The first-ever visible light images of the surface of Venus have been captured by NASA’s Parker Solar Probe, revealing how the planet’s rocky interior glows red hot. Veiled beneath a thick layer of unbroken cloud, the Evening Star’s surface had never previously been glimpsed using optical equipment, and scientists now hope to learn about Venus’ geology and evolution by analyzing the probe’s images.
As its name suggests, the Parker Solar Probe is on a mission to study the Sun, and has conducted a series of flybys of Venus in order to boost its trajectory towards our star using the planet’s gravitational field. In a new study in the journal Geophysical Research Letters, NASA scientists reveal that on two of those flybys – conducted in July 2020 and February 2021 – the probe’s Wide-Field Imager (WISPR) “unexpectedly penetrated [Venus’] thick atmosphere, detecting thermal emission from the surface.”
“Venus is the third brightest thing in the sky, but until recently we have not had much information on what the surface looked like because our view of it is blocked by a thick atmosphere,” explained study author Brian Wood in a statement. “Now, we finally are seeing the surface in visible wavelengths for the first time from space.”
While the probe’s imaging software is primarily intended to detect features of the solar atmosphere, scientists at NASA thought they might also be able to use WISPR to observe the clouds of Venus as Parker passed by the planet. During the fourth flyby on February 20, 2021, the probe’s orbit happened to line up in such a way that the imager was able to capture the entire nightside of Venus before beaming the images back to Earth.
To their surprise, the researchers found that they were able to see surface features peeking through the planet’s famously dense clouds. Such an observation was unexpected as most wavelengths of visible light are unable to penetrate the planet’s thick atmosphere, yet the study authors report that on the planet’s nightside, some of the longest visible wavelengths are in fact capable of passing through.
“The surface of Venus, even on the nightside, is about 860 degrees [F, 460°C],” said Wood. “It's so hot that the rocky surface of Venus is visibly glowing, like a piece of iron pulled from a forge.”
On the dayside, the light from these glowing surface features is lost amid the intense sunlight reflecting off the clouds, yet WISPR was able to capture the glow emanating from the planet’s super-hot surface on the nightside. Because higher altitude regions are slightly cooler than lowland areas, the researchers were able to distinguish between features such as the continental region Aphrodite Terra, the Tellus Regio plateau, and the Aino Planitia plains.
“The WISPR images also show a bright rim of emission at the limb, associated with nightglow emission from molecular oxygen, somewhat analogous to auroral emissions observed at Earth,” write the study authors.
Interestingly, they go on to explain that “there have actually been many reports of faint emission from the Venusian night side from credible amateur and professional astronomers, dating back to the 1600s.” However, because this so-called “ashen light” phenomenon has never been successfully imaged, scientists had dismissed it as an optical illusion.
The images provided by the Parker Solar Probe prove that the planet does indeed give off a visible nightside glow, and offers opportunities for researchers to learn about the composition of the planet’s crust. For example, by studying the wavelengths of this surface glow, scientists may be able to identify the minerals that are present and gain clues as to how the planet came to be such an inferno.
Further observations are now planned during the probe’s upcoming Venus flybys, the last of which is set to take place in November 2024.