There are many exciting spacecraft studying the solar system at the moment. Messenger, launched in 2004, has been studying Mercury. Rosetta is currently in orbit around the comet 67P Churyumov/Gerasimenko, New Horizons is about to encounter the dwarf planet Pluto/Charon system whilst Dawn has recently entered orbit around the dwarf planet Ceres, the largest body in the asteroid belt.
Launched in 1997, and now nearing the end of its mission in 2017, is the spacecraft Cassini which is currently in orbit around Saturn studying the planet and its ring system. Cassini carried a small robotic lander called Huygens.
On Christmas Day 2004 Huygens said goodbye to its partner and headed off to Titan the largest moon of Saturn and at 5,152 kms across, considerably bigger than the planet Mercury, dwarfs our own Moon by 50%, and is twice the size of demoted planet Pluto.
What it would encounter was almost impossible to say as Titan remained an enigma for years because of its impenetrably thick atmospheric haze.
So welcome to the surface of Saturn’s giant moon Titan!
Imagine a gentle landscape of hilly sand dunes leading down to a tranquil lake, whose surface starts rippling in the afternoon wind, disturbing the reflection of the few white clouds drifting above. On the opposite shore, a sudden rainstorm wets the stones and pebbles. It feels as if a sunset is unfolding because the entire sky is pumpkin coloured. It is the only known satellite with an appreciable atmosphere and all the changing weather that goes with it. The air is 1.5 times thicker than our own and is also similarly composed, mainly of nitrogen. Combined with its low gravity this soupy air would allow you to fly with the most simple of wings. But hold on, Titan is not so much enjoyably weird as frighteningly perilous! Methane rain, water-ice terrain, and hints of cryovolcanism make Saturn’s largest moon one of the most dynamic places in the solar system.
When the Huygens probe descended through the smog, the results astonished everyone. Here was the only celestial body besides Earth with lakes of liquid and rain falling from clouds.
The super-cold temperature of -167 degrees Celsius, however, meant that liquid water was out the question. Instead, the terrestrial seeming landscape of boulders and countless lakes offered a twist; the stones were solid water ice, which at such temperatures is hard as rock. And the lakes and seas were filled with liquid petrochemicals made primarily from molecules such as methane, propane and ethane (which on earth are extremely flammable gases).
Two of the largest lakes have been named ‘Kraken Mare’ at 1,170kms and ‘Ligeia Mare’ 420kms. Radar penetration records depths of over 200mts, and even strange islands have been detected. The latest hypotheses suggest that these are waves or bubbles, or floating debris like ice rafts that have melted away from the mainland as Titan’s northern hemisphere heats up denoting the onset of summer.
Naturally we assume life requires water, but astrobiologists suggest extraterrestrial life forms could take in hydrogen instead of oxygen, where it would react internally with acetylene instead of glucose. The by-product would be methane instead of the carbon we exhale. NASA planetary scientist Chris McKay suggested life that consumed methane would measurably alter the atmosphere and be detectable from Earth. In 2010 a John Hopkins University scientist claimed there was just such evidence in an odd excess of hydrogen in Titan’s upper atmosphere, while it is nearly totally absent at the surface, despite strong downdrafts. One implication is that methane-addicted organisms eat the hydrogen.
Life Jim… but not as we know it? Possibly, but far too early to say, many other non-life chemistry could account for these observed oddities.
So a fascinating world, tantalizingly mysterious and not about to give up its secrets so readily. For the moment we’re left with a cold, thick nitrogen atmosphere containing intriguingly abundant organic substances, a dynamic weather system that transports gases and liquids in strong dune; creating winds and a landscape that is forever resculpted.