Stephen is an online writer and former English teacher who is interested in sociology, economics, and literature.
William Herschel, using what was then the world's largest telescope, discovered Enceladus in 1789. It's fair to say that his find didn't exactly set the scientific world alight.
Saturn was known as Cronus in Greek mythology and Cronus was the leader of the Titans, Enceladus, by tradition, was the opponent of Athena during the war between the Titans and the gods. William's son, John, came up with the idea of naming the known moons of Saturn after the Titans.
For around 200 years, Enceladus was little more than a curiosity. Astronomers made rough calculations about its density, mass, and albedo(1) but didn't spend too much time worrying about it.
When Voyagers 1 and 2 were launched in 1977, there was so much to look at that Enceladus wasn't very high on NASA's list of priorities. Nevertheless, the two probes had a look.
If you look at our moon, you can easily see that meteorite craters have pitted its surface. You might expect this would be the case for Enceladus, but not quite. Images from Voyager 2 showed that a lot of the terrain looked smooth and showed no evidence of impacts. This must mean that the surface in these areas was quite young and was probably the result of water volcanism.
Intrigued, when Cassini was launched in 1997, part of its mission was to take a closer look at Enceladus. It arrived around Saturn in 2004 and detected water plumes geysering out of the moon's south pole. Surely then, there was water under the ice. But how was this possible?
Enceladus is 500 kilometers in diameter which makes it the sixth largest moon in Saturn's system. Much of the surface is covered in ice that reflects back almost all of the sunlight that reaches the surface. This makes Enceladus even colder than it would be otherwise. A balmy day on most of Enceladus might see the temperature rise to minus 198 degrees Celsius.
At that sort of temperature, you might expect that the moon would be a solid ball of ice. It isn't. In 2005, plumes of water vapor were discovered and analyzed. The surface temperature was higher than in other regions. The source of this heat is still not fully understood and various theories have been put forward.
What is generally accepted is that there is an ocean of liquid water under the south pole.
A full analysis of the ejected water has shown that all the chemical elements necessary to life are present in Enceladus' ocean.
Cassini flew just 50 kilometers over the surface and sampled the jets of water to better understand their chemistry.
Is There Life on Enceladus?
Nearly 3 kilometers below the surface in South Africa's Mponeng gold mine, water flows in through a fracture in the rock that leads to even deeper depths. This hostile environment is home to a bacterium called Candidatus Desulforudis audaxviator (2).
Life on the surface of our planet depends upon sunlight and, for many years, we assumed that this must be true for all life. But it isn't, Candidatus doesn't need sunlight at all. It lives off minerals that decay because of radiation, it's not at the bottom of a food chain where the higher members need light. It's not in a food chain at all - nothing else lives in its environment.
Such creatures are called extremophiles because they thrive in hostile environments and there are many other examples on our planet.
What was once a fairly uninteresting rock orbiting Saturn like over 80 others is now the focus of considerable scientific interest and speculation.
My bet is that there is life on Enceladus. It will undoubtedly be primitive and somewhat similar to Candidatus. When we find life there, and we will, it will show that life can develop on other worlds. Planets with more varied environments than Enceladus will surely host a wider range of creatures. And planets with conditions similar to Earth's might be home to advanced life forms.
Life will be the rule rather than the exception. Intelligent life will be much rarer but, in a vast universe. it will be out there somewhere.
NASA has decided that Enceladus deserves a closer look. The plan is to launch the Enceladus Orbilander in 2038. Orbilander will orbit, land, and analyze what it finds. We might get the answers that we want but we'll have to wait. Orbilander will not reach the icy moon until 2050.
Still, no need to rush. Enceladus isn't going anywhere.
1 - Albedo: Albedo is the amount of light that is reflected by a surface. The measure runs from 0 - no light is reflected at all, to 1 - the body reflects all the light that falls on it.
2 - The audaxviator part of the name comes from Jules Verne's "Journey to the Center of the Earth" in which the hero, Professor Lidenbrock, comes across an inscription in Latin that reads "Go down, bold traveler (audax viator), and you will reach the center of the earth.". In fact, Candidatus doesn't travel - it's happy in its pools.
- One is the loneliest number for mine-dwelling bacterium | Nature
Sole member of world's first single-species ecosystem depends on rocks and radioactivity for life.
- Enceladus | Science – NASA Solar System Exploration