Sunday, April 27, 2014

Astrobiology : Follow the Water

The more we've learned about life on our planet, the more we've come to realize the conditions that we consider livable are only a small fraction of the conditions that living things on this planet are happy to have. The two factors which remain are the need for an energy source and the presence of at least some liquid water.

Almost any sort of energy can be utilized by living things (Light, organic chemical, inorganic chemical, ion gradient, electrical, radiation) even when present in minimal amounts. Energy isn't the limiting factor on our planet

Water is ubiquitous on Earth, from the upper atmosphere to miles below the surface. We find life everywhere we find water, even if that water is horrendously toxic (acid/alkali/heavy-metal/etc.) to us. We find life subsisting between grains of sand subsisting on the trace of moisture provided by dew. We find life in the deepest mines we've dug. We find life living in lakes isolated from the surface for thousands of years of ice.

On Earth, wherever there is water, there is life.



The name of our planet is synonymous with solid ground, but most of the surface of our world is covered in water. From a distance, a glance at our home reveals it to be a water-world first. No other planet (under any definition of 'planet') in our system is anything like it. However, water is common in our part of the universe.

During the formation of a planetary system, volatile elements and compounds are pushed out from the star until ambient space cools enough for those volatiles to condense and freeze. The place where water freezes is referred to as the ice-line and represents the start of the region where icy bodies are formed.

The formation of planets produces a great deal of heat. The kinetic energy of rocky/icy bodies as they merge under gravitational attraction is converted to heat. If the resulting bodies are large enough, they melt and the different components form layers ranging from densest to lightest going from the core to the surface. Water is very low density and so ends up largely on the surface of such bodies. Because they formed far enough out from the sun for water to freeze, the surfaces begin to cool and freeze soon after they form. The residual heat of formation is tremendous, and combined with new heat generated through radioactive decay and tidal interactions can keep temperatures below the surface elevated above the freezing point of water for quite some time.

Several bodies in our solar system appear to have under-ice oceans.

Calisto : science1.nasa.gov/science-news/science-at-nasa/1998/ast22oct98_2/
Enceledus : www.theguardian.com/science/2014/apr/03/ocean-enceladus-alien-life-water-saturn-moon
Europa : www.space.com/23880-jupiter-moon-europa-hidden-oceans.html

There are potentially living things on these moons, prospering in the warm water of thermal vents or creeping along in the cold waters near the ice.

I can't wait until we go and look.



References :
  1. Follow-the-water.
  2. Light energy for biology.
  3. Electrical energy for biology.
  4. Radiation energy for biology.
  5. Ice-line.
  6. Oxygenation of Earth.
    1. http://en.wikipedia.org/wiki/Great_Oxygenation_Event
  7. Snowball-Earth.
    1. http://en.wikipedia.org/wiki/Snowball_earth