/Johnson Space Center announced that a recent study strengthens the argument that chemical and structural features in a Martian meteorite—ALH84001—may be evidence of fossilized microbial life on Mars from the distant past. While not absolutely conclusive that the meteorite bears the remains of ancient Martian life, the results of the study show that alternate, non-biological explanations for some of the meteorite's properties are not consistent with new findings.

Meteorite ALH84001, discovered in Antarctica in 1984 and chemically identified as having originated on Mars, hit the news in 1996 when researchers hypothesized that microscopic features and chemical constituents in the rock could possibly be the fossilized remains of ancient Martian microbial life. The hypothesis was controversial among scientists, and alternate, non-biological processes were offered by opponents as possible explanations for the meteorite's features.

The recent reexamination of the meteorite was focused on one of the leading non-biological explanations for the existence of magnetite crystals in the sample. Magnetite is an iron-bearing, magnetic mineral that can be produced both biologically and through inorganic processes. Some forms of life on Earth—including microbes–produce magnetite crystals in their cells that help them orient to Earth's magnetic field.

The NASA/JSC team that performed the new analysis of ALH84001 concluded that new data on the magnetite crystals, obtained with more powerful analytic instrumentation than used in the 1996 study, are not consistent with the leading non-biological explanations. This, they argue, strengthens the biological explanation for the origin of the magnetite.

The new analysis also obtained scanning electron microscope data that yielded more detail on shapes within the alleged microbe fossils. The new shapes that emerged from the data closely resemble shapes within Earthly microbe fossils—further strengthening the hypothesis that the meteorite contains fossils of life, and thus that life at one time existed on Mars.

The evidence for the possibility of life on Mars, past or present, has been growing over the past decade, or longer—evidence that Mars was once much warmer and wetter than it is now, and that it had rivers, lakes, and possibly oceans of water, making it an environment possibly conducive to the formation of life. We have also detected methane rising out of the soil of Mars, which some suggest could be a byproduct of current biological activity, underground.

NASA will continue to examine the Martian meteorite, focusing their study on further detailing the structures of alleged microbe fossils and possible chemical signatures of life that remain in the rock.

So, we're still waiting for the day—but with all the tantalizing clues emerging from our exploration of Mars and the Martian meteorite, it feels very much like that day is somewhere on the horizon. But, wouldn't it be ironic if we were to make the first definitive detection of extraterrestrial life right here on Earth, with evidence that's been just laying around since before the beginning of human civilization?




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Lunar Ice Smack-down a Success!

November 20th, 2009 by Ben Burress

The view from the control room of Chabot's planetarium during
the live LCROSS lunar impact eventIt's official: NASA's LCROSS mission found water on the Moon, no bones about it. Though NASA is still analyzing all the data they reaped from the LCROSS impact event on October 9th, and will be for a long time to come, they seem confident enough about the preliminary findings to make this a definite declaration of discovery!

Rewind to October 9th. It was a lot of fun watching the event up here at Chabot. We'd hoped to observe the impact through our 36-inch telescope, Nellie, but were clouded out. Fortunately, the main part of the show was brought to us via satellite from NASA—and from the vantage point of the LCROSS spacecraft, on its collision course with the Moon, where terrestrial weather was not a factor.

Our planetarium was filled—overfilled actually; we had to open up our theater across the hall as an overflow viewing area! Mind you, it was 3:00 in the morning on a Friday, and still over 300 people showed up in various states of caffeination.

I set up the planetarium to resemble the control room of a futuristic starship: a huge spinning animation of the Moon overhead, and several large projections showing simulations of the impending impact, recent images from other lunar missions, and, front and center, the view from NASA, which alternated between Mission Control at Ames Research Center and a live view from the LCROSS spacecraft itself.

The view from LCROSS showed an ever-nearing wall of lunar craters and topography as LCROSS homed in on its fate. The announcement was made that the primary impactor, LCROSS's Centaur upper rocket stage, had impacted, and we all strained our eyes looking for the plume of dust the impact was hoped to produce. But, the impact didn't create as visible an ejecta plume as expected; we stared on, but only saw the wall of craters loom closer and closer.

The four minutes between Centaur impact and the inevitable impact by LCROSS itself ticked by, and we held our breaths. Then, the image went blank, and NASA announced that LCROSS had impacted the Moon. Though we didn't see the plume, it was exciting to ride along with LCROSS to its end, and live to tell about it. Next better thing to being there….

