Scientists now believe that Deep Impact's 820-pound impactor vaporized deep inside comet Tempel 1's surface when the collision took place on July 4. Moving at 23,000 miles per hour, the impact would have been severe, generating temperatures of several thousand degrees Kelvin, and creating what Dr. Pete Schultz of Brown University calls "...our own incandescent photo flash." Even 50 minutes after Tempel 1 and the impactor collided, the visual effects were still striking, as shown in this spectacular photo from the flyby probe. In the second photograph, taken from the impactor probe, the comet is seen in startling detail. Note the topographical features, which include what may be ancient impact craters and a variety of ridge lines. Clearly, Deep Impact wasn't the first object to hit this comet! Image credit for both photos: NASA/JPL-Caltech/UMD. Meanwhile, x-rays from Tempel 1 have been confirmed by the XMM-Newton space observatory. Previous observations of comets had suggested that...

The Hubble images below (click to enlarge) give an idea of the size of the Deep Impact event. At left is the comet Tempel 1 before the collision. In the middle image, taken 15 minutes after impact, the comet is four times brighter than before and shows a substantially increased cloud of dust and gas. The image at far right was taken over an hour after the collision. Note the fan shape of the ejecta -- the debris, according to this Hubble news release, is pushing outward at about 1800 kilometers per hour. Image: The potato-shaped comet is 14 kilometres wide and 4 kilometres long. Tempel 1's nucleus is too small even for the Hubble telescope to resolve. These visible-light images were taken by the Advanced Camera for Surveys' High Resolution Camera. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA). Data from Deep Impact continue to accumulate. Images taken by ESA's XMM-Newton observatory (an x-ray observatory based in space) show the emissions of hydroxyl ions, the direct...

Deep Impact gave mission scientists what they bargained for -- and more-- when its impactor collided with comet Tempel 1 last night. The collision occurred at 0152 EDT (0652 GMT), with the first image returning at 0157. Calling the impact 'spectacular,' principal investigator Dr. Michael A'Hearn of the University of Maryland, College Park added, ""With this much data we have a long night ahead of us, but that is what we were hoping for. There is so much here it is difficult to know where to begin." Note the use of autonomous navigation aboard the impactor, which was released from the mothership at 0207 EDT (0607 GMT) on the 3rd. On its own, the impactor needed to make three targeting maneuvers as it closed on the comet, the first of these 90 minutes before impact, followed by two more at 35 and 12.5 minutes respectively. The result: a 10 kilometer per second collision with the comet, while the mothership monitored events from nearby, and legions of telescopes followed the action from...

Deep Impact successfully released its 820-pound impactor this morning at 2:07 EDT (0607 GMT), some 880,000 kilometers from the Tempel 1 comet. The Jet Propulsion Laboratory has also reported that six hours before release of the impactor, the spacecraft performed a successful trajectory correction, using a 30-second burn to change Deep Impact's velocity by about one kilometer per hour. Another burn occurred twelve minutes after impactor release, when the flyby spacecraft began a 14-minute burn designed to move it out of the path of the oncoming comet and place it in the best position to observe the impact. Image: One hundred and seventy-one days into its 172-day journey to comet Tempel 1, NASA's Deep Impact spacecraft successfully released its impactor at 2:07 a.m. Sunday, Eastern Daylight Time. This image of Deep Impact's impactor probe was taken by the mission's mother ship, or flyby spacecraft, after the two separated. Image credit: NASA/JPL-Caltech.

No one knows quite what to expect when the Deep Impact probe slams into comet Tempel 1, but countless amateur astronomers plan to be watching to see if the comet brightens following the collision. And it might, given the amount of material that could be dislodged by the event. A telescope or set of binoculars will probably be required, although dedicated skywatchers can still see the spot in the sky where the big event will occur even without the aid of such equipment. The time of impact is 1:52 EDT (0552 GMT) on the morning of July 4, a time when the comet will be best placed for viewing from the American southwest, although Kelly Beatty, executive editor of SKY & TELESCOPE magazine, is now saying that anyone west of the Mississippi has a good chance of seeing it. From a news release just issued by the magazine, here is where to look: After dark, find Jupiter shining high in the southwest. It's the brightest "star" in that part of the sky (brighter Venus sets in the west-northwest...

