With the Dawn spacecraft on its approach to Vesta, I've been scouting around for science fiction that involves this interesting asteroid. The one story that stands out is famous for its author more than its quality. It's "Marooned Off Vesta," which turns out to be Isaac Asimov's first published story. John Campbell rejected it at Astounding Science Fiction, so it was left to Amazing Stories' Ray Palmer to publish the Good Doctor's first, written at the age of 18. "Marooned Off Vesta" appeared in Amazing's issue of March 1939 and would have faded into obscurity if its author hadn't gone on to his spectacular career in fiction and non-fiction. The era when Asimov didn't make the cover of a magazine he was writing for didn't last for long. I don't particularly recommend you hunt this story down, although it appears (for sentimental reasons, I suppose) in 1973's The Best of Isaac Asimov. Here a trio of space travelers in trouble look out at the surface of Vesta from their crippled craft....

Our Voyager spacecraft are in a fascinating place indeed, where the stream of charged particles flowing out from the Sun -- the solar wind -- bumps up against what we might call the 'interstellar wind,' the tenuous material expelled from other stars in our neighborhood. We've looked at the solar wind's possibilities for propulsion many times, pondering whether it could push a 'magsail' at high velocity to the outer system, and whether such a push would be controllable (it looks to be a turbulent ride indeed). But new work reminds us that the Sun's magnetic field lines are likewise pushed outward by the solar wind. Merav Opher (Boston University) comments: "The sun's magnetic field extends all the way to the edge of the solar system. Because the sun spins, its magnetic field becomes twisted and wrinkled, a bit like a ballerina's skirt. Far, far away from the sun, where the Voyagers are, the folds of the skirt bunch up." We're learning from those same Voyagers as they move through the...

I'm sometimes asked why I write so seldom about Mars, a very interesting place indeed. The answer is that so many excellent sites are out there tracking events on the planet that I'm happy to keep my focus on the outer system and the starry gulf beyond. But now and then Mars news interrelates with broader stories about planet formation and what we might find in other solar systems. Such is the case with new work from Kevin Walsh (Southwest Research Institute) that looks at the migration of Jupiter during the formation of the Solar System. At issue is the question of why Mars is so small, because if you run simulations of the planet formation process for the four inner planets of our system, you get a Mars that's much heavier than the one we see. Tweaking the simulation parameters isn't enough -- it still doesn't produce the smaller Mars. But a major migration scenario involving Jupiter can help to explain the situation. The trick is that it relies upon an initial distribution of...

We looked recently at Titan Mare Explorer (TiME), a mission to land a probe on Titan's Ligeia Mare, a methane-ethane sea that would be observed for an extended period by this floating observatory. But I don't want to pass too quickly over Comet Hopper, one of the other missions being considered by NASA's Discovery Program. This one is a proposal out of the University of Maryland that would land on comet 46P/Wirtanen not once but multiple times, observing the changes on the comet and in its innermost coma as it interacts with the Sun. The innermost coma is the comet's atmosphere immediately above the nucleus, where cometary jets and outgassing originate. Jessica Sunshine, principal investigator for Comet Hopper, says the idea is to watch how surface and coma change through a solar approach: "We've had some amazing cometary flybys but they have given us only snapshots of one point in time of what a comet is like. Comets are exciting because they are dynamic, changing throughout their...

The Dawn mission is going to command our attention this summer, with orbital capture around Vesta in mid-July and science data collection beginning a scant two weeks later as the spacecraft produces topographical maps from an altitude of approximately 2700 kilometers. Orbiting the main belt asteroid for one year, Dawn will close to within 200 kilometers to obtain closer images and perform other scientific measurements. And then it's back into cruise mode for the trip to Ceres, another object of intense interest regarding Solar System formation. This ambitious mission is the first ever mounted to orbit two Solar System targets. The image below is Dawn's first look at Vesta, a mere five pixels across in these early approach images. This is the first image of the asteroid Dawn has taken, and images like it will be used to help scientists analyze Vesta's precise location against background stars, helping to tune up the spacecraft's trajectory on the approach. The image was taken when...

Back in the days when the Solar System seemed a simpler place, asteroids were thought to be chunks of rocks whose features could be explained by impacts with other such objects. Comets were altogether different, laden with icy material that erupted when heated by the Sun. It was a straightforward picture, at a time when the system had nine planets, icy 'dwarf planets' were not yet in vogue, and distinctions between orbiting objects were clearly drawn. Today we work with a more complicated scenario, one in which some objects once thought of as asteroids develop comet-like features that can last for months. Thus the interest in the asteroid called (596) Scheila, which late last year developed plumes after brightening unexpectedly in December. Orbiting the Sun every five years, Scheila has a diameter of about 110 kilometers, and evidence from both the Hubble Space Telescope and the Swift satellite now indicates that the unusual activity here was caused by a collision with a smaller...

