NASA's Hubble, Spitzer and Chandra space telescopes will all be watching in July when the Deep Impact spacecraft releases its impactor module (about the size of a coffee table) into the path of onrushing comet Tempel 1. Deep Impact's flyby module will be watching, too, as the impactor creates a crater that may be anywhere from two to fourteen stories deep, releasing cometary dust and ice and exposing underlying materials that have remained unchanged since the formation of the Solar System. Now in the cruise phase of its flight, Deep Impact has been through a test of its autonomous navigation system, and its high gain antenna is operating nominally. A mission status report provides some details about the early stages of the flight, when critical subsystems were put through their paces: Another event during commissioning phase was the bake-out heating of the spacecraft's High Resolution Instrument (HRI) to remove normal residual moisture from its barrel. The moisture was a result of...

How does a moon that would fit within the state boundaries of Arizona manage to hold an atmosphere? That's the question following Cassini's most recent flyby of Enceladus. The spacecraft found magnetic field oscillations that scientists now attribute to ionized water vapor. The odd magnetic field signature has shown up on both Cassini flybys, the second of which, on March 9, came to within 500 kilometers of the Saturnian moon's surface. Image: This artist conception shows the detection of an atmosphere on Saturn's icy moon Enceladus. The Cassini magnetometer instrument is designed to measure the magnitude and direction of the magnetic fields of Saturn and its moons. During Cassini's two close flybys of Enceladus -- Feb. 17 and March 9 -- the instrument detected a bending of the magnetic field around Enceladus. Credit: NASA/JPL. Because Enceladus is too small to hold an atmosphere for long, a continuous source of replenishment is suspected. The most likely candidate: volcanoes or...

The Cassini Imaging Team has published its first findings about Titan in the journal Nature. The complexity of Titan's surface and the extent to which it is continually modified draws the most attention. Where are the craters that should have pocked its surface over the past billion years? Thanks to Cassini/Huygens, some answers are beginning to emerge. Working with the last eight months of imagery from the orbiter, the team reports that thirty percent of the satellite's surface has now been mapped with resolutions high enough to pick out features as small as one to ten kilometers. From a press release from the Cassini Imaging Central Laboratory for Operations (CICLOPS): At this scale, what has been discovered are geologically young terrains with signs of tectonic resurfacing, erosion by liquid hydrocarbons, streaking of the surface materials by winds and only a few large circular features thought to be impact craters formed in the ice 'bedrock'. (The largest of these - a...

Twenty-four craters on Saturn's tiny moon Phoebe have now been deemed prominent enough to receive their own names. Phoebe was honored by the names of the Argonauts, the explorers who sailed with Jason to find the golden fleece; its largest crater has been christened Jason. The tale was known in the days of Homer and may have served as a pattern for the wanderings of Odysseus. It is most famously told in a four-book epic by Apollonius of Rhodes, one time custodian of the fabulous library of Alexandria. "We picked the legend of the Argonauts for Phoebe as it has some resonance with the exploration of the Saturn system by Cassini-Huygens," said Dr. Toby Owen, of the University of Hawaii at Manoa. He is the chairman of the International Astronomical Union Outer Solar System Task Group and an interdisciplinary scientist on the Cassini-Huygens mission. "We can't say that our participating scientists include heroes like Hercules and Atalanta, but they do represent a wide, international...

What Cassini heard from Huygens as it descended to Titan's surface is now available as an audio file from the European Space Agency, but it may be easier to download it from Ralph Lorenz' home page. Lorenz is an assistant research scientist at the University of Arizona's Lunar and Planetary Laboratory and a co-investigator on Huygens' Surface Science Package; he created the sound file based on Cassini data. The file compresses four hours of real-time audio into about a minute. What the listener hears is a tone whose frequency depends on the strength of the Huygens signal as received by Cassini. The probe's antenna emitted radio energy unevenly, "...like the petals of a flower rather than the smooth shape of a fruit," as Lorenz puts it. As the probe's orientation changed durings its long descent, its spin rate slowed, causing rapid changes in the tone. "You can hear how the motion becomes slower and steadier later in the descent," Lorenz said. A UA press release on Lorenz' work can be...

