Io doesn't come into play very much on Centauri Dreams, probably because of the high astrobiological interest in the other Galilean satellites of Jupiter -- Europa, Callisto and Ganymede -- each of which may have an internal ocean and one, Europa, a surface that occasionally releases material from below. Io seems like a volcanic hell, as indeed it is, but we saw yesterday that its intense geological activity produces interactions with Jupiter's powerful magnetosphere, leading to radio emissions that might be a marker for exomoon detection. The exoplanet hunt has diverse tools to work with, from the transits that result from chance planetary alignments to radial velocity methods that measure the motion of a host star in response to objects around it. Neither is as effective at planets in the outer parts of a solar system as we'd like, so we turn to direct imaging for large outer objects and sometimes luck out with gravitational microlensing, finding a planetary signature in the...

How do you close on a comet? Very carefully, as the Rosetta spacecraft has periodically reminded us ever since late January, when it was awakened from hibernation and its various instruments reactivated in preparation for operations at comet 67P/Churyumov-Gerasimenko. The spacecraft carried out ten orbital correction maneuvers between May and early August as its velocity with respect to the comet was reduced from 775 meters per second down to 1 m/s, which is about as fast as I was moving moments ago on my just completed morning walk. What a mission this is. When I wrote about the January de-hibernation procedures (see Waking Up Rosetta), I focused on two things of particular interest to the interstellar-minded. Rosetta's Philae lander will attempt a landing on the comet this November even as the primary spacecraft, now orbiting 67P/Churyumov-Gerasimenko, continues its operations. We're going to see the landscape of a comet as if we were standing on it, giving Hollywood special...

I'll wrap up this week's outer planet coverage with a look at recent Cassini flybys of Titan, but I also want to put these accomplishments in the context of what we might do with future missions to the ice giants Uranus and Neptune like the proposed ODINUS missions we looked at yesterday. One-off missions to explore a planet and its satellites collect highly detailed data, but comparative studies of the giant planets require accumulating datasets separated by decades. Are there alternatives? Let's hold that thought as we look at Cassini in this light. The flyby designated T-101 occurred on May 17 and was highlighted by Cassini beaming radio signals over Ligeia Mare and Kraken Mare, the two largest seas on Titan. The idea here is to bounce the signals off the surface of the lakes so that they are received by the ground stations of the Deep Space Network here on Earth. Image: Signals bounced off Titan can reveal important details about the moon's surface. Credit: NASA/JPL-Caltech....

Once New Horizons has performed its flyby of Pluto/Charon and, let's hope, its reconnaissance of a Kuiper Belt object (KBO), what comes next in our exploration of the outer Solar System? Pushing further out, Innovative Interstellar Explorer grew out of a NASA 'Vision Mission' study and has been developed at Johns Hopkins University Applied Physics Laboratory by Ralph McNutt and team. Boosted by a Jupiter gravity assist, IIE would explore the interstellar medium some 200 AU and further from the Sun, using a plutonium-fueled 1 kW electric radioisotope power supply. And then there's Claudio Maccone's FOCAL mission, which would target the Sun's gravitational focus beginning at 550 AU, continuing well past 1000 AU for observations exploiting gravitational lensing effects. FOCAL has been the subject of intense study -- Maccone's 2009 book Deep Space Flight and Communications grew out of this decades-long work -- and with both IIE and FOCAL we have the prospect of making observations of the...

My guess is that the public thinks of the Hubble Space Telescope largely in relation to deep space objects. The Hubble Ultra Deep Field is a case in point, a region of the sky in the constellation Fornax that is no more than a tenth of the width of a full moon, but one that contains 10,000 galaxies. An image of the HUDF augmented by near-ultraviolet data has had considerable play in the media, showing star birth in galaxies five to ten billion years ago. It's too lovely not to show here. Image: The Hubble Ultra Deep Field with near-ultraviolet data, a false-color image that is the result of data acquisition from 841 orbits between 2003 and 2012. Credit: NASA/ESA/Caltech/Arizona State. The HUDF attests to Hubble's range, but we also know from Hubble's studies of objects in our own Solar System that it can support ongoing planetary missions. Astronomers will now use the space observatory to help find tiny objects against the background of an immense starfield in Sagittarius. After...

