Water Rules on Europa

Jupiter’s moon Europa continues to amaze and educate us about conditions in the “mid-range” region of the solar system. If you look at an image of Europa, you’ll notice right away that it appears to have jagged breaks in its icy crust, almost like a cracked egg. Yet, that surface is very smooth, which means it’s relatively young. There aren’t too many craters from impactors, and even the cracks look “iced over”.

We’ve long suspected that Europa has a significant fraction of water hiding in an ocean under its frozen crust. That’s led scientists to dub it an ‘ocean world’ or a ‘water world’.

Data from missions as far back as Voyager and the Galileo spacecraft helped us suss out Europa’s true nature. The Juno mission, currently in orbit around Jupiter, has also imaged Europa, mostly from a distance. Its data add to the collection of amazing observations we’ve been able to make. Europa’s appearance and the presence of a possible subsurface ocean inspire many questions: Why is it so smooth? What else is happening there? Could Europa support life? Does it HAVE life now? The answers lie in those ice-covered oceans.

Stretching Europa

We’ve long known that Europa is subject to tidal forces from Jupiter. It’s tidally locked to its parent planet. That is, Europa doesn’t spin on its axis the same way our planet does. That means the same side of Europa faces Jupiter as it orbits the planet. The tidal forces cause its surface to flex and stretch and similar flexing stretches and heats Europa’s rocky core. In addition, as Europa stretches, its oceans experience tides. Heat from the core and the action of the tides could affect the surface through warming and cracking. The cracks could be conduits for water to “leak out” to the surface and freeze.

Exploring Europa from Earth Orbit

In addition to spacecraft missions, scientists have also used HST over many years to study Europa. Their long-term observations also yielded intriguing facts about the place. For example, in 2013, Hubble Space Telescope found spectral evidence for plumes of water ice jetting out from Europa’s southern polar region. The most recent discovery from Hubble data shows a persistent water vapor “cloud” at Europa. Those data come from observations made between 1999 to 2015.

During that time, HST took more images and spectra of this moon, building up a significant database of information. A recent analysis of the images and data turned up an interesting fact. That water vapor “atmosphere” really only persists over the trailing hemisphere of Europa. Nobody’s quite sure why. That remains to be figured out. Now, the goal is to figure out where the vapor cloud originates. Is it primarily from the plumes? Or is something else going on, too?

Finding out More at Europa

Europa isn’t exactly a garden spot, despite its abundance of water. The surface is highly reflective, and it’s cold. The surface temperature at midday is around -260 F. You’d think it would be low enough to keep the surface relatively, well, frozen in place. Yet, it appears that the water ice on the surface is sublimating, that is, changing from an icy state to a vapor state. That could be contributing to the massing of water vapor over the trailing hemisphere, along with action from the plumes. We need more to pin this down, however.

The best way to directly find out the causes of Europa’s vapor atmosphere is to go there. It’s not likely that humans are going to travel to Europa and take surface and atmospheric measurements. It would be a lethal experience, due to the extremely high radiation associated with Jupiter’s magnetic field. It blasts Europa with a constant bath of high-energy particles. You could stand on the surface of this moon, but you wouldn’t last long. Even with radiation protection, in one day, the radiation you experience would be 1,800 times the radiation you’d get if you stayed here on Earth and lived at sea level. That’s enough to cause illness or death in a very short time.

Send in the Robotic Probe

The next best thing is to send spacecraft, which we’ve been doing. Another one is on the drawing boards, called the NASA Europa Clipper mission. It will do at least 45 flybys of Europa, using a variety of instruments to map and study the surface. It will also use gravitational measurements to confirm the existence and extent of that subsurface ocean. The main goal, however, is to determine whether or not Europa could, or does, support life. If all goes well, the mission could launch as early as 2024.

The post Water Rules on Europa appeared first on The Spacewriter’s Ramblings.