Although the main mission is facing the sun, NASA’s Parker Solar Probe will use any opportunity to send data back home.
The planet Venus represents just such an event, or rather, seven of them. The probe will swing around Venus seven times during its mission for gravity aids, using the planet’s gravity as a slingshot for rate and speed corrections as it gets closer to the sun.
The solar probe made the third of these maneuvers on July 11, 2020, and as it approached, it took a glare shot from the planet’s night side using the Wide-field Imager for Parker Solar Probe (WISPR) instrument.
Parker is not the only investigator who can take photos of Venus as it moves through the inner Solar System. BepiColombo, a joint European and Japanese space agency Mercury probe, took a video of Venus while making a gravity maneuver last year.
BepiColombo is Venus flyby. (ESA / BepiColombo / MTM)
These images show the planet as relatively smooth and without features. This is not at all surprising – Venus is shrouded in a thick, toxic atmosphere with clouds of predominantly sulfuric acid reflecting about 70 percent of the light they hit. Therefore, Venus is one of the brightest objects in the night sky.
The Parker team expected to see a similar sphere – but that’s not what they saw when they processed the WISPR data.
If you look at the picture, you see a bright glow around the edge of the planet. The team believes it is night light.
It is produced by atoms in the upper atmosphere. On the day of the planet, solar radiation divides carbon dioxide in the upper atmosphere into oxygen and carbon monoxide. As evening falls, the atoms combine again to carbon dioxide, causing a glow.
This is something that also occurs on Earth and on Mars, and it has been seen before on Venus; its presence in the Parker statue is not surprising.
The white stripes are not either – although the Parker team is not sure what they are, there are a number of candidates, including dust, cosmic rays, material ejected from the spacecraft after being struck by dust, or a combination thereof.
(NASA / Johns Hopkins APL / Naval Research Laboratory / Guillermo Stenborg and Brendan Gallagher)
What’s amazing is that dark smear on the planet’s face. This is a region called the Aphrodite Terra, the largest highland region on the surface of the planet.
WISPR, designed to represent the solar corona and coronal ejections, is suitable for observations of visible light – but somehow it looked through Venus’ clouds.
However, the scientists think they know what happened. Venus currently has one active mission, the Japanese space agency’s Akatsuki probe. It sends back similar images, taken using the infrared camera, which is sensitive to temperature changes.
The 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 has effectively captured the thermal emission of the Venusian surface,” said astrophysicist and WISPR team member Brian Wood of the U.S. Naval Research Laboratory. “It looks a lot like images the Akatsuki spacecraft acquired at near-infrared wavelengths.”
This means that WISPR can be more sensitive to infrared light than it is designed to be – which in turn offers new possibilities for Parker’s main mission to study the sun. The Parker team is currently taking a closer look at the instrument’s specifications to find out exactly what it did.
“Either way,” said WISPR project scientist Angelos Vourlidas of the Johns Hopkins Applied Physics Laboratory, “some exciting scientific opportunities await us.”