* Astronomy

Images from the European Space Agency's Huygens probe descent imager/spectral radiometer side-looking imager and from the medium resolution imager, acquired after landing, were merged to produce this image.



The horizon's position implies a pitch of the imager/spectral radiometer, nose-upward, by 1 to 2 degrees with no measurable roll. "Stones" in the foreground are 10 to 15 centimetres in size, presumably made of water ice, and these lie on a darker, finer-grained substrate. A region with a relatively low number of rocks lies between clusters of rocks in the foreground and the background and matches the general orientation of channel-like features in the panorama of the previous image. The scene evokes the possibility of a dry lakebed.

Images recorded by the European Space Agency's Huygens probe descent imager/spectral radiometer between 17 and 8 kilometres were assembled to produce this panoramic mosaic. The probe ground track is indicated as points in white.


Expand (181kb, 1541 x 1571)

North is up. Narrow dark linear markings, interpreted as channels, cut through the brighter terrain. The complex channel network implies precipitation (likely as methane "rain") and possibly springs.

Cassini/Huygens scientists have discovered exactly where on Saturn's largest moon, Titan, the European Space Agency's (ESA) Huygens probe landed last January.

Expressed in Titan longitude and latitude, the Huygens probe landed within about 5 kilometres of 192.4 degrees west longitude (or 167.6 degrees east longitude) and minus 10.2 degrees south latitude. That's a mere 7 kilometres away from where Cassini/Huygens scientists predicted the probe would land.


Expand (2.6Mb, 3000 x 3000)

"It's important that we know from an orbital perspective what kind of terrain the Huygens probe landed in. It allows us to connect what Huygens found in detail about a small patch of Titan's surface to what the orbiter is accumulating now. We had a pretty good notion of what the landing site was before, but connecting it with the radar data allowed us to use the magnificent, absolute knowledge of the location transferred through the Cassini orbiter" - Bashar Rizk, University of Arizona Lunar and Planetary Laboratory .

Overall, the entire set of Descent Imager-Spectral Radiometer (DISR) observations from 150 kilometres high in Titan's atmosphere through landing outlines the major role methane plays in shaping Titan's surface and controlling its meteorology.
DISR was enveloped in thick haze as soon as it began taking data at 150 kilometres altitude, and the haze reaches undiminished all the way to the surface. The haze was so thick that DISR's three different cameras began discerning surface features only at about 55 kilometres altitude.

Landing site animation! (~300Mb, .Avi)

DISR scientists used the different camera views to reconstruct the probe's descent trajectory and measure wind velocities. At 50 kilometres high , 90 kph winds swept the probe eastward. But at about 7 kilometres altitude, windspeed dropped to less than 3kph and the winds changed direction. This may be a convective region where local winds disconnect from Titan's main jet-streams.

At 700 meters altitude, DISR turned on a landing lamp so spectrometers could analyse light reflected from the near-surface atmosphere and the surface itself. The spectrometers measured five percent methane in Titan's mostly nitrogen atmosphere at 20 meters altitude.
That's three times more methane than in Titan's stratosphere and confirms that methane is condensing near Titan's surface.
The team had planned to measure light reflected from Titan's surface to learn just what that surface is made of. The dark, frigid surface would look reddish to the human eye. It reflected no more than 15 percent to 20 percent at infrared (longer-than-visible) light wavelengths. Light reflected from Titan's surface showed there are organic materials (carbon-and-hydrogen containing compounds) and water ice, but also water ice laced with an unknown constituent.
Scientists will have to further analyse DISR data and organic materials manufactured in the laboratory to identify the unknown constituent.

But it's the DISR images of Titan's striking landscape that have thrilled millions of people worldwide. When DISR scientists assembled the descent images into panoramic mosaics, they saw bright, high terrain cut by deep channels and flat, darker, lower terrain that resembled a dried lakebed. It is Earth-like desert topography clearly marked by fluid flow.


Zoom view

There appear to be two types of channel networks. Steeply sloped main drainage channels from 100 to 200 meters wide and 50 to 100 meters deep branch through the bright highlands. They are believed to have been cut by rapidly flowing rivers of liquid methane. A second type are the short, stubby channels that often begin - or end - in dark circular areas. They are thought to be spring-fed channels.

One of DISR's most memorable images is the well-known view from Titan's surface taken after landing. Fifteen-centimetre rounded water-ice cobbles lie scattered over a darker, fine-grained "ice gravel."
It's more evidence for powerful erosion by flowing liquid.

Read More

This map of Saturn's moon Titan shows the location mapped with the Cassini radar mapper using its synthetic aperture radar imaging mode during the October 28, 2005, flyby.


Expand (63kb, 1051 x 972)

The radar swath is superimposed on a false-colour image made from observations by NASA's Hubble Space Telescope. The location of the Huygens landing site is marked in red on the far right. The overlap between the Huygens data and the radar data will give new clues to the nature of the surface seen by the Huygens probe, which landed on Titan in January 2005.

The October 28 swath is about 6,150 kilometres long, extending from 7 degrees north to 18 degrees south latitude and 179 degrees west to 320 degrees west longitude. The spatial resolution of the radar images ranges from about 300 meters per pixel to about 1.5 kilometres per pixel.

Cassini's four radar passes revealed a variety of geologic features, including impact craters, wind-blown deposits, channels and cryovolcanic features.