New NASA instrument will identify composition of Enceladus' plumes

Instrument sensitivity is being enhanced to detect even small quantities of water.
By Laurel Kornfeld | Nov 08, 2017
As a next step in determining whether microbial life exists in the subsurface ocean of Saturn's moon Enceladus, NASA plans to construct a sub-millimeter wave or radio instrument capable of identifying the chemicals in the moon's geysers.

Engineers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, have been given the go-ahead to build a technologically advanced, remote-sensing instrument known as the Submillimeter Enceladus Life Fundamentals Instrument or SELFI.

A significant improvement over submillimeter devices currently in use, SELFI will study the chemical makeup of Enceladus' plumes of water and ice, from which scientists believe they will be able to determine whether the underground ocean is capable of hosting life.

At the bottoms of Earth's oceans, hydrothermal vents have been found to be teeming with microbes, a discovery that has led scientists to question whether ocean worlds such as Enceladus also have these hydrothermal vents, and if they do, whether these could host simple life forms.

Studying the composition of Enceladus' plumes could enable scientists to also identify the composition of the subsurface ocean.

Before NASA's Cassini mission, scientists thought Enceladus was frozen solid. However, the spacecraft detected a slight wobble in the the moon's orbit that indicates a subsurface ocean might be present. Cassini also discovered the plumes of water vapor and icy particles coming from fissures on the surface of Saturn's sixth largest moon.

Tidal forces from Saturn appear to generate heat within Enceladus by pulling and squeezing the moon, warming its interior enough to hold liquid water and crack the ice shell.

"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," said Gordon Chin, SELFI Principal Investigator.

"We can scan through all the plumes to see what's coming out of Enceladus. Water vapor 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."

Spectrometers analyze the chemical compositions of both gases and solids in astronomical objects, revealing key information about the objects' properties.

"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 explained.

"The spectral lines are so discrete that we can identify and quantify chemicals with no confusion whatsoever," said chief systems engineer Paul Racette of Goddard.

SELFI will be capable of detecting and analyzing 13 molecular species at the same time, Chin noted.

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