Europa—A World Worth Exploring

Europa is one of the most interesting objects in the solar system. It is a promising place to search for life elsewhere in the solar system despite being over 5 times further away from the Sun than the earth (on average 485 million miles), no larger than our own moon, and tidally locked towards Jupiter. In 2022, NASA’s Europa Clipper mission will set sail to explore this icy ocean world and assess its prospects for habitability.

Europa, and other icy ocean worlds, have redefined what we mean by habitable. This new frontier was explored during the Cassini mission where plumes were discovered at the south pole of Enceladus (a moon of Saturn). To follow up from the Cassini mission, NASA is now turning its search to Jupiter’s satellites and, in particular, Europa. The current plans for Europa Clipper involve 42 flybys of Europa as well as a potential separate lander to sample from the surface.

Mission 1: Characterize Europa’s ice shell and study the formation of its complex surface features

Europa has the smoothest surface of any known solid object in the Solar System. Its surface is made up of a global shell of ice that seems to be undergoing continual resurfacing. Based on the small number of craters observed, the icy surface of this moon appears to be no more than 40 to 90 million years old, which is quite young in geologic terms.

The Galileo space probe, launched in 1989, allowed us to see Europa’s surface like never before. It brought this strange world into focus and from it we discovered the diversity of Europa’s surface geology. Large cracks and ridges span the surface indicating an active surface that is constantly being pushed and pulled by Jupiter’s tidal forces. There are chaotic regions where the icy crust has frozen and refrozen into complex shapes. The thick ice shell shows evidence of a mobile lithosphere and tectonic activity only seen before on the Earth. The Europa Clipper mission will perform 42 flybys of Europa and provide high resolution images of the surface and allow us to examine it in greater detail.

credit: NASA Close up of Europa surface

The surface of Europa is very different from that of Earth. The surface temperature never rises above minus 230 degrees Fahrenheit. Its surface is constantly bombarded by ionised particles originating from its volcanic neighbour Io and Jupiter’s strong magnetic field. Despite this hostile surface environment, Europa is widely considered to be one of the most promising places in the solar system for habitability. Not on its surface, but beneath it.

Mission 2: Understand the habitability of Europa’s ocean

Underneath Europa’s ice shell is a global liquid water ocean. In fact, scientists believe that there is more liquid water in Europa’s oceans than there is water on the Earth.

Water, the cornerstone for life as we know it, seems to be abundant under the surface of Europa’s icy shell. The water is kept liquid thanks to tidal heating from Jupiter. Europa’s ocean may also be in contact with a rocky surface below it, potentially providing a platform for the building blocks for life. Whilst the jury is still out on where life on Earth originated, one good bet is that life emerged deep underwater in hydrothermal vents. Conditions so far indicate that Europa is a great place to look for these kinds of habitable conditions, although these hydrothermal vents have not yet been discovered. Hypothetical Interior of Europa. Current evidence suggests that the moon has a fully differentiated core, rocky mantle and global subsurface ocean.

credit: NASA
Model of Europa’s interior. The moon is thought to have a metallic core surrounded by a rocky interior, and then a global ocean on top of that, surrounded by a shell of water ice.
http://photojournal.jpl.nasa.gov/catalog/PIA01669

Current plans for the Clipper mission include a lander that will touch down on the surface and remain operational for multiple days. However, a lander is not going to be able to sample the sub-surface ocean directly since the ice shell is estimated to be between 3 and 30km deep. What it might be able to do though is sample material from the oceans that has made its way onto the surface.

Jupiter should be visible from New York throughout the month of February. Europa, alongside Io, Callisto, and Ganymede, was first discovered by Galileo in 1610. With his handmade telescope he saw 4 specks of light hovering around Jupiter and noticed that each night their positions relative to Jupiter were different. He quickly realized these four specks were actually moons in orbit around Jupiter. This provided some of the first evidence for the Copernican universe, that the earth is not at the center of everything.

Even with the most basic telescope you can distinguish the four closest moons, just as Galileo did over 400 years ago. Take a little extra time to look at Europa. That small light in the sky could be our best chance for finding life elsewhere in the solar system. The Europa Clipper mission may not be able to answer this question definitively, but it will certainly go a long way in helping us to understand this ocean world.

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