Europa's Epsom Salt May Indicate Ocean Biosphere

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If you’ve ever found yourself wanting to know if there’s extraterrestrial life on Europa, this latest study into the Jovian moon’s icy crust should whet your appetite.

Using data from the powerful Keck II Telescope atop Mauna Kea in Hawai’i, astronomers Mike Brown, of the California Institute of Technology (Caltech), and Kevin Hand, of NASA’s Jet Propulsion Laboratory (JPL), have found strong evidence that suggests chemicals from Europa’s sub-surface ocean are leaking to the surface. In turn, chemicals from the surface are likely cycling into the ocean too. The research has been published in the Astrophysical Journal.

This discovery is profound when considering the live-giving potential of one of Jupiter’s largest moons — it is further proof that the sub-surface ocean isn’t cut off from the surface; chemicals are cycling into the ocean, potentially supporting a hypothetical Europan biosphere.

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“We now have evidence that Europa’s ocean is not isolated — that the ocean and the surface talk to each other and exchange chemicals,” said Brown, in a Caltech press release. “That means that energy might be going into the ocean, which is important in terms of the possibilities for life there. It also means that if you’d like to know what’s in the ocean, you can just go to the surface and scrape some off.”

Using a high-resolution spectroscope attached to Keck’s infrared eye, Brown and Hand detected the spectroscopic fingerprint of magnesium sulfate salt — also known on Earth as epsomite, or, more commonly, Epsom salt — a mineral that could have only been formed through the oxidation of a mystery mineral that originated below the ice in a liquid environment.

“Magnesium should not be on the surface of Europa unless it’s coming from the ocean,” said Brown. “So that means ocean water gets onto the surface, and stuff on the surface presumably gets into the ocean water.”

It has long been known that sulfur ejected from sibling Jovian moon Io rains down on one of Europa’s hemispheres. Being tidally locked — as in, one side of Europa is always facing Jupiter — one hemisphere is always leading the moon’s orbit, while the other hemisphere is always trailing. The sulfur ejected from Io is directed down to Europa’s trailing hemisphere by Jupiter’s magnetic field. This process was first inferred during the Galileo mission to Jupiter from 1989 to 2003.

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When analyzing the spectrum of the water ice and other minerals embedded in Europa’s surface, Brown and Hand detected a tiny, previously unnoticed “dip” in the spectrum at low latitudes in the trailing hemisphere.

At Hand’s JPL lab, the pair tested a variety of chemicals — including household chemicals like Draino — to see if they could replicate this dip in the spectrum. The most likely candidate was identified as magnesium sulfate. The chemical is likely formed when ionized sulfur (from Io) makes contact with another chemical on Europa’s surface: magnesium chloride.

Although it may sound like you need a degree in chemistry to understand these chemical reactions, the upshot is straightforward. Although magnesium chloride isn’t easy to detect, magnesium sulfate is. We know where the sulfur came from (Io) and we know that the magnesium could have only come from Europa’s oceans. The authors therefore deduce that Europa’s oceans are salty, just like Earth’s.

“If we’ve learned anything about life on Earth, it’s that where there’s liquid water, there’s generally life,” said Hand. “And of course our ocean is a nice salty ocean. Perhaps Europa’s salty ocean is also a wonderful place for life.”

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This is another piece of evidence in favor of a ripe environment for life to thrive in Europa’s oceans. Below the cracked icy surface, a 100 kilometer-deep ocean exists in a liquid state, heated by the tidal stresses inflicted on Europa’s core. Previous observations have detected the presence of liquid water “lakes” in pockets near the surface — indicative that some of that water escapes to the surface, allowing nutrients through the cracks in the ice.

In 2009, University of Arizona scientist Richard Greenberg caused a stir when he made an estimate of how much oxygen could potentially cycle into the Europan ocean. By his reckoning, 6.6 billion pounds of macrofauna could be supported. Yes, we’re talking about complex organisms not dissimilar the marine life we’re familiar with on Earth.

Brown and Hand’s research into the spectroscopic signature of chemistry on Europa’s surface further strengthens that not only could there be sufficient quantities of oxygen cycling, nutrients could be doing the same.

I, for one, welcome our Europan jellyfish overlords.

Publication: Salts and radiation products on the surface of Europa, Brown & Hand, arXiv:1303.0894 [astro-ph.EP]

Image credit: NASA

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