Zeroing in on an alien ocean: Water vapor found around moon of Jupiter

Wladimir Lyra | Star News

When one thinks of extraterrestrial life, one usually conjures the image of little green men on planet Mars.

But what if the closest extraterrestrial life out there is sushi?

While Mars shows signs of ancient lakes and dry riverbeds, at present it is drier than the driest desert on Earth. On Mars we are not looking for present life, but for fossils from a wetter past billions of years ago.

Based on what we know about life, it seems to require three fundamental ingredients: suitable chemical elements, a source of energy and a liquid medium. On Earth, these are carbon, the Sun (mostly) and water. But while the same elements are found everywhere and energy sources abound, water is a little trickier.

Yet, there are a few places in the solar system with liquid water beyond our precious Earth. One of them is Europa, a moon of planet Jupiter.

Discovered by the Italian astronomer Galileo over 400 years ago, Europa is thought to hold as much as twice the amount of water than all of Earth’s oceans combined. The ocean itself is under a thick layer of ice, about 10 miles deep.

The evidence for an ocean came from the twin spacecraft launched in the 70s, the Voyagers, that took a close look at Europa. The Voyagers showed a young icy surface, cracked in a crisscrossed pattern. This would be expected if the ice was floating on top of liquid, fracturing along faults, like on Earth. In the 90s a third spacecraft, Galileo, named after the discoverer, made an important finding, showing that Jupiter’s magnetic field was modified around Europa. The principle is the same one behind metal detectors at airports. The metal detector is a magnetic field. If you cross it carrying something that conducts electricity, the magnetic field will produce a current. This current in turns produces a smaller magnetic field. Measuring this magnetic field betrays the presence of the coin in your pocket. Beep! — to your annoyance. The Galileo spacecraft measurement implies that something under the ice was a very good conductor of electricity. A salty ocean was the best explanation.

An ocean! Europa was now the ice princess of the solar system (think Elsa).

But while all that’s good, the evidence was indirect. Galileo heard the roaring waves, but it did not see the water.

More direct evidence came in 2012 when the Hubble Space Telescope detected oxygen and hydrogen, the components of water, in a very thin atmosphere around Europa. The observations implied that plumes of water are jetted into space through cracks in the ice. Now, a recent study confirms the Hubble detection.

The scientists used the 10m Keck telescope in Hawaii and, instead of looking for hydrogen and oxygen individually, looked for signs of water itself. They monitored Europa for 17 nights, detecting water on one of them. The amount detected, over 528,000 gallons (an Olympic swimming pool has about 660,000 gallons), is consistent with the amount of oxygen and hydrogen detected by Hubble.

This is the most direct evidence for Europa’s subsurface ocean to date. It is still not spotting the ocean, but it is smelling the briny air of the surf.

So what is in the future?

In a few years, a new generation of instruments, like the Thirty Meter Telescope and the James Webb Space Telescope, should be able to better localize and help us understand the plumes. Even more enticing, NASA and ESA (the European Space Agency) are planning the missions Europa Clipper and JUICE (JUpiter Icy moons Explorer). These missions should reach Jupiter in the 2030s and will be able to see the plumes. These missions should also map the ice thickness everywhere on Europa, locating a suitable spot for a meltprobe to reach the ocean.What will we find?

We have no idea.

Microbes? Alien fishes? Nothing?

It’s all speculation at this point. What seems certain is that Europa does have a briny ocean under its blanket of ice. Insulated from the cold of space, the temperatures in the ocean are Earthly and familiar.

One cannot help but wonder at the far future of human exploration of the solar system, when diver astronauts will swim in an alien ocean teeming with strange life. There, with stormy Jupiter looming enrapturing in the sky, a crew far from home may complement their space diet with a fresh catch; and debate if a better sushi is found in Tokyo or right there, on the icy bores of a brave new world.

Wladimir Lyra is an assistant professor of astronomy at New Mexico State University. He can be reached at wlyra@nmsu.edu.