If selected at another future opportunity, the ELF mission would search for
biosignature and
biomolecules in the geysers of Enceladus. The south polar jets loft water, salts and
organic 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 measure
amino acids — the building blocks of
proteins — analyze
fatty acids, and determine whether
methane (CH4) found in the plumes could have been produced by living
organisms.[2]
In 2008, the Cassini orbiter was flown through a plume and analyzed the material with its neutral
mass spectrometer. The orbiter detected simple organics, including methane (CH4),
carbon monoxide (CO),
carbon dioxide (CO2)
nitrogen, and complex
organic 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 the
plumes of Enceladus, of
hydrogen cyanide, a possible chemical essential for
life as we know it, as well as other
organic molecules, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant
microbial communities or drive complex
organic synthesis leading to the
origin of life."[9][10]
Mission concept
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 of
Cassini 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 over a period of 3 years through plumes of water launched above the south pole of
Enceladus.[2] The geysers could provide easy access for sampling the moon's subsurface ocean, and if there is
microbial life in it, ice particles from the sea could contain the evidence
astrobiologists need to identify them.[11] The Principal Investigator is
Jonathan Lunine of
Cornell University in Ithaca, New York.
Objectives
The goals of the mission are derived directly from the most recent decadal survey: first, to determine primordial sources of
organics and the sites of
organic synthesis today; and second, to determine if there are current
habitats in Enceladus where the conditions for
life 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 by Cassini, 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 two
mass spectrometers to assess
habitability of the interior oceanic environment. The payload consists of
the MASPEX and the ENIJA, optimized to analyze respectively the gas and grains:[1][8]
The
Cassini spacecraft has measured small
silica particles, normally formed at 90 °C or higher, streaming from Enceladus.[12] The size and composition of the particles suggest that they come from current
hydrothermal 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 of
amino acids (the building blocks of
proteins). The second test would determine whether the
carbon number distribution in
fatty acids or
isoprenoids is biased toward a particular rule (even, odd, or divisible by a small integer). The third would measure carbon and
hydrogenisotopic ratios, together with the abundance of
methane 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 from
the original on August 16, 2014. Retrieved April 8, 2015.