With launch of the Dawn mission to Ceres and Vesta coming up on July 7, NASA has announced a news conference for next Tuesday, the 26th, to discuss details of the four year journey to the asteroids. Held at NASA headquarters, the event is due to be streamed on the agency's homepage. The Hubble Space Telescope, meanwhile, has provided these images, shown below as a montage, of the two target asteroids. The debris of the asteroid belt, which may house 100,000 or more asteroids as large as ten kilometers across, provides an idea of the kind of materials available for planet-building some 4.6 billion years ago. For those who follow robotic missions with fascination for the rapid strides in technology they represent, consider that Dawn is the first mission sent to orbit two different targets. Vesta will be the first, in 2011, with Ceres following in 2015. The Vesta image (on the right) shows the asteroid's southern hemisphere, which is dominated by an impact crater so large that the...

Centauri Dreams doubts that most space scientists expected to find as much activity around Saturn as the Cassini probe has revealed. Enceladus was spectacular enough, with its geysers spewing material hundreds of kilometers above the surface. And now we find indications that two other moons -- Tethys and Dione -- are active worlds as well. More Cassini close passes will be needed to firm this up. For that matter, data already collected from previous flybys may contain still more clues, which is how things work in planetary science these days -- we collect information at a rate far surpassing our ability to keep up with the inflow. In any event, Cassini's arrival in Saturn space in 2004 made it clear that centrifugal forces caused by the planet's fast rotation (10 hours and 46 minutes) compressed plasma into a disc from which cold, dense plasma from the planet's inner magnetosphere was being flung into space. Hotter plasma from the outer magnetosphere quickly moves in to fill up the...

An underground ocean on Titan? The apparent detection of low frequency radio waves makes liquid water beneath the surface of the huge Saturnian moon a possibility, according to research led by Fernando Simoes (Centre d'Etudes Terrestres et Planetaires, Saint Maur, France). Simoes and team have been studying what New Scientist is describing as an 'enigmatic radio signal' that the European Space Agency's Huygens probe detected as it descended to Titan's surface in 2005. The signal seems not dissimilar to what lightning produces on Earth, where low frequency signals bounce between the ground and the upper atmosphere, in the process attenuating some frequencies while enhancing others. But Titan's surface seems to be a poor reflector, meaning there may be a better one below. Thus the talk of an ocean, although it's just one candidate. "We do not need a subsurface ocean but require a subsurface reflector," Simoes told New Scientist. "If a subsurface ocean exists, the solid-liquid interface...

New Horizons' recent encounter with Jupiter seems to have gone off flawlessly, returning stunning imagery in the bargain. For the Pluto-bound spacecraft, the giant planet turned out to be more than a simple gravitational slingshot. Jupiter was also a shakedown for the even more intriguing planetary encounter to come in 2015, letting both spacecraft systems and operators here on Earth work through a real-time event. This image of the moon Io, showing a volcanic eruption in progress on that tortured world, was only one of many scenes the spacecraft captured (including excellent views of Jupiter's rings). If you look at the Io picture carefully, you can see another plume, from the volcano Masubi at about the 7 o'clock position. On the nightside, the volcano Loki is visible as illuminated by Jupiter. The images that went into this animation were taken over an eight-minute span on March 1. Image: This five-frame sequence of New Horizons images captures the giant plume from Io's Tvashtar...

An object in an elliptical, egg-shaped orbit experiences interesting gravitational stresses. Enough so that the changing forces it endures may be the cause of the plumes of water vapor that Cassini found on Saturn's moon Enceladus in 2005. In essence, the tiny moon is being alternately squeezed and stretched as it makes its way around the planet. These tidal forces cause existing fault lines to rub against each other, producing enough heat to turn ice into water vapor and ice crystals. That's the conclusion of new work by Francis Nimmo (University of California -- Santa Cruz) and team, who note the warmer surface of Enceladus' southern pole and the presence of the famous 'tiger stripes,' which appear to be tectonic fault lines. "We think the Tiger Stripes are the source of the plumes," says Nimmo, "and we made predictions of where the Tiger Stripes should be hottest that can be tested by future measurements." Image: This is a mosaic of Enceladus compiled from 21 images taken by the...

