Looking for Life Beyond Earth: Ocean Worlds
How NASA missions to ocean-bearing moons in the outer solar system are addressing one of the greatest mysteries of all.
Enceladus Cutaway View (Artist Concept) (2015-10-26) by NASA/JPL-CaltechNASA
THE PROMISE OF ICY "OCEAN WORLDS"
Robotic probes cast into the depths of space over the past few decades have
made one thing crystal clear: Our solar system is a very wet place. Surveys of the
giant planets Jupiter, Saturn, Uranus and Neptune -- places far from the warmth
of the Sun -- have exposed the secrets of their enigmatic moons, and it turns
out that some of the moons harbor hidden oceans locked inside an outer shell of
ice.
On Earth, itself an ocean world, liquid water is essential to life as we know it. Thousands of meters below the surface, in permanent darkness, hydrothermal vents belching plumes of heated, mineral-laden water often host rich ecosystems.
Scientists believe similar conditions may exist in the far reaches of our solar system, deep within icy moons orbiting giant Jupiter and Saturn.
Searching For Life on an Icy Moon (Artist Concept) (2017-02-08) by NASA/JPL-CaltechNASA
Thus it is a topic of great interest whether the dark, alien oceans of the outer solar system could be habitable for simple life forms. In fact, these may be the best places in the solar system to search for present-day life beyond Earth.
Enceladus the Storyteller (2006-03-09) by NASA/JPL/Space Science InstituteNASA
It's likely that any life in these oceans would be simple and small, that is, microbial in nature. But the implications of finding another origin of life in our solar system -- one truly independent from Earth -- would be staggering.
Although Earth and Mars have been exchanging material in the form of meteorites for much of the history of the solar system, it's difficult for meteorites blasted off our planet to make their way all the way out to the moons of the outer planets.
Thus, a discovery of even simple, microbial life on one of these worlds would profoundly affect our understanding of life as a universal process that happens readily given the right ingredients and enough time.
Cassini Flies Through The Enceladus Plume (Artist Concept) (2016-04-20) by NASA/JPL-CaltechNASA
Between 2004 and 2017, NASA's Cassini spacecraft studied the Saturn system up close. On Saturn's dynamic moon Enceladus, Cassini found geyser-like jets of water vapor and icy particles venting the contents of a global, subsurface ocean far into space.
Cassini also determined that there likely are hydrothermal vents at the bottom of that ocean, spewing warm, mineral-rich water that could potentially power an alien ecosystem there.
A future mission could sweep up "free samples" from the plume, while a surface-crawling robot might plumb the depths of the geysers themselves.
Colorful Colossuses and Changing Hues (2012-08-29) by NASA/JPL-Caltech/SSINASA
Saturn's giant moon Titan could be home to life as we *don't* know it.
The Cassini-Huygens mission performed the first detailed exploration of Titan, revealing an alien world with some startlingly Earth-like characteristics.
Ligeia Mare on Saturn's Moon Titan (2013-05-22)NASA
Shrouded in a dense atmospheric haze, Titan is the only other body in the solar system with liquid on the surface, plus it has rain, flowing rivers and lakes.
But there's a catch: on Titan, where the temperature is a balmy -290 degrees Fahrenheit, water is as hard as rock. On Titan's surface, the liquids are all hydrocarbons like methane, not water.
The complex chemistry at work on Titan might be similar to that of the early Earth before life got started. Studying this chemistry provides a unique window into processes that might have contributed to our planet's habitability.
Titan Touchdown (Video) (2015-01-01) by NASA/ESA/JPL-CaltechNASA
The Cassini spacecraft carried a European probe called Huygens to Saturn, which parachuted to Titan's surface in 2005.
Boats or blimps might one day be deployed on the haze-enshrouded moon, to navigate its methane seas and its smoggy, nitrogen-rich atmosphere. (Titan also has a salty, subsurface ocean beneath its icy shell, although not much is known about that ocean just yet.)
Sunlight Glinting Off A Titan Sea (2014-08-21) by NASA/JPL-Caltech/University of Arizona/University of IdahoNASA
While unlikely, finding life that could survive on Titan would be a game-changer.
If we find the seas of Titan are hosting a kind of biological chemistry, even a primitive one, where the first steps toward life are being taken, it would tell us that the drive toward life, that kind of chemical complexity we see in life on Earth, can occur in many different kinds of environments.
Europa: Ocean World (Video) (2014-11-21) by NASA/JPL-CaltechNASA
In the next decade, NASA is planning to send a spacecraft on repeated flybys of an icy moon of Jupiter called Europa to learn whether it possesses the right ingredients for life.
Based on data from previous missions to Jupiter, scientists believe a salty ocean lies beneath Europa's icy crust. It is thought to be an immense ocean -- containing twice the water in Earth's seas -- and it likely has been around for most of the history of the solar system -- more than 4 billion years.
This should be plenty of time for life to evolve, if the right conditions exist there.
Europa Mission Spacecraft (Artist Concept) (2016-04-20) by NASA/JPL-CaltechNASA
It's possible a kind of double ecosystem exists on Europa: one on the sea floor and one on the underside of the moon's icy shell.
The upcoming NASA mission, called Europa Clipper, will seek to understand whether Europa indeed has the ingredients for life. Its mission to understand if the icy moon is habitable could eventually be followed by missions to land on the surface and explore what lies beneath the ice.
For more information about NASA's Europa Clipper mission, visit https://europa.nasa.gov/.
For more information about Cassini and Huygens, along with many more stunning images, visit https://saturn.jpl.nasa.gov.
Visit https://solarsystem.nasa.gov for information about all of the ocean worlds mentioned in this exhibit.
