If selected at another future opportunity, the ELF mission would search forbiosignature andbiomolecules in the geysers of Enceladus. The south polar jets loft water, salts andorganic molecules dozens of miles over the moon's surface from an underground regional ocean. The hypothesis is that the water is warmed by thermal vents similar to features found deep in Earth's oceans. ELF's instruments would measureamino acids — the building blocks ofproteins — analyzefatty acids, and determine whethermethane (CH4) found in the plumes could have been produced by livingorganisms.[2]
In 2008, theCassini orbiter was flown through a plume and analyzed the material with its neutralmass spectrometer. The orbiter detected simple organics, including methane (CH4),carbon monoxide (CO),carbon dioxide (CO2)nitrogen, and complexorganic compounds.[8]Cassini also detected sodium and potassium at a concentration implying a salty liquid ocean.[8] However,Cassini did not have the equipment with the sensitivity required for direct analyses.[1][8]
On 14 December 2023, astronomers reported the first time discovery, in theplumes of Enceladus, ofhydrogen cyanide, a possible chemical essential forlife as we know it, as well as otherorganic molecules, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extantmicrobial communities or drive complexorganic synthesis leading to theorigin of life."[9][10]
Composite map of Enceladus's south polar region showing cracks dubbed'tiger stripes' where the geysers are located.
The Enceladus Life Finder (ELF) mission would pursue the implications ofCassini orbiter's 2005 discoveries of active jetting from, and existence of an ocean within, Enceladus. The mission concept would have the ELF orbiter fly 8 to 10 times through plumes of water launched above the south pole of Enceladus over a period of 3 years.[2] The geysers could provide easy access for sampling the moon's subsurface ocean, and if there ismicrobial life in it, ice particles from the sea could contain the evidenceastrobiologists need to identify them.[11] The Principal Investigator isJonathan Lunine ofCornell University in Ithaca, New York.
The goals of the mission are derived directly from the most recent decadal survey: first, to determine primordial sources oforganics and the sites oforganic synthesis today; and second, to determine if there are currenthabitats in Enceladus where the conditions forlife could exist today, and if life exists there now.[1] To achieve these goals, the ELF mission has three objectives:[1]
To measure abundances of a carefully selected set of neutral species, some of which were detected byCassini, to ascertain whether the organics and volatiles coming from Enceladus have been thermally altered over time.
To determine the details of the interior marine environment —pH,oxidation state, available chemical energy, and temperature — that permit characterization of the life-carrying capacity of the interior.
To look for indications that organics are the result of biological processes through three independent types of chemical measurements that are widely recognized as diagnostic of life.
The ELF spacecraft would use twomass spectrometers to assesshabitability of the interior oceanic environment. The payload consists ofthe MASPEX and the ENIJA, optimized to analyze respectively the gas and grains:[1][8]
TheCassini spacecraft has measured smallsilica particles, normally formed at 90 °C or higher, streaming from Enceladus.[12] The size and composition of the particles suggest that they come from currenthydrothermal activity,[13][14][15][16] where the moon's ocean meets the underlying rock, a prime habitat for life.[12][17]
ELF's instruments would conduct three kinds of tests in order to minimize the ambiguity involved in life detection.[1][8] The first would look for a characteristic distribution ofamino acids (the building blocks ofproteins). The second test would determine whether thecarbon number distribution infatty acids orisoprenoids is biased toward a particular rule (even, odd, or divisible by a small integer). The third would measure carbon andhydrogenisotopic ratios, together with the abundance ofmethane relative to other alkanes, to assess whether the values fall in the range for biological processes.[8]
^Gronstal, Aaron (July 30, 2014)."Enceladus in 101 Geysers".NASA Astrobiology Institute. Archived fromthe original on August 16, 2014. RetrievedApril 8, 2015.
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