The search for extraterrestrial life just got more interesting as a team of
scientists including Southwest Research Institute’s Dr. Christopher Glein
has discovered new evidence for a key building block for life in the
subsurface ocean of Saturn’s moon Enceladus. New modeling indicates that
Enceladus’s ocean should be relatively rich in dissolved phosphorus, an
essential ingredient for life.
“Enceladus is one of the prime targets in humanity’s search for life in our
solar system,” said Glein, a leading expert in extraterrestrial
oceanography. He is a co-author of a paper in the Proceedings of the
National Academy of Sciences (PNAS) describing this research. “In the years
since NASA’s Cassini spacecraft visited the Saturn system, we have been
repeatedly blown away by the discoveries made possible by the collected
data.”
The Cassini spacecraft discovered Enceladus’s subsurface liquid water and
analyzed samples as plumes of ice grains and water vapor erupted into space
from cracks in the moon’s icy surface.
“What we have learned is that the plume contains almost all the basic
requirements of life as we know it,” Glein said. “While the bioessential
element phosphorus has yet to be identified directly, our team discovered
evidence for its availability in the ocean beneath the moon’s icy crust.”
One of the most profound discoveries in planetary science over the past 25
years is that worlds with oceans beneath a surface layer of ice are common
in our solar system. Such worlds include the icy satellites of the giant
planets, such as Europa, Titan and Enceladus, as well as more distant bodies
like Pluto. Worlds like Earth with surface oceans must reside within a
narrow range of distances from their host stars to maintain the temperatures
that support surface liquid water. Interior water ocean worlds, however, can
occur over a much wider range of distances, greatly expanding the number of
habitable worlds likely to exist across the galaxy.
“The quest for extraterrestrial habitability in the solar system has shifted
focus, as we now look for the building blocks for life, including organic
molecules, ammonia, sulfur-bearing compounds as well as the chemical energy
needed to support life,” Glein said. “Phosphorus presents an interesting
case because previous work suggested that it might be scarce in the ocean of
Enceladus, which would dim the prospects for life.”
Phosphorus in the form of phosphates is vital for all life on Earth. It is
essential for the creation of DNA and RNA, energy-carrying molecules, cell
membranes, bones and teeth in people and animals, and even the sea’s
microbiome of plankton.
Team members performed thermodynamic and kinetic modeling that simulates the
geochemistry of phosphorus based on insights from Cassini about the
ocean-seafloor system on Enceladus. In the course of their research, they
developed the most detailed geochemical model to date of how seafloor
minerals dissolve into Enceladus’s ocean and predicted that phosphate
minerals would be unusually soluble there.
“The underlying geochemistry has an elegant simplicity that makes the
presence of dissolved phosphorus inevitable, reaching levels close to or
even higher than those in modern Earth seawater,” Glein said. “What this
means for astrobiology is that we can be more confident than before that the
ocean of Enceladus is habitable.”
According to Glein, the next step is clear: “We need to get back to
Enceladus to see if a habitable ocean is actually inhabited.”
Reference:
Jihua Hao, Christopher R. Glein, Fang Huang, Nathan Yee, David C. Catling,
Frank Postberg, Jon K. Hillier, Robert M. Hazen. Abundant phosphorus expected
for possible life in Enceladus’s ocean. Proceedings of the National Academy of
Sciences, 2022; 119 (39)
DOI: 10.1073/pnas.2201388119
Tags:
Space & Astrophysics