Ocean Discovery On Enceladus Spur Life-Hunting Missions to Icy Moons

Saturn's moon Enceladus, covered in snow and ice, resembles a perfectly packed snowball in this image from NASA's Cassini mission released on Dec. 23, 2013.

This view was taken by Cassini on March 10, 2012. It shows the leading side of Enceladus. 

North on Enceladus is up and rotated 6 degrees to the left.

Credit: NASA/JPL-Caltech/Space Science Institute

Astronomers are hoping that the existence of a subsurface ocean on Saturn's icy moon Enceladus will build momentum for life-hunting missions to the outer solar system.

Researchers announced their discovery of the deep watery ocean on Enceladus on Thursday (April 3) in the journal Science, confirming suspicions held by many scientists since 2005, when NASA's Cassini spacecraft spied geysers of ice and water vapor erupting from Enceladus' south pole.

The discovery vaults Enceladus into the top tier of life-hosting candidates along with Europa, an ice-sheathed moon of Jupiter that also hosts a subterranean ocean. Both frigid satellites bear much closer investigation, researchers say.



"I don't know which of the two is going to be more likely to have life. It might be both; it could be neither," study co-author Jonathan Lunine of Cornell University told reporters yesterday (April 2).

Jonathan Lunine

"I think what this discovery tells us is that we just need to be more aggressive in getting the next generation of spacecraft both to Europa and to the Saturn system once the Cassini mission is over."

Cassini arrived in orbit around Saturn in 2004 and is currently scheduled to go out in a blaze of glory in September 2017, when it will dive headlong into the giant planet's thick atmosphere.

Enceladus' geysers blast material hundreds of miles into space, offering a way to sample the moon's subsurface ocean from afar.

(Researchers think the ocean is feeding the geysers, though they can't be sure of this at the moment.)

NASA Galileo spacecraft: Could Jupiter become a star? - Video

Galileo at Jupiter. Credit: NASA

NASA's Galileo spacecraft arrived at Jupiter on December 7, 1995, and proceeded to study the giant planet for almost 8 years.

It sent back a tremendous amount of scientific information that revolutionised our understanding of the Jovian system.

By the end of its mission, Galileo was worn down.

Instruments were failing and scientists were worried they wouldn't be able to communicate with the spacecraft in the future.

If they lost contact, Galileo would continue to orbit the Jupiter and potentially crash into one of its icy moons.

Galileo would certainly have Earth bacteria on board, which might contaminate the pristine environments of the Jovian moons, and so NASA decided it would be best to crash Galileo into Jupiter, removing the risk entirely.

Although everyone in the scientific community were certain this was the safe and wise thing to do, there were a small group of people concerned that crashing Galileo into Jupiter, with its Plutonium thermal reactor (RTG), might cause a cascade reaction that would ignite Jupiter into a second star in the Solar System.

Hydrogen bombs are ignited by detonating plutonium, and Jupiter's got a lot of hydrogen.Since we don't have a second star, you'll be glad to know this didn't happen.

Could it have happened? Could it ever happen? The answer, of course, is a series of nos. No, it couldn't have happened. There's no way it could ever happen… or is there?

Jupiter is mostly made of hydrogen, in order to turn it into a giant fireball you'd need oxygen to burn it. Water tells us what the recipe is.

There are two atoms of hydrogen to one atom of oxygen. If you can get the two elements together in those quantities, you get water.



In other words, if you could surround Jupiter with half again more Jupiter's worth of oxygen, you'd get a Jupiter plus a half sized fireball.

It would turn into water and release energy but that much oxygen isn't handy, and even though it's a giant ball of fire, that's still not a star anyway. In fact, stars aren't "burning" at all, at least, not in the combustion sense.

Our Sun produces its energy through fusion. The vast gravity compresses hydrogen down to the point that high pressure and temperatures cram hydrogen atoms into helium. This is a fusion reaction.

It generates excess energy, and so the Sun is bright. And the only way you can get a reaction like this is when you bring together a massive amount of hydrogen.

In fact… you'd need a star's worth of hydrogen. Jupiter is a thousand times less massive than the Sun. One thousand times less massive.

In other words, if you crashed 1000 Jupiters together, then we'd have a second actual Sun in our Solar System.

Jupiter as captured by Michael Phillips on July 25th, 2009 

But the Sun isn't the smallest possible star you can have.

In fact, if you have about 7.5% the mass of the Sun's worth of hydrogen collected together, you'll get a red dwarf star.

So the smallest red dwarf star is still about 80 times the mass of Jupiter.

You know the drill, find 79 more Jupiters, crash them into Jupiter, and we'd have a second star in the Solar System.

There's another object that's less massive than a red dwarf, but it's still sort of star like: a brown dwarf.

This is an object which isn't massive enough to ignite in true fusion, but it's still massive enough that deuterium, a variant of hydrogen, will fuse.

You can get a brown dwarf with only 13 times the mass of Jupiter. Now that's not so hard, right? Find 13 more Jupiters, crash them into the planet?

As was demonstrated with Galileo, igniting Jupiter or its hydrogen is not a simple matter.

We won't get a second star unless there's a series of catastrophic collisions in the Solar System.

And if that happens… we'll have other problems on our hands.

ESA JUICE Mission to Jupiter's Icy Moons

An artist's illustration of the JUpiter ICy moons Explorer spacecraft in the Jovian system. The mission will launch in 2022 and arrive at Jupiter in 2030 to study the planet and its largest moons.

CREDIT: ESA/AOES

An ambitious European mission that will launch a robotic probe to explore Jupiter's icy moons in 2022 has got its science gear.

The European Space Agency has picked 11 instruments for the planned JUpiter ICy moons Explorer, or JUICE, spacecraft.

The mission is expected to reach Jupiter, the largest planet in the solar system, in 2030 and spend at least three years studying the gas giant's major moons Callisto, Europa, and Ganymede.

The Jovian satellites are intriguing to scientists because they are thought to have vast oceans beneath their icy outer crust.

"Jupiter and its icy moons constitute a kind of mini-Solar System in their own right, offering European scientists and our international partners the chance to learn more about the formation of potentially habitable worlds around other stars," said Dmitrij Titov, JUICE study scientist for ESA, in a Feb. 21 statement.

The JUICE mission will observe Jupiter's atmosphere and magnetosphere, as well all four Galilean moons: Europa, Callisto, Ganymede and the volcanic Io.

The spacecraft is expected to make 12 flybys of crater-covered Callisto, as well as two close passes of Europa in an attempt to gather the first-ever measurements of the thickness of that moon's frozen crust, ESA officials said.



The spacecraft will eventually end up orbiting Ganymede, the largest moon in our solar system, to study its surface and internal structure. Ganymede is also the only known moon in the solar system with its own magnetic field, and JUICE will closely observe the moon's interactions with Jupiter's magnetosphere, ESA officials said.

The collection of approved instruments to help scientists complete these tasks includes cameras, spectrometers, a laser altimeter and an ice-penetrating radar, as well as a magnetometer, plasma and particle monitors, and radio science hardware, ESA officials said. Teams from 15 European countries and the United States and Japan will develop the tools.

"The suite of instruments addresses all of the mission's science goals, from in-situ measurements of Jupiter's vast magnetic field and plasma environment, to remote observations of the surfaces and interiors of the three icy moons," Luigi Colangeli, coordinator of ESA's solar system missions, said in a statement.