In the time since Parker Solar Probe captured its first visible light images of Venus’ surface from orbit in July 2020, a subsequent flyby has allowed the spacecraft to gather more images, creating a video of Venus’ entire nightside. A full analysis of the images and video, published on Feb. 9, 2022, in the journal Geophysical Research Letters, is adding to scientists’ understanding of the planet likened as Earth’s twin.
NASA’s Parker Solar Probe has taken its
first visible light images of the surface of Venus from space.
Smothered in thick clouds, Venus’ surface is usually
shrouded from sight. But in two recent flybys of the planet, Parker used its
Wide-Field Imager, or WISPR, to image the entire nightside in wavelengths of
the visible spectrum – the type of light that the human eye can see – and
extending into the near-infrared.
The images, combined into a video, reveal a faint glow
from the surface that shows distinctive features like continental regions,
plains, and plateaus. A luminescent halo of oxygen in the atmosphere can also
be seen surrounding the planet.
“We’re thrilled with the science insights Parker Solar
Probe has provided thus far,” said Nicola Fox, division director for the
Heliophysics Division at NASA Headquarters. “Parker continues to outperform our
expectations, and we are excited that these novel observations taken during our
gravity assist maneuver can help advance Venus research in unexpected ways.”
Such images of the planet, often called Earth’s twin,
can help scientists learn more about Venus’ surface geology, what minerals
might be present there, and the planet’s evolution. Given the similarities
between the planets, this information can help scientists on the quest to understand
why Venus became inhospitable and Earth became an oasis.
“Venus is the third brightest thing in the sky, but until recently we have not had much information on what the surface looked like because our view of it is blocked by a thick atmosphere,” said Brian Wood, lead author on the new study and physicist at the Naval Research Laboratory in Washington, DC. “Now, we finally are seeing the surface in visible wavelengths for the first time from space.”
NASA’s Parker Solar Probe has taken its first visible light images of the surface of Venus from space. Credits: NASA's Goddard Space Flight Center/Joy Ng
Unexpected Capabilities
The first WISPR images of
Venus were taken in July 2020 as Parker embarked on
its third flyby, which the spacecraft uses to bend its orbit closer to the Sun.
WISPR was designed to see faint features in the solar atmosphere and wind, and
some scientists thought they might be able to use WISPR to image the cloud tops
veiling Venus as Parker passed the planet.
“The objective was to measure the speed of the clouds,” said WISPR project
scientist Angelos Vourlidas, co-author on the new
paper and researcher at Johns Hopkins University Applied
Physics Laboratory.
But instead of just seeing clouds, WISPR also saw through to the surface of
the planet. The images were so striking that the scientists turned on the
cameras again during the fourth pass in February 2021. During the 2021 flyby,
the spacecraft’s orbit lined up perfectly for WISPR to image Venus’ nightside
in entirety.
“The images and video just blew me away,” Wood said.
As Parker Solar Probe
flew by Venus on its fourth flyby, its WISPR instrument captured these images,
strung into a video, showing the nightside surface of the planet. Credits:
NASA/APL/NRL
Glowing like an Iron
from the Forge
Clouds obstruct most of the visible light coming from Venus’ surface, but
the very longest visible wavelengths, which border the near-infrared
wavelengths, make it through. On the dayside, this red light gets lost amid the
bright sunshine reflected off Venus’ cloud tops, but in the darkness of night,
the WISPR cameras were able to pick up this faint glow caused by the incredible
heat emanating from the surface.
“The surface of Venus, even on the nightside, is about 860 degrees,” Wood
said. “It's so hot that the rocky surface of Venus is visibly glowing, like a
piece of iron pulled from a forge.”
As it passed by Venus, WISPR picked up a range of wavelengths from 470
nanometers to 800 nanometers. Some of that light is the near-infrared –
wavelengths that we cannot see, but sense as heat – and some is in the visible
range, between 380 nanometers and about 750 nanometers.
Venus in a New Light
In 1975, the Venera 9 lander sent the first tantalizing glimpses of the
surface after landing on Venus. Since then, Venus’ surface has been revealed further
with radar and infrared instruments, which can peer through the thick clouds by
using wavelengths of light invisible to the human eye. NASA’s Magellan mission
created the first maps in the 1990s using radar and JAXA’s Akatsuki spacecraft
gathered infrared images after reaching orbit around Venus in 2016. The new
images from Parker add to these findings by extending the observations to red
wavelengths at the edge of what we can see.
