Marsquakes and Meteorites Unveil the Potential for Subterranean Alien Lifeforms on Mars
Boulder, Colo., USA: Are subterranean lifeforms viable on Mars? A new interpretation of Martian
seismic data by scientists Ikuo Katayama of Hiroshima University and Yuya
Akamatsu of Research Institute for Marine Geodynamics suggests the presence
of water below the surface of Mars. “If liquid water exists on Mars,”
Katayama says, “the presence of microbial activity” is possible.
This analysis is based on seismic data from SEIS (Seismic Experiment for
the Interior Structure), deployed from NASA’s InSight lander that landed on Mars in 2018 (Fig. 1). This robotic lander is unique
because it was able to use its robotic arm to place a seismometer on the
surface of Mars. The SEIS
instrument, which contains the seismometer, uses the seismic waves
naturally generated on Mars from Marsquakes or meteorite impacts to scan
the planet’s interior (Fig. 1). When a Marsquake or meteorite impact occurs
on Mars, SEIS can read the energy emitted
as P-waves,
S-waves, and surface
waves to create an image of the planet’s interior (Fig.
2). Scientists can use P-waves and S-waves to determine a lot about the
rocks that make up Mars, including the density of the rocks or potential
composition changes within the rocks. For example, S-waves cannot travel
through water and move at a slower speed than P-waves. Therefore, the
presence, absence, and arrival time of S-waves can determine what the
subsurface looks like. Moreover, P-waves can travel faster through
higher-density material and slower through less dense material, so their
velocity can help determine the density of the material the wave is
traveling through, as well as if there are any changes in density along its
path. The seismic data collected with SEIS shows a boundary at 10 km depth
and 20 km depth from measured discrepancies in seismic velocity.
This boundary has previously been interpreted as sharp transitions in the
porosity (the percentage of open space in a rock) or chemical composition
of the Martian interior. However, Katayama and Akamatsu have interpreted
these cracks as potential evidence for water within the Martian subsurface.
The seismic data indicate a boundary between dry cracks and water-filled
cracks in the Martian subsurface (Fig. 3). To test their hypothesis, they
measured the seismic velocity passing through rocks with the same
structures and composition of a typical Martian crustal rock under wet,
dry, and frozen conditions. A typical Martian rock is similar to the
diabase rocks from Rydaholm, Sweden, due to their evenly sized plagioclase
and orthopyroxene grains. In the lab, Katayama and Akamatsu measured P-wave
and S-wave velocity using a piezoelectric transducer, which uses
“electrical energy . . . as a wave source” that “monitor[s] seismic wave
energy” on dry, wet, and frozen diabase samples. Experimentation revealed
that the seismic velocities of the dry, wet, and frozen samples are
significantly different, which supports the interpretation that the
boundary at 10 km and 20 km could be from a change from dry rock to wet
rock.
These laboratory experiments back up Katayama and Yuya’s hypothesis that
the boundary measured by seismic data indicates a transition from dry rock
to wet rock rather than a change in porosity or chemical composition. The
findings, therefore, provide compelling evidence for the existence of
liquid water beneath the surface of Mars. “Many studies suggest the
presence of water on ancient Mars billions of years ago,” Katayama
explains, “but our model indicates the presence of liquid water on
present-day Mars.”
FEATURED ARTICLE
Seismic discontinuity in the Martian crust possibly caused by water-filled cracks
I. Katayama and Y. Akamatsu
Contact: Ikuo Katayama, Hiroshima University, katayama@hiroshima-u.ac.jp
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