Let me suggest that you mark August 25th on your calendar. It's the day we celebrate the 25th anniversary of Voyager 2's closest approach to Neptune in 1989. That would be reason enough to look back and remember -- marveling all the while at the Voyagers' continuing mission -- but it's also the day when New Horizons will cross the orbit of Neptune. At work, as principal investigator Alan Stern points out in his latest PI's Perspective, is 'cosmic coincidence not design,' but what a moment it will be as New Horizons moves at last into 'Pluto space.' 90 percent of the long journey is over, with a bit more than 300 million miles to go before the encounter with Pluto/Charon next summer. Newly awakened from hibernation, the spacecraft will be put through a complete checkout of its onboard systems and scientific instruments, as well as conducting its first optical navigation campaign to study the approach into Pluto. Stern also reports that the upcoming cruise science will include imaging...

I love a long journey by car or rail, but not by airplane. Back in my flight instructing days, I used to love to take a Cessna 182 on a long jaunt, but these days the flying I do means sitting in the cheap seats in the back of a gigantic jet and suffering the various indignities of security checks, long lines and tightly packed quarters. Hence my 1000 mile rule: If the trip is less than that distance, I'll drive it or look for a rail connection. My recent trip back to the Midwest reminded me how much I enjoy seeing the scenery at my own pace and having plenty of time to think. One of the things I thought about was how to extract maximum value from spacecraft. A decade or so ago, JPL's James Lesh explained to me how the signal from a distant probe passing behind a planet would be affected by that planet's atmosphere. An elementary way to do atmospheric science! I've mused ever since about how to do complicated things with existing resources and how to put technology in the right place...

Our recent discussions of the Jovian moons Ganymede and Europa highlight a fact that not so long ago would have seemed absurd. Three of the four bright dots that Galileo saw through his primitive telescope around Jupiter are potential habitats for life. Even battered Callisto gives evidence of an internal ocean, as do, of course, both Ganymede and Europa. But why stop there? Further out, Titan is worth exploring both on the surface and under it, and tiny Enceladus may be both the easiest to study and the most bizarre astrobiological possibility we've yet found. The 'easy to study' part comes from the fact that Enceladus conveniently spews vapor from its own internal reservoirs into space, making it possible for a space probe to analyze the contents without ever touching down on the surface. The 'bizarre' part comes from the fact that those fissures exist, surely a sign of Saturn's gravitational grip upon the flexing moon, but also a reminder that these outer moons have leaped into...

Remember as you ponder NASA’s Request for Information about a Europa mission that the agency is contributing three instruments to the European Space Agency’s JUpiter ICy moons Explorer (JUICE) mission, to be operational in Jupiter space in the 2030s. The goal here is to explore Europa, Callisto and Ganymede through numerous flybys, with the craft finally settling into orbit around Ganymede. This would be the first serious look at multiple Jupiter moons by a visiting spacecraft since the Galileo mission, which explored the system from 1995 to 2003. The large Jovian moons have always been of interest, with not just Europa but Callisto and Ganymede also thought to have deep oceans beneath their icy crusts. Galileo, in fact, found evidence for salty seas within Ganymede, probably containing magnesium sulfate. At the Jet Propulsion Laboratory, a team led by Steve Vance is offering new research showing that what we may have on Ganymede is more than a simple sea between two layers of ice....

Stanley G. Weinbaum is best known for the 1934 short story "A Martian Odyssey," lionized by readers and critics alike after it appeared in the July issue of Wonder Stories. Isaac Asimov would later opine that "A Martian Odyssey" was one of a handful of stories that changed the way all later science fiction was written. But Weinbaum's depiction of a genuinely alien being called Tweel sometimes obscures his other work, which you can find collected in The Best of Stanley G. Weinbaum (1974), a worthwhile addition to the library of any SF fan, and a reminder of the loss the genre suffered when the author died at age 33. This morning I've been thinking back to a little known Weinbaum story called "Redemption Cairn," which ran in the March, 1936 Astounding Stories and which, because I have a good run of Astounding issues from that era, sits not ten feet away from me on my shelf. I don't know if this is the first appearance of Europa in science fiction, but "Redemption Cairn," with its...

