No one ever said that Uranus was anything but a strange world. Nineteen times farther from the Sun than the Earth, the planet's equator is tilted 98 degrees from its orbital plane. The tilt is so profound that if you work out the averages, the Uranian poles get more sunlight than the equator. That could lead to interesting weather patterns on a world with an 84-year orbit where seasons last twenty-one years. Such seasonal subjects have been the subject of recent study using imagery from the Keck II instrument in Hawaii, the results presented at the Division for Planetary Sciences meeting this week in Ithaca, NY. Uranus reached equinox in 2007 when the Sun attained a position directly over the planet's equator. Having equal amounts of sunlight over northern and southern hemispheres is obviously not a routine occurrence for this planet, but it's a good chance to look at what's happening on the meteorological front. Lawrence Sromovsky (University of Wisconsin) notes that seasonal...

The last time Cassini flew past Saturn's moon Enceladus (August 11), temperatures over one of the so-called 'tiger stripe' fractures at the south pole were lower than had been measured on an earlier flyby in March. Two October encounters, one of them scheduled for today, may provide enough additional data to help us understand what's going on. The fracture in question is known as Damascus Sulcus, which showed temperatures between 160 and 167 Kelvin in August, but 180 degrees Kelvin during the March flyby. Then again, nothing about Enceladus should surprise us any longer, including an apparent change in the intensity of the plume, within which trace amounts of organics have been detected. The October 9 approach takes us to a distance closer than any previous flyby of a Saturnian moon, a mere 25 kilometers from the surface, a key objective being to study the composition of the plume with the spacecraft's field and particle instruments. Thus Tamas Gambosi (University of Michigan, Ann...

The transit method -- observing a distant planet as it moves in front of its star as seen from Earth -- is a prime tool for exoplanet detection. But transits are hardly limited to planets around their primaries. The Taiwanese-American Occultation Survey (TAOS) is demonstration of that, an attempt to find tiny Kuiper Belt objects (KBOs) in the range between 0.5 and 28 kilometers. As you would imagine, at a distance like this such objects cannot be seen directly, but an occultation -- the dimming of a star when one of the KBOs passes in front of it -- should be apparent. The image below shows the method applied to a cometary nucleus. Image: Looking for dimmed starlight -- the basic method at work in the TAOS survey. The experiment follows 3000 stars five times per second in its search. Credit: TAOS. TAOS works with small, wide-field robotic telescopes on peaks near the Yu-Shan (Jade Mountain) National Park in Taiwan. The current results represent 200 hours of collected data using these...

Fine work by Rosetta on the Steins flyby. Check here for more imagery of the 'diamond in the sky,' with cratering suggesting extreme age. Image: Asteroid Steins seen from a distance of 800 km, taken by the OSIRIS imaging system from two different perspectives. The effective diameter of the asteroid is 5 km, approximately as predicted. At the top of the asteroid (as shown in this image), a large crater, approximately 1.5-km in size, can be seen. Scientists were amazed that the asteroid survived the impact that was responsible for the crater. Credits: ESA ©2008 MPS for OSIRIS Team MPS/UPM/LAM/IAA/RSSD/INTA/UPM/DASP/IDA.

With the Steins encounter looming, let's keep the focus on the asteroid belt, in this case by examining a connection between that distant region and our own planet. Cosmic dust particles -- tiny bits of pulverized rock up to a tenth of a millimeter in size -- move continuously through the Solar System, a kind of micro-thin fog of micrometeorites that contributes hundreds of billions of particles to Earth's atmosphere. New research into the makeup of some 600 of these particles now reveals their chemical and mineral content, allowing an overview that points to their origin. The suspected source: A group of asteroids between Mars and Jupiter. You can see one of the Koronis asteroids in the image at left, which shows 243 Ida as photographed by the Galileo probe. What we now believe about the Koronis asteroids is that they were formed some two billion years ago by the breakup of a much larger asteroid. Within the Koronis family are the ninety or so Karin asteroids, which seem to be in a...

