Cassini mission engineers are referring to its final pass by Titan as 'the goodbye kiss,' a phrase that sounds like something from a Raymond Chandler novel. Maybe it's the juxtaposition of intimacy and death that Chandler exploited so well. In any case, what counts in the last of Cassini's hundreds of passes over Titan in its 13-year exploration of the system is the gravitational nudge that is sending the spacecraft into Saturn's atmosphere tomorrow. "Cassini has been in a long-term relationship with Titan, with a new rendezvous nearly every month for more than a decade," said Cassini Project Manager Earl Maize at NASA's Jet Propulsion Laboratory in Pasadena, California. "This final encounter is something of a bittersweet goodbye, but as it has done throughout the mission, Titan's gravity is once again sending Cassini where we need it to go." Closest approach for the final pass at Titan occurred at 1504 EDT (1904 UTC) on September 12, at an altitude of 119,049 kilometers, with data...

While we track hurricane Irma and its path of devastation in the Caribbean, another kind of storm is affecting the skies over more northerly areas. A strong geomagnetic storm watch continues in effect, making it possible that the aurora borealis -- northern lights -- will be visible further south than usual, in Scotland and southern Scandinavia but perhaps into the continental United States as well, while the aurora australis could be active for those in the more southerly latitudes below the equator. All of this is due to sunspot AR2673, which is the source of a flare and coronal mass ejection hurled out of the Sun on Monday. I've seen the northern lights in Iceland on one spectacular October night, but only once -- in Iowa, in 1970 -- have I seen them in the US. The phenomenon results from electrons accelerated as they encounter the Earth's magnetosphere, following the magnetic field lines to the polar regions, where from 500 kilometers down to 80 kilometers up, they collide with...

The Jet Propulsion Laboratory has just published details about Cassini's last days and its final plunge into Saturn on September 15. That last act turns the craft into our first planetary probe of Saturn, to use Linda Spilker's memorable phrase. A Cassini project scientist at JPL, Spilker goes on to note that the probe will be "sampling Saturn's atmosphere up until the last second. We'll be sending data in near real time as we rush headlong into the atmosphere -- it's truly a first-of-its-kind event at Saturn." Image: Cassini streaks across Saturn's sky in its final moments. Credit: NASA/JPL-Caltech. I want to lift the Cassini final calendar out of this JPL news release, as many Centauri Dreams readers have expressed an interest particularly in the mission-ending atmospheric entry. We will likely lose radio contact within, JPL estimates, one to two minutes after the descent into the atmosphere begins. Eight of the twelve science instruments will be operating throughout the plunge,...

Knowing that he was busy in Australia, I hadn't thought that Alan Stern would get off a new report on New Horizons quite this fast (he wrote it over the Pacific on the flight back). But there's enough here that I want to supplement this week's earlier post about the three occultations of 2014 MU69, the distant Kuiper Belt Object toward which the spacecraft now moves at roughly a million kilometers a day. I'm also taken with an image in Stern's latest, seen below. What we're looking at is the spacecraft as it approaches what we now think may be a binary object, with the dense starfield in Sagittarius stretching out behind. Nice work by artist Carlos Hernandez. Image: Artist's concept of the New Horizons spacecraft flying by a possible binary MU69 on Jan. 1, 2019. Credit: Carlos Hernandez. The three occultations observed in June and July were examined in particular for evidence of debris, rings or other hazards that could cripple the spacecraft during the close approach. The encounter...

I'm going to miss the Cassini mission as much as anyone, but I have to say it's fascinating to watch how mission controllers are wringing good science out of every last moment of the spacecraft's life. We're now in the Grand Finale phase of the mission, in which Cassini has moved between the planet and its rings in a series of weekly dives. Now we're about to push into a new series of close passes, actually moving through Saturn's upper atmosphere. Notice the language that Linda Spilker, Cassini project scientist at the Jet Propulsion Laboratory, uses to describe what's next: "As it makes these five dips into Saturn, followed by its final plunge, Cassini will become the first Saturn atmospheric probe. It's long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn, and we're laying the groundwork for future exploration with this first foray." Image: This artist's rendering shows Cassini as the spacecraft makes one of its final five dives through...

