Discovered in 1610 by Galileo Galilei, Europa is a moon of the planet Jupiter. At 3100 kilometers in diameter, the sixth-largest moon and the fifteenth-largest object in the Solar System, Europa is about the same size as Earth’s moon.
Europa is a candidate for housing extraterrestrial microbes. This moon holds the necessary conditions for life: subsurface oceans attached to rocks, an icy surface connected to oceans below, salts on the surface that create energy gradient, organic material from comet or asteroid impacts, and a source of heat, from tidal heating that occurs due to Jupiter’s gravity.
Ice and Oceans
The key to life is water. Scientists have formed a consensus that there are subsurface oceans beneath Europa’s frozen surface. The surface ice is estimated to be 100 kilometers thick, marking Europa’s average temperature at -160°C at the equator and -220°C at the poles. Nevertheless, scientists believe the subsurface oceans are a result of tidal heating, when orbital and rotational energy are dissipated as heat in the crust of the moon.
In 2011, the United States’ National Aeronautics and Space Administration (NASA) discovered a new ocean with floating ice shelves that were collapsing, transferring nutrients and energy between the surface and subsurface oceans.
Britney Schmidt, at Institute for Geophysics in Austin, Texas, said this discovery further supports life on Europa: “One opinion in the scientific community has been, ‘If the ice shell is thick, that is bad for biology —that it might mean the surface is not communicating with the underlying ocean.’ [But] now we see evidence that even though the ice shell is thick, it can mix vigorously. That would make Europa and its oceans more habitable.”
Like terrestrial planets Mercury, Venus, Earth, and Mars, underneath the frozen surface, Europa is composed of silicate rocks — rather than a combination of gases (commonly hydrogen, helium, and water) like gaseous plants.
Europa’s surface is exceedingly smooth, with very few craters. Its surface appears to be very young and active, around 30 million years old (the Earth is 4.54 billion years old). Additionally, Europa has a small metallic core, made up of iron and sulphur.
Earth, like Europa, is also made up of silicate rocks and an iron core; specifically Earth’s core contains iron and nickel. Scientists believe these similarities further support life on Europa.
In 2013, NASA scientists were able to see clay-like minerals on images from Galileo taken in 1998. The most likely explanation for their existence is due to comet or asteroid hits to the moon’s surface at an angle, since it is unlikely that they originated from the moon’s interior and made their way to the surface, because the moon’s icy crust is thick and impenetrable.
The types of space rocks that deliver such minerals also often carry organic material. Jim Shirley, a research scientist at NASA’s Jet Propulsion Laboratory, says, “ Organic material, which are important building blocks for life, are often found in comets and primitive asteroids. [And] finding the rocky residues of this comet crash on Europa’s surface may open up a new chapter in the story of the search for life on Europa.”
In December 2012, the Hubble Space Telescope observed plumes of water vapour venting from Europa’s south pole. Now scientists are trying to determine if the water vapour is coming from the moon’s surface or subsurface oceans.
“If those plumes are connected with the subsurface water ocean we are confident exists under Europa’s crust, then this means that future investigations can directly investigate the chemical makeup of Europa’s potentially habitable environment without drilling through layers of ice,” says Lorenz Roth of the Southwest Research Institute in San Antonio, Texas. “And that is tremendously exciting.”
The plumes of water vapour makes it easier to study the subsurface oceans, since samples can be retrieved from the orbit without landing on the moon or drilling through the ice. For now, scientists are watching Europa closely to make sure the plumes are a regular occurrence, not an anomaly, so they can conduct a mission at the right time to retrieve the vapour.
Europa and Earth
Scientists are looking for Europa-like conditions on Earth. They found Lake Vostok, a body of water located beneath the Russian research station in Antarctica, which has similar conditions to Europa. The lake is buried under 4 kilometers of ice, with liquid water underneath it, probably heated by geothermal heat.
So far, scientists have found microorganisms in the ice, such as cyanobacteria, bacteria, fungi, spores, pollen grains, and unidentified organisms that have never been seen before.
On 5 February 2012, after a decade of digging, Russian scientists broke through 3.2 kilometers of ice and reached Lake Vostok, which has been cut off from the surface for 14 million to 34 million years.
“When it comes to Europa, there is no better analog on Earth than Lake Vostok,” says Kevin Hand, deputy chief scientist of solar system exploration for NASA’s Jet Propulsion Laboratory. “In both cases, the liquid water envelope trapped beneath the ice is cut off from the sun.”
Any discovery in Lake Vostok will provide valuable and transferable information regarding Europa.
Scientists have been lobbying for future missions. They want to examine the moon’s chemical compositions and collect vapour samples.
NASA hopes to launch a mission a decade or so from now. The White House’s 2015 federal budget request allocated $15 million toward the mission.
NASA chief financial officer Beth Robinson said, “Europa is a very challenging mission operating in a really high radiation environment, and there is lots to do to prepare for it. We are looking for a launch some time in the mid-2020s.”
Currently, the NASA officials suggest the Europa Clipper is the most likely the earlier project, which is planned to launch in 2025. The Europa Clipper would orbit Jupiter and make flybys of Europa to study its ice shell and subsurface oceans. It would cruise through the plumes of water vapour on the south pole of the moon, providing a way to sample the ocean from afar. The total cost of the clipper would be $2 billion.
Mission scientist Robert Pappalardo of NASA’s Jet Propulsion Laboratory says the clipper will return with images with a resolution six times sharper than Galileo’s images, and 3000 times more data.
“The drumbeat is getting louder,” says Hand at California Institute of Technology in Pasadena, California.
Atoms that made up the Earth today were created through nuclear fusion reactions in ancient stars and supernova explosions. Under the right conditions, life was created. Is it possible that that the same process is happening on other planets?
The scientific community is enthusiastic to launch missions to Europa; however, there are people who are skeptical on what they will find on Europa and wonder if it is worth the money.
Scientists search for life on other planets to explain life on Earth. Where did we come from? Why are we here? Where will we be going? There is not scientific evidence to confirm hypothesis, scientists are still searching for answers.