Venus is so hot that its surface glows visibly at night through the thick clouds.
That’s what photos taken by NASA’s Parker Space Probe have revealed.
The planet’s average temperature hovers around 860 degrees Fahrenheit, and thick clouds of sulfuric acid obscure visibility. So far, the only photos of the surface of Venus were taken by four Soviet spacecraft that successfully landed there in the 1970s and 1980s, operating shortly before succumbing to the infernal environment.
While flying past Venus, the Parker spacecraft aimed its cameras at the night side of Venus. It was able to see the visible wavelengths of light, including the reddish colors adjacent to the infrared that can pass through the clouds.
“It’s a new way of looking at Venus that we’ve never tried before — we weren’t even sure it was possible,” said Lori Glaze, director of NASA’s planetary division.
In Parker’s photos, warmer places like low-lying volcanic plains appeared brighter, while those at higher elevations, like Aphrodite Terra, one of three regions the size of a continent on Venus, were about 85 degrees cooler and darker.
“It’s like heating up a piece of iron,” said Brian Wood, a physicist at the Naval Research Laboratory in Washington, DC, and the lead author of a study published this month in Geophysical Research Letters detailing the findings. “It starts to glow a little bit at very red wavelengths. And so that’s what we see: the surface of Venus is glowing at very red wavelengths, because it’s so hot.”
The photos also showed a halo of luminescent oxygen in the atmosphere.
“We were able to capture these really, really beautiful, stunning images,” said Nicola Fox, NASA’s director of heliophysics.
for dr. Wood and other scientists working on the mission, the research was a crash course in planetary science. “I’ve never studied planets,” said Dr. Wood. “We are all solar physicists. We are experts on the sun, not planets.”
As its name implies, the Parker Solar Probe’s mission to probe the sun is to withstand scorching temperatures as it plunges through the sun’s outer atmosphere. By design, the trajectory of the Parker spacecraft makes several close flybys of Venus, using the planet’s gravity as a brake to keep it closer to the sun.
The single-camera instrument, known as the Wide-Field Imager for Parker Solar Probe, or WISPR, is not designed to look directly at the sun, which is far too bright, especially at close range. Instead, WISPR peers to the side, at charged particles known as the solar wind, which emanate from the sun at a speed of a million miles per hour.
Before launching the Parker Solar Probe in 2018, Dr. Glaze and Dr. Fox, then the project scientist for the mission, the ability to turn on the instruments during the Venus flybys. But firm plans were not made until after launch, and the Parker Space Probe worked flawlessly.
“That was only because of safety concerns,” said Dr. Fox. “Until you’re in orbit, you don’t really know how your spacecraft flies.”
WISPR, designed to capture faint solar wind particles, proved adept at discerning the faint glow on the night side of Venus.
It took some trial and error to figure that out. In July 2020, during the first flight with the camera turned on, the scientists found that if part of the dayside of Venus was in field of view, the photo turned out to be far too overexposed.
“We didn’t really know what we were doing,” said Dr. Wood. “We soon found out that that leads to a completely unusable image.”
But there were two images of only the night side. “Those are the images that revealed to us, ‘Wow, okay, so now we see something,'” said Dr. Wood.
The scientists were better prepared when their spacecraft flew past again in February last year, capturing enough footage to make into a movie.
Other spacecraft orbiting Earth, including Japan’s Akatsuki and the European Space Agency’s Venus Express, have observed similar patterns at longer infrared wavelengths, which are not visible to the human eye. (Whether an astronaut orbiting above the night side of Venus would see the glow Parker detected is unclear, Dr. Wood said, because the human eye can barely detect these wavelengths.)
Because different materials glow with different intensities at different wavelengths, it may be possible to combine the Parker data with the other spacecraft’s infrared observations to identify some minerals on the surface.
“This is where we want to go with this data, but we’re not that far yet,” said Dr. Wood.
The data will also help future Venus missions, such as NASA’s DAVINCI+, which is due to launch by the end of the decade and send a probe to the surface by parachute. “I think it’s going to be” a really exciting time,” said James Garvin, DAVINCI+ principal investigator. “Venus is going to come alive.”
The Parker Space Probe will not be able to properly view the night side of Venus until its final flight in November 2024.
dr. Wood noted a historical symmetry in his Venus findings. In 1962, the first successful interplanetary probe, NASA’s Mariner 2 mission to Venus, confirmed the existence of the solar wind. That was a prediction from Eugene Parker, an astrophysicist who is the namesake of the mission he is now working on.
“I just find it fascinating that this connection between research on Venus and research on solar wind has been there from the beginning,” said Dr. Wood.