Get out to about 2.4 AU from the Sun (2.41 AU, to be precise) and your radio signals have a long travel time. It takes 20 minutes to cross the 360 million kilometers between Earth and the Rosetta spacecraft, and that, of course, is one-way. As we've learned from all our deep space missions, spacecraft are largely on their own for the brief and critical window of an encounter, like the one with asteroid Steins that is coming up for Rosetta. Opportunities for possible trajectory correction maneuvers exist both on September 4 and 5th, but it's on the 4th that Rosetta's controllers will have their last chance to acquire optical images for navigation. Uplink commands for asteroid fly-by mode will be sent on the morning of the 5th and then we wait for results as the vehicle flips for observation and tracking. Rosetta will close to within 800 kilometers of the asteroid, passing it at a speed (relative to Steins) of 8.6 kilometers per second. Image: The approach of Rosetta's spacecraft to...

A symposium called Sloan Digital Sky Survey:Asteroids to Cosmology, held in Chicago this past weekend, is producing interesting news, not the least of which is the discovery of a 'minor planet' that is currently inside the orbit of Neptune. 2006 SQ372 is only in the neighborhood briefly, already setting out on a journey that will take it 150 billion miles from the Sun. Its orbit is an ellipse four times longer than it is wide, not dissimilar from the dwarf world called Sedna, which was discovered in 2003. But SQ372 strays even further out and takes twice as long to complete its orbit. You'll need to click to enlarge the image below to see the details. Image (click to enlarge): The orbit of the newly discovered solar system object SQ372 (blue), in comparison to the orbits of Neptune, Pluto, and Sedna (white, green, red). The location of the Sun is marked by the yellow dot at the center. The inset panel shows an expanded view, including the orbits of Uranus, Saturn, and Jupiter inside...

As someone who has always been interested in how we name things, the choices on Enceladus have been particularly pleasing. On the remote Saturnian moon, place names are chosen from the The Arabian Nights, which is how we wind up with Damascus Sulcus, as seen in the photo below. A sulcus is a large fracture, a 'tiger stripe,' as they're called on Enceladus. The four most prominent are named Alexandria, Cairo, Baghdad and Damascus, adding yet a further tinge of exotica to a tiny world that has already shown itself to be highly unusual. Cassini's August 11 flyby is, as the photo shows, paying off big. The intent was to focus in on sources for the jets that spew water vapor, ice and trace organics into space -- the yellow circles in the image show two particular sources of jets. What we're after, of course, is a closer look at geological activity in the sulci, in hopes of determining whether liquid water exists beneath the surface. The new details show that the fractures are some 300...

Although the Cassini spacecraft has just passed no more than fifty kilometers from the surface of Saturn's moon Enceladus, the investigation of the intriguing object will only intensify in October, when Cassini moves to within half that distance. With astrobiological interest high, Enceladus is a hot place to be. Data from the most recent flyby began streaming in to the Deep Space Network station in Canberra last night, with the downlink scheduled to continue into the afternoon of the 12th (EST). The prime target, using every camera resource available and covering infrared, visible light and ultraviolet, is the area of the moon's southern pole that houses the fissures now known as 'tiger stripes.' Under intense scrutiny will be the terrain of the fissures as well as the composition of the ice grains inside, and tuning up our data on temperature should provide a better idea of whether or not liquid water lies close to the surface. Cassini will be looking for other elements -- oxygen,...

Remember those oceans of methane we thought might exist on Titan? They were an exciting thought (I recall hypothetical images of the Huygens probe bobbing in such an ocean at the end of its journey, before we knew what it would actually land on). It's exciting to confirm that liquid does exist on Titan's surface in the form of liquid hydrocarbons, with a positive identification of ethane. At least one of the large lakes the Cassini orbiter has found there contains the substance, but we also know that numerous other lake-like areas exist beneath the smog. Image: The Imaging Science System aboard NASA's Cassini orbiter took the image, left, of Ontario Lacus in June 2005. (Image credit: NASA/JPL/Space Science Institute.) Cassini's Visual and Infrared Mapping Spectrometer took the image, right, of Ontario Lacus in December 2007. This view, taken at 5-micron wavelengths from 1,100 kilometers (680 miles) away, shows the part of the lake that is visible on Titan's sunlit side. What appears...