After yesterday's look back at the ambitious Project Orion planners and their hopes of reaching Saturn's moons by the 1970s, let's stay in the same vicinity today to look at what may be the emergence of an entirely new moon. As always, we have Cassini to thank for this work, which shows a disturbance at the outer edge of Saturn's A ring. This is the outermost of the large, bright rings, with a width of approximately 14,600 kilometers. Its inner boundary is the Cassini division, a 4800 kilometer wide region between it and the B ring. The image below shows the disturbance, an area in the shape of an arc that is about 20 percent brighter than its surroundings. The region is some 1200 kilometers long and 10 kilometers wide, and it is accompanied by breaks in the otherwise smooth profile at the edge of the ring. The current thinking is that both the arc and the protuberances are the result of gravitational effects caused by a nearby object. Are the rings, then, giving birth to a new moon?...

The recent news about an ocean on Enceladus had me thinking over the weekend about a trip my wife and I took years ago to Michigan's Upper Peninsula. There we had rented a cabin for the week on the shores of Lake Superior, twenty miles from the nearest town, unless you counted the small grocery store, art gallery and scattered houses up the highway as a town -- if so, it was a tiny one. Looking out across the silver and gunmetal gray waves of Superior, you could imagine it an ocean, a cold, frothing place of treacherous currents and, that October, raw winds. Lake Superior appears as the comparison in many of the reports on the Enceladus findings as they sketch out what appears to be a sea just as large, perhaps ten kilometers deep covered by an ice shell four times as thick. Given that the well known plumes of Enceladus are already known to contain organic molecules in addition to salty water, the inevitable question arises: Could some form of life exist beneath this frozen surface?...

The European Space Agency's Rosetta spacecraft, having traveled for ten years, is on track for its close-up investigation of comet 67P/Churyumov-Gerasimenko to begin later this year. Three years ago we had the first actual image of the comet, a 13-hour exposure taken shortly before the craft entered a lengthy period of hibernation. On the 20th of January, Rosetta was 'awakened' and controllers are in the process of commissioning its onboard instruments. As part of the process, we have two 'first-light' images taken on March 20 and 21. Image: Comet 67P/Churymov-Gerasimenko in the constellation Ophiuchus. This image was taken on 21 March by the OSIRIS Narrow Angle Camera. The comet is indicated by the small circle next to the bright globular star cluster M107. The image was taken from a distance of about 5 million kilometres to the comet. A wide-angle image was taken on 20 March. Credit & copyright: ESA © 2014 MPS for OSIRIS-Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA. We're seeing...

The second largest sea on Titan is Ligeia Mare, made up of methane and ethane in a body of liquid that is larger than Lake Superior. Now we have word that the surface of Ligeia Mare is so utterly still that it would appear like glass. The news comes from Stanford University, where geophysicist Howard Zebker had led a new study based on Cassini measurements made in 2013. "If you could look out on this sea," said Zebker, "it would be really still. It would just be a totally glassy surface." Titan seizes the imagination not only because it is planet-like, with seas and a thick atmosphere, but because we know of no other body in the Solar System besides Earth that has a complex cycle involving solid, liquid and gas. Because the thickness of Titan's atmosphere compromises optical observations, Cassini bounced radio waves off the surface and analyzed the resulting echo. Wave action could be measured by the strength of the returning echo. Zebker explains in this Stanford news release that...

Just how early we are in our thinking about traveling beyond the Solar System is revealed in a comment made by Ned Wright, principal investigator of the WISE mission. "We don't know our own sun's backyard as well as you might think," said Wright. And he goes on to say, "We think there are even more stars out there left to find with WISE." That's a wake-up call indeed given how much WISE has already told us, and what two new studies have brought to light. Davy Kirkpatrick (Caltech) led one of these, examining data from the Wide-field Infrared Survey Explorer mission that performed two full scans of the sky in 2010 and 2011, capturing images of almost three-quarters of a billion galaxies, stars and asteroids. Analyzing data using NASA's AllWISE program, which makes it possible to compare the datasets more effectively, Kirkpatrick's team found 3,525 new stars and brown dwarfs within 500 light years of the Sun. These objects, says Kirkpatrick, were totally overlooked before now. In any...

