Potentially Habitable Worlds Are Wet & Wild

March 28, 2009

I recently had fun making a baking soda powered tabletop volcano to the delight of my grandson Leo, who just loves watching the thing explode. You know, that popular middle school science fair project where vinegar (acetic acid) neutralizes baking soda and causes it to give off carbon dioxide, creating pressure that blows the liquid up a toy volcano cone.

But on other planets there may really be volcanoes gushing out water rather than molten rock. And, mud volcanoes that belch out a slurry of organic-rich material, if not subterranean microbes.

The possible discovery of wet slushy volcanoes on Titan and Mars, and damp soils, is ratcheting up the possibility of finding extraterrestrial life. A number of papers were presented last week at the 40th Lunar and Planetary Science Conference in The Woodlands, Texas.

Cryovolcano

In the frigid outer solar system, where daytime temperatures are at -300 degrees Fahrenheit or lower, a different type of geology may be taking place – cryovolcanos. These mountains are suspected of spewing out a Slurpee of ice, propane, butane and other liquid hydrocarbons.

The best candidate is an area known as Hotei Arcus, thought not everyone agrees it is really a volcano. Photos on different flybys taken by the NASA/ESA Cassini orbiter have been interpreted as cryo-lava outflows. 

The lobe-like fingers, each hundreds of feet high, have a shape and thickness consistent with highly viscous lava on Earth. Like an advancing flow of lava, the lobes also appear to cut off several small streams apparently carved by liquid methane.

You need a subterranean heat source close to liquid reservoirs to spew out this stuff. It’s sort of nature’s recreation of the famous 1952 Miller-Urey experiment that mixed pre-biotic compounds, such as water, methane and ammonia (an ideal antifreeze for Titan) to make amino acids – the building block of life.

Mud Volcanoes

Closer to home, Mars orbiting spacecraft have identified dozens of mounds in the northern plains that bear a striking resemblance to mud volcanoes on Earth. High-resolution images reveal small knobs or patches. They frequently have one or more craters and an irregular shape.

As on Earth, a mud volcano would form when pressurized gas and water from as much as several miles down, blows out the surface like a popped Champaign cork. This shoots out a gooey mess of water, mud, rocks, as well as methane.

 Mud volcanoes would accomplish what a martian drilling rig would have a tough time doing, transporting rocks from several miles beneath the martian surface, and placing them within reach of sample-return rovers.

Microbial life could be flourishing deep below the martian surface, perhaps driven there as surface conditions became hostile over geologic time. It may be warm enough miles below the surface for water to remain a liquid. The volcanoes, which may be as young as 10 million years, offered an elevator for microbes to reach the surface – in a martian twist on the closing chapter of Jules Verne’s 1864 novel Journey to the Center of The Earth.

 

Briny Droplets

A highly publicized surprise from NASA’s Mars Phoenix Lander was the discovery of perchlorates in the planet’s arctic region. Perchlorate is the stuff used to make rocket fuel and explode fireworks. On Mars these salts could keep water in a liquid state at temperatures of -160 degrees Fahrenheit.

Pockets of brine might form when the perchlorate mixes with the water ice that Phoenix found near the north pole. In fact there has been a lively debate whether Phoenix photographed briny liquid water droplets on the lander legs, which would have been kicked up by its landing thrusters. Some scientists think they move like a liquid in successive exposures. Others say it’s just frost.

The perchlorates may explain why the mid 1970s Viking biology experiments did not find any organic compounds in the soil. The soil was heated in the Viking biology experiments. Heated perchlorates release their oxygen and burn up and organic material! So maybe the release of carbon dioxide seen in the Viking experiments was actually from the disintegration of trace organic material.

These findings show that the road to indentifying extraterrestrial life is long and arduous, with potential dead ends and misinterpretations. But the payoff of a positive detection is so staggering, the long haul and lively debate among scientists is well worth it.