Now in press at Astrobiology is a look at the possibilities of life on Enceladus that holds out hope for detecting biomarkers with data gathered during a Cassini flyby. That's an exciting possibility, depending as it does not on an orbiter or lander mission from an indefinite future but on equipment we've currently got in Saturn space. And the Enceladus picture remains fascinating because of the possibility that some microbial systems on Earth that operate far beneath the surface may offer examples of how life could evolve on a cold and distant moon of Saturn. We've already found a dozen icy particle jets coming out of Enceladus' south polar regions, all pumping material into a plume that extends for thousands of kilometers. A 2005 Cassini flyby revealed, among other things, water vapor, methane and simple organic compounds, even as other Cassini instrumentation showed the moon's south polar region to be anomalously warm. If there is liquid water under the south polar region, could...

The latest Carnival of Space is now available at the Space Disco site, where Dave Mosher has put together a helpful slideshow of entries handsomely illustrated and linked to the originals. With seven new blogs coming online at Discovery Space, we'll doubtless be seeing contributions from many of these fine writers, people such as Ray Villard, Chris Lintott and Mosher himself. I'm particularly looking forward to Jennifer Ouellette's Twisted Physics blog, which this week offers a backgrounder on tachyons. In terms of our usual beat, deep space from the outer planets into interstellar space, I'll send you to David S.F. Portree's Altair VI site, where the author has gone to considerable trouble to present the results of a study by Science Applications, Inc. (SAI) on the possibilities of futuristic missions to Titan. This material was originally presented in 1983 at a NASA workshop and offers a view of what should still be a viable game plan: To seed the clouds of Titan with floating...

Much can be learned from a close look at an asteroid, as the European Space Agency's Rosetta spacecraft will demonstrate this September. For one thing, interactions between the solar wind and the asteroid can deepen our knowledge both of the object and the forces that act upon it. For another, studying what's around the asteroid can be useful, especially now that we know some asteroids have even smaller asteroid 'moons.' But Rosetta's September target, asteroid (2867) Steins, is an interesting case in and of itself. E-type asteroids, which this one is, are relatively common in regions closer to the Sun but uncommon within the main belt itself. They're typically small and show a high albedo, reflecting more light from the Sun than the average asteroid. Moreover, while they're apparently made of silicates and basalts, their composition is only poorly understood. Thus the choice of (2867) Steins as a target within a larger mission plan that culminates in 2014 at comet 67/P...

Does anybody remember an old science fiction movie involving an attempt to snatch meteors from space? We're talking something made probably in the 1950's, and all I remember is a group of one-man spaceships sent up -- for reasons that escape me -- to go after meteors. You can imagine the dynamics of trying to catch a meteor with a scoop on a spacecraft. All subsequent attempts to identify this film have failed, but I was reminded of it by the discovery of a new mineral in a sample of interplanetary dust. Collecting the dust wasn't quite as terrifying as the meteor-grabbing depicted in the movie, and the motivation for it was surely sounder. In any case, it's clear that you don't have to go into deep space to collect interesting things. It was Scott Messenger (Johnson Space Center) who suggested that interstellar dust particles (IDPs) from a particular comet could be captured in the stratosphere if scientists chose their time carefully. Messenger zeroed in on comet...

Calcium aluminum-rich inclusions (CAIs) are bright, ancient materials found in carbonaceous chondrite meteorites. Their story in terms of modern astronomy goes back to February 8, 1969, with the fall of the so-called Allende meteorite, the largest carbonaceous chondrite yet discovered. This meteorite, which fell over Chihuahua, Mexico, was found to be rich in CAIs, seen as inclusions of up to several centimeters in size. The link between CAIs and the early Solar System was soon established. Carbonaceous chondrites are meteorites with high levels of water and organic compounds. the presence of which leads scientists to believe that they are relatively pristine examples of material from the birth of the Solar System. They are also known for the round grains known as chondrules. Now a team of astronomers has found asteroids likewise enriched in calcium and aluminum, and hence considered to be among the oldest yet identified. Says Tim McCoy (National Museum of Natural History): "I find...

