This illustration of the large Quetzalpetlatl Corona located in Venus’
southern hemisphere depicts active volcanism and a subduction zone, where the
foreground crust plunges into the planet’s interior. A new study suggests
coronae reveal locations where active geology is shaping Venus’ surface. Credits: NASA/JPL-Caltech/Peter Rubin
The research uses archival NASA data to show that Venus may be losing heat
from geologic activity in regions called coronae, possibly like early tectonic
activity on Earth.
Earth and Venus are rocky planets of about the same size and rock
chemistry, so they should be losing their internal heat to space at about the
same rate. How Earth loses its heat is well known, but Venus’ heat flow
mechanism has been a mystery. A study that uses three-decade-old data
from NASA’s Magellan
mission has taken a new look at how Venus cools and
found that thin regions of the planet’s uppermost layer may provide an answer.
Our planet has a hot core that heats the surrounding mantle, which carries
that heat up to Earth’s rigid outer rocky layer, or lithosphere. The heat is
then lost to space, cooling the uppermost region of the mantle. This mantle
convection drives tectonic processes on the surface, keeping a patchwork of mobile plates in motion. Venus
doesn’t have tectonic plates, so how the planet loses its heat and what
processes shape its surface have been long-running questions in planetary
science.
The study looks at the mystery using observations the Magellan spacecraft
made in the early 1990s of quasi-circular geological features on Venus called
coronae. Making new measurements of coronae visible in the Magellan images, the
researchers concluded that coronae tend to be located where the planet’s
lithosphere is at its thinnest and most active.
This composite radar image of Quetzalpetlatl Corona was created by
overlaying data from about 70 orbits of NASA’s Magellan mission into an image
obtained by the Arecibo Observatory radio telescope in Puerto Rico. The rim of
the corona indicates possible tectonic activity. Credits: NASA/JPL-Caltech
“For so long we’ve been locked into this idea that Venus’ lithosphere is
stagnant and thick, but our view is now evolving,” said Suzanne Smrekar, senior
research scientist at NASA’s Jet Propulsion Laboratory in Southern California,
who led the study published in Nature Geoscience.
Just as a thin bedsheet releases more body heat than a thick comforter, a
thin lithosphere allows more heat to escape from the planet’s interior via
buoyant plumes of molten rock rising to the outer layer. Typically, where
there’s enhanced heat flow, there’s increased volcanic activity below the
surface. So coronae likely reveal locations where active geology is shaping
Venus’ surface today.
The researchers focused on 65 previously unstudied coronae that are up to a
few hundred miles across. To calculate the thickness of the lithosphere
surrounding them, they measured the depth of the trenches and ridges around
each corona. What they found is that ridges are spaced more closely together in
areas where the lithosphere is more flexible, or elastic. By applying a
computer model of how an elastic lithosphere bends, they determined that, on
average, the lithosphere around each corona is about 7 miles (11 kilometers)
thick – much thinner than previous studies suggest. These regions have an
estimated heat flow that is greater than Earth’s average, suggesting that
coronae are geologically active.
“While Venus doesn’t have Earth-style tectonics, these regions of thin
lithosphere appear to be allowing significant amounts of heat to escape,
similar to areas where new tectonic plates form on Earth’s seafloor,” said
Smrekar.
This radar image from NASA’s Magellan mission shows circular fracture
patterns surrounding the “Aine” corona, located in Venus’ southern hemisphere.
The corona is about 124 miles (200 kilometers) across and shows various
features that may be associated with volcanic activity. Credits: NASA/JPL-Caltech
A Window Into Earth’s Past
To calculate how old a celestial body’s surface material is, planetary
scientists count the number of visible impact craters. For a tectonically
active planet like Earth, impact craters are erased by the subduction of
continental plates and covered by molten rock from volcanoes. If Venus lacks
tectonic activity and the regular churn of Earth-like geology, it should be
covered in old craters. But by counting the number of Venusian craters,
scientists estimate that the surface is relatively young.
Recent studies suggest the youthful appearance of Venus’ surface is likely
due to volcanic activity, which drives regional resurfacing today. This finding
is supported by the new research indicating higher heat flow in coronae regions
– a state that Earth’s lithosphere may have resembled in the past.
“What’s interesting is that Venus provides a window into the past to help
us better understand how Earth may have looked over 2.5 billion years ago. It’s
in a state that is predicted to occur before a planet forms tectonic plates,”
said Smrekar, who is also the principal investigator of NASA’s forthcoming
Venus Emissivity, Radio science, InSAR, Topography, And Spectroscopy (VERITAS) mission.
VERITAS will pick up where Magellan left off, improving upon that mission’s
data, which is low resolution and comes with large margins of error. Targeting
launch within a decade, the mission will use a state-of-the-art synthetic
aperture radar to create 3D global maps and a near-infrared spectrometer to
figure out what the surface is made of. VERITAS will also measure the planet’s
gravitational field to determine the structure of Venus’ interior. The
instruments will together fill in the story of the planet’s past and present
geologic processes.
“VERITAS will be an orbiting geologist, able to pinpoint where these active
areas are, and better resolve local variations in lithospheric thickness. We’ll
be even be able to catch the lithosphere in the act of deforming,” said
Smrekar. “We’ll determine if volcanism really is making the lithosphere
‘squishy’ enough to lose as much heat as Earth, or if Venus has more mysteries
in store.”
Source: Study
Finds Venus’ ‘Squishy’ Outer Shell May Be Resurfacing the Planet | NASA
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