Huygens's second landing anniversary -- the surprises continue(Forwarded)

ESA News
http://www.esa.int

12 January 2007

Huygens's second landing anniversary -- the surprises continue

Two years ago, planetary scientists across the world watched as Europe and
the US did something amazing. The Huygens descent module drifted down
through the hazy atmosphere of Saturn's moon Titan, beaming its data back
to Earth via the Cassini mothership. Today, Huygens's data are still
continuing to surprise researchers.

Titan holds a unique place in the Solar System. It is the only moon
covered in a significant atmosphere. The atmosphere has long intrigued
scientists as it may be similar to that of the early Earth but the deeper
mystery was: what lies beneath the haze?

The European Space Agency built the Huygens spacecraft to find out. The
probe, carrying scientific investigations involving both sides of the
Atlantic, hitched a ride on NASA's Cassini spacecraft. Together Cassini
and Huygens make an unprecedented joint space mission -- as a major
milestone, Huygens parachuted to the surface of Titan on 14 January 2005.

While Cassini keeps flying by this moon of Saturn collecting new amazing
data, one can say that the data collected by Huygens's six instruments
during its 2.5-hour descent and touch-down have provided the most
spectacular view of this world yet and first dramatic change in the way we
now think about it.

"When you put all the data together, we get a very rich picture of Titan,"
says Athéna Coustenis, Observatoire de Paris, France, "The Descent
Imager/Spectral Radiometer (DISR) pictures were an enormous surprise. We
had expected a much smoother landscape." Instead, they saw a varied
landscape of channels that had been formed by some kind of flowing liquid.

"At the landing site we also saw rounded ice pebbles," says Jonathan
Lunine, University of Arizona. The Surface Science Package (SSP) provided
the final piece in this particular puzzle. The impact it detected when
Huygens touched down indicated that the spacecraft had come to rest in
compacted gravel. "Put it all together and it is clear that Huygens landed
in an outflow wash," says Lunine.

The Gas Chromatograph and Mass Spectrometer (GCMS) instrument confirmed
the nature of the liquid that shapes the surface of Titan. It detected
methane evaporating from the Huygens landing site. "Methane on Titan plays
the role that water plays on Earth," concludes Lunine. But there are still
mysteries. It is not yet clear whether the methane falls mostly as a
steady drizzle or as an occasional deluge.

The GCMS also detected two isotopes of argon. Both have important stories
to tell. The Ar40 indicates that the interior of Titan is still active.
This is unusual in a moon and indicates that perhaps an insulating layer
of water ice and methane is buried in the moon itself, close to the
surface, trapping the heat inside it. Occasionally, this heat causes the
so-called cryo-volcanoes to erupt. Icy 'lava' flows from these
cryo-volcanoes have been seen from the orbiting Cassini spacecraft.
Because Ar40 is so heavy, it is mostly concentrated towards the base of
the atmosphere, so having Huygens on the surface was essential for its
detection.

Daniel Gautier, Observatoire de Paris, France, thinks that the other
isotope, Ar36, is telling scientists that Titan formed after Saturn, at a
time when the primeval gas cloud that became the Solar System had cooled
to about 40 K (-233 C).

The atmosphere of Titan held surprises too. "Huygens made a fantastic and
unexpected discovery about the wind," says Gautier. At an altitude of
around 60 kilometres, the wind speed dropped, essentially to zero.
Explaining this behaviour presents a challenge for theoreticians who are
developing computer models of the moon's atmospheric circulation.

The Huygens Atmosphere Structure Instrument (HASI) provided the
temperature of the atmosphere from 1600 kilometres altitude down to the
surface. "This has helped put all the other data into context," says
Coustenis. Huygens measured the composition profile of the atmosphere to
be a mixture of nitrogen, methane and ethane. The methane and ethane
provide humidity, as water does in Earth's atmosphere. At the surface of
Titan, Huygens measured the temperature to be 94 K (-179 C) with a
humidity of 45 percent.

Even though the Huygens data set is now two years old, the discoveries
have not yet stopped. "There are lots of surprises still to come from this
data," says Francesca Ferri, Università degli Studi di Padova. In
addition, Huygens gives planetary scientists a wealth of 'ground-truth' to
complement and help interpret the observations still coming from Cassini.
At the beginning of 2007, Cassini showed that liquid methane is present on
Titan in lakes.

Cassini, whose experiments also see a joint US and European participation,
will make another 22 fly-bys of Titan -- the first on 13 January --
between now and the end of its scheduled mission in the summer of 2008.
The Cassini-Huygens scientists are discussing their options to extend the
mission. One idea, says Christophe Sotin, Université de Nantes, France,
would be to use Cassini to study the newly discovered lakes.

Huygens has exceeded expectations and shown Titan to be an 'alien earth',
giving planetary scientists a new world of fascination to explore.

Note to editors:

Cassini-Huygens is a project of international collaboration between NASA,
ESA and ASI.

For more information:

Jean-Pierre Lebreton, ESA Huygens Project Scientist
Email : jean-pierre.lebreton @ esa.int

[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEM7QJRMTWE_index_1.html ]

More about ...

* At Saturn and Titan
http://www.esa.int/SPECIALS/Cassini-Huygens/index.html
* More on Cassini-Huygens spacecraft
http://sci.esa.int/science-e/www/obj...objectid=35026

Related articles

* Titan has liquid lakes!
http://www.esa.int/esaSC/SEMXJIRMTWE_index_0.html
* Tallest mountains ever seen on Titan imaged by Cassini
http://www.esa.int/esaSC/SEMAJIZTIVE_index_0.html
* Vast polar ethane cloud observed on Titan's north pole
http://www.esa.int/esaSC/SEMCI08LURE_index_0.html
* Huygens Scientific Archive data set released
http://www.esa.int/esaCP/SEM8TYIZBQE_index_0.html
* How the world watched Huygens
http://www.esa.int/esaCP/SEMJ83EQMPE_index_0.html
* Titan's pebbles 'seen' by Huygens radio
http://www.esa.int/esaCP/SEM23SVT0PE_index_0.html
* Cassini's radar spots 'Great Lakes' on Titan
http://www.esa.int/esaCP/SEMR8OBUQPE_index_0.html
* Landing on Titan -- the new movies
http://www.esa.int/esaSC/SEMKVQOFGLE_index_0.html
* Movie of Titan's surface in the infrared
http://www.esa.int/esaSC/SEMLMXLVGJE_index_0.html
* A simulated view from Huygens
http://www.esa.int/esaSC/SEMA7UMZCIE_index_0.html

Related links

* Titan lakes -- JPL podcast
http://www.jpl.nasa.gov/multimedia/p...sini-20070103/
* ESA Planetary Science archive (PSA)
http://www.rssd.esa.int/PSA
* Cassini-Huygens at JPL
http://saturn.jpl.nasa.gov/home/index.cfm
* Cassini-Huygens at NASA
http://www.nasa.gov/cassini
* Italian Space Agency (ASI)
http://www.asi.it