Last week's look at Europa examined the possibility of primordial impacts there that might have brought organic materials to the moon, focusing especially on clay-like minerals that a JPL team found in data from the Galileo mission. I had barely finished that article before the news from Hubble arrived with observations of water vapor above the southern pole of Europa, a possible indication of water plumes erupting from the moon's surface. That work ran in Science Express and was reported at the meeting of the American Geophysical Union in San Francisco. Lead author Lorenz Roth (Southwest Research Institute) described it this way: "By far the simplest explanation for this water vapor is that it erupted from plumes on the surface of Europa. If those plumes are connected with the subsurface water ocean we are confident exists under Europa's crust, then this means that future investigations can directly investigate the chemical makeup of Europa's potentially habitable environment...

Europa continues to fascinate those hopeful of finding life elsewhere in our Solar System, and it's easy to see why. Consider everything the Jovian moon has going for it. Although it's a long way from the Sun (Jupiter is 5 AU out), Europa gets internal heat from its interactions with the gravitational well around Jupiter, which causes the moon to be stretched and squeezed. We have an ocean whose occasional eruptions into the ice above allow mixing with surface materials and, as this JPL news release points out, salts on the surface that create an energy gradient. These factors have been in place on Europa since the moon first formed. Now an analysis of data from the Galileo mission has turned up something else needed for life: The likelihood of organic materials. The assumption has been that comet or asteroid impacts could provide these, and the data that Jim Shirley (JPL) will discuss tomorrow at the American Geophysical Union meeting in San Francisco show the presence of clay-type...

I don't usually have much to say about Mars, for this site's focus is on deep space -- the outer Solar System and beyond. But with both the Mangalyaan and MAVEN Mars missions in progress, I'll take this opportunity to mention new work out of MIT that deals with the effect of Mars on asteroids. The topic is 'space weathering,' the result of impacts from high energy particles and more. Richard Binzel and colleague Francesca DeMeo have been looking at disruption to asteroid surfaces, finding that close planetary encounters can explain an unusual fact: The surfaces of most asteroids appear redder than the remnants of asteroids that have crashed as meteorites to Earth. Back in 2010, Binzel established what he sees as the basic mechanism. Main belt asteroids, orbiting between Mars and Jupiter, are exposed to cosmic radiation that changes the chemical nature of their surfaces. But take an asteroid out of the main belt and give it a close pass by the Earth and 'asteroid quakes' will occur,...

With the Cassini mission continuing through 2017, we'll doubtless have many fine views of Saturn to come, but the images below merit special attention, enough so that I decided to close the week with them. We're looking at an annotated, panoramic mosaic made by processing 141 wide-angle images, sweeping across 651,591 kilometers. That covers the planet, its inner ring system and all its rings out to the E ring. Moreover, the view presented here is in natural color, so we see the color as it would be seen by human eyes rather than as distorted during observations at other wavelengths. You may remember the 'Wave at Saturn' campaign from last summer, when the word went out that Cassini would be snapping a view of the Earth from Saturn space. In the mosaic (click the image to zoom in) we can see the Earth as a blue dot to the lower right of Saturn, but Venus is visible too to the upper left, and Mars shows up as the faint red dot above and to the left of Venus. A close look will reveal...

New views from Cassini are giving us a much better look at Titan's north pole and the seas and lakes that make the region so distinctive. This is particularly interesting because most of the moon's lakes are concentrated at its northern latitudes, a fact that demands an explanation. The new near-infrared images show an area of bright terrain in this northern region that had not been observed before. This news release from the Jet Propulsion Laboratory suggests that the surface thus revealed is unique on Titan. If we can figure out what's going on here, we may have an explanation for the concentration of lakes and seas in these latitudes. Image: The vast hydrocarbon seas and lakes (dark shapes) near the north pole of Saturn's moon Titan sprawl out beneath the watchful eye of NASA's Cassini spacecraft. Scientists are studying images like these for clues about how Titan's hydrocarbon lakes formed. Titan is the only world other than Earth that is known to have stable bodies of liquid on...

