NASA designs advanced new SELFI instrument to help search for life on Enceladus

The plumes of Enceladus: SELFI would study their composition in more detail than ever before. Photo Credit: NASA/JPL/Space Science Institute

Is there life on Enceladus? Are there any Enceladan bacteria or other little critters swimming in that alien ocean on this tiny moon of Saturn? We don’t know yet, but there is compelling evidence from the Cassini mission for at least a habitable environment in the dark waters below the icy crust. What’s needed now is to return to Enceladus with new and better instruments, designed especially to search for signs of active biology, which Cassini couldn’t do. Now, a new instrument has been designed by NASA which would further study the water vapour plumes erupting from the moon’s south pole and analyze what’s in them in more detail than previously possible. Those plumes are tantalizingly connected to the salty subsurface ocean below the surface ice.

The new instrument is called the Submillimeter Enceladus Life Fundamentals Instrument (SELFI) which would measure trace chemicals in the plumes. SELFI would be able to simultaneously detect and analyze 13 molecular species, including water in various isotopic forms, as well as methanol, ammonia, ozone, hydrogen peroxide, sulfur dioxide, and sodium chloride (the same salt in Earth’s oceans). These measurements would provide specific clues as to the composition and habitability of the subsurface ocean.

Diagram of an interior cross-section of the crust of Enceladus, showing how hydrothermal activity is thought to be causing the plumes of water vapour on the surface. Image Credit: NASA-GSFC/SVS/NASA/JPL-Caltech/Southwest Research Institute
Map of the Tiger Stripe fractures at the south pole of Enceladus, with plume locations marked by white circles. Cassini’s flight path during one close flyby is marked by the red line. Image Credit: NASA/JPL-Caltech/Space Science Institute

“Submillimeter wavelengths, which are in the range of very high-frequency radio, give us a way to measure the quantity of many different kinds of molecules in a cold gas. We can scan through all the plumes to see what’s coming out from Enceladus,” said SELFI Principal Investigator Gordon Chin. “Water vapour and other molecules can reveal some of the ocean’s chemistry and guide a spacecraft onto the best path to fly through the plumes to make other measurements directly.”

“Molecules such as water and carbon monoxide, and others, are like little radio stations that broadcast on very specific frequencies that say, ‘hey, I’m water, I’m carbon monoxide,’” Chin added.

“SELFI is really new,” Chin said. “This is one of the most ambitious submillimeter instruments ever built.”

Close-up view of plume activity in one of the Tiger Stripe fractures at the south pole of Enceladus. Photo Credit: NASA/JPL/Space Science Institute
Another close-up view of rough surface terrain on Enceladus. Photo Credit: NASA/JPL/Space Science Institute
A more global view of Enceladus. Photo Credit: NASA/JPL/Space Science Institute

SELFI would be much more sensitive than previous similar submillimeter instruments. With it, scientists could measure very small amounts of trace gases, even at the extremely cold temperatures of the moon’s surface, and explore the system of the surface vents themselves.

“The spectral lines are so discrete that we can identify and quantify chemicals with no confusion whatsoever,” said Paul Racette, a Goddard engineer who is the project’s chief systems engineer.

The water vapour plumes were previously analyzed by Cassini, and found to also contain ice particles, organics, carbon dioxide, methane and salts. The plumes erupt through huge cracks called Tiger Stripes in the icy surface crust, originating from a global subsurface ocean. There is also now evidence from Cassini for active hydrothermal vents on the bottom of that ocean, much like in oceans on Earth.

SELFI would be a great tool in the search for life on Enceladus (and perhaps Europa also?). Now all that’s needed is a mission to send it on.

This article was first published on AmericaSpace.






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