Only time and energy for an abbreviated post today -- I'm down with the flu! But Cassini comes through in the pinch. Below is a spectacular image of Mimas seen against the blue northern latitudes of Saturn. From the JPL description (more of which can be found here): Mimas drifts along in its orbit against the azure backdrop of Saturn's northern latitudes in this true color view. The long, dark lines on the atmosphere are shadows cast by the planet's rings. Saturn's northern hemisphere is presently relatively cloud-free, and rays of sunlight take a long path through the atmosphere. This results in sunlight being scattered at shorter (bluer) wavelengths, thus giving the northernmost latitudes their bluish appearance at visible wavelengths. At the bottom, craters on icy Mimas (398 kilometers, or 247 miles across) give the moon a dimpled appearance. Image credit: NASA/JPL/Space Science Institute.

One way to explain the existence of the Moon is through a giant collision, one that tore off enough material to build a satellite in a planetary orbit. Can Pluto and its moon Charon be explained the same way? Robin Canup thinks so. Canup is assistant director of Southwest Research Institute's Department of Space Studies; she argues the case in the January 28 issue of Science. The Moon may seem large in our skies, but it makes up only about 1 percent of Earth's mass. Charon, on the other hand, is 10 to 15 percent the mass of Pluto, which suggests to Canup that the corresponding collision must have been with an object almost as large as Pluto itself. She also believes that Charon probably formed intact as a result of the collision. "This work suggests that despite their many differences, our Earth and the tiny, distant Pluto may share a key element in their formation histories. This provides further support for the emerging view that stochastic impact events may have played an...

Exactly how big is the Solar System? We used to talk about Pluto as the outermost planet, implying the Solar System ended when you crossed its orbit. Now we talk in terms of the Kuiper Belt, a band of debris and planetesimals far beyond Pluto's orbit; beyond the Kuiper Belt looms the vast Oort Cloud, a spherical halo of comets that may extend a light year from our Sun. And if one thing is clear from current research, it's that our old notions of boundaries have to be readjusted. Take recent work at the Southwest Research Institute, which shows that the process of planetary formation once extended far beyond the orbit of Pluto. As reported in the January 2005 issue of The Astronomical Journal, SwRI's Alan Stern used planetary formation software to explore how objects like Sedna, a huge planetoid fully 2/3 the diameter of Pluto, could have formed at distances from 75 AU to 500 AU. The two distances represent Sedna's closest approach and farthest distance from the Sun. "The model...

The European Space Agency's Paris conference on the 21st gave us a further look at Titan's exotic weather systems. In particular, the Gas Chromatograph Mass Spectrometer carried by Huygens produced data showing the malleable nature of methane on the surface of the frigid world. According to John Zarnecki, principal investigator for the Huygens Surface Science Package: "The Gas Chromatograph Mass Spectrometer has detected a 'whiff' of methane evaporating off the surface and the SSP data has also shown indications of gas flowing into its sensing area. These gaseous outbursts were released as heat generated by Huygens warmed the soil beneath the probe. This is a tantalising glimpse of the processes at work on Titan and shows how the weather systems operate with methane forming clouds and raining down on to the surface - producing the drainage channels, river beds and other features that we see in the images." And back to that 'creme brulee' comparison -- Huygens' penetrometer evidently...

ESA's Paris press conference produced new images and an analysis of data from the six instruments that Huygens took to the surface of Titan. "We now have the key to understanding what shapes Titan's landscape," said Dr Martin Tomasko, Principal Investigator for the Descent Imager-Spectral Radiometer (DISR), adding: "Geological evidence for precipitation, erosion, mechanical abrasion and other fluvial activity says that the physical processes shaping Titan are much the same as those shaping Earth." That statement appears in this ESA news release, which goes on to discuss the remarkable surface features Titan has yielded up to scrutiny. And while calling Titan an 'extraordinarily Earth-like world,' as ESA does here, seems to be stretching the point (especially at surface temperatures cold enough to produce liquid methane), the new images,like the one below, do show a complex meteorology. Available in both a gaseous and liquid state, methane forms clouds and precipitates onto the...