Last week we looked at the possibility of using a planet's aurora as an exoplanet detection tool, speculating that the LOFAR radio telescope in Europe might be able to detect such an emission, and I reminisced about listening for emissions from Jupiter on an old shortwave receiver. Jonathan Nichols' work at the University of Leicester makes the case for exoplanet detections, and recent news from analysis of Cassini data indicates that planetary aurorae can do more than just flag the presence of a planet. In some cases, they can provide information about that planet's moons, as in the case of Saturn, where careful analysis may offer us new insights into Enceladus. For it turns out that the electrical connection between Saturn and Enceladus is rather robust. Moreover, it was a connection that scientists had anticipated, given that in the Jovian system, Io creates a glowing auroral footprint near Jupiter's north and south poles. Why not expect something similar in the case of Enceladus,...

The study of carbon monoxide found in the atmosphere of Pluto -- a strong signal rendered in data from the James Clerk Maxwell Telescope in Hawaii -- gives us insight into the significant changes happening to the dwarf planet on its 248-year orbital path around the Sun. Pluto is one of a kind, offering us a cold planetary atmosphere that shows marked changes over time, an atmosphere that may at times freeze out and settle to the surface. No other dwarf planet is known to have an atmosphere, and Pluto's is now known to vary in pressure and probably in composition. Jane Greaves (University of St. Andrews) led the team doing the new Pluto work, and she's the first to admit that what the data revealed was a surprise. Pluto reached perihelion in 1989, its closest approach to the Sun, so astronomers assumed that as it began to recede, the atmosphere would contract. But as measured by the occultation of background stars, the atmospheric pressure and size actually increased between 1988 and...

These days funding for missions to some of the most interesting places in the Solar System is much in question. But sooner or later we're going into the outer system to investigate the possibilities for life on worlds like Europa, Enceladus or Titan. The case for Europa seems particularly compelling, but we have to be careful about our assumptions. When the Europa Orbiter Science Definition Team developed a strategy for Europan exploration in 1999, it was generally believed that any Europan ocean would be covered by a thick and impermeable layer of ice. Life, then, might exist around deep sub-oceanic volcanic vents if it existed at all. Thus the strategy for Europan exploration that evolved: Three missions, beginning with an orbiter, followed up by a lander and, finally, a third mission that would drill down through the presumably many kilometers of surface ice to explore whatever lay beneath. Even in more financially optimistic times, that strategy didn't get us into Europa's ocean...

Back in December, scientists from the Cassini team presented evidence for ice volcanoes on Titan, looking at a region called Sotra Facula, which bears some resemblance to volcanoes on Earth like Mt. Etna in Italy and Laki in Iceland. An ice volcano, also known as a cryovolcano, would draw on geological activity beneath the surface that warms and melts parts of the interior and sends icy materials through a surface opening. Sotra Facula's two 1000-meter peaks combine what appear to be deep volcanic craters with finger-like flows of material, a kind of surface sculpting that could explain some of the processes occurring on other ice-rich moons. But work like this is part of an ongoing dialogue testing various hypotheses, and the latest round takes us in a sharply different direction. In a new paper in Icarus, Jeff Moore (NASA Ames) and Robert Pappalardo (JPL) argue that Titan is in fact much less geologically active than some have thought. A cool and dormant interior would be incapable...

Send a spacecraft into the outer Solar System and unexpected things can happen. We're all anticipating the arrival of the New Horizons probe at Pluto/Charon in 2015, but the work the spacecraft has done along the way has recently been highlighted again. Moving toward Jupiter in 2007, New Horizons was programmed to image Jupiter's ring system in the hope of catching details about an odd effect. Back in the 1990s, the Galileo probe had shown unusual patterns in the Jovian ring, and the New Horizons imagery was able to spot not only the patterns Galileo had seen but two new ripple patterns as well, evidence of recent events in the Jovian system. Image: The New Horizons spacecraft took the best images of Jupiter's charcoal-black rings as it approached and then looked back at Jupiter in February 2007. The top image was taken on approach, showing three well-defined lanes of gravel- to boulder-sized material composing the bulk of the rings, as well as lesser amounts of material between the...

Studying the heliosphere and its interactions with the interstellar medium isn't easy, which is one among many reasons we follow the fortunes of the Voyager probes with such continuing fascination. They're pushing up against the boundary between the Sun's local 'bubble' and deep space beyond, where charged particles from the solar wind are no longer a factor and the deeper rhythms of the galaxy take hold. Now our other probe of this exotic region is back in the news in a new paper. IBEX (the Interstellar Boundary Explorer) is telling us much about how our system interacts with the interstellar medium and the effects of the galactic magnetic field upon the heliosphere. IBEX has provoked much discussion in these pages -- I was amazed to see I had written fully thirteen articles on the mission in the last six years, going back to pre-launch speculations. The mission caught my eye because it was the first ever sent with the express purpose of studying the outer edges of the Solar System....

As the Dawn spacecraft continues on its way to Vesta, which it will reach in July, mission controllers have been putting it through its paces with a series of maneuvers that test the vehicle's capabilities, a rehearsal for the high- and low-altitude mapping orbits it will operate in. It's interesting to consider Dawn's ion thrusters, which after more than 2.2 years of powered flight, continue to work flawlessly, now with a bit less than half of the original supply of xenon propellant (the spacecraft started with 425 kilograms of xenon). The velocity change in this period has been 5.7 kilometers per second, marking a record for on-board propulsion systems. Dawn's approach to Vesta is slow and spiraling, closing in on the asteroid at 0.7 kilometers per second as the orbital paths of target and spacecraft become more and more similar. In this mission report, chief engineer Marc Rayman (JPL) describes the trajectory, which is made possible by the high fuel efficiency of the ion...