Tholins are interesting molecules, large and complex. They're organic aerosols -- particles small enough to remain suspended in the atmosphere for some time -- formed from methane and nitrogen. Their presence on Titan is intriguing because they're thought to contain some of the chemical precursors of life. That makes studying how they form there a preoccupation with those wanting insight into how life appears. Titan is a wonderful laboratory for such studies. We already knew that nitrogen and methane dominated its atmosphere. New measurements from Cassini now show that tholins form much higher in that atmosphere than was previously believed. The most recent Cassini flybys, though, have also demonstrated the presence of benzene, a key component in the formation of aromatic hydrocarbon compounds. Moreover, Cassini's Ion Beam Spectrometer (IBS) and Electron Spectrometer (ELS) have picked up the presence of large positive and negative ions. Here's Andrew Coates (University College,...

Shrouded in the night of a 15-year winter, Saturn's north pole demands specialized instruments to yield its secrets. Enter Cassini's visual and infrared mapping spectrometer, whose data on the region have disappointed no one. A six-sided honeycomb-shaped feature has emerged that was first found by the Voyager 1 and 2 spacecraft over twenty years ago. Now Cassini has, for the first time, captured the entire hexagon in a single image. What exactly is it? Think of Earth's polar regions, where winds move in a circular pattern around the pole, but ponder this difference: Saturn's vortex is a hexagon nearly 25,000 kilometers across. Four Earths would fit inside it. Click here for a QuickTime movie of the odd feature. This makes Saturn possibly the Solar System's most intriguing object when it comes to polar anomalies. The south pole sports an enormous hurricane, while the north is dominated by clouds moving along the hexagon at great rate. Indications are that the hexagon extends fully 100...

What is it about Enceladus? I doubt anyone would have thought the tiny moon would weigh so heavily in our thinking about Saturn before Cassini, but now comes the news that Enceladus is distorting the planet's magnetic field to the point that it becomes tricky to measure the length of the Saturnian day. Count the electrically charged particles originating in the moon's geysers as the culprit -- they're actually causing Saturn's magnetic field lines to slip relative to the planet's rotation. The process seems to work like this: Gas particles are ejected from the geysers on Enceladus and become electrically charged. Captured by Saturn's magnetic field, they form a disk of plasma that wraps around the planet's equator. The rotation of the plasma disk slows down enough due to interactions with the magnetic field that the rotation period Cassini has been measuring -- based on radio emissions -- is not actually the length of Saturn's day. Instead, it's the rate of rotation of the plasma...

I remember talking to the exuberant astrophysics professor Sheridan Simon about a football-shaped planet he had created one Super Bowl eve. This was at a science fiction convention and it must have been fifteen years ago. Simon frequented such venues because he had built a cottage industry around creating planets for various science fictional settings. As a lark, he had run the numbers on what would happen to the atmosphere of a world shaped like a pigskin and wound up announcing the result: "It's plaid! That's what you would see. A plaid football!" I think he was pulling my leg, and that wouldn't have been out of character either for this generous, gregarious man who died all too young. But Mike Brown's new paper in Nature brought back memories of that conversation with Sheridan Simon in spades. Brown (California Institute of Technology), who specializes in the exotica at the fringes of our Solar System, has been examining an object his team originally found. 2003 EL61 is also...

If the dark features Cassini has found near Titan's north pole really are filled with liquid, they're seas more than lakes, one of them larger than any of the Great Lakes in North America. The image below says it all, comparing the largest of these features with Lake Superior. This work is being done through radar imaging, detecting dark radar surfaces that imply smoothness. Cassini's visual and infrared mapping spectrometer is also at work as the liquid hypothesis at Titan's surface is explored. Image: This feature on Titan is at least 100,000 square kilometers (39,000 square miles), which is greater in extent than Lake Superior (82,000 square kilometers or 32,000 square miles), which is one of Earth's largest lakes. The feature covers a greater fraction of Titan than the largest terrestrial inland sea, the Black Sea. The Black Sea covers 0.085 percent of the surface of the Earth; this newly observed body on Titan covers at least 0.12 percent of the surface of Titan. Because of its...

Every time we get new information about Enceladus, I keep thinking about how the original Orion team would have felt if they really had made the trip to Saturn they once discussed for their fabled atomic rocket. Enceladus, thought Freeman Dyson, looked to be a logical place to refuel because it was believed to be rich in ice and hydrocarbons. But no one in those pre-Cassini days could have imagined what Dennis Matson (Jet Propulsion Laboratory) is now talking about: "Deep inside Enceladus, our model indicates we've got an organic brew, a heat source and liquid water, all key ingredients for life. And while no one is claiming that we have found life by any means, we probably have evidence for a place that might be hospitable to life." All of which falls into the 'never in my wildest dreams' category, for Enceladus has hardly led the list when one discusses life's possible venues in the Solar System. But Cassini found geysers ejecting water vapor and ice from the moon's south polar...

