Big news came from the Hubble Space Telescope today. Observations from the famous telescope made in ultraviolet light show a large plume of hydrogen and oxygen spewing from, Jupiter’s moon, Europa’s south polar region. Europa is one of Jupiter’s four largest moons, known as the Galilean Moons, after their discoverer Galileo Galilei in the 17th century. The plume is guessed to be water gushing from cracks in the ice that covers the entire surface of Europa. This is the first observation of geysers on Europa although it has been suspected for some time now.
Europa is roughly the same size our our moon and is covered with ice. This has been known for centuries since Galileo discovered the moon in 1610. Europa is easily visible in binoculars and small telescopes and is extremely bright. It was correctly guessed that Europa was covered in a layer of ice because it reflects a very high amount of sunlight. Ice is one of the most reflective materials, about 70% of sunlight is reflected back off the surface. The spacecraft we have sent to Jupiter such as Voyagers 1 and 2 and the Galileo probe confirmed the existence of an icy surface.
The surface of Europa is interesting because it doesn’t contain any craters or any marks of impacts like the vast majority of moons in the solar system. That means that Europa is constantly re-making its surface. The same way glaciers and tectonic plates reform the surface of Earth, giant cracks along the surface of Europa indicate that the surface is geologically active. Where there is surface tectonics there should be geological events such as volcanoes or geysers. That’s what Hubble confirmed today.
The observations from Hubble showed a massive plume of water gushing from the moon’s south polar region. The plume extends approximately 200 km (125 miles) into space. Europa has no atmosphere and much less gravity than Earth so the vapor is able to spew well beyond the surface of Europa. The water from the geyser was blasted from beneath the icy surface at a whopping 700 kilometers per hour (1,500 mph). That’s three times faster than a commercial jet! Two questions remain to be answered: How do we know the geyser is shooting out water and where does that water come from?
A Veritable Waterworld
The existence of water on Europa has actually been known for a long time. To know how this works we have to know a little bit about Europa’s orbital properties. Europa orbits Jupiter, the solar system’s largest planet. Jupiter’s gravity is so intense that it actually effects the insides of its closest moons. Europa’s orbit is slightly elliptical, meaning that it isn’t a perfect circle, an ellipse or oval-shaped orbit. Most celestial bodies have slightly elliptical orbits but Europa’s is more pronounced. When Europa is closer to Jupiter the massive gravity of the planet literally squeezes the moon and stretches the rocky core. This pressure and friction creates heat under the icy surface and has created a subsurface ocean on Europa. It is guessed that Europa actually contains more water than Earth as Europa’s ocean is global, there are no landmasses. NASA and the European Space Agency hope to eventually send a probe to Europa to explore this massive subsurface ocean because where water exists the possibility of life also exists.
The Giant Plume
We’ve answered where the water comes from, but how are scientists sure it is indeed water that was spewed from the surface and how does such a tiny moon have geysers that powerful? Hubble doesn’t just do visible light observations. The telescope is also equipped with a camera that can image in ultraviolet light. The actual images taken by Hubble don’t show what we think of as a geyser like Old Faithful in Yellowstone National Park. What Hubble observed was actually individual hydrogen and oxygen atoms in the plume. Since Europa has no atmosphere the hydrogen and oxygen atoms were in space. Jupiter, like Earth, generates an magnetic field in its solid metal core. When the water from the geyser interacts with the electrons from Jupiter the water separates into its constituent hydrogen and oxygen atoms which glow in ultraviolet light. That’s the best possible explanation for why Hubble observed these two individual atoms.
But where did the geyser come from? Well as we saw earlier about Europa’s elliptical orbit, the moon is closer at some points and further away at others. As Europa moves closer to Jupiter it is squeezed and crunched by Jupiter’s immense gravity. Then as Europa moves further away from Jupiter cracks in the ice open up and allow the subsurface water to rise up and spew out. As it so happens, Hubble recorded these observations while Europa was moving away from Jupiter so it makes sense that the cracks in the icy surface were opened up.
Teeming With Life?
The prospect of life swimming in Europa’s ocean has long been intriguing. The discovery of geysers on Europa make the question even more worth exploring. As we see from geysers on Earth, a lot of power in needed to blast material out from under the surface. On Earth this comes from heat and pressure that builds up beneath cracks in the Earth’s crust. When the heat and pressure becomes too great water and gases burst forth in a steaming awesome display of geological activity.
One of the theories of how life began involves water and heat in the prehistoric oceans of Earth. Hydrothermal vents on the ocean floor mix heat and amino acids to create the first organic materials. To this day life thrives around hydrothermal vents despite the extremely alien conditions. We know there is heat in Europa’s oceans due to the gravitational heating of the core from Jupiter and there’s water which is a universal solvent. Could the mixing of amino acids, water, and heat have occurred on Europa as well? The prospect is certainly intriguing and worthy of further exploration. Curiosity is one of humanity’s definite traits so hopefully in a decade or two we will have a spacecraft on its way to Europa to explore the subsurface ocean and attempt to find evidence of life. Imagine fish (or something totally alien) swimming around on the moon of a distant planet! How that would change our views of life and its frequency throughout our galaxy!