The Huygens probe will usher in 2005 with its landmark mission at Titan. After a seven-year journey strapped to the side of the Cassini Orbiter,
Huygens will be set free on Dec. 25, 2004. The Probe will coast for 21 days en route to Titan.
Huygens will be the first spaceprobe to land on a world in the outer Solar System. It will land on the surface of Titan, Saturn's largest moon, and
the only moon in the Solar System to possess a thick atmosphere.
Descent Through Titan's Atmosphere
Huygens will make a parachute-assisted descent through Titan's atmosphere, collecting data as the parachutes slow the probe from super sonic speeds.
Five batteries onboard the probe are sized for a Huygens mission duration of 153 minutes, corresponding to a maximum descent time of 2.5 hours plus at
least 3 additional minutes (and possibly a half hour or more) on Titan's surface. These batteries are capable of generating 1800 Watt-hours of
Huygens's investigations may reveal how life began on Earth. Jean-Pierre Lebreton, ESA's Project Scientist for Huygens says, "One of the key
questions we hope to address is how complex the organic molecules have grown in Titan's atmosphere."
However, organic molecules are still a long way from life itself. So, what defines life? What is the difference between the living and the non-living?
Scientists are still unsure. No satisfactory definition has been found so far. Any attempt to define life's characteristics either excludes some
types of life or includes some inanimate objects. When looking for an appropriate definition of life, there is one property all scientists seem to
agree on: all life needs energy to sustain its metabolism. For example, plants use sunlight, while animals extract energy from organic molecules in
the food they eat. This happens not only in these higher-level organisms, but also in the simplest forms of life on Earth, microbes. Microbes are
single-cell organisms that capture their life-energy from a dizzying array of inorganic chemical reactions. Such chemical metabolisms are so different
from those in the animals and plants of Earth, that astrobiologists now wonder if life could arise in any place that can sustain a rich network of
chemical reactions, such as on Titan.
NASA's Voyager 1 provided the first detailed images of Titan in 1980. They showed only an opaque, orange atmosphere, apparently homogeneus. It was so
thick that you could not see the surface. However, other data revealed exciting things. Similarly to Earth, Titan's atmosphere is mostly nitrogen but
there is also methane and many other organic compounds.
Organic compounds form when sunlight destroys the methane. If sunlight is continuously destroying methane, how is methane getting into the atmosphere?
On Earth today, it is life itself that refreshes the methane supply. Methane is a by-product of the metabolism of many organisms. Could this mean
there is life on Titan?
Titan is not a pleasant place for life. It is far too cold for liquid water to exist, and all known forms of life need liquid water. Titan's surface
is -180?C. According to one exotic theory, long ago, the impact of a meteorite, for example, might have provided enough heat to liquify water for
perhaps a few hundred or thousand years. However, it is unlikely that Titan is a site for life today. Jean-Pierre Lebreton, Huygens Project Scientist,
is puzzled by the amount of methane that persists in Titan's atmosphere. Could there be oceans of methane on or under the surface?
Solid landing or ocean landing?
Over the years, scientists have dramatically changed their minds about Titan's surface. In the mid-nineties, the NASA-ESA Hubble Space Telescope
spied an area on Titan that was brighter than the rest. More recent observations show the same feature better. What are these bright and dark patches?
Lebreton wonders if, "the bright area could be a continent and the rest oceans. We don't know yet. There is no doubt, though, that the surface
appears very diverse, not uniform. There are a lot of surprises waiting for us there."
Where will Huygens land? On the bright patch or on a dark one? "Closer to the bright surface, but not on it," answers Lebreton. "Just imagine! We
could be landing in an ocean! It would be really exciting, the first landing in an ocean outside the Earth!" To land on an ocean would probably mean
better data from Huygens. Even if the probe lasted only a few minutes before sinking, it would at least stay in an upright position. Being the right
way up is essential for sending the data back to the Cassini orbiter and to the scientists on Earth. Moreover, some of Huygens's instruments are
better prepared to analyse liquids. If Huygens lands on a solid surface instead, there is a higher risk of falling in the wrong direction and not
being able to easily communicate with Cassini.
What do you guys think about this mission? I think the most interesting find would be organic compounds. They are formed when sunlight destroys the
methane. If there are organic compound on Titan, what is replenishing the methane? Here on Earth it is life itself that replenishes it. Any
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