by Michael Hammerschlag
Early Friday (Jan 14) morning (4:50am EST),
the last grand space mission –the 11 year
$3 billion Cassini mission to Saturn, dropped
a landing probe into the most earthlike atmosphere
in the Solar System, the heavy clouds of
massive moon Titan. Titan is, with Ganymede,
the largest moon in the solar system*- at
3200 mi. diameter, bigger than planets Mercury
or Pluto, and possessed with an amazing primeval
blanket of supercooled air- 94+ % nitrogen
(Earth is 79%), 2-6% methane, and the remainder
a dirty orange smog of complex organics.
Though having only 1/7th
the gravity of Earth, Titan’s atmosphere is 1.5 times Earth’s pressure
at the surface (equal to 20ft underwater) and 4½ times as dense, and extends out 120 miles
(compared to Earth’s 30 miles). But unlike
Earth, the distant frigid world, which gets
only 1% of the sunlight of Earth, is a bone
chilling –178C (-290F, 95K), where the methane and ethane would be liquid, and very close to solid- leading
to speculation
of lakes, oceans, and volcanoes
of methane or ethane. Although radar pics of the
surface from the flybys of Cassini don’t seem to
show any such thing- they’ve only shot a
small portion of the surface. The only other
solid body in the solar system with an appreciable
atmosphere, Venus, has sulfuric acid clouds
in CO2 at 100 times Earth's pressure and hellish
700° temperatures.
Although the extreme cold would prevent life,
liquid organics react much better than gases
or solids, which are too unconcentrated or
immobile, so Titan is an organic cauldron
with compounds and gases thought to be similar
to the dawn life on Earth- 4 billion years
ago. And it is an ice world: much of the
moon is believed to be composed of a 50/50
(water) ice/rock mixture- the density is
only 1.88 times that of water (Earth is 5.5,
surface rocks about 2.8, and gas giant Saturn
is only .7 and would float in water), so
there may be liquid water at depths to combine
the complex snow of organic compounds into
amino acids and proteins.. the building blocks
of DNA. “Methane is irreversibly destroyed
by solar UV radia
tion at high altitudes in 50 million years,”
says Johns Hopkins Univ. Cassini-Huygens
scientist Darrell Strobel from Darmstadt,
Germany, the European Space Agency’s Operation
Center. (They built the Huygens) “If this
process continued over the age of the solar
system, that’s enough to create 200-300 meters
(layer) of complex hydrocarbons (on the surface).”
Cassini scientists have found diacetylene
and benzene hundreds of miles out in the
atmosphere, amazing for such large molecules,
and can see high white cirrus like clouds.
Titan keeps one side locked to its magnificent
master Saturn and its spectacular rings (which
is now the closest it gets to Earth-visible
all night at opposition) and whips around
it in 16 days at about 3 times the distance
that the Moon is from Earth.
The discus shaped 9 ft. 700lb. shell of the Huygens probe, released Christmas Eve, will slam into the Titanic atmosphere at about 13,500mph (3¾ miles a second) at about 170 miles altitude, heat to 2700 degrees on the shuttle-like ceramic tiles, and violently slow (14G deceleration) to about 900 mph at 90 miles up, where a little 8ft parachute yanks off the top half of the discus and deploys a 27ft parachute. “Titan's atmosphere is much more extended (4 times farther for equivalent pressure) than Earth’s because of the low gravity,” says Strobel. At 65 miles, that parachute is cut away and a smaller 10ft parachute deploys, so that the lithium batteries won’t be used up in the 2 hour 20min drop to the surface. A gas chromatograph, and spectrometer will heat and analyze the atmospheric gases at many altitudes and cameras will madly blast away at the surface. 35 Plutonium pellet heaters keep the craft from freezing blind in the bitter alien skies, and Doppler-shift radio analysis may determine winds [over 310mph measured!] and rocking (inc. of a liquid landing). Radar and acoustic receptors will measure the distance to the surface, the speed of sound, the roughness and constitution of the surface (and depth?). clouds of Titan fm 750 mi Nov '04
Just above the
surface brilliant lights are turned on for the spectrograph and cameras, as the
discus crunches onto the surface at 12 ft/sec (15mph), blasting up data to the
mother ship. The heated gas trap will vaporize the solid or liquid surface and
analyze it with the
spectrometer/chromatograph. The JPL/ESA scientists dream it might land
in a methane and/or ethane lake (it floats),
but admit that would quickly freeze it and
damage components; hopefully many sensors
would first measure the density, temperature,
waves, electrical, optical, acoustic, and
thermal characteristics. Even if it works
perfectly, the surface life is only expected
to be 2¼ hours [lasted longer], when Cassini, about
40,000 miles away, will disappear over the
Titanic horizon; but Cassini will make over
40 more passes by it, as close as 590 miles.
