Scientists find evidence of complex organic molecules from Enceladus
Discovery indicates Saturn's
moon meets critical requirements for life
June 27, 2018
Southwest Research Institute
Using mass spectrometry data
from NASA's Cassini spacecraft, scientists found that large, carbon-rich
organic molecules are ejected from cracks in the icy surface of Saturn's moon
Enceladus. Scientists think chemical reactions between the moon's rocky core
and warm water from its subsurface ocean are linked to these complex molecules.
"We are, yet again, blown
away by Enceladus. Previously we'd only identified the simplest organic
molecules containing a few carbon atoms, but even that was very
intriguing," said SwRI's Dr. Christopher Glein, a space scientist
specializing in extraterrestrial chemical oceanography. He is coauthor of a
paper in Nature outlining this discovery. "Now we've found organic
molecules with masses above 200 atomic mass units. That's over ten times
heavier than methane. With complex organic molecules emanating from its liquid
water ocean, this moon is the only body besides Earth known to simultaneously
satisfy all of the basic requirements for life as we know it."
Prior to its deorbit in
September of 2017, Cassini sampled the plume of material emerging from the
subsurface of Enceladus. The Cosmic Dust Analyzer (CDA) and the SwRI-led Ion
and Neutral Mass Spectrometer (INMS) made measurements both within the plume
and Saturn's E-ring, which is formed by plume ice grains escaping Enceladus'
gravity.
"Even after its end, the
Cassini spacecraft continues to teach us about the potential of Enceladus to
advance the field of astrobiology in an ocean world," Glein said.
"This paper demonstrates the value of teamwork in planetary science. The
INMS and CDA teams collaborated to reach a deeper understanding of the organic
chemistry of Enceladus' subsurface ocean than would be possible with only one
data set."
During Cassini's close flyby
of Enceladus on Oct. 28, 2015, INMS detected molecular hydrogen as the
spacecraft flew through the plume. Previous flybys provided evidence for a
global subsurface ocean residing above a rocky core. Molecular hydrogen in the
plume is thought to form by the geochemical interaction between water and rocks
in hydrothermal environments.
"Hydrogen provides a
source of chemical energy supporting microbes that live in the Earth's oceans
near hydrothermal vents," said SwRI's Dr. Hunter Waite, INMS principal
investigator who also was a coauthor of the new paper. "Once you have
identified a potential food source for microbes, the next question to ask is
'what is the nature of the complex organics in the ocean?' This paper
represents the first step in that understanding -- complexity in the organic
chemistry beyond our expectations!"
"The paper's findings
also have great significance for the next generation of exploration,"
Glein said.
"A future spacecraft
could fly through the plume of Enceladus, and analyze those complex organic
molecules using a high-resolution mass spectrometer to help us determine how
they were made. We must be cautious, but it is exciting to ponder that this
finding indicates that the biological synthesis of organic molecules on
Enceladus is possible."
Story Source:
Materials provided by Southwest Research Institute. Note:
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Journal Reference:
Frank Postberg, Nozair
Khawaja, Bernd Abel, Gael Choblet, Christopher R. Glein, Murthy S. Gudipati,
Bryana L. Henderson, Hsiang-Wen Hsu, Sascha Kempf, Fabian Klenner, Georg
Moragas-Klostermeyer, Brian Magee, Lenz Nölle, Mark Perry, René Reviol, Jürgen
Schmidt, Ralf Srama, Ferdinand Stolz, Gabriel Tobie, Mario Trieloff, J. Hunter
Waite. Macromolecular organic compounds from the depths of Enceladus. Nature,
2018; 558 (7711): 564 DOI: 10.1038/s41586-018-0246-4
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