The WISPR images show features on the Venusian surface, such as the continental
region Aphrodite Terra, the Tellus Regio plateau, and the Aino Planitia plains.
Since higher altitude regions are about 85 degrees Fahrenheit cooler than lower
areas, they show up as dark patches amidst the brighter lowlands. These
features can also be seen in previous radar images, such as those taken by
Magellan.
Surface features seen in the WISPR images (left) match ones seen in those from the Magellan mission (right). Credits: NASA/APL/NRL (left), Magellan Team/JPL/USGS (right)
Beyond looking at surface features, the new WISPR images will help
scientists better understand the geology and mineral make-up of Venus. When
heated, materials glow at unique wavelengths. By combining the new images with
previous ones, scientists now have a wider range of wavelengths to study, which
can help identify what minerals are on the surface of the planet. Such
techniques have previously been used to study the surface of the Moon. Future
missions will continue to expand this range of wavelengths, which will contribute
to our understanding of habitable planets.
This information could also help scientists understand the planet’s
evolution. While Venus, Earth, and Mars all formed around the same time, they
are very different today. The atmosphere on Mars is a fraction of Earth’s while
Venus has a much thicker atmosphere. Scientists suspect volcanism played a role
in creating the dense Venusian atmosphere, but more data are needed to know
how. The new WISPR images might provide clues about how volcanos may have affected
the planet’s atmosphere.
In addition to the surface glow, the new images show a bright ring around
the edge of the planet caused by oxygen atoms emitting light in the atmosphere.
Called airglow, this type of light is also present in Earth’s atmosphere, where
it’s visible from space and sometimes from the ground at night.
Flyby Science
While Parker Solar Probe’s primary goal is solar science, the Venusian
flybys are providing exciting opportunities for bonus data that wasn’t expected
at the mission’s launch.
WISPR has also imaged Venus’ orbital dust
ring – a doughnut-shaped track of microscopic
particles strewn in the wake of Venus’ orbit around the Sun – and the FIELDS
instrument made direct measurements of radio waves in the
Venusian atmosphere, helping scientists understand how the
upper atmosphere changes during the Sun’s 11-year cycle of activity.
In December 2021, researchers published new findings about
the rediscovery of the comet-like tail of plasma streaming out behind Venus,
called a “tail ray”. The new results showed this tail of particles extending
nearly 5,000 miles out from the Venusian atmosphere. This tail could be how
Venus’ water escaped from the planet, contributing to its current dry and
inhospitable environment.
While the geometry of the next two flybys likely won’t allow Parker to
image the nightside, scientists will continue to use Parker’s other instruments
to study Venus’ space environment. In November 2024, the spacecraft will have a
final chance to image the surface on its seventh and final flyby.
The Future of Venus
Research
Parker Solar Probe, which is built and operated by the Johns Hopkins
Applied Physics Laboratory in Laurel, Maryland, isn’t the first mission to
gather bonus data on flybys, but its recent successes have inspired other
missions to turn on their instruments as they pass Venus. In addition to
Parker, the ESA (European Space Agency) BepiColombo mission and the ESA and
NASA Solar Orbiter mission have decided to gather data during their flybys in
the coming years.
More spacecraft are headed to Venus around the end of this decade with
NASA’s DAVINCI and VERITAS missions and ESA’s EnVision mission. These missions
will help image and sample Venus’ atmosphere, as well as remap the surface at
higher resolution with infrared wavelengths. This information will help scientists
determine the surface mineral make-up and better understand the planet’s
geologic history.
“By studying the surface and atmosphere of Venus, we hope the upcoming missions will help scientists understand the evolution of Venus and what was responsible for making Venus inhospitable today,” said Lori Glaze, director of the Planetary Science Division at NASA Headquarters. “While both DAVINCI and VERITAS will use primarily near-infrared imaging, Parker’s results have shown the value of imaging a wide range of wavelengths.”
By Mara Johnson-Groh
NASA’s Goddard Space Flight Center in Greenbelt, Md
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