All the observing time on comet Tempel 1 as the Deep Impact spacecraft approaches is really paying off. Scrutinized by ground and space-based telescopes, the comet was seen to emit a small outburst of materials on June 14. Now Deep Impact has seen a much more massive ejection of ice and other particles that occurred on June 22. Although six times larger than the earlier one, the new outburst dissipated quickly, within about half a day. Intriguingly, the spectrometer aboard Deep Impact showed that the amount of water vapor in the coma doubled during this event, while the amount of other gases, including carbon dioxide, increased even more. From a University of Maryland news release, quoting Michael A'Hearn, who leads the Deep Impact mission: "Outbursts such as this may be a very common phenomenon on many comets, but they are rarely observed in sufficient detail to understand them because it is normally so difficult to obtain enough time on telescopes to discover such phenomena," said...

Here's the Deep Impact target, as seen by the Hubble Space Telescope in a dramatic set of images that show a jet of dust blowing away from the comet's nucleus. At the time the photos were taken -- seven hours apart on June 14 -- Hubble was 120 million kilometers away; the images come from the space observatory's Advanced Camera for Surveys' High Resolution Camera. Tempel 1, it is hoped, will provide an even more spectacular show when Deep Impact reaches it on July 4, releasing an 820 lb. copper impactor that will slam into the comet. The image on the left shows the comet before the new jet formed. In the center of the image, the bright dot is the reflection of light off the comet's nucleus, which is too small at these distances for Hubble to resolve. The nucleus is thought to be about 14 kilometers wide and 4 kilometers long, about as hard to see, according to an ESA press release, "...as someone trying to spot a potato in Stockholm from Madrid." At the right, a bright area in the...

What can you do with a vertical gun range? NASA's Ames Research Center has one, a three story tall machine that fires objects into the surface of your choice. Of late, Brown University professor of geology Peter Schultz has been using it to fire marble-sized beads into surfaces ranging from dust to ice and snow. Moving faster than a speeding bullet -- ten times as fast -- the objects create craters, and craters are something Schultz has made a career studying. As you might imagine, this expertise has caught NASA's eye, and the agency hopes to use Schultz' work to analyze the results of the fireworks set to go off on July 4, when comet Tempel 1 runs headlong into the Deep Impact probe. The professor is one of 13 co-investigators overseeing the mission, which is designed to study what comes out of the comet when the spacecraft's 820-pound copper impactor separates from the mothership and becomes a cometary target. From a Brown University news release: "This is heady stuff," Schultz...

New Horizons, the doughty spacecraft soon to be sent to Pluto, Charon and on into the Kuiper Belt, has been shipped from its birthplace -- the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, MD -- to NASA's Goodard Space Flight Center in nearby Greenbelt. At Goddard, New Horizons will begin another round of pre-launch tests, with liftoff scheduled for next January. What I hear from people associated with this project is that New Horizons is ready to go. As mentioned here earlier, APL's David Dunham gave a talk about upcoming missions at the recent New Trends in Astrodynamics conference in Princeton. I had been concerned about the review process that New Horizons must undergo, required because it carries a radioisotope thermoelectric generator (RTG) that produces energy from fissionable materials. The final environmental impact statement produced by this process is due in the summer, with final NASA decision on the mission in the fall. But when I talked to him at...

By now, our outer Solar System probes have brought us so many surprises that finding yet another one should be passé. But it never is, and imagine the wonders we'll find, for example, when New Horizons arrives at Pluto/Charon and moves on to the Kuiper Belt beyond. Now Cassini has once again made news with the discovery of what may be described as an 'ice volcano.' The beauty of the concept is that it may explain the presence of atmospheric methane on Titan. "Before Cassini-Huygens, the most widely accepted explanation for the presence of methane in Titan's atmosphere was the presence of a methane-rich hydrocarbon ocean," said Dr. Christophe Sotin, distinguished visiting scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. That otherworldly ocean was the most exotic of constructs, creating images of the Huygens lander bobbing about amidst frigid swells as its batteries failed. What the probe parachuted into was quite different. In a way, it's a shame to lose the...

Deep Impact's arrival at Comet Tempel 1 should be spectacular. Due to reach the comet on July 4 of this year, the two-part probe will launch a 360 kg impactor designed to produce a crater on the comet's nucleus and a plume of gas and dust. Getting inside a comet is a key mission goal: the ejected material should tell us much about the early days of the Solar System. Right now astronomers are engaged in making baseline observations through Earth-based telescopes to characterize Tempel 1 as completely as possible. By examining its albedo (reflectivity), rotation period and size, the mission team will be able to differentiate between impact effects and the natural activity of the comet during the Deep Impact encounter. The photograph on the right (click to enlarge) shows an image of Tempel 1 together with a number of visual artifacts. What has happened here is that images were taken through various filters, one after the other. The motion of the comet against background objects accounts...