The first global geological map of Ganymede has become available through the efforts of a team led by Wes Patterson (Johns Hopkins Applied Physics Laboratory) and Geoffrey Collins (Wheaton College). The map doesn't reproduce well in the small space I have available, but the image below gives you an idea of its layout and is linked to the download site at the U.S. Geological Survey, which is publishing it as USGS Scientific Investigations Map 3237. Image: Ganymede is the largest satellite of Jupiter, and its icy surface has been formed through a variety of impact cratering, tectonic and possibly cryovolcanic processes. Images of Ganymede suitable for geologic mapping were collected during the flybys of Voyager 1 and Voyager 2 (1979), as well as during the Galileo mission in orbit around Jupiter (1995-2003). This map represents a synthesis of scientists' understanding of Ganymede geology after the Galileo mission. Credit: Wheaton College/JHUAPL/Brown University/JPL/USGS. Ganymede is...

The MACH-11 program (Measurements of 11 Asteroids and Comets Using Herschel) uses data from the European Space Agency's space-based Herschel observatory to look at small bodies that are targeted by our spacecraft. With the Dawn mission on its way to Ceres, the Herschel data have now revealed the existence of water vapor on the dwarf planet. To my knowledge, this is the first time water vapor has been detected in an asteroid, or I should say, an object that used to be considered an asteroid before the International Astronomical Union decided to re-classify it because of its large size. Herschel ran out of coolant in the spring of 2013, but not before making a series of observations of Ceres in the two previous years that show a thin water vapor atmosphere. As with so many of our missions (Kepler comes immediately to mind), we still have plentiful data to look through. In this case, we'll be examining the increasingly fuzzy distinction between asteroids and comets as we try to figure...

In the first post of 2014, I wrote about what the following year -- 2015 -- would bring, the New Horizons flyby of Pluto/Charon as well as the arrival of the Dawn spacecraft at Ceres, a fascinating object with a possible internal ocean. But let's not forget about the European Space Agency's Rosetta spacecraft, which is now nearing the end of a decade-long journey to comet 67P/Churyumov-Gerasimenko. The spacecraft is scheduled to awake from a two-year stretch in sleep mode today, with arrival at the comet's core in November. The orbiter will operate there until the end of 2015. We've had missions to comets before, many of them discussed in these pages, but none as ambitious as this one. Rosetta's Philae lander will attempt a landing on the comet in November while the orbiter will continue tracking it as the comet is transformed by its approach to the Sun into an erupting, churning mass of ice and dust. With gravity about a thousand times less than that of Earth, this is a tricky...

Over the New Year transition I saw a number of tweets to the effect that as of January 1, the first flyby of Pluto was going to occur next year, a notable thought when I ponder how fast this long journey has seemed to move. Was it really way back in 2006 that New Horizons launched? We can only wonder what surprises the Pluto/Charon system has in store for us in 2015. The same can be said for Ceres, a body which, as of December 27, is now closer to the Dawn spacecraft than Vesta, the asteroid around which it orbited so many interesting times. Christopher Russell (UCLA) is Dawn's principal investigator, a man whose thoughts on the mission naturally carry weight: "This transition makes us eager to see what secrets Ceres will reveal to us when we get up close to this ancient, giant, icy body. While Ceres is a lot bigger than the candidate asteroids that NASA is working on sending humans to, many of these smaller bodies are produced by collisions with larger asteroids such as Ceres and...

Titan has about 9000 cubic kilometers of liquid hydrocarbon, some forty times more than in all the proven oil reservoirs on Earth. That's just one of the findings of scientists working over the data from recent Cassini flybys of the Saturnian moon. Each flyby snares our attention because this is the only other place in the Solar System that has stable liquid on the surface, even if it's not water. That's part of Titan's fascination, of course, because it's similar to the Earth in terms of basic interactions between liquids, solids and gases but completely alien in terms of temperatures. Just how extensive are those seas and lakes we've found in Titan's northern hemisphere? Cassini's radar instrument has given us our best views to date with the mosaic shown below, one that's based on multiple images from flybys tracking areas at various angles. Kraken Mare, Titan's largest sea, and Ligeia Mare, the second largest, appear along with nearby lakes. We learn not only that Kraken Mare is...