Huygens mission scientists will gather tomorrow in Paris to discuss the results of the experiments aboard the probe. Huygens delivered plenty of data: the probe transmitted for several hours from the surface of Titan, even after the Cassini orbiter moved below the horizon. Cassini received one hour and twelve minutes worth of solid information; all told, we have some 474 megabits that include 350 pictures of the descent and landing area. Early results show that the upper atmosphere is what the European Space Agency calls 'a uniform mix of methane with nitrogen in the stratosphere.' As the probe descended, the concentration of methane increased. One unexpected issue was the haze, which the Huygens team assumed the probe would clear at between 75 and 50 kilometers. In fact, Huygens only emerged from the haze at 30 kilometers above the surface. Methane or ethane fog was detected near the ground. On the table tomorrow in Paris will be data about the texture of Titan's surface (the famous...

Of all the Titan images released so far, this one may be the most provocative. Surely these are drainage channels, and is it possible we're looking at a coastline in the lower part of the picture? Is there still liquid out there? If so, it's not water but liquid methane or ethane, and it may have drained long ago into the surface. Months of analysis will be needed before we start getting answers to such questions. The image was taken at approximately 8 kilometers altitude. Note what may be fog near the 'shoreline.' Image: A boundary between high, lighter-coloured terrain and and darker lowland area on Titan. Credit: European Space Agency. More images from ESA are here. The Huygens Atmospheric Structure Instrument (HASI) recorded the sounds of Huygens' descent, now available online. A member of the HASI science team describes the descent audio as including a 'lot of acoustic noise,' which I assume refers to the sound you would have heard within the probe during the descent; the audio...

The first images coming back from Titan are raw (i.e., unprocessed), and we'll have more (up to 350, apparently) available soon. The first picture shows what appear to be drainage channels, as you can see below. This is one of the first raw, or unprocessed, images from the European Space Agency's Huygens probe as it descended to Saturn's moon Titan. It was taken with the Descent Imager/Spectral Radiometer, one of two NASA instruments on the probe. Credit: ESA/NASA/University of Arizona The second image (via Emily Lakdawalla in Darmstadt) seems to be from the surface. Notice the rounded rocks, perhaps evidence of erosion from some kind of liquid (though I notice JPL is calling these ice blocks rather than 'rocks'). Now comes the fun part: we'll be getting details and more images all night long and unravelling the data will take months. What a story, and what a triumph for ESA, NASA and the Italian Space Agency!

Incoming data shows that Huygens' instruments were functioning nominally throughout the descent. From this morning's (EST) press conference, this statement by Jean-Jacques Dordain, ESA's Director General: "The morning was good; the afternoon is better. We were an engineering success this morning, but we can say this afternoon that we are also a scientific success. We are the first visitors to Titan, and scientific data that we are collecting now shall unveil the secrets of the new world. In fact we have got on the ground station data from Huygens long after the touchdown, more than two hours. I must say that we are short of ground stations! The batteries are much more solid than the number of ground stations which can receive the signal. Cassini has just started to deliver the data collected by Huygens, and we might be able to see the results during the night." And this fascinating detail from Emily Lakdawalla's weblog for the Planetary Society: One thing that may have helped the...

Huygens, now on the surface of Titan, has been transmitting data for five hours now, twice the expected time. Signals received by the Parkes Observatory in Australia first confirmed that the probe had survived the landing. It has also been confirmed that at least one experiment -- the Doppler Wind Experiment -- has been successful. Update: Cassini has turned toward Earth and is now transmitting Huygens data, with about forty minutes of preliminaries before the crucial science data are sent. ESA scientists should start looking at the first datasets around 1130 EST. The key question remains: how sound are the data? From John Noble Wilford's story on the New York Times Web site (free registration required): The possibility remains that a design flaw in Cassini's radio receiver system will hopelessly scramble the data. Engineers anticipated that signals from the wind-tossed Huygens would vary widely in frequency and strength, and thus compensated for it in the receiver's design. But they...