Rains have come to the equatorial regions of Titan, a vivid marker of the changing seasons on the distant Saturnian moon. A large storm system appeared in the equatorial regions in late September of last year as spring came to the low latitudes, and extensive clouds followed in October. When they dissipated, the Cassini orbiter was able to capture surface changes in a 500,000 square kilometer region along the southern boundary of the Belet dune field, along with smaller areas nearby, all of which had become darker. The likely cause: Methane rain. Tony Del Genio (Goddard Institute for Space Sciences) is a member of the Cassini imaging team: "These outbreaks may be the Titan equivalent of what creates Earth's tropical rainforest climates," says Del Genio, "even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of Earth's behavior over the tropical oceans than over tropical land areas." That's an interesting take on these...

What do we make of the ‘tiger stripes’? The intriguing terrain in the south polar region of Saturn’s moon Enceladus is geologically active and one of the most fascinating finds of the Cassini mission. The ‘stripes’ are actually four trenches, more or less in parallel, that stretch 130 kilometers, each about 2 kilometers wide. What Cassini showed us was that geysers of ice particles and water vapor are being ejected into space from the interior of the moon, setting off astrobiological speculations that elevated Enceladus to a new and deeply intriguing status. Is there liquid water under the surface? You could make that case based on recent work showing that some ice particles ejected from the moon are rich in salt, a sign that they may be frozen droplets from a saltwater ocean in contact with Enceladus’ mineral-rich core. Interesting place indeed -- we’ve got a serious possibility of liquid water and an energy source in the form of tidal effects from Enceladus’ orbit as it changes in...

Of all the interesting targets the WISE (Wide-Field Infrared Explorer) mission might find, I've focused primarily on two in Centauri Dreams: A small star, doubtless a brown dwarf, that might be found closer to us than the Alpha Centauri trio, and a large planet out in the Oort Cloud that might be disturbing cometary orbits. That latter scenario turned up again last March in Finding the Real Planet X, when we looked at various theories about large objects in the outer system, including the thinking of John Matese and Daniel Whitmire (University of Louisiana at Lafayette). Parameters of a Perturber Matese has studied the possibility of small stars near our Sun for two decades, but his view now, as revealed in a paper just published in Icarus, is that an object three to five times larger than Jupiter may be the perturber we're looking for. Matese and Whitmire's paper on the matter has been available as a preprint since April, but its publication in Icarus has caught the eye of the...

Our view of the Solar System has changed utterly in the last fifty years. Mention that at a cocktail party and your listener will assume you're talking about Pluto, the demotion of which has stirred more response than any other recent planetary news. But in addition to all we've learned through our spacecraft, our view of the Solar System has gone from a small number of orbiting planets to huge numbers of objects at vast distances. Fifty years ago, a Kuiper Belt many times more massive than the main asteroid belt was only theory. And the early Solar System models I grew up with never included any representation of a vast cloud of comets all the way out to 50,000 AU. We've also begun to learn that liquid water, once thought confined to the Earth, may be plentiful throughout the system. Caleb Scharf goes to work on this in a recent post in Life Unbounded, noting what our models are telling us about internal oceans on a variety of objects: Much can be done with purely theoretical models...

Adaptive optics changes everything for ground-based telescopes, removing the worst of the distortion caused by a changeable atmosphere and allowing astronomers to see objects with a clarity akin to a space-based platform. But the recent adaptive optics work at the Keck II telescope in Hawaii really put the technology to the test. Normally, astronomers use a laser to create an artificial 'star' that computers can monitor, using information about atmospheric conditions and distortions to adjust the telescope up to 2000 times per second. But if Jupiter is your target, you've got a problem. The giant planet is bright enough to obscure the laser 'star,' meaning you need a guide star that is brighter still and close to Jupiter to do the work. Europa turned out to be the target of choice, positioned perfectly on November 30, 2010 to allow the adaptive optics system to work and to allow the capture of the image below. What you're seeing is Jupiter in infrared light at a wavelength of nearly...

Back in December, NASA published its report on the Europa Jupiter System Mission (EJSM), noting how mission goals that were separately developed by NASA itself and the European Space Agency have now melded into a unified strategy. We're looking at orbiters around two of Jupiter's moons, a NASA vehicle around Europa and an ESA orbiter around the other Jovian 'water world,' Ganymede. The December report explained the derivation of each mission: The Europa Jupiter System Mission (EJSM) would be an international mission with an architecture of two independently launched and operated flight elements. Its theme and goals are derived from the US National Research Council's Planetary Science Decadal Survey [SSB 2003] and the ESA Cosmic Vision document [ESA 2005]. These reports emphasize as key questions for solar system exploration: 1) the origin and evolution of habitable worlds, and 2) processes operating within the solar system. Image: The NASA Jupiter Europa Orbiter would address the...