Before getting into the distant regions near Pluto/Charon, let's pause for a moment with a reflection on speed. New Horizons left Earth orbit traveling faster than any other vehicle launched into interplanetary space, although it has since slowed. Now the Juno mission is getting press for its velocity, perhaps impelled by this quote from Bill Knuth (University of Iowa), who is lead investigator for one of the probe's nine scientific instruments. Of Juno's recent close approach to Earth, Knuth says: "Juno will be really smoking as it passes Earth at a speed of about 25 miles per second relative to the Sun. But it will need every bit of this speed to get to Jupiter for its July 4, 2016, capture into polar orbit about Jupiter. The first half of its journey has been simply to set up this gravity assist with Earth." The speed is impressive, about 40 kilometers per second, and far above Voyager 1's 17.1 kilometers per second, as well as New Horizons' expected 14 kilometers per second at...

A paper just published online by the journal Astrobiology examines what a Europa lander could accomplish on the surface. It’s part of the process of future mission building even if that future is deeply uncertain -- we’re a long way from a Europa lander, and funding even a far less demanding flyby mission is problematic in the current environment. But Robert Pappalardo, lead author of the study at JPL, explains the rationale for a close-up study of the icy world: "If one day humans send a robotic lander to the surface of Europa, we need to know what to look for and what tools it should carry. There is still a lot of preparation that is needed before we could land on Europa, but studies like these will help us focus on the technologies required to get us there, and on the data needed to help us scout out possible landing locations. Europa is the most likely place in our solar system beyond Earth to have life today, and a landed mission would be the best way to search for signs of...

I've come to believe that building the system-wide infrastructure we'll eventually need for interstellar flight will depend on satisfying two imperatives: Planetary defense and astrobiology. The first demands the ability to move payloads quickly to distant targets, allowing plenty of time to change the trajectory of problematic objects. The second is all about science and answering key questions about our place in the cosmos. I know few people who think life doesn't exist elsewhere, but if it really is out there, finding and cataloguing it will involve human crews operating deep in the Solar System. After all, we're learning how widespread internal oceans may be, and it's possible that even places as remote as Triton may have spawned some kind of organisms. And while we've had our eye on Europa's hidden ocean for some time now, Enceladus is a recent entrant into the astrobiology sweepstakes with its jets of water ice and organic particles emmanating from the so-called 'tiger stripes'...

We're just past the 35th anniversary of the discovery of Pluto's moon Charon. Or more precisely, we just passed the July 7 date when the announcement of that discovery, which had actually happened in June of 1978, was made. That turned my thoughts back to Larry Niven's story "Wait It Out," which tells the tale of two astronauts who are stranded on Pluto's surface. Removing his helmet to die quickly, the narrator discovers that he lives on in a strange semi-stasis, his brain now a superconductor. First published in 1968 (in All the Myriad Ways), the story contains no Charon, but the scene lingers with me. I'll quote just a patch of it, though I've quoted it before: A superconductor is what I am. Sunlight raises the temperature too high, switching me off like a damned machine at every dawn. But at night my nervous system becomes a superconductor. Currents flow; thoughts flow; sensations flow. Sluggishly. The one hundred and fifty-three hours of Pluto's rotation flash by in what feels...

One of the themes I often use in my talks is the 'filling out' of our picture of the Solar System. In addition to the asteroid belt, we've added the icy bodies of the Kuiper Belt and the vast expanse of the Oort Cloud into what once seemed a relatively simple, nine-planet solar system. I could easily add to the ranks the population of so-called 'Centaurs,' small bodies that populate the space between the giant planets and show characteristics of both comets and asteroids. 10199 Chariklo is the largest Centaur yet discovered (260 kilometers in diameter), and Saturn's moon Phoebe may be a captured Centaur, in which case images of it from the Cassini orbiter offer us our first detailed view of such an object. Both Chiron (discovered in 1977) and 60558 Echeclus show signs of a cometary coma; both are classified as asteroids and comets (as is 166P/NEAT). Although differences in definition exist, most agree that Centaurs orbit the Sun between Neptune and Jupiter and eventually cross the...

