Free-floating planets -- planets moving through interstellar space without stars -- may not be unusual. If solar systems in their epoch of formation go through chaotic periods when the orbits of their giant planets are affected by dynamical instability, then ejecting a gas giant from the system entirely is a plausible outcome. David Nesvorny (SwRI) has been studying the possibilities for such ejections in our Solar System, using computer simulations of the era when the system was no more than 600 million years old. Clues from the Kuiper Belt and the lunar cratering record had already suggested a scattering of giant planets and smaller bodies then. An ejected planet makes sense. Studies of giant planets interacting with the protoplanetary disk show that they tend to migrate and wind up in a configuration where pairs of neighboring planets are locked in a mean motion resonance. Such a resonance occurs when two planets exert a regular, periodic gravitational influence on each other...

We've often considered the effect of interstellar dust on a spacecraft moving at a substantial percentage of the speed of light. The matter becomes even more acute when we consider an interstellar probe arriving at the destination solar system. A flyby mission moving at ten percent of the speed of light is going to encounter a far more dangerous environment just as it sets about its critical observations, which is why various shielding concepts have been in play to protect the vehicle. But even at today's velocities, spacecraft can have unexpected surprises when they arrive at their target. We're now looking toward a 2015 encounter at Pluto/Charon. New Horizons is potentially at risk because of the fact that debris in the Pluto system may not be found in a plane but could take the form of a thick torus or even a spherical cloud around the system. We don't yet know how much of a factor impactors from the Kuiper Belt may be, but strikes at 1-2 kilometers per second would kick up...

?Sometimes our spacecraft take us past an asteroid, and other times the asteroid comes to us. Asteroid 2005 YU55 pays Earth a visit soon, closing to a bit less than the distance of the Moon on November 8. The Deep Space Network dish at Goldstone (CA) and the Arecibo facility in Puerto Rico will track the object, with images from Goldstone expected to achieve resolutions as fine as 2 meters per pixel, which should give us a wealth of information about the asteroid’s surface features. About the size of an aircraft carrier, 2005 YU55 was also observed by Arecibo in 2010, when it was found to be roughly spherical in shape with a rotation period of 18 hours. You’ll also recall asteroid 21 Lutetia, which we covered here when the European Space Agency’s Rosetta probe flew past it in July of 2010. The imagery from that encounter showed a cracked and battered surface, but new analysis now indicates that the asteroid may once have had a hot metallic core. Lutetia may, in other words, be a...

Back when I was writing my Centauri Dreams book in 2004, I remember talking to JPL's James Lesh about various aspects of communicating with distant spacecraft. Lesh had written an interesting paper on how we might communicate with an Alpha Centauri probe, and we went on to discuss laser communications in the context of today's Deep Space Network. What stuck in my mind about that conversation was how much we can learn when one thing moves in front of another. Lesh pointed out how useful it is to examine a radio signal when a spacecraft moves behind a planet, studying the attenuation of the signal and learning more about the planet itself. When a celestial object moves in front of a distant star, we also get useful results, as has recently happened in our studies of the dwarf planet Eris. You'll recall that it was Eris that kicked off a new round of controversy about Pluto, for the early estimates were that the diameter of Eris (then thought to be 3000 kilometers) was actually 25...

So much has been happening in recent weeks that I haven't had the chance to keep up with all the stories in the queue, and that's not a bad thing considering that a high level of activity usually means we're learning new and interesting things. Consider the Dawn mission, which has been orbiting the asteroid Vesta since the middle of July. The Dawn team has been sharing results about Vesta in multiple locations, including the European Planetary Science Congress and the Division of Planetary Sciences Joint Meeting 2011 in Nantes and the annual meeting of the Geological Society of America in Minneapolis. As expected, Vesta turns out to be an intriguing place. The image below is a look at Vesta's topography in the southern polar region, with the overall curvature of the tiny world removed, so you're seeing what it would look like on a flat surface. You wouldn't have this view on Vesta because many of the features would wrap around below the horizon, but the image gets across the scale of...