Back to the water. Though no plume of dust was seen by LCROSS's main visible camera, that's not all it had in its toolbox of instruments. Most revealing was data collected by LCROSS's spectrometer—the device that sorts out the wavelengths of light and discriminates the specific wavelengths emitted by specific chemicals. Water (H2O) and hydroxyl (OH) seem to have been present in the dust plumes kicked up from the permanently shadowed floor of Cabeus crater, at the lunar south pole.

And more: other volatile chemicals—whose identities will no doubt be revealed by NASA in coming months in the due course of their data analysis—appear to have been detected in the impact plume.

How much water? Are we talking vast sheets of solid ice, glaciers, and land-locked icebergs? Well…though NASA hasn't yet characterized the quantities of water inferred by LCROSS's detection, the serene waters of Cabeus likely are a mixture of lunar soil and ice—a substance you'd have to work at to extract pure water from.

For more exciting discoveries to come, stay tuned to the Moon….




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Posted in Astronomy, KQED, Partners, TV | 3 Comments

Oakland Teachers Scope Out What Galileo Saw

November 6th, 2009 by Ben Burress

Oakland Unified teachers assembling Galileoscopes at ChabotWhat was it like for Galileo, the first time he put an eye to his telescope to see things in the heavens as never before seen? As anyone who has seen a planet or a star cluster or a nebula—or the Moon—through even a small telescope knows, the sight can be quite breathtaking. For Galileo, it must have been a universe-changing experience….

Through a generous donation by a concerned citizen (concerned that kids today aren't seeing enough of the sky), Chabot just completed a pair of workshops for Oakland teachers that places in their capable hands and in their classrooms "Galileoscopes"—special telescopes designed and manufactured for the 2009 International Year of Astronomy. The Galileoscope is a low cost, simple, but good-quality telescope designed to simulate the power and field of view of Galileo's original telescope, which opened up the universe in such a profound way.

In September and October, a total of 23 Oakland teachers received training, activities, and one Galileoscope each (plus tripod), enabling them to share the experience with their students and, hopefully, spark their imagination and curiosity about the world around us in a way that nothing but astronomy does.

A look through a telescope—any telescope, big or small—does put a spark in the eye and the imagination. At least, that was my experience. Growing up in Oakland back in the 60's, I didn't have access to any small telescopes, but Chabot Observatory was only a couple miles away, and my family often went up on a weekend night for a classroom demo, a planetarium show, and thoroughly enjoyable viewing through the two antique telescopes, Leah and Rachel. Something about the actual light from Saturn or Jupiter or a distant galaxy tickling the receptors in your retina places you out there—or puts those objects directly into your brain.

The Oakland teachers now armed with their Galileoscopes will use these simple but effective tools to show their students the difference between seeing Saturn as a spot of light and Saturn as a disk with "ears" (the appearance of its rings through a Galileoscope), or the difference between Jupiter as a brighter spot of light and Jupiter as a world with a giant storm in its clouds and four smaller "worlds" (moons) in orbit around it, or the difference between the Moon as a disk with light and dark areas that make interesting shapes in our imaginations and the Moon with mountain ranges, vast plains, thousands upon thousands of craters, and shadows stretching across the landscape.

By the way, Galileoscopes can still be ordered, through the Galileoscope website, for a short time still, in case you're interested in getting your toe into the door of a much bigger universe….




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Web of Stars

October 23rd, 2009 by Ben Burress

Students in Cork, Ireland interacting live via Skype with Chabot
during real-time observing session.What do Chabot's 36-inch telescope, Nellie, and a classroom full of 14-year-old girls in Cork, Ireland have in common? In a few words, the International Year of Astronomy and the Web of Stars!

Wednesday morning around 1:00 AM, Chabot staff astronomer Conrad Jung and I fired up the systems in the 36-inch observatory and made a Skype video call to the Blackrock Castle Observatory in Cork, Ireland. Staffers Frances McCarthy and Alan Giltinan answered—it was 9:00 AM for them, and Frances had already been up four hours to prepare for our premiere session of Web of Stars. A bus-load of girls from a local school were on their way through the downpours of rain Cork was experiencing at the time.

On our end, everything technological was working fine: Nellie, our 36-inch telescope, was stoked, motors humming and ready to drive us to faraway celestial locales; computers were singing (in their own particular way), and the webcam-Skype interlink was green. The webcam view nicely framed the telescope, making a great background for the session.