Cassini's recent pass through the plumes of Enceladus resulted in a number of intriguing finds, perhaps the most interesting of which is the temperature along the 'tiger stripes.' These are the fissures from which Enceladus' famous geysers erupt. Cassini's Composite Infrared Spectrometer found them to be warm along almost their entire length, reaching no less than minus 93 degrees Celsius (-135 F). The warmest regions correspond to two visible geyser locations. The contrast in temperatures is striking: The differential between these regions and other areas on Enceladus is a whopping 93 degrees Celsius (200 F). This heat map gives a sense of what we're dealing with. The brightest fracture, known as Damascus Sulcus and visible at lower left in the image, shows the highest temperatures. In this image, the false color infrared data are superimposed on a grayscale mosaic of the south pole that dates back to the summer of 2005. The map was made at a distance of between 14,000 and 32,000...

One question jumps out at me from the blog entries that Cassini team members have been posting on the probe's dazzling close pass by Enceladus. It's from deputy project scientist Linda Spilker, who says: "I am thinking about the two Voyager flybys of the Saturn system that took place over 25 years ago. How in the world did we miss the Enceladus plumes back then???" Indeed, but that's the nature of exploration, to learn something new each time you revisit a place, especially one that's fully 10 AU out. The process is addictive, and breathtaking. Do be aware of the flyby blog, offering an inside view of one of the most interesting of Cassini's encounters thus far (also be aware that the entries are oddly out of order, a problem apparently being fixed). With the data downlink now started (as of about 0201 UTC today) via the Deep Space Network's Goldstone station, we can ponder the chutzpah of taking a spacecraft so close to the huge geysers erupting out of the south pole of Enceladus....

As if we didn't have enough trouble getting to the outer Solar System, now comes word that the US inventory of plutonium-238 is diminishing. That's what NASA administrator Mike Griffin told a House appropriations subcommittee this past week, pointing out that after the Mars Science Laboratory launches in 2009, the agency will find itself running out of the plutonium needed to fuel radioisotope power systems. Even New Horizons, on the way to Pluto/Charon, is using Russian plutonium, the periodic purchase of which has been forced by NASA's dwindling supplies. New Horizons' principal investigator Alan Stern told the committee that beyond the Mars Science Laboratory, NASA probably has enough plutonium on hand or on order to fuel the outer planets flagship mission targeted at 2017 and an interim Discovery class mission scheduled to fly a few years earlier, the latter intended, ironically enough, to test more efficient radioisotope power systems now under development. Meanwhile, the outer...

Sometimes nature does what huge telescopes can't manage. Tomorrow night, a careful amateur astronomer may be able to provide information not only about the tiny asteroid 45 Eugenia but also about the two moons that orbit it. At play is an occultation, in which these moons and Eugenia itself helpfully occlude a star for observers in various parts of the southern US and Mexico. Sky & Telescope is reporting the relevant times to be 5:42 to 5:45 UTC on March 9. Image: Eugenia and its larger moon, Petit-Prince. With a density only 20 percent greater than water, this main belt asteroid is either a loose pile of rubble or an icy object with sparse rocky materials. Petit-Prince orbits it at a radius of 1,190 kilometers. Not shown here is the smaller moon, Petite-Princesse. The animation was assembled from infrared images of the objects. Credit: William Merline (SwRI), Laird Close (ESO), et al., CFHT. Moons have been discovered in their dozens around asteroids ever since 1994, when the...

Saturn's rings turn out to be more dynamic than expected, and it's clear that what Cassini has to tell us about them -- and about the rest of the Saturnian system -- is only beginning. Throw Enceladus into the picture and things get even more complicated, and interesting. Geysers on the moon have already been found to supply content to the so-called E-ring, while material flowing from it in the form of the gas of electrically charged particles called plasma is now known to influence Saturn's magnetosphere. The latest discovery is that this plasma is, in turn, being drawn into Saturn's A-ring, where it is being absorbed. Image: Enceladus seen across the un-illuminated side of Saturn's rings. A hint of the moon's active south polar region can be seen as a just slightly dark area at bottom. This view was obtained from about 1 degree above the ringplane. Enceladus is 505 kilometers (314 miles) across. Credit: NASA/JPL/Space Science Institute. Unlike Jupiter, then, Saturn seems to have...