Why europa could have life

To start with, in an overall sense, it's quite smooth, with few towering mountains or deep basins. Myriad ridges and grooves crisscross the surface, breaking up the landscape. Many of these features coincide with long, curving streaks that are dark and reddish in color — some stretching across the surface in great arcs over miles kilometers long.

Elsewhere, domes, pits and chaotic jumbles of icy blocks hint that warm ice may be rising from deep below. Models suggest that Europa's icy shell is relatively thin.

The icy moon gets stretched and released by the tug of Jupiter's gravity, in an endless cycle, as Europa orbits the giant planet. This squeezing in and out is a process called tidal flexing, which may be creating heat inside Europa; the warmed ice from this heat may be pushing the surface upward to create the ridges. The tidal flexing also may be creating enough heat inside Europa to maintain a liquid ocean beneath the moon's icy surface.

Most of the heat would be focused at the boundary between the ocean and the icy crust. For Europa to be potentially habitable, it would need to have the essential chemical ingredients for the chemistry of life. These include carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, which are common elements, and scientists think it's likely they were present on Europa as it formed.

Later on, asteroids and comets impacted the moon and would have deposited even more organic, or carbon containing, materials. The chemical elements for life might be found within Europa's icy shell, as well as its ocean.

Tidal heating could be powering a system that cycles water and nutrients between the moon's rocky interior, ice shell and ocean, creating a watery environment rich with chemistry conducive to life.

This is why studying Europa's chemistry — on the surface and within the suspected ocean — is important for understanding its habitability, because living things extract energy from their environments by chemical reactions. All lifeforms need energy to survive. Where would life on an icy world far from the Sun get energy? The type of life that might inhabit Europa likely would not be powered by photosynthesis — but by chemical reactions.

Europa's surface is blasted by radiation from Jupiter. That's a bad thing for life on the surface — it couldn't survive. But the radiation may create fuel for life in an ocean below the surface. And just how many microbes might exist in Europa's sea? Chyba's conservative estimate: one per cubic centimeter -- a far cry from the hundreds of thousands of organisms that occupy each cubic centimeter of water on Earth.

Could life on our planet have its origins on Europa? Probably not, according to Chyba. Chyba emphasizes that all theories about life on Europa hinge on proof that a liquid body of water actually exists between the moon's surface and its rocky core.

As a student, Chyba's interest in extraterrestrial life led him to the Cornell University laboratory of famed astronomer Carl Sagan, a long-time advocate of planetary exploration. Chyba received his Ph. From to , Chyba served as a White House adviser on national security. Beginning Feb. All Rights Reserved. Stanford, CA Terms of Use Copyright Complaints. Spacecraft observations determined that the surface of Europa is covered with water ice. That ice and other materials on Europa's surface are bombarded with radiation from Jupiter that could alter them into some of the chemical building blocks of life.

If these compounds reach the subsurface ocean, they can be valuable nutrients to start and sustain life. The ocean water can react with the rocks and minerals of the subsurface ocean's floor to liberate other nutrients to support life.

Europa's position in space is within the powerful gravitational field of Jupiter. This strong gravitational "pull" has the moon locked into an orbit with one hemisphere constantly facing Jupiter. The elliptical orbit takes Europa alternatively closer to and farther away from the planet.

This alternating increase and decrease of gravitational force on Europa results in the moon elongating and relaxing with each trip around the planet. This internal movement, combined with gravitational forces exerted by neighboring moons, produces internal friction and heat within Europa.

Europa's internal heat could be the energy source that keeps the subsurface ocean from freezing and sustains any life that exists there. There could be hot water vents on the floor of the subsurface ocean that deliver energy and nutrients from the planet's interior.

Organisms on Earth have been discovered in the subglacial lakes of Antarctica and in the hot ion-rich waters of hydrothermal vents. Life in Europa's subsurface oceans could be supported in similar ways.

Europa from Galileo: An image of the trailing hemisphere of Europa. It shows very few impact structures but numerous ridges and fractures that suggest a rigid crust moving over a mobile layer below.

Image by NASA. NASA gives three pieces of evidence that strongly support the presence of Europa's subsurface ocean. This suggests a large body of conductive material salty water at a depth of 30 kilometers about 20 miles or less.

These suggest a mobile layer below Europa's crust that supports the crust and allows it to move. The presence of magnesium compounds on the surface of Europa suggests that water from the subsurface ocean reaches the surface through springs or vents.