Cloud World: Probe About To Smash Into Titan

Published: Fri 14 Jan 2005 09:11 AM
Cloud World: Mission To Titan
By Michael Hammerschlag
Michael Hammerschlag has written articles about the Voyager missions to the Outer planets, the SETI project, and worked on the Subaru telescope on the summit of Mauna Kea, Hawaii, the biggest astronomical complex on Earth.
Early Friday (Jan 14) morning (3:50am EST), the last grand space mission –the 11 year $3 billion Cassini mission to Saturn, will smash 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- 90+ % nitrogen (Earth is 79%), 6%? methane, and the remainder a dirty orange smog of complex organics.
Image of Titan, courtesy of NASA .
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.
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 of Earth. 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 1.8 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. “Methane is irreversibly destroyed by solar UV radiation at high altitudes in 50 million years,” says Johns Hopkins Univ.
Huygens scientist Darrell Strobel from Darmstadt, Germany, the European Space Agency’s Operation Center. (They designed many of the Huygens instruments.) “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.
“Titans 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 and rocking (inc. of a liquid landing). Radar and acoustical receptors will measure the distance to the surface, the speed of sound, the roughness and constitution of the surface (and depth
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, 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 30-90 minutes and within 2¼ hours 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 fifth of which looks like it is covered with shiny asphalt, the rest white. 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.
Titan PICS from Cassini:
TITAN Facts: Big JPL Press Release:
Huygens Instruments: European Space Agency- Huygens: ESA Pictures
State of Space ’97: Mir problems, Cassini launch and foretold Mars missions failures and shuttle disaster.

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