Titan has been in the news quite a bit recently for its
relevance to astrobiology research. But why all the
attention? This week, Astrobiology Features takes a closer
look that this frigid, haze-covered world.

Conditions on Titan

Long hailed as a natural astrobiology laboratory, Saturn’s
largest moon Titan is certainly on the minds of many
scientists today. This moon is the second largest in the
solar system (Jupiter’s Ganymede is the largest); its
diameter is about 3200 miles (larger than the planet
Mercury), or approximately the distance across the United
States. Titan is interesting because it is unique: it is the only
moon in the solar system known to have a thick
atmosphere. The composition of the atmosphere is largely
nitrogen (about 90%). By comparison, Earth’s atmosphere
has a nitrogen content of about 78%. There are also
smaller amounts of ethane and methane in Titan’s
atmosphere; these molecules are created when energetic
ultraviolet light from the sun reacts with gasses (e.g.
ammonia) released from its interior. Due to the very cold
temperatures (about -290 degrees Fahrenheit!), scientists
believe that these molecules could exist in liquid form and
could thus drizzle out of the atmosphere onto the surface,
creating perhaps large lakes of methane and ethane.

Since Titan is so cold, it is devoid of the liquid water that
makes life possible here. Thus, scientists skeptical that we
will find life there, but they are just the same optimistic
about learning more about the pre-biotic chemistry that
might have occurred on our own planet. Titan can be
regarded as a time machine: it will allow researchers to
study the photochemistry and chemical reactions that were
possibly taking place on early Earth.

Early Observations

Titan was first discovered by Christian Huygens in 1655,
and since that time, scientists have learned about its
composition and structure from measurements at a
distance. Ground based observations, coupled with
measurements from Voyager and the Hubble Space
Telescope, have already told us something about the
nature of this moon. Scientists are confident of our
knowledge about some aspects of Titan, such as its size
and average density. However, they are less certain about
the exact nature of the surface underneath the hazy
shroud. The thick atmosphere (about 1.5 times the
pressure of Earth’s) precluded any direct images of the
surface during the Voyager mission, although subsequent
infrared imaging by the Hubble revealed lighter and darker
areas on the moon.

Getting a Closer Look

Although there is still much that scientists don’t know
about Titan, many of the outstanding questions may soon
become in reach. The Huygens Probe, an integral part of
the Cassini mission to Saturn, will plunge through Titan’s
atmosphere early in 2005. Even though it took a
seven-year voyage while piggybacked on the Cassini
orbiter, it will only have a functional lifetime of about three
hours. During this time, the probe will be very busy
simultaneously collecting aerosols for chemical analyses,
making spectral measurements, and measuring physical
and electrical properties of the atmosphere. But before and
after the demise of the probe, the Cassini orbiter will
undertake several close fly-bys of the moon. With onboard
radar and various spectrometers, the orbiter will give
insights about the moon from a more global perspective.
Some of the astrobiology-related science objectives for
the Cassini-Huygens mission include:

–Determine the relative amounts of different components
of the atmosphere.
–Observe vertical and horizontal distributions of trace
gases; search for complex molecules; investigate energy
sources for atmospheric chemistry; study formation and
composition of aerosols .
–Determine the physical state, topography, and
composition of Titan’s surface; characterize its internal
structure.
(taken from the JPL Cassini-Huygens webpage)

NAI’s Role

Both during and after Cassini-Huygens, scientists will be
pouring over the data from the mission. Many of these
scientists will be also involved with the NASA
Astrobiology Institute’s Titan Focus Group, a collection of
about 30 members from all over the country. This group,
chaired by Jonathan Lunine of the University of Arizona,
will have a functional lifetime of about three years. The
Titan Focus Group’s core objective is to “ensure the
conceptualization and initial study of appropriate
techniques for advanced organic analysis on Titan, after
Cassini-Huygens.” The members are especially interested
in helping to shape future requirements for subsequent
Titan surface missions.

Many important questions remain about Titan and what it
can tell us about pre-biotic chemistry that occurred during
early Earth evolution. It will take a close-up look and
collaborations from several different scientists to
effectively answer them. You can learn more about the
mission and actively monitor the updates at JPL’s
Cassini-Huygens’ homepage: http://saturn.jpl.nasa.gov

Ariane Flight 157 November 29: A rapid rescheduling for liftoff of the “10-ton Ariane 5”

The launch of Arianespace’s first “10-ton” Ariane 5 will be rescheduled
following yesterday’s postponement that resulted from a ground-related
anomaly.

Arianespace Chief Executive Officer Jean-Yves Le Gall said the launch will
be pushed back by a few days from the original November 28 target, with the
new date to be announced early next week.

Le Gall said the anomaly was related to data from operation of external
pyrotechnic igniters that are mounted on the Ariane 5’s launch table. These
devices are used to burn off the accumulation of hydrogen that is used to
chill down the launcher’s Vulcain 2 cryogenic main engine before it begins
operation.

Speaking to reporters at a Spaceport briefing this morning, Le Gall said
the launch table-mounted igniters functioned after being commanded by the
automated countdown sequence. This command was given at 6.8 seconds before
the Vulcain main engine was to have started.

However, data confirming the igniters’ proper operation was not received by
the automated ground control system – and the countdown was automatically
halted at 3 seconds prior to the Vulcain engine’s startup.

Le Gall stressed the anomaly that interrupted Flight 157 countdown was not
related to the Ariane 5 launcher itself, and added that the automated ground
control system worked perfectly – preventing the Ariane 5’s main engine from
starting when a data problem occurred.

The launch vehicle and its dual satellite payload immediately were placed in
a safe mode on the pad at the Spaceport’s ELA-3 launch complex.

Operations are now underway to drain and purge cryogenic propellants from
Ariane 5’s main stage and the ESC-A upper stage. Once completed, the Ariane
5 will be rolled back to the final assembly building Saturday morning –
where it will be reconfigured for launch.

Le Gall said Arianespace still plans to conduct the two remaining missions
scheduled before year-end: Flight 157 in the coming days with its HOT BIRDTM
7 and Stentor satellite payloads; and Flight 165, which will use an Ariane 4
to loft the NSS-6 telecommunications platform for New Skies Satellites N.V.