One of the things we're going to be looking for at Pluto is evidence of a sub-surface ocean. About eighteen months ago I wrote about the work of Guillaume Robuchon and Francis Nimmo (University of California at Santa Cruz). With Pluto's outer surface thought to be a thin shell of nitrogen ice covering a shell of water ice, these researchers have been asking what surface features might flag an ocean deep inside. An equatorial bulge left over from the days when Pluto was spinning more rapidly - or the lack of one - could be the evidence they're looking for. The thinking is this: Such a bulge could be as much as 10 kilometers high and New Horizons should be able to spot it. The presence of the bulge would indicate no ocean beneath, for the movement of liquid water would over time have reduced or eliminated the protrusion. But if New Horizons finds instead evidence of tensional stresses, indicating the outer shell was stretched because of temperature changes over time, then the...

Last week's post about the chemistry of Europa's ocean is nicely complemented by new work on the moon's interior by Brad Dalton (JPL) and colleagues. Like JPL's Kevin Hand, who has been looking at the role of hydrogen peroxide in possible subsurface life there, Dalton is in the hunt for ways to learn more about the composition of Europa's ocean. Both scientists have been using data from the Galileo mission, refining its results to produce new insights. Usefully, the surface chemistry on Europa is affected by the charged particles continually striking the tiny world. That allows us to get a read on which parts of Europa would be the best targets for future spacecraft missions, for Dalton's work helps us find the places where charged particles have had the smallest impact. It's there -- on parts of the leading hemisphere in Europa's orbit -- that material from within the ocean is most likely to be found in pristine condition, with the least chemical processing by incoming charged...

The news that hydrogen peroxide is found across much of the surface of Europa is intriguing. The global ocean beneath the moon’s icy crust would turn hydrogen peroxide into oxygen, assuming there is some mixing between the surface and the ocean. We don’t know if that mixing occurs, but if it does, then we may be looking at a useful chemical energy source for life. Given that I spent much of last week writing about Arthur C. Clarke, this thought invariably brings up a recent viewing of 2010: Odyssey II and the injunction beamed to Earth: “All these worlds are yours except Europa. Attempt no landing there.” Europa is increasingly irresistible the more we learn about it. Here’s Kevin Hand (Jet Propulsion Laboratory) on the question of hydrogen peroxide’s possible role: "Life as we know it needs liquid water, elements like carbon, nitrogen, phosphorus and sulfur, and it needs some form of chemical or light energy to get the business of life done. Europa has the liquid water and elements,...

Europa continues to fascinate us with the possibility of a global ocean some 100 kilometers deep, a vast body containing two to three times the volume of all the liquid water on Earth. The big question has always been how thick the icy crust over this ocean might be, and we've looked closely at Richard Greenberg's analysis, which shows surface features he believes can only be explained by interactions between the surface and the water, making for a thin crust of ice. See Unmasking Europa: Of Ice and Controversy for more, and ponder the prospects of getting some kind of future probe through a thin ice layer to explore the potentially habitable domain below. Possible interactions between the surface and the ice are considered in a new paper by Mike Brown (Caltech) and Kevin Hand (JPL), one that makes the case that there are two ways of thinking about Europa. One is to see the Jovian moon purely as an ice shell upon which the bombardment of electrons and ions have created a chemical...

It's reasonable to call the two Voyager spacecraft our first interstellar probes, in the sense that they are approaching the heliopause and are still transmitting data. Long before controllers shut them down -- which should occur somewhere in the 2020s -- Voyager 1 will have left the Solar System and we'll have data on what happens when the solar wind gives way to the stellar winds from beyond. A case could be made for the Pioneer craft as interstellar probes as well, but while Pioneer 10 has reached a distance of 107 AU, the Pioneers are no longer transmitting data. Voyager 1 is now 123.45 AU out, for a round-trip light time of 34 hours, 15 minutes. But does leaving the Solar System mean we've truly entered interstellar space? An entertaining piece called Postcards from the edge, published in early February by The Economist, notes that much depends on how we define 'interstellar.' Gravity, says its author, defines the universe at the largest scales, and if we're talking about...