Back in June we tracked what the New Horizons team was doing to refine our knowledge of 2014 MU69, the Kuiper Belt Object toward which New Horizons is now moving (see New Horizons: Occultations in Preparation for MU69). There were actually three of these events, on June 3, July 10 and July 17 of this year, studied not only by team members on the ground in Argentina and South Africa but by observatories like SOFIA (the airborne Stratospheric Observatory for Infrared Astronomy) and the Hubble Space Telescope. Hubble and the European Space Agency's Gaia satellite were critical in calculating where the shadow of MU69 would fall. Learning more about the distant KBO is a key part of the encounter, given the possibilities of debris around MU69 in the upcoming flyby. You'll recall that the Pluto/Charon system was analyzed painstakingly in advance of the New Horizons flyby for the same reason. The occultations, in which the object passes in front of a distant star, allowed the team to take...

The Voyagers' continuing interstellar mission reminds us of how little we know about space just outside our own Solar System. We need to learn a great deal more about the interstellar medium before we venture to send fast spacecraft to other stars. And indeed, part of Breakthrough Starshot's feasibility check re small payloads and sails will be to assess the medium and determine what losses are acceptable for a fleet of such vehicles. The definitive work on the matter is Bruce Draine's Physics of the Interstellar and Intergalactic Medium, and thus it's no surprise that Draine has been involved as a consultant with Starshot. As we saw yesterday, we have only one spacecraft returning data from outside the heliosphere (soon to be joined by Voyager 2), making further precursor missions explicitly designed to study 'local' gas and dust conditions a necessity. Another reminder of the gaps in our knowledge comes from an analysis of WISE data. The Wide-field Infrared Survey Explorer...

All of the Juno spacecraft's instruments -- including JunoCam -- were operational during its July 10 flyby, giving us a close-up look at the Great Red Spot. Now 16,000 kilometers wide, the storm has been studied since 1830 and may be considerably older than that. Juno's orbit took it to perijove (closest to Jupiter's center) at 2155 EDT on the 10th (0155 UTC on the 11th), when it closed to about 3500 kilometers above the cloud tops. The passage across the Great Red Spot occurred eleven minutes later at some 9000 kilometers above the clouds. While the data are being unpacked and analyzed, we can enjoy the efforts of citizen scientists who went to work on the raw images posted on the JunoCam site and processed them, a procedure done in coordination with the Juno team. "These highly-anticipated images of Jupiter's Great Red Spot are the 'perfect storm' of art and science. With data from Voyager, Galileo, New Horizons, Hubble and now Juno, we have a better understanding of the...

The human expansion into the Solar System will demand our being able to identify sources of water, a skill we're honing as explorations continue. On Mars, for example, the study of so-called 'pitted craters' has been used as evidence that the low latitude regions of the planet, considered its driest, nonetheless have a layer of underlying ice. The Dawn spacecraft discovered similar pitted terrain on Vesta, as you can see in the image below. Image: These enhanced-color views from NASA's Dawn mission show an unusual "pitted terrain" on the floors of the craters named Marcia (left) and Cornelia (right) on the giant asteroid Vesta. The views show that the physical properties or composition of the material in which these pits form is different from crater to crater. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/JHUAPL. Vesta's Marcia crater contains the largest number of pits on the asteroid. The 70-kilometer feature is also one of the youngest craters found there. So what accounts for this...

I love the image of Jupiter below because of the detail -- a mosaic of 27 images taken on closest approach by Cassini in 2000, it shows visible features down to 60 kilometers across. Nine images covering the entire planet were acquired in red, green and blue to provide color much like what our eyes would see if we were there. The Great Red Spot, nestled among the clouds of ammonia, hydrogen sulfide and water, is obvious. But we'll soon learn much more, for the Juno spacecraft is scheduled to fly directly over the Great Red Spot on July 10. Image: This true color mosaic of Jupiter was constructed from images taken by the narrow angle camera onboard NASA's Cassini spacecraft on December 29, 2000, during its closest approach to the giant planet at a distance of approximately 10 million kilometers. Credit: NASA/JPL/Space Science Institute. Launched on August 5, 2011, Juno completed its first year in Jupiter orbit on July 4, a reminder of how well shielded its instruments are in this...