A little after 2:00 AM PDT, the girls from North Presentation Secondary School rolled into the classroom, and there was a great deal of excitement. Eight or nine of them immediately descended upon the microphone and webcam and started chirping "helloes" and "hi's" at us across the 5,000 mile gulf (what's an ocean and a continent to get in the way of the Internet?).

After the greeting buzz died down, and the girls' teacher and the facilitators at Blackrock Castle got them to their computer stations, the morning's work began….

"We regret," Conrad and I had to inform them, "that the weather at Chabot is damp, and we're completely fogged out." This was a disappointment, of course, but we had a Plan B lined up in the event of bad astronomy weather. From Conrad's archive of astrophotography, we pulled up some un-processed astronomical images from months past and dumped them to our FTP server, where Alan at Blackrock Castle immediately downloaded them to the girls' computers: Comet Lulin, the Andromeda Galaxy (M-31), the Hercules globular cluster (M-13), the Apollo 15 landing region on the Moon, the Great Nebula in Orion (M-42), and the Ring Nebula (M-57) were the fare for the session.

With the astro-image processing software Salsa-J, the Cork girls proceeded to process the images—taking each set of three color channel (red, green, blue) black and white images and combining them into composite full-color images. Throughout the 2-hour session, the girls broke away from their computers two and three at a time to come to the microphone and chat with Conrad and I—we were even treated to a song or two from the girls, one by the entire class: On the Banks of My Own Lovely Lee.

The Web of Stars program was conceived of by Blackrock Castle Observatory, and Chabot became the partner observatory through proximity to San Francisco, which is a sister city of Cork. In Ireland, classrooms competed over the summer to earn one of the six pilot observing sessions with Chabot, and the program will unfold from October through March with one session each month.

Though we had to resort to our bad weather Plan B ("B" for "bad" weather) for our kick-off session, the A plan ("A" as in "actual active astronomy") will be for us to acquire and image objects with Nellie from lists of targets sent to us by the students in Cork, and deliver them in real time to the classroom at the Castle, where they will conduct the image processing and measurement activities in lock step.

Please wish us and the students in Cork good weather!




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Posted in Astronomy, KQED | 3 Comments

Equinox on Saturn Reveals Ring Ripples

October 9th, 2009 by Ben Burress

Bumps and ripples in the otherwise flat ring system of Saturn cast long shadows at equinox. Image credit: NASA/CassiniImagine a vast, flat plain spreading out before you for tens of thousands of miles in all directions, with no Earthly curvature to give the horizon its slightly finite look. Instead, it stretches seemingly to the infinite blackness of space in one direction, and slices straight into the streaky, wind-smoothed clouds of Saturn in the other…

Hard to imagine what it would be like to float just above the rings of Saturn, but what a sight it must be! As a kid, one of my favorite astronomical pass-times was imagining the view from other places in the Solar System.

Now imagine a towering bulge of frosty mist rising up out of this super-flat plane of ice chunks, literally the size of a mountain. Such is what was beheld by NASA's Cassini spacecraft last month–albeit, from a distance–when it turned its cameras to Saturn's vast rings during the few days surrounding Saturn's equinox (August 29, 2009), giving us a view never before seen.

Equinox on Earth, when the Sun is positioned directly over our equator, happens twice a year. Due to Earth's tilted rotational axis, as we orbit the Sun the latitude over which the Sun shines directly cycles north and south between the latitudes of the Tropics. On its way north to warm our (Northern Hemisphere) summers or south to leave us in the chill, the Sun crosses the equator on the equinoxes (Fall and Spring).

The same thing happens on Saturn, with two differences. First, Saturn takes nearly 30 years to orbit the Sun, so equinox comes only about every 14 years. Second, Saturn has its system of rings that encircle the planet directly above its equator, serving as a visible extension of the equator. At Saturn's equinox, the Sun is not only directly over the equator, but sunlight strikes the rings edge-on, like a flashlight shining on a flat piece of paper from the edge, the light just grazing over the surfaces on either side.

When this happens, any deviations from the flatness of the ring system—bumps and ripples–cast long shadows across the rings, making the features much easier to see. The same thing is seen on that piece of paper with shadows from creases and bumps leaping across the page.

