A fireball blazes across the overcast, peach-colored sky streaking lower and lower. Soon it burns out and a small object is hanging from a parachute. It drifts steadily lower in the breeze until finally it splashes down into the dark, frigid sea far from any land. It bobs ceaselessly on a gloomy twilight world even though it is noon and the temperature hovers at -290 degrees F. Such a scenario will someday become reality when a spacecraft splashes down on Titan.
The Cassini spacecraft has been orbiting Saturn since June 30, 2004 and one of its major discoveries was lakes of liquid hydrocarbons on Titan in 2006 with some being true seas. Cassini has observed storms on Titan, minus lightning, that rain liquid methane onto the surface and has observed dry lowlands become flooded with liquid methane. Lakes and ponds have been observed evaporating and new storms form elsewhere on Titan pouring more rain onto its surface. Titan has an active hydrologic cycle like Earth with rain, clouds, fog, mist, streams, rivers, lakes, and seas, except that it is driven by methane instead of water. Chemical reactions aided by the feeble sunlight create complex organic compounds and the lakes also contain a mixture of ethane, propane, and acetylene in addition to methane. The first nautical exploration of an extraterrestrial sea and the chance to analyze it, and possibly a shoreline, is an opportunity that is hard to pass up.
A Titan lake lander or a similar probe would be able to tell how this cycle works and the similarities and differences to the hydrological cycle on Earth. Titan is also suspected of having active cryovolcanoes, a cold type of volcanism involving erupting slush of methane and water ice from the warmer interior. The primary target for any lake lander would be a huge lake called Ligeia Mare near the north polar region of Titan. This lake is a sea in its own right and is larger than Lake Superior. It is one of the largest and deepest lakes on Titan with a surface area of around 60,000 square miles and about 560 feet deep. The backup target lake is Kraken Mare, which is almost as large. Five science objectives are specific to exploring the sea:
•determine the chemistry of a Titan sea,
•determine the depth of a Titan sea,
•constrain marine processes on Titan,
•determine how local meteorology over the sea varies during a Titan day (about 16 Earth days),
•characterize the atmosphere above the sea such as lake effect phenomena, precipitation, clouds, wind, temperature variation, hazes, mists, fog, and any lightning, if it exists.
The probe would have two cameras. One would take pictures during its descent to Ligeia Mare and the other would take pictures after splashdown. The scenery could be interesting as the lake is near the North pole so the already feeble light at Titan might be even fainter. Sunlight at the surface is only 1/10 of 1 percent as bright as on Earth so it will be like a very bright moonlight. Fortunately, it should not be much dimmer than the photo of the surface from Huygens on January 14, 2005, therefore imaging will be possible. The haze and mists could reduce visibility, but if there is a good breeze close to the surface, visibility would be good. The sea would be bathed in a deep, peach-colored light due to the thick, smoggy atmosphere. The air pressure on the surface of Titan is actually higher than on Earth, about 1.6 times. It would be possible to walk around in this atmosphere for brief periods before the higher pressure makes it a bit uncomfortable, but unfortunately it is not breathable and it is a frigid -290 degrees F, therefore spacesuits would be mandatory for future explorers.
The first photos from the sea might not be too impressive if the probe hits its mark and splashes down directly in the middle of the sea. The horizon would appear like a flat, black line in every direction with no land visible. The lake itself should appear darker than the sky and probably black. It may have ripples from the anticipated breezes and there could be glints of sunlight on it if the Sun manages to break through any thin spots in the smoggy haze high aloft. Unfortunately, the smog would be too thick to see the beauty of Saturn with its nearly edge-on rings. The probe is expected to last up to six months so it is hoped that the wind will eventually bring the bobbing probe ashore. Land would be first spotted across the sea on the distant horizon and grow steadily larger until finally making landfall. The probe would then analyze the shoreline, which could really be interesting because it is not known what would wash ashore from an alien sea.
This exciting mission will someday become reality even though a spacecraft called the Titan Mare Explorer (TiME) was not approved for development last year and lost out to InSight, a Mars geothermal mission. Tough orbital mechanics and a tight budget may keep such a mission to Titan's seas forever beyond our lifetimes, but Titan will always be there. The first nautical exploration of an extraterrestrial sea and the chance to analyze it, and possibly a shoreline, is an opportunity that is hard to pass up. TiME is still excellent technology and either it or a similar mission will fly someday.
This article almost seems like science fiction and could not have even been written ten years ago. Now thanks to Cassini's great technology leading to the discovery of free-standing liquid on Titan, the only other world in the Solar System besides Earth to have stable liquid on its surface, a mission to explore an alien sea will become a reality, hopefully sooner than later. Only time will tell if this exciting mission will succeed with vistas and discoveries that at one time were only stuff of dreams and science fiction.