Last July, NASA's Parker Solar Probe swung around the planet Venus during a gravity-assist maneuver designed to bring the spacecraft ever closer to the sun. During its seven-year mission the probe will whip around Venus seven times. Each time it does, the planet's gravity bends the spacecraft's orbit closer and closer to the sun.

NASA's Parker probe travels deep inside the sun's corona to study the solar wind close to its source. To keep its cool, the spacecraft uses a heat shield made of a carbon composite foam sandwiched between two carbon plates and coated with white ceramic paint. It can withstand temperatures of 3,000° F (1,650° C) at the same time the spacecraft sits comfortably in the shade at 85° F (30° C). (NASA)
NASA's Parker probe travels deep inside the sun's corona to study the solar wind close to its source. To keep its cool, the spacecraft uses a heat shield made of a carbon composite foam sandwiched between two carbon plates and coated with white ceramic paint. It can withstand temperatures of 3,000° F (1,650° C) at the same time the spacecraft sits comfortably in the shade at 85° F (30° C). (NASA)

NASA is putting Parker in the hot seat so it can better study the solar wind — the high-speed stream of particles our star pew pews — close to its source rather than 93 million miles away. By mission's end in late 2025, the spacecraft will skim just 4 million miles (6 million km) from the sun's searing surface.

This topographic map of Venus is color-coded with blue regions lowest and red highest. I circled the highland region Aphrodite Terra. While Venus doesn't appear to have moving plates (plate tectonics), it shows abundant evidence of past (present?) volcanic activity and faults that have cracked its crust. (NASA)
This topographic map of Venus is color-coded with blue regions lowest and red highest. I circled the highland region Aphrodite Terra. While Venus doesn't appear to have moving plates (plate tectonics), it shows abundant evidence of past (present?) volcanic activity and faults that have cracked its crust. (NASA)

As during any journey there are often surprises along the way. During the mission’s third Venus gravity assist on July 11, 2020, Parker's wide-field camera called WISPR (Wide-field Imager for Parker Solar Probe) captured a striking and unexpected image of the planet’s nightside from 7,693 miles (12,381 km) away.

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WISPR is designed to take photos in visible light just like your camera does. Its subjects are the solar corona, the pearly bonnet of light surrounding the blackened moon during a total solar eclipse, as well as the solar wind and its structures as they approach and fly by the spacecraft.

Astronauts on the space station took this photo of airglow (left) as they traveled around the Earth's nightside with city lights below. Atmospheric gases absorb ultraviolet (UV) light from the sun during the day and re-emit it in a variety of colors at night. Oxygen glows green and sodium yellow-orange. (NASA)
Astronauts on the space station took this photo of airglow (left) as they traveled around the Earth's nightside with city lights below. Atmospheric gases absorb ultraviolet (UV) light from the sun during the day and re-emit it in a variety of colors at night. Oxygen glows green and sodium yellow-orange. (NASA)

At Venus, the camera detected a bright rim around the edge of the planet from airglow. Space station astronauts have photographed a similar phenomenon that shows up as a green or yellowish "rind" around the circumference of the Earth from orbit. It's also visible as streaks of faint light to ground observers under dark skies. On Venus, ultraviolet (UV) light in sunlight breaks up carbon dioxide (CO2) molecules, liberating oxygen (O) atoms. The atoms travel around to the nightside of the planet and recombine into oxygen molecules (O2), emitting infrared and other colors of light in the process.

This diagram looks technical, but it basically shows how UV light (labeled EUV here) from the sun breaks up carbon dioxide in the Venusian atmosphere. Freed oxygen atoms migrate to the backside of the planet and emit light as they recombine into oxygen molecules (O2). (ESA/VIRTIS-VenusX/IASF-INAF, Observatoire de Paris (R.Hueso, Univ. Bilbao)
This diagram looks technical, but it basically shows how UV light (labeled EUV here) from the sun breaks up carbon dioxide in the Venusian atmosphere. Freed oxygen atoms migrate to the backside of the planet and emit light as they recombine into oxygen molecules (O2). (ESA/VIRTIS-VenusX/IASF-INAF, Observatoire de Paris (R.Hueso, Univ. Bilbao)

Venusian airglow is a fascinating topic of its own, but here's the really bizarre thing. No one expected to see that prominent, dark feature just above the center of the image. Named Aphrodite Terra, it's the largest highland region on Venus, comparable in size to Africa. The feature appears dark because it's about 85° F (30° C) cooler than its surroundings.

Remember, WISPR is a visual light camera, so naturally, scientists expected to see nothing but clouds, which Venus possesses in abundance. On the dayside alone, the cloud layer is some 12.4 miles (20 km) thick. So by what magic did Parker's camera see all the way down to the surface?

Venus is currently in the morning sky and very near the sun, making it difficult to see from the ground but not from the orbiting Solar and Heliospheric Observatory (SOHO). One of SOHO's cameras used a special mask to block the sun's glare when it took this photo of the solar corona and Venus on March 1, 2021. (ESA / NASA)
Venus is currently in the morning sky and very near the sun, making it difficult to see from the ground but not from the orbiting Solar and Heliospheric Observatory (SOHO). One of SOHO's cameras used a special mask to block the sun's glare when it took this photo of the solar corona and Venus on March 1, 2021. (ESA / NASA)

“WISPR effectively captured the thermal (heat) emission of the Venusian surface,” said Brian Wood, an astrophysicist and WISPR team member. Heat emission is another word for light emitted in the infrared part of the spectrum. If you ever wondered what color shines just beyond the red edge of the rainbow arc, it's infrared. Pity, we can't see it with the human eye.

This pleasant surprise sent the WISPR team back to the lab to test the camera's sensitivity to heat emissions. If WISPR can somehow see infrared light, scientists could use it to photograph dust around the sun and in the inner solar system. Dust glows in infrared when it absorbs sunlight. How serendipitous would that be?

But WISPR's apparent superpowers may have a more intriguing explanation. If the team discovers the camera is blind to infrared, it may have revealed a previously unknown “window” through the Venusian atmosphere instead. And that would be an exciting new discovery. Good news either way.

This is the full-frame view of Venus taken by NASA’s Parker Solar Probe during its close flyby in July 2020. (NASA/Johns Hopkins APL/Naval Research Laboratory/Guillermo Stenborg and Brendan Gallagher)
This is the full-frame view of Venus taken by NASA’s Parker Solar Probe during its close flyby in July 2020. (NASA/Johns Hopkins APL/Naval Research Laboratory/Guillermo Stenborg and Brendan Gallagher)

Similar nightside observations were planned on Feb. 20, 2021 during the fourth flyby. Data and images from that encounter are expected to arrive by the end of April, so we should know what's up soon. Sometimes in science, it's what you don't anticipate that leads to the most interesting discoveries. Already, a mission sent to the sun has unintentionally enlightened us about Venus. And who knows what else may be in the pipeline. Stay tuned.

"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.