[meteorite-list] Latest Titan Pictures Show Details of Geography

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Jan 19 20:08:01 2005
Message-ID: <200501200107.RAA06757_at_zagami.jpl.nasa.gov>

http://www.nature.com/news/2005/050117/full/050117-5.html

Latest Titan pictures show details of geography
Mark Peplow
www.nature.com
January 18, 2005

More images from Titan have confirmed scientists' expectations that a
complicated cycle of weather is shaping the surface of Saturn's largest
moon.

"It looks as if there are rivers, cliffs, lakes and clouds," says Tony
McDonnell, part of the Huygens probe's surface-science team from the
Open University, Milton Keynes, UK. "It's the full range of geography."

The pictures show terrain that is covered with sinuous drainage channels
winding around a range of hills towards a dark area that looks like an
ocean.

The interpretation of these pictures should be obvious to anyone who has
seen an aerial view of Earth, says Peter Smith from the University of
Arizona, Tucson, who helped to develop Huygens' descent imaging system.
"We see the same features every time we fly over a coastline."

"There's no evidence yet of liquid in these rivers, they look more like
Arizona's dried-up river beds," Smith adds. "But those canyons didn't
carve themselves."

The surface rubble snapped by Huygens also bears the marks of flowing
liquid hydrocarbons such as methane and ethane: "They're very smooth,
there's definitely some fluvial process that shaped them," says Andrew
Ball, another member of the Open University team.

Scientists had speculated that Titan could be a cold analogue for
conditions on the primordial Earth, and these early discoveries bear
that out, says McDonnell.

"There's no evidence for life," he cautions. "But we do see all three
phases of matter, and transport mechanisms between them: evaporation,
clouds, rain and rivers. This provides the opportunity for the
development of complex organic molecules."

Fresh surface

Titan's surface also seems to be remarkably fresh. Counting the number
of craters on a moon and comparing it with the number of meteoroids in
the area gives astronomers a way to calculate the age of a moon's
surface. The younger the crust, the fewer craters are visible.

"One thing's for sure: Titan's not cratered. I haven't seen a single
one," says Smith.

Unlike the other moons in the Solar System, Titan has a thick
atmosphere, so smaller meteors may burn up before they hit the ground.
This makes it more difficult to estimate the age of the surface, but
"it's probably less than 10 million years old", Smith says.

"In some areas, the surface is very bright," he adds. This suggests that
liquids wash dark tars from the icy surface quite regularly. This might
be a sign of methane rain.

Smith is now piecing together images taken in the last kilometre above
the landing site, which was illuminated by a lamp on the bottom of the
probe.

Big bang

In the meantime, McDonnell has been studying results from Huygens'
impact sensors. "It had quite a big bang, hitting the surface at about
3.5 metres per second," he says. That's equivalent to 12.6 kilometres
per hour.

The probe has made a dent in Titan's surface that is a few centimetres
deep. The soil seems to be made up of grains of water ice glued together
by sticky hydrocarbons such as methane, giving it the consistency of
putty, says McDonnell.

Huygens hit the ground just 8? from vertical, suggesting that winds were
not strong enough to blow it around much. The mosaic image released
today confirms this. Because Huygens' on-board camera was looking down
at a slight angle, it took pictures of the ground beneath looking in all
directions as the falling probe spun round. But it was not able to see
directly downwards.

If the probe had been drifting during its descent this wouldn't have
mattered, but the dark patch in the centre of the mosaic means that the
probe must have remained over the same area of ground as it fell.

Smith admits he was surprised that Huygens survived its crash landing.
"We had more than an hour of extra data from the surface, and that's a
wonderful addition," Smith says. "Thank God the parachute didn't fall on
top of the probe."

Mission scientists expect to release more details on 21 January. A
series of scientific meetings over the next two months will allow the
different teams to compare their data to get a better understanding of
Titan's geography.
Received on Wed 19 Jan 2005 08:07:49 PM PST