Centaurs are intriguing objects, and not just because of the problem in figuring out what they are. For one thing, the farthest points in their orbits take them between the orbits of the outer planets in our Solar System. That makes them unstable, yielding lifetimes on the order of a few million years. They also show characteristics of both asteroids and comets, which makes objects like 174P/Echeclus so intriguing. Discovered in 2000, it was classified as a minor planet before a cometary coma appeared. Thus its current cometary designation. So what exactly do we have here? In 2005, a large piece of 174P/Echeclus broke off, possibly the result of an impact or, despite a distance at the time of over 13 AU from the Sun, perhaps the release of volatiles. We saw another outburst in 2011 at a distance of 8.5 AU from the Sun. Maria Womack (University of South Florida), who is lead author of a new paper on Echeclus, calls it “a bizarre solar system object,” which sounds about right, though...

Perhaps the image of Uranus just below helps explain why the planet has been treated so sparsely in science fiction. Even this Voyager view shows us a featureless orb, and certainly in visible light the world has little to make it stand out other than its unusual axis of rotation, which is tilted so that its polar regions are where you would expect its equator to be. Geoff Landis' "Into the Blue Abyss" (2001) is the best fictional treatment I know, but the fog-shrouded Uranus of Stanley G. Weinbaum's "The Planet of Doubt" (1935) has its own charms, though obviously lacking the scientific verisimilitude of the Landis tale. My admiration for Gerald Nordley's "Into the Miranda Rift" (1993) is unabated, taking us into this strange world's most dramatic moon, while I should also mention Kim Stanley Robinson's visit to Uranus in Blue Mars (1997), where the moon is established as a protected wilderness site while the rest of the Uranian satellite system is under colonization. Fritz Leiber's...

When you find a protoplanetary disk that displays unusual properties, the suspicion grows that an unseen planet is causing the phenomenon. The young Beta Pictoris is a classic case in point: Here we see disk asymmetry, with one side of the disk appearing longer and thinner than the other, and a warp that could be caused by the planet known as Beta Pictoris b. Or consider an extreme case, HD 142527. A T Tauri star in Lupus, HD 142527 displays an inner disk that is tilted by about 70 degrees (see HD 142527: Shadows of a Tilted Disk). Such a striking offset could be caused by an encounter with another star, though there no good candidates. Are we seeing the effects of proto-planets? All this comes to mind because of what Kat Volk (JPL) and Renu Malhotra (Lunar and Planetary Laboratory, University of Arizona) are seeing in our own Solar System. Their analysis of the more distant regions of the Kuiper Belt shows that objects there display an offset of about eight degrees from the...

Our spacecraft have never encountered an object as far from Earth as 2014 MU69, but New Horizons will change all that when it races past the Kuiper Belt object on New Year's Day of 2019. This summer is an interesting part of the project because planners will use it to gather as much information as possible about what they'll find at the target. We have three occultations to work with, one of them just past, and they are as tricky as it gets. But before I get to the occultations, let me offer condolences to the family and many New Horizons friends of Lisa Hardaway, who died in January at age 50. Hardaway helped to develop the LEISA (Linear Etalon Imaging Spectral Array) spectrometer that brought us such spectacular results during the Pluto/Charon flyby. She was program manager at Ball Aerospace for the Ralph instrument that contains LEISA. Mission scientists used data from the instrument package to make geological, color and composition maps of Pluto and its moons. The mission team...

How to make sense of Enceladus? The moon's famous jets of water vapor, mixing with organic compounds, salts and silica, first revealed the possibility of an ocean beneath the icy surface, and the Cassini orbiter has treated Enceladus as a high priority target ever since. But why the asymmetry here? After all, while the south polar region includes the active 'tiger stripe' fractures associated with the plumes in a geologically young area, the northern pole shows much more cratering, evidence for a considerably older surface and, obviously, no plumes at all. Perhaps, say astronomers from NASA, the University of Texas and Cornell, we're dealing with an ancient impact, one that completely re-oriented Enceladus by tipping it about 55 degrees away from its original axis. Thus we get fractures well over 100 kilometers long in the south, evidence for an asteroid strike in what would have once been an area close to the moon's equator. Radwan Tajeddine (Cornell University) is a Cassini imaging...