Once again it's time to catch up with Enceladus, the little moon that has such a huge impact on the planetary system it moves through. We're learning, for example, how much water vapor is erupting from the features in the moon's south polar region known as the 'tiger stripes.' Cassini measurements (using the Ultraviolet Imaging Spectrograph aboard the spacecraft) had pegged the rate of discharge at 200 kilograms of water vapor every second. New measurements from ESA's Herschel space observatory match up closely to these findings. Saturn's E-ring, formed from plume particles, would dissipate in a few hundred years without discharges like these. You may recall that back in June, Herschel results were announced that showed a huge torus of water vapor circling Saturn itself, one that appeared to be the source of water found in Saturn's upper atmosphere. More than 600,000 kilometers across and 60,000 kilometers thick, the enormous cloud was produced by Enceladus and picked up by...

Among all the planets, Uranus seems to get the least play in science fiction, though it does have one early advocate whose work I've always been curious about. Although he wrote under a pseudonym, the author calling himself 'Mr. Vivenair' published a book about a journey to Uranus back in the late 18th Century. A Journey Lately Performed Through the Air in an Aerostatic Globe, Commonly Called an Air Balloon, From This Terraquaeous Globe to the Newly Discovered Planet, Georgium Sidus (1784) seems to be reminiscent of some of Verne's work, even if it pre-dates it, in using a then cutting-edge technology (balloons) to envision a manned trip through space. Image: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which it is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory. When 'Vivenair' wrote, Uranus had just been discovered (by William Herschel in 1781). The author used it as the occasion for political...

We can thank the British astronomer John Herschel (1792-1871) for giving the moons of Saturn their classical theme, resulting in the familiar names Mimas, Dione, Enceladus, Tethys, Titan, Rhea, and Iapetus for the seven moons known to him when he wrote his Results of Astronomical Observations Made at the Royal Observatory, Cape of Good Hope (1847). It was a natural, then, that the moon discovered shortly thereafter would get a name like Hyperion (although it wasn't Herschel but merchant and astronomer Willam Lassell who suggested the name). Hyperion was an elder brother of Cronos (Saturn), and was associated with watchfulness and observation. Only recently have we discovered just how unusual Hyperion turns out to be, as the unprocessed image from the Cassini mission below clearly demonstrates. Its shape is irregular, indicating it may be the remnant of a larger body broken by some ancient impact. Its low density indicates large amounts of water ice mixing with small amounts of rock....

2007 OR10 is an innocuous enough designation (discoverer Mike Brown calls it 'an official license plate number' based on date of discovery), but 'Snow White' isn't. The dwarf planet that acquired the latter monniker from Caltech astronomer and KBO-hunter Brown seemed to deserve its name because at the time, Brown thought it was an icy chunk that had broken off from the dwarf planet Haumea. Ice in the outer system is almost always white, and that's what you would expect on a world called 'Snow White.' But recent spectral analysis has revealed that while 'Snow White' is indeed covered in water ice, it's not white at all. In fact, it is one of the reddest objects in the Solar System, about half the size of Pluto in its orbit at system's edge. What to make of this? It turns out that another dwarf planet fits the same characteristics, in being both red and covered with water ice. Although a bit smaller than Snow White, Quaoar is thought to have had an atmosphere and to have once been...

New Horizons continues on its inexorable way to Pluto/Charon, now some 21 AU out, which places it between the orbits of Uranus and Neptune. The latest report from principal investigator Alan Stern tells us that the 2011 checkout of the spacecraft was completed on July 1, a two-month process that included a test of the REX radio occultation experiment, coordinating with the Deep Space Network as the Moon interrupted a radio signal from Earth. According to Stern, spacecraft tracking over May and June shows New Horizons on a 'perfect course' toward the distant world, one that will demand no course correction until, at the earliest, 2013. I wanted to bring Stern's report into play here because of the image below, which shows Pluto's newly discovered moon P4 along with the other moons now known in the system. The fact that I hadn't yet run it told me that it was time to do some catching up with this impressive mission. Image: These two images, taken about a week apart by NASA's Hubble...

