Sky & Telescope - July 2023 - 8

NEWS NOTES
to search for those changes, " notes team
member Scott Hensley (Jet Propulsion
Laboratory). Computers have gotten
quite good at pattern recognition, but
spotting differences in Magellan images
requires taking into account the different
viewing angles of each image.
Since his search was manual, Herrick
SOLAR SYSTEM
Finally! Scientists Find Active Volcano on Venus
FOR DECADES, scientists have both
suspected the existence of and searched
for active volcanoes on Venus. Its surface
is geologically young, perhaps only
tens of millions of years old, meaning
that lava flowed recently on our sister
planet. Now, a new analysis of threedecade-old
radar images from NASA's
Magellan orbiter has resulted in a
definitive detection: In 1991, there was
volcanic activity on the surface.
" We've never had evidence as strong
as this, " says Paul Byrne (Washington
University in St. Louis), who was not
involved with the study.
Magellan orbited Venus from 1990
until 1994, when it plunged into the
hellish atmosphere. But before the mission's
end, the spacecraft's synthetic
aperture radar mapped almost all of the
pThis computer-generated 3D model of Venus's
surface shows the summit of Maat Mons.
Venusian surface, showing features as
small as 120 meters (390 feet) across.
These maps were sent back to Earth
and stored digitally on CDs. It took
years for in-depth probing of the surface
to become possible. " You need to be
able to load in a few hundred-gigabyte
data sets, pan around on the surface,
and zoom in and out, " says Robert Herrick
(University of Alaska Fairbanks).
Herrick presented the study on March
15th in Science and at the 54th Lunar
and Planetary Science Conference in
Woodlands, Texas.
Herrick searched the data the oldfashioned
way - by eye. " There's no
automatic algorithm that will allow you
New lava flows
Vent 1
Vent 2
Distance (km)
5
Vent 1
Vent 2
narrowed his scope to the most likely
volcanic areas. He'd pored through only
1.5% of the planet's area when he hit
paydirt. On Maat Mons, which is itself
a volcano, Herrick spotted a caldera
that had enlarged over an eight-month
period, changing from circular to
kidney bean-shaped. The caldera also
became shallower and its floor darkened,
possibly indicating it had filled
with lava.
To verify that the detection wasn't a
trick of the light, so to speak, Herrick
and Hensley used Magellan's topography
map to correct their radar images
so that they both appear as if viewed
from straight above, a process called
orthorectification. They conclude that
the caldera's changes in size, shape, and
brightness are real.
One scenario is that the first radar
image caught the caldera in between
eruptions. " If the magma chamber is
still down there and still getting fed
every now and again, you might get a
later eruption in the exact same place, "
Herrick explains. Although the fuzzy
images make it difficult to say for
certain, he thinks this caldera could be
acting much like Kīlauea in Hawai'i, a
shield volcano that last erupted earlier
this year. There might also have been
accompanying lava flows, which show
up in the second image as a brightened
area north of the caldera, but the
changing illumination makes it difficult
to say for sure.
" It's not clear that there's been volcanic
activity, i.e., stuff coming out of the
ground, " Byrne says. " It's possible that
what we're seeing in their new paper is
magmatic activity, i.e., the movement of
10
pTwo images, the left taken in February 1991 and the right taken in October of the same year but
from a different viewing angle, show a volcanic vent (Vent 2) that became bigger, changed shape,
and darkened. (Vent 1 remained unchanged over the same time period.) The dashed line encircles a
region that became brighter in that time period; whether these are new lava flows is still uncertain.
8
JULY 2023 * SKY & TELESCOPE
magma in the subsurface. "
" But either way, " he adds, " this finding
is a big deal! "
¢MONICA YOUNG
Read more at https://is.gd/Venusvent.
VOLCANO ON VENUS: NASA / JPL-CALTECH; RADAR IMAGES
OF VENTS: USGS ASTROGEOLOGY SCIENCE CENTER / NASA
PLANETARY DATA SYSTEM

https://www.is.gd/Venusvent

Sky & Telescope - July 2023

Table of Contents for the Digital Edition of Sky & Telescope - July 2023