Although its main mission is to look at the Sun, NASA’s Parker Solar Probe will take every opportunity to send data home to Earth.
The planet Venus represents exactly such an opportunity, or rather seven of them. Seven times during its mission, the probe will rotate around Venus to help gravitationally, using the planet’s gravity as a slingshot for course and speed corrections as it gets closer and closer to the Sun.
The solar probe made the third of these maneuvers on July 11, 2020 and, as it approached, took a glamorous photo of the night part of the planet using the Wide-field Imager for Parker Solar Probe (WISPR).
Parker is not the only spacecraft to photograph Venus as it travels through the inner solar system. BepiColombo, a mixed European and Japanese space agency, the Mercury spacecraft, made a video of Venus, which performed a gravitational assistance maneuver last year.
BepiColombo’s Venus Struggle. (ESA / BepiColombo / MTM)
These images show the planet as relatively smooth and without features. This is not at all surprising – Venus is surrounded by a thick and toxic atmosphere, with clouds of sulfuric acid, which reflects about 70% of the light that hits them. That is why Venus is one of the brightest objects in the night sky.
The Parker team expected to see a dazzling globe in a similar way – but that’s not what they saw when they processed the WISPR data.
If you look at the picture, you can see a bright glow around the edge of the planet. This, the team believes, is a nightmare.
It is produced by the atoms in the upper atmosphere. On the edge of the planet’s day, solar radiation divides carbon dioxide from the upper atmosphere into oxygen and carbon monoxide. When night falls, the atoms recombine into carbon dioxide, causing a glow.
This happens on Earth and Mars and has been seen before on Venus; his presence in Parker’s image is not surprising.
And there are no white stripes – while the Parker team isn’t sure what they are, there are a number of candidates, including dust, cosmic rays, material evacuated from the spacecraft after being hit by dust, or a combination of all of them.
(NASA / Johns Hopkins LPA / Naval Research Laboratory / Guillermo Stenborg and Brendan Gallagher)
What is surprising is that the dark spot on the face of the planet. This is a region called Aphrodite Terra, the largest mountain region on the planet’s surface.
WISPR, designed to imagine the solar corona and coronary ejections, is optimized for visible light observations – however, somehow, it looked through the clouds of Venus.
Scientists think they still know what happened. Venus currently has an active mission, the Akatsuki spacecraft of the Japanese Space Agency. It sends back similar images, made with the help of its infrared camera, sensitive to temperature variations.
Aphrodite Terra, with its higher altitude, is much cooler than the surrounding terrain, so that it would be visible in infrared or near-infrared images of the planet.
“WISPR has effectively captured the thermal emission of the Venusian surface,” said astrophysicist and WISPR team member Brian Wood of the US Naval Research Laboratory. “It’s very similar to the images acquired by the Akatsuki spacecraft at near-infrared wavelengths.”
This means that WISPR may be more sensitive to infrared light than it was designed to be – which in turn opens up new possibilities for Parker’s main mission to study the Sun. The Parker team is currently reviewing the instrument’s specifications to find out exactly what it did.
“Anyway,” said Angelos Vourlidas, a WISPR scientist at the Johns Hopkins Laboratory of Applied Physics, “some interesting scientific opportunities await us.”