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...

The Green Bank radio telescope in West Virginia has picked up the Huygens carrier signal, which should have been activated after the opening of the main chute and the dropping of the heat shield. The signal carries no data other than this: Huygens made it through the entry into Titan's atmosphere. We should have data available by 1310 EST, routed from Huygens through Cassini. From an ESA press release: What the Green Bank radio telescope has detected is only a 'carrier' signal. It indicates that the back cover of Huygens must have been ejected, the main parachute must have been deployed and that the probe has begun to transmit, in other words, the probe is 'alive'. This, however, still does not mean that any data have been acquired, nor that they have been received by Cassini. The carrier signal is sent continuously throughout the descent and as such does not contain any scientific data. It is similar to the tone signal heard in a telephone handset once the latter is picked up. Says...

The Planetary Society's Emily Lakdawalla is covering Huygens events from Darmstadt here. From her latest post: Another item that was news to me came from Marty Tomasko, the University of Arizona researcher who heads the Descent Imager Spectral Radiometer team (that's the main camera on Huygens). His last images are expected to come from about 150 meters off the ground. But, if Huygens survives the landing, DISR could still take pictures. What's cool about that is if Huygens lands in a liquid, it would be taking pictures through that liquid, seeing what's suspended in it. But I've been taking an informal poll of the science team to find out what they think they will land on, and no one has predicted liquid. The predictions range from "icy" to "squelchy" (the latter is how Surface Science Package investigator John Zarnecki described it ). After a few of these questions during the press briefing, Tomasko finally said, "This is probably not the best day to speculate. Probably you should...