New Horizons' close approach to Jupiter on the 28th of February set up some intriguing observational possibilities. The Pluto-bound spacecraft now moves beyond the giant planet in a trajectory that takes it down Jupiter's 'magnetic tail,' where sulfur and oxygen particles from its magnetosphere eventually dissipate. Since no spacecraft has ever been in this region before, coordinating what New Horizons sees with other instruments -- both space-based and terrestrial -- can tell us much about the Jovian environment. The image below is a composite of data from the Chandra X-ray Observatory superimposed upon the latest Hubble image. Notice the x-ray activity near the poles, where Chandra is detecting aurorae. The operative mechanism seems to be interaction between the solar wind and the sulfur and oxygen ions in Jupiter's magnetic field, creating aurorae a thousand times more energetic than what we see on Earth. Image: In preparation for New Horizon's approach of Jupiter, Chandra took...

Most speculation about finding life on Europa revolves around drilling through the perhaps kilometers-deep ice to sample the ocean beneath. But paleobiologist Jere H. Lipps (University of California, Berkeley) envisions a different exercise. Lipps, who has studied polar environments for twelve years in Antarctica, notes that turnover of ice on that continent often brings organisms to the surface that would otherwise be hidden. Is ice shifting similarly on Europa? Absolutely. Looking at images of that fractured surface, we see a dynamic environment where water from beneath seems to have welled up and re-frozen. The surface is strewn with domes, ridges and tilted ice rafts. Evidence of life might be found in places where blocks of ice have pushed up to form ridges and rills. Lipps puts it this way: "This is a paleontological search strategy, which is what I do. If I want to collect fossils in Nevada, I get a map and look for likely spots, like rock outcroppings, where fossils will be...

Perhaps ten to twenty kilometers under Europa's global shell of ice there looks to be an ocean. That ice sheet is pretty thick for even our best drilling rigs but, says William B. McKinnon (Washington University, St. Louis), the deformities make a good case for its being relatively thin in comparison to the world it encircles. The smooth and largely uncratered surface implies that the ice has been active in recent geological time. McKinnon made the case for a Europa mission at the American Geophysical Union meeting last December and continues to advocate close study of the Jovian moon, which seems to offer one of the most intriguing habitats for life's development in our Solar System. The Galileo mission, due to its serious antenna problems, couldn't get enough images to see active geysering, as we've found on Saturn's moon Enceladus, but we do see what McKinnon calls "...lots of interesting ice tectonics, and surface eruptions with weird colors and spectral signatures whose...

Centauri Dreams' view is that the more we can learn about asteroids, the better. And the interest isn't purely scientific. One day we may have to set about nudging an approaching asteroid so as to prevent a collision with Earth, and if that day comes, we'll need to have a plan in place that depends upon a thorough understanding of these objects and their composition. In the long run, asteroid studies are anything but optional. The European Space Agency's Rosetta mission is filling in some of the gaps enroute to comet 67P Churyumov-Gerasimenko. In its sights are two asteroids -- 2867-Steins and 21-Lutetia -- orbiting between Mars and Jupiter. We'll learn a lot more about both between now and July of 2010, by which time Rosetta will have viewed each at close range. Meanwhile, the spacecraft has taken a first look at 21-Lutetia using the onboard OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) instruments. At the time of its observations, the vehicle was roughly 245...

Somehow I missed Mike Brown's recent thoughts on 2003 EL61, the oddly elongated Kuiper Belt object that's as big as Pluto along its longest dimension. Fortunately, the BBC recently covered the story. At the American Astronomical Society meeting in Seattle, Brown (Caltech) had discussed the instability of the object's orbit, pointing out that it is headed for an eventual encounter with Neptune. A possible outcome: Two million years from now, 2003 EL61 may be a comet. "When it becomes a comet," says Brown, "It will be the brightest we will ever see."

When I interviewed the Jet Propulsion Laboratory's James Lesh several years ago, he explained how space scientists could use radio signals to do science. It's the ultimate technique for taking advantage of what's at hand. If your spacecraft is moving behind a planet it's investigating as seen from Earth, the changes to its signal as it disappears behind the disk tell you much about the composition of the planetary atmosphere. "One person's noise," said Lesh, "is another person's signal." Of course, that kind of work isn't limited to radio. Twice on November 14, 2003 Titan passed in front of a star, the events separated by just seven and a half hours. As you would expect, the occultation tracks were different, one visible from the Indian Ocean and southern Africa, the other from the Americas and western Europe. The effects of Titan's atmosphere on the starlight have, in each case, supplied information about the movement of gases around the frigid world. This work required observations...