Yesterday we looked at the possibility of colonizing worlds much different from the Earth. Seen in one light, pushing out into the Kuiper Belt and building settlements there is part of a slow migration to the stars that may occur without necessarily being driven by that purpose. Seen in another, experimenting with human settlements in extreme environments is a way of exploiting the resources of nearby space, pushing the human presence out into the Oort Cloud. Either way, we can find places that, while not 'habitable' in the classic sense of liquid water at the surface, are nonetheless colonizable. In his Tale of Two Worlds, novelist Karl Schroeder works on a definition of a colonizable world. It has to have an accessible surface, for one thing, meaning one we can work with -- obviously a surface gravity of 4 g's is going to be a problem. Much smaller worlds like Pluto, as we saw yesterday in Ken Roy's work on possible colonies there, pose less of a challenge, as we can imagine...

Yesterday's look at a major river on Titan took on a decidedly science fictional cast, but then Titan has always encouraged writers to speculate. Asimov's "First Law" (1956) tackles a storm on Titan as a way of dealing with the Three Laws of Robotics. Arthur C. Clarke filled Titan with a large human colony in Imperial Earth (1976), and Kim Stanley Robinson used Titanian nitrogen in his books on the terraforming of Mars. As far back as 1935, Stanley G. Weinbaum was writing about a frozen Titan and the struggles of early explorers on that world. The list could go on, but right now the focus stays on Cassini, which with funding continued through 2017 will continue to give us new and striking discoveries like the river dubbed the moon's 'little Nile' feeding into Ligeia Mare. Nor do I want to ignore the recent work from Howard Zebker (Stanford University) and team, who have been working with Cassini radar data and new gravity measurements to tell us more about the internal structure of...

One of the wonderful things about daily writing is that I so often wind up in places I wouldn't have anticipated. Today's topic includes the discovery of a long river valley on Titan that some are comparing to the Nile, for reasons we'll examine below. But the thought of rivers on objects near Saturn invariably brought up the memory of a Frank R. Paul illustration, one that ran as the cover of the first issue of Hugo Gernsback's Amazing Stories in April of 1926. The bizarre image shows sailing ships atop pillars of ice, a party of skaters, and an enormous ringed Saturn. Is this Titan? The answer is no. The illustration is drawn from the lead story in the magazine, Gernsback's serialized reprint of Jules Verne's Off on a Comet, first published in French in 1877 under the title Hector Servadac. A huge comet has grazed the Earth and carried off the main characters, who must learn how to survive the rigors of a long journey through the Solar System, much of the time exploring their...

Even as New Horizons continues to push toward Pluto, now just past the halfway point between the orbits of Uranus and Neptune, we're continuing to get excellent data from the much closer Cassini spacecraft around Saturn. Cassini's composite infrared spectrometer (CIRS) is probing the circulation and chemistry of Titan's atmosphere, tracking how gases like benzene and hydrogen cyanide are distributed and affected by changes in temperature and circulation. We're getting a closeup view of how chemistry and atmospheric circulation modify climate on the distant moon, information that shows a good deal of change over a short period of time. The latest from Cassini, written up in a paper just published in Nature, involves a shift in seasonal sunlight that is apparently tied to the reversal in circulation around the moon's south pole. Earlier in the mission the air here was rising. Now there is strong evidence for sinking air. Nick Teanby (University of Bristol, UK) notes how quickly the...

Now that we have vast numbers of Kuiper Belt Objects assumed to be orbiting outside the orbit of Neptune, not to mention possible Oort Cloud interlopers (Sedna may be one of these), the question of names gets ever more interesting. Great entertainment awaits, as witness the KBO known as 2005 FY9. Discovered not long after Easter in 2005, it quickly gained the nickname Easterbunny. It’s now, after several years, been re-christened Makemake, but I like what Mike Brown, who led the discovery team, has to say about this dwarf planet and its earlier monicker: Three years is a long time to have only a license plate number instead of a name, so for most of the time, we simply referred to this object as “Easterbunny” in honor of the fact that it was discovered just a few days past Easter in 2005. Three years is such a long time that I think I’m going to have a hard time calling Makemake by its real name. For three years we’ve been tracking it in the sky, observing it with telescopes on the...