Have a look at the design of the Psyche spacecraft now being built by Space Systems Loral in Palo Alto. What's intriguing here is the five-panel x-shaped design of the solar array, reconfigured from a four-panel array on either side of the spacecraft. The juiced up array offers this asteroid-bound spacecraft higher power capabilities for its solar electric propulsion system, helping to support the recently adjusted higher velocity requirements of its journey. Image: This artist's-concept illustration depicts the spacecraft of NASA's Psyche mission near the mission's target, the metal asteroid Psyche. The artwork was created in May 2017 to show the five-panel solar arrays planned for the spacecraft. Credit: NASA/JPL-Caltech/Arizona State Univ./Space Systems Loral/Peter Rubin. For the Psyche mission has been re-thought, with the interesting result that arrival at the unusual metal asteroid will take place a full four years earlier than the original timeline. "We challenged the mission...

Although there are no plans at present to send a lander to Europa, we continue to work on the prospects, asking what kind of operations would be possible there. NASA is, for example, now funding a miniature seismometer no more than 10 centimeters to the side, working with the University of Arizona on a project called Seismometers for Exploring the Subsurface of Europa (SESE). Is it possible our first task on Europa's surface will just be to listen? The prospect is exciting because what we'd like to do is find a way to penetrate the surface ice to reach the deep saltwater ocean beneath or, barring that, any lakes that may occur within the upper regions of the ice shell. The ASU seismometer would give us considerable insights by using the movements of the ice crust to tell us how thick it is, and whether and where ocean water that rises to the surface can be sampled by future landers. Image: Close-up views of the ice shell taken by the Galileo spacecraft show uncountable numbers of...

Cassini's final months are stuffed with daring science, the kind of operations you'd never venture early in a mission of this magnitude for fear you'd lose the spacecraft. With the end in sight for Cassini, though, ramping up the science return seems worth the risk. And while diving through the narrow gap between Saturn and its rings seems to be asking for trouble, the results of the first plunge on April 26 show that the region is more dust-free than expected. "The region between the rings and Saturn is 'the big empty,' apparently," says Cassini Project Manager Earl Maize of NASA's Jet Propulsion Laboratory in Pasadena, California. "Cassini will stay the course, while the scientists work on the mystery of why the dust level is much lower than expected." Image: This artist's concept shows an over-the-shoulder view of Cassini making one of its Grand Finale dives over Saturn. Credit: NASA/JPL-Caltech. The region between Saturn and its rings was thought, based on previous models of the...

Sometimes it pays to step back and try to look at spaceflight with fresh eyes. Go out and find Saturn in the sky and consider it as the ancients did, a moving celestial ember. And as you stand there, realize all over again that we've built a spacecraft that has been operating around that world since 2004, feeding us a datastream as its path was tweaked to look at interesting targets. The sheer magnitude of this accomplishment -- Cassini is now operating between the planet and its rings! -- is cause for celebration even as the mission's end approaches. Image: Artist's concept of Cassini diving between Saturn and its innermost ring. Credit: NASA/JPL-Caltech/Space Science Institute. Today's good news is that controllers have reacquired Cassini's signals following its plunge through the ring/planet gap on April 26, a time during which its 4-meter high-gain antenna was re-oriented to serve as an ad hoc shield against whatever dust grains or particles might be in its path. Critical...

Jim Green, who is director of the Planetary Science Division at NASA headquarters, clearly loves his job, and he got so excited during Thursday's news conference that he kept interchanging Enceladus with Europa in his remarks. Both were in play during the discussion, and the context made it clear what he intended, but I always get a kick out of seeing that kind of enthusiasm showing forth in scientists and academics. It's a reminder of why they got involved in the first place, and for that matter, what drew me into writing about the field myself. The news delivered in the press conference and through two new papers involves two older space missions that are driving planning for yet a third, the Europa Clipper mission, a Jupiter orbiter that is still in the design and planning stages. And with Cassini in its final months of operation, it's fitting that a Cassini flyby through the Enceladus plumes in 2015 should result in what Cassini project scientist Linda Spilker (JPL) called a...