As seen from Earth, equinox on Saturn means the rings appear to vanish as we look at them edge-on. This behavior puzzled astronomers long ago before they understood the rings for what they are. During the August 2009 Saturn equinox, however, for the first time in history we had a bird's-eye view of the rings during equinox, from Cassini. Cassini has been in orbit around Saturn for five years now.

Cassini spotted a number of prominent shadows trailing bright spots and ridges—bumps and ripples of different sorts rising above the ring plane.

Some of the bumps–icy ring material kicked up by the gravitational disturbance of a small moonlet inside the rings–were measured at over two miles high, the height of the Rocky Mountains. Other rippling features, such as long ridges running along the direction the rings encircle Saturn, are waves created by the gravity of moons orbiting outside the ring system. Still other types of disturbances observed are possibly caused by the impact of meteoroids or chunks of ice with the rings.

Saturn's rings are tens of thousands of miles across, but are extremely thin—perhaps no thicker than the height of a four-story building! So a bump or ripple as high as a mountain is a big deal!

Ah, to be on Saturn, now that equinox is here…




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MOON Spells "Water"

September 25th, 2009 by Ben Burress

Map of Moon water; blue indicates higher concentrations of detected water molecules. Credit: NASA/Moon Mineralogy Mapper instrument.Here it comes! A veritable tidal wave of discovery on Earth's Moon….

In one short week, NASA's LCROSS (Lunar Crater Observation and Sensing Satellite) mission will quite literally come to an end—a fiery, spectacular end as it deliberately crashes into the lunar South Pole crater Cabeus A in hopes of kicking up enough material for us to detect the presence of water. If you want to see the action as it happens, come up to Chabot Space & Science Center on Friday morning, October 9, 3:00 AM to watch NASA's live simulcast and–weather and the gods of astronomy permitting–the view through Chabot's 36-inch telescope, "Nellie."

In recent months, NASA has been sending a lot of acronyms—excuse me: spacecraft—to the Moon: LRO with it's LROC, LEND, and LOLA instruments; LCROSS (which I've heard some call "LaCROSS," for the record) with its VIS, NIR, MIR, TLP, VSP, NSP—oh, the list goes on!

The fact of the matter is MOON spells "Moon." Whether or not we do end up returning humans to the Moon in the next decade, which is partly what reconnaissance by LRO and LCROSS and their arrays of acro-instrumentation is for, there are still things to be learned about our nearest neighbor in space—and water is the word at present.

Even as LCROSS and its Centaur-booster-rocket-turned-lunar-clobbering-device follow their final fatal trajectory toward Cabeus A, its launch buddy LRO, now in an orbit around the Moon and beginning to send back scientific results and images, may have already detected telltale signs of the wet stuff—which on the Moon won't be wet, but frozen solid, of course; liquid water cannot persist in the Moon's airless environment.

LRO's LEND (Lunar Exploration Neutron Detector) instrument is designed to find signs of water molecules by measuring neutron radiation emanating from the lunar surface. The Moon is constantly bombarded by high energy cosmic radiation, which forms radioactive isotopes in the soil that in turn emit neutrons. By measuring the abundance and speed distribution of the neutrons, details of soil chemistry can be inferred. The presence of light atomic nuclei–in particular the lightest of all, hydrogen, a component of water—in the soil reduces the levels of neutron emission. That drop in neutron radiation is the telltale scientists are looking for.

While LRO scientists want to make further measurements before concluding the presence water ice concentrations, observations from three other spacecraft—NASA's M3 instrument (Moon Mineralogy Mapper) aboard India's Chandrayaan-1 spacecraft and the Cassini and EPOXI spacecraft—have mutually confirmed the presence of water and hydroxyl molecules (hydroxyl is a water molecule missing one of its two hydrogen atoms) in the soils of the Moon, across much wider expanses than the confines of dark polar crater floors.

Cassini and EPOXI made measurements as they flew past the Moon to their respective destinations (Saturn, and a comet), and measurements have been made by M3 from lunar orbit. The detection of water by these spacecraft doesn't mean seas of liquid or glaciers of ice, or even blanketing layers of gaseous water vapor, but rather relatively small amounts of water and hydroxyl molecules attached to, or "stuck to," other materials in the top few millimeters of soil.

This thin "confetti" of water molecules appears to come and go with lunar daytime, forming during the cold, dark two-week-long lunar night and diminishing under the baking light of the Sun.

So, right now, MOON spells water (M3 et al), water (LRO), and possibly more water (LCROSS, on October 9th)—at least, the evidence seems to be mounting!




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