For the first time, the surface of Venus has been imaged in visible wavelengths from space. The camera on the Parker Solar Probe pierced through the thick Venusian cloud cover and captured blurred but extremely valuable images of the highlands and lowlands of the planet.
The breakthrough images came thanks to a spacecraft with an entirely different mission — the Parker Probe, which has been exploring and progressively nearing the Sun in unprecedented ways. And to get ever closer, it uses trips around Venus to slow down and thereby fly closer to the Sun.
It was during two of those trips around Venus in 2000 and 2001 that the Parker camera, which sees in visible and near infrared wavelengths, was able to image the night side of Venus. This was a first and totally unexpected, since Venus is known to have a dense cover of clouds.
The planet is also, of course, stunningly hot, with a mean temperature of 867 degrees Fahrenheit on the surface. But the temperatures are lower on the elevated Aphrodite Terra, the largest highland region on the Venusian surface, and that is the area that shows as being dark in the images.
“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,” said Brian Wood, lead author on the new study in Geophysical Research Letters and a physicist at the Naval Research Laboratory in Washington. “Now, we finally are seeing the surface in visible wavelengths for the first time from space.”
The presentation below, put together by NASA, the John’s Hopkins University Applied Physics Lab and Naval Research Lab, is a stitched together video of the Parker Probe’s Feb. 20, 2021 pass by the dark side of the planet.
Clouds of sulfur dioxide and sulfuric acid obstruct most of the visible light coming from Venus’ surface and so observing from both the ground and from space has relied on radar and observing wavelengths in the infrared that can pierce through the clouds.
But on two passes, the the Parker Probe’s Wide-field Imager for Solar Probe (WISPR) picked up a range of wavelengths from 470 nanometers to 800 nanometers. Some of that light is the near-infrared – wavelengths that we cannot see, but sense as heat – and some is in the visible range, between 380 nanometers and about 750 nanometers.
The WISPR images all come from the nightside of the planet because on the dayside this red light gets lost amid the bright sunshine reflected off Venus’ cloud tops. But in the darkness of night, the Parker Probe cameras were able to pick up this faint glow caused by the incredible heat emanating from the surface.
“It’s so hot that the rocky surface of Venus is visibly glowing, like a piece of iron pulled from a forge,” Wood said in a statement. “The images and video just blew me away.”
Reflecting the surprise that visible light images had been collected, WISPR project scientist Angelos Vourlidas, co-author on the new paper and researcher at Johns Hopkins University Applied Physics Laboratory said that the original science objective on the first 2000 flyby “was to measure the speed of the clouds.”
But instead of just seeing clouds, WISPR also saw through to the surface of the planet — and one early image was released to the public in Feb. 2021.
Those early images were so striking that the scientists turned on the cameras again during the fourth Parker pass by Venus that same month. During the 2021 flyby, the spacecraft’s orbit lined up perfectly for WISPR to image Venus’ nightside in entirety and images and then a video were produced.
In addition to the surface glow, the new images show a bright ring around the edge of the planet caused by oxygen atoms emitting light in the atmosphere. Called airglow, this type of light is also present in Earth’s atmosphere, where it’s visible from space and sometimes from the ground at night.
NASA and most other national space agencies have focused in recent decades on exploring Mars, our other neighboring planet, which has been found to have been warmer and wetter in its early days. Because Venus is so hot and shrouded in noxious clouds, it has not seen the same level of exploration.
But that will be changing due to renewed interest in a nearby planet that is similar in size to Earth (Mars is quite a bit smaller) has similar mass and bulk composition, and has a proximity to the Sun that is also somewhat similar. Venus is also very different, however, with an atmosphere consisting of 96 percent carbon dioxide, crushing surface air pressure, ground temperatures hotter than Mercury and no moon.
There have been some reports (highly controversial) of possible biosignature compounds in the Venusian atmosphere, but the current NASA scientific interest is focused on how and why Venus has such different conditions from its sister planet, Earth. And as with Mars, there is a possibility that early Venus was quite different from the planet today.
Two new NASA missions — VERITAS (Venus Emissivity, Radio science, InSAR, Topography, And Spectroscopy) and DAVINCI+ — were announced last year and are scheduled to orbit Venus in the late 2020s. The European Space Agency also plans to launch its EnVision mission to Venus in the early 2030s.
All of these spacecraft are currently planned to carry near infrared imaging capabilities, allowing further study of the nightside surface. With WISPR having demonstrated the possibility of extending surface observations into the optical, the mission development teams will surely explore the feasibility of adding cameras that use these shorter wavelengths.
As for future Parker and WISPR observations, the encounter geometry for the most recent flyby in 2021 was not favorable for nightside imaging and the flyby in 2023 August will be no better. So scientists (and the public) will have to await the final flyby in November 2024 for the new WISPR imagery of Venus.
The only nation to land mission on Venus is the former Soviet Union, which had a very active Venus program from 1962 to 1984. During that time, the Soviets managed to put thirteen probes in orbit around Venus, with ten hardened devices reaching the planet’s hellish surface to send back scientific data and even images of the planet.
Because of the severe conditions, none of the landers lasted on the surface for long. But they did take the only up-close pictures that exist of the surface of Venus.