The launch of the Juno spacecraft last Friday gets us back in business around the Solar System's largest planet, but also has useful exoplanet implications. To understand why, consider just one of the instruments carried aboard the spacecraft. The Jupiter Energetic-particle Detector Instrument (JEDI) is designed to measure how energetic particles flow through Jupiter's magnetosphere and interact with its atmosphere. Developed at Johns Hopkins Applied Physics Laboratory, JEDI will be looking at the interactions that produce the most powerful auroral phenomena in our system, and what we will learn has broad applications. After all, new tools like the Low Frequency Array (LOFAR) are coming online, bringing hitherto unavailable sensitivity to radio frequencies below 250 MHz. Not so long ago, Jonathan Nichols (University of Leicester) proposed using LOFAR to look for aurorae similar to those on Jupiter in exoplanetary systems. In fact, his research shows that gas giants in orbits up to 50...

Considering the nature of the Dawn spacecraft's slow, spiraling entry into orbit around Vesta, it's a little unclear precisely when orbital insertion was, but NASA is pegging an approximate time of 0447 UTC on July 16. The event is leading to closer and better imagery all the time, the example below being the first full-frame image, taken from the spacecraft's framing camera on July 24. Here we're looking at the asteroid from a distance of 5200 kilometers, seeing for the first time the kind of surface detail that has long been hidden from even the most powerful telescopes. Image: NASA's Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA. Dawn's principal investigator Chris Russell (UCLA) likes what he sees: "We have been calling Vesta the smallest terrestrial planet. The latest imagery provides much justification for our expectations. They show that a variety of processes were once at...

When the German astronomer Johann Gottfried Galle discovered Neptune on September 23, 1846, he found a world so distant from the Sun that its orbit takes 165 years to complete. With Neptune reaching its first complete revolution since discovery, an event that occurred yesterday, we can enjoy some celebratory Hubble imagery of the planet. I especially like the shot below, which not only shows atmospheric features but also has been tweaked to reveal some of Neptune's moons. The planet has about thirty moons, most of them too faint to appear in these images. Image: This illustration was composed from numerous separate Hubble Wide Field Camera 3 images. A color image composed of exposures made through three color filters shows the disk of Neptune, revealing clouds in its atmosphere. Forty-eight individual images from a single filter were brightened to reveal the very faint moons and composited with the color image. The white dots are Neptune's inner moons moving along their orbits during...

I had been intending to cover recent news about Saturn in an upcoming post anyway, but the images below sealed the deal. They're further wonders from Cassini, pictures of a massive storm in Saturn's northern hemisphere that encircles the planet. First detected on December 5, 2010, the storm has been on the rampage ever since at about 35 degrees north latitude. It covers approximately 4 billion square kilometers. Cassini's radio and plasma wave science instrument has been showing a lightning flash rate 10 times that of any other storms the spacecraft has monitored since its arrival in Saturn orbit back in 2004. The flashes were so frequent at one point that Cassini could no longer resolve individual strokes, although the intensity has now eased. Image: The huge storm churning through the atmosphere in Saturn's northern hemisphere, seen here in a true-color view from NASA's Cassini spacecraft. This view looks toward the sunlit side of the rings from just above the ring plane. The...

If you're trying to figure out how fast a gas giant rotates, you have your work cut out for you. Jupiter seems to present the easiest case because of the famed Red Spot, first observed by the Italian astronomer Giovanni Cassini. But gas giants are thought to have a relatively small solid core, one that is completely obscured by their atmospheres. Rotation involves atmospheric effects as the gases slosh and swirl. No wonder astronomers were glad to find Jupiter's pulsating radio beams, discovered in the 1950s. Rotation of the planet's inner core results in a magnetic field that produces these signals, offering our best estimate on the planet's actual rate of rotation. We now know that the largest of the planets is also the fastest rotating, completing one rotation every 9.9 hours. But even this turns out to be an average because the gaseous nature of the planet causes it to experience differential rotation. Head for the poles and you find a slightly slower rotation period than you do...