Huygens' Descent Imager Spectral Radiometer (DISR) team has now produced mosaic images of the probe's descent to Titan's surface. These were created by combining images taken by Huygens as it rotated on its axis, the first image showing the view from approximately 20 kilometers altitude. The photos were taken in groups of three as the probe descended through the atmosphere last January. Image: (click to see enlargement): This stereographic projection of DISR images from ESA's Huygens probe combines 60 images in 31 triplets, projected from a height of 3000 metres above the black 'lakebed' surface. The bright area to the north (top of the image) and west is higher than the rest of the terrain, and covered in dark lines that appear to be drainage channels. Credits: ESA/NASA/JPL/University of Arizona. The stereoscopic image shown above is intriguing because of what appears to be going on in the north and west (top and top left of the image). Be sure to click on the image to see it in...

Titan continues to live up to its billing as a model of the early Earth. Recent observations by Cassini tell us much about the moon's atmosphere, about 98 percent nitrogen (with most of the remainder being methane), and laden with organic molecules. Sunlight appears to break these molecules apart as they rise in the atmosphere, where their fragments form heavier organic molecules -- propane, ethane, acetylene, hydrogen cyanide. Cold air over the winter pole then causes this material to sink, with the result that heavy organics build up in the stratosphere over the course of the winter. Supplying the data is Cassini's Composite Infrared Spectrometer instrument (CIRS); a paper on its findings is scheduled to appear in the May 13 issue of Science. The polar vortex phenomenon is similar to what occurs on Earth; strong winds circulating around Titan's north pole isolate the atmosphere over the pole during the polar night, inhibiting mixing with the lower regions of the atmosphere....

The Kuiper Belt yields up its secrets grudgingly, but sometimes we get help from objects much closer to the Sun. Cassini's flyby of Saturn's moon Phoebe on June 11, 2004 has provided all the information scientists needed to declare the ancient object a relic from the outer Solar System, much like Pluto and other Kuiper Belt members. Two papers in Nature provide our best look yet at Phoebe. Determining a planetary object's origin isn't easy, but Phoebe can be analyzed in terms of its density, which is calculated on the basis of the moon's mass studied in relation to volume estimates from the Cassini images. The resulting figure is 1.6 grams per cubic centimeter, lighter than most rocks but heavier than pure ice, and suggesting an ice/rock composition similar to Pluto and Neptune's moon Triton. "Cassini is showing us that Phoebe is quite different from Saturn's other icy satellites, not just in its orbit but in the relative proportions of rock and ice. It resembles Pluto in this regard...

Scientists anticipated that Titan would be a model laboratory for studying the organic chemistry that eventually led to life on the primitive Earth. So the discovery of complex mixtures of hydrocarbons and carbon-nitrogen compounds came as no surprise. What was unusual was where they found them: in Titan's upper atmosphere. Organic materials were expected on Titan because nitrogen and methane, the two primary components of its atmosphere, should form complex hydrocarbons when exposed to sunlight or energetic particle radiation from Saturn's magnetosphere. But the frigid temperatures on the Saturnian moon led most researchers to believe such hydrocarbons would condense and eventually wind up on the moon's surface. Instead, Cassini's ion and neutral mass spectrometer helped them find hydrocarbons galore in Titan's outer atmosphere. Image: This natural color composite (taken during the April 16 flyby) shows approximately what Titan would look like to the human eye: a hazy orange globe...

The mystery of Sedna's spin seems to be solved. The enigmatic Kuiper Belt object whose orbit reaches as far as 500 AU from the Sun (and as close as 80) appeared to have an unusually slow rotation rate when first observed. Some astronomers speculated that an unseen moon could be the cause, even though the best Hubble images showed no such object. It has taken a set of new measurements by Scott Gaudi, Krzysztof Stanek and colleagues at the Harvard-Smithsonian Center for Astrophysics (CfA) to solve the mystery. Sedna's rotation period isn't the previously thought 20 days, but ten hours, which is consistent with other planetoids in the Solar System. The need for the missing moon has vanished. Not that Sedna doesn't remain unusual. In addition to its highly elliptical orbit, the planetoid is one of the largest Kuiper Belt objects known, three-quarters the size of Pluto, or about 1,000 miles across. Another oddity: Sedna's ruddy color, which remains unexplained. Image: CfA astronomer Scott...