The 6.3 ton (with fuel) Cassini, launched
in 1997, only could reach Saturn by using
convoluted gravity assists- twice from Venus,
once from earth, and once from Jupiter; so
it had to be built to take the furnace heat
inside Venus’s orbit as well as the billion
mile cold of Saturn. At the time, I thought
it
was very risky- they shielded it from the sun by hiding
behind the dish antenna (the Galileo main
dish was crippled on its Jupiter mission).
Arriving at Saturn on June 30th, Cassini
had to twice pass through the hazardous bands
of ice and rock in the rings. Everything
has gone tremendously well: on New Years
Day, they flew by the bizarre moon of Iapetus,
one fourth of which looks like it is covered
with shiny asphalt, the rest light. The mission
should function till at least 2008, with
69 fly bys of the moons, and extensive photography
and analysis of Saturn’s moons, clouds, gases,
winds, magnetic fields, and unique rings;
and help to understand the dawn of life. Radar image of Titan surface fm Cassini
Started in 1983- this is the culmination
of a quarter century effort for the cheering
scientists in Darmstadt and Pasadena.
Jan 14 11:30pm The first Huygens picture from 16 km (~10mi)
shows channels that they claim are rivers,
but to me it looks like it could be the tops
of clouds. Incredible, the pic of rocks-
ah, to see the lap of a methane sea, but
surprising how much one rockfield looks like
any other (Mars). The 5 mile high shot shows
a jumble with what looks like patches of liquid. They lost one radio
channel from the Huygens, but every bit of
data was recieved from the other- with the
8 time redundant transmission, into the twin
2.2 gig hard drives on the Cassini- top of
the line in 1996.
moon Iapetus 888 mi. diameter
Michael Hammerschlag has written articles about the Voyager missions to the Outer planets, the SETI project, and worked as a chemist and on the Subaru telescope on the summit of Mauna Kea, Hawaii, the biggest astronomical complex on Earth.
Titan PICS from Cassini: http://saturn.jpl.nasa.gov/news/events/titana/index.cfm
TITAN Facts: http://kvtr.elte.hu/tnp/nineplanets/titan.html
Big JPL Press Release: http://saturn.jpl.nasa.gov/news/press-kits/cassini-arrival.pdf
Huygens Instruments: http://saturn.jpl.nasa.gov/spacecraft/instruments-huygens.cfm
European Space Agency- Huygens: http://www.esa.int/SPECIALS/Cassini-Huygens/index.html
State of Space ’97: http://members.surfbest.net/mikehammer/mhmir2.htm Mir problems, Cassini launch and foretold
Mars missions failures and shuttle disaster
*for a long time they thought Titan was the
biggest, which it is, if you include atmosphere,
but Ganymede has a 69mi. bigger diameter. As far as I'm concerned Titan is still Titanic. composite panorama of surface as landing (top left shore closeup below) methane sea w whitecaps
shore of methane lake??? shoals on left
GASES of TITAN ATMOSPHERE
melting point (°C) -182
-183
-188
-210
boiling point (°C) -162
-89 -42 -196
Methane
Ethane
Propane
Nitrogen
formula CH4 C2H6 C3H8 N2
To determine Kelvin temp subtract number
from 273