It's always good to dream big, but sometimes dreams take you in unexpected directions. Growing up with science fiction, I reveled in tales of manned exploration of the Solar System and nearby stars, many of which I assumed would eventually become reality. But I never dreamed about personal computers. You can go through the corpus of science fiction in the first two-thirds of the 20th Century and find many a computer, but there are few tales involving personal computers on the desktop. An exception is Murray Leinster's short story 'A Logic Named Joe,' which ran in the March 1946 issue of Astounding Science Fiction. Leinster invokes something like today's massively networked computers in a story that anticipates the Internet. How did science fiction fail to see something as huge as the PC revolution coming down the tracks? Maybe it's because the future still surprises even those whose business it is to imagine it. I'm musing about all this because of my own desktop PC and the views...

The return of the Genesis mission in 2004 was a spectacular event, its parachute failing to deploy upon re-entry, leading to a crash in the Utah desert that seemed to have destroyed the mission's solar wind collectors. But Genesis was a tough bird and we're getting good science from its remains. The latest news comes from study of an instrument designed to enhance the flow of solar wind onto a small target, with the aim of measuring oxygen and nitrogen. The Solar Wind Concentrator worked well and new papers out of Los Alamos National Laboratory have now appeared, with isotopic measurements of the Sun that illuminate our system's formation. It's astonishing that we have these results -- Genesis flight payload lead Roger Wiens (LANL) calls Genesis "...the biggest comeback mission since Apollo 13" -- but ponder what we've got here. The spacecraft spent two years at the Sun-Earth L1 Lagrange point, some 1.5 million kilometers from Earth, collecting atoms of the solar wind, the stream of...

The latest work involving Cassini's Cosmic Dust Analyzer (CDA) gives us fresh information about Saturn's intriguing moon Enceladus and the likelihood of an internal ocean there. You'll recall that plumes of water vapor and grains of ice have been found spewing from the 'tiger stripe' fractures at the moon's southern pole, feeding material to Saturn's E ring. Three times during the spacecraft's passes through the plumes of Enceladus in 2008 and 2009, the CDA measured the composition of plume grains. Some of these icy particles struck the detector moving at speeds of up to 17 kilometers per second, vaporizing them on impact. The particle constituents could then be separated for close study. What we find is that the ice grains most distant from Enceladus are poor in ice and match the composition of Saturn's E ring. But move closer to the moon and large, salt-rich grains begin to appear. If the plumes came only from surface ice, we would expect little salt rather than the 'ocean-like'...

New Horizons' encounter with Pluto/Charon in 2015 is eagerly anticipated, but let's not forget that the spacecraft will be operational afterwards as it moves deeper into the Kuiper Belt. Fuel will be tight, but there should be enough available for one and possibly a second encounter with a Kuiper Belt Object (KBO), assuming we can identify a likely candidate. I'm often asked how such targets would be chosen, and here's one answer: A new site called IceHunters has been set up at Southern Illinois University that will draw the public into the hunt for icy objects. At the heart of the IceHunters project are images made by some of the world's largest telescopes (most come from the 6.5-meter Magellan telescope in Chile and the 8-meter Subaru telescope on Mauna Kea), of the region where potential targets will be found. Like SETI@Home, IceHunters leverages widely distributed PCs in the hands of end-users worldwide. Check the site and you'll see that instead of conventional astronomical...

We've certainly gotten our money's worth out of the spacecraft once called 'Deep Impact.' A mission designed for close study of a comet (Tempel 1) winds up making extrasolar planet investigations in an extended mission called EPOCh (Extrasolar Planet Observations and Characterization), sends back imagery of the Earth and its moon that deepens our knowledge of terrestrial world observations, and flies by another comet, Hartley 2, in its DIXI phase (Deep Impact Extended Investigation ). Add it all up and you get the combined acronym EPOXI. Have a look at the range of comets that have been studied by spacecraft thus far: Image: Images at the same scale for all cometary nuclei observed by spacecraft. Differences in overall shape are dramatic, as are the differences in contrast between the nuclei and their associated jets, which are brighter than the nucleus at Halley and Hartley 2 and much fainter than the nucleus at other comets. Credit: Science/AAAS. Now we have further analysis of the...