Although its main mission is to stare at the Sun, NASA’s Parker solar probe will use every opportunity to send data back home to Earth.
The planet Venus represents just such an opportunity, or rather seven of them. Seven times during its mission, the probe will swing around Venus as a gravity assistant, using the planet’s gravity as a slingshot to adjust course and speed as it gets closer to the Sun.
The solar probe performed the third of these maneuvers on July 11, 2020, and as it approached, made a dazzling shot on the night side of the planet using the Parker Solar Probe Scanner (WISPR)
Parker is not the only probe to take pictures of Venus as it penetrates the inner solar system. BepiColombo, a joint probe for the European and Japanese space agencies Mercury, made a video of Venus when it made a maneuver to support gravity last year.
These images show the planet as relatively smooth and impersonal. This is not surprising at all – Venus is shrouded in a dense, toxic atmosphere with clouds of mostly sulfuric acid, which reflect about 70 percent of the light that hits them. That is why Venus is one of the brightest objects in the night sky.
Parker’s team expected to see such an impersonal orb – but they didn’t see it when processing WISPR data.
If you look at the image, you can see a bright glow around the edge of the planet. This, according to the team, is a night glow.
This is produced by atoms in the upper atmosphere. In the daily part of the planet, solar radiation separates carbon dioxide in the upper atmosphere into oxygen and carbon monoxide. When night falls, the atoms recombine into carbon dioxide, causing a glow.
This is something that is found on both Earth and Mars, and it has been seen before on Venus; his presence in the image of Parker is not surprising.
Nor are the white stripes – while Parker’s team isn’t sure what they are, there are a number of candidates, including dust, cosmic rays, material ejected from the spacecraft after a dust strike, or a combination of all.
What is surprising is this dark smear on the face of the planet. This is a region called Aphrodite Terra, the largest mountainous area on the planet’s surface.
WISPR, designed to depict the solar corona and coronal ejections, is optimized for visible light observations – but still somehow peeks through the clouds of Venus.
However, scientists think they know what happened. Currently, Venus has an active mission – the Akatsuki spacecraft of the Japanese space agency. It sends back similar images taken with its infrared camera, sensitive to temperature fluctuations.
Aphrodite Terra, with its higher altitude, is much cooler than the surrounding terrain, so in infrared or near-infrared images of the planet it would be visible.
“WISPR effectively captures heat emissions from the Venusian surface,” said BIS Wood, an astrophysicist and WISPR team member at the U.S. Naval Research Laboratory. “It’s very similar to the images obtained from the Akatsuki spacecraft with close infrared wavelengths.”
This means that WISPR may be more sensitive to infrared light than it is designed to be – which in turn opens up new possibilities for Parker’s main mission to study the Sun. The Parker team is currently taking a closer look at the features of the tool to find out exactly what it did.
“Anyway,” said WISPR scientist Angelos Vurlidas of the John Hopkins Laboratory of Applied Physics, “some exciting scientific opportunities await us.