Stunning views of Venus were captured by NASA’s Parker Solar Probe during its close flyby of the planet in July 2020. For more information, the WISPR team planned a series of similar observations of Venus’s nightside during Parker Solar Probe’s latest Venus flyby on Feb. 20, 2021. Scientists on the mission team expect to receive and process the data for analysis by the end of April.
Though the Parker Solar Probe’s primary focus is the Sun, Venus plays an important role in the mission: the spacecraft passes by Venus seven times during its seven-year mission, using the planet’s gravity to bend the spacecraft’s orbit. These Venus gravity assists allow Parker Solar Probe to fly closer and closer to the Sun on its mission to study the dynamics of the solar wind close to its source.
But — along with the orbital dynamics — these passes can also yield some unique and even unexpected views of the inner solar system. During the mission’s third Venus gravity assist on July 11, 2020, the onboard Wide-field Imager for Parker Solar Probe, or WISPR, captured a striking image of the planet’s nightside from 7,693 miles away.
WISPR effectively captured the thermal emission of the Venusian surface. It’s very similar to images acquired by the Akatsuki spacecraft at near-infrared wavelengths.Brian Wood
WISPR is designed to take visible-light images of the solar corona and inner heliosphere, as well as images of the solar wind and its structures as they approach and fly by the spacecraft. The camera detected a bright rim around the edge of Venus that could be nightglow – light emitted by oxygen atoms high in the atmosphere that recombine into molecules in the nightside. The prominent dark feature in the image’s center is Aphrodite Terra, Venus’s largest highland region. The feature appears dark due to its lower temperature, which is approximately 85 degrees Fahrenheit (30 degrees Celsius) cooler than its surroundings.
That aspect of the image took the team by surprise, said Angelos Vourlidas, the WISPR project scientist from the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, who coordinated a WISPR imaging campaign with Japan’s Venus-orbiting Akatsuki mission. “WISPR is tailored and tested for visible light observations. We expected to see clouds, but the camera peered right through to the surface.”
“WISPR effectively captured the thermal emission of the Venusian surface,” said Brian Wood, an astrophysicist and WISPR team member from the U.S. Naval Research Laboratory in Washington, D.C. “It’s very similar to images acquired by the Akatsuki spacecraft at near-infrared wavelengths.”
This unexpected finding prompted the WISPR team to return to the lab to test the instrument’s sensitivity to infrared light. If WISPR can detect near-infrared wavelengths of light, the unexpected capability will open up new avenues for studying dust around the Sun and in the inner solar system. If it is unable to detect extra infrared wavelengths, these images, which show signatures of features on Venus’ surface, may have revealed a previously unknown “window” through the Venusian atmosphere.
“Either way,” Vourlidas said, “some exciting science opportunities await us.”
The WISPR team planned a series of similar observations of Venus’s nightside during Parker Solar Probe’s latest Venus flyby on Feb. 20, 2021, to gain more insight into the July 2020 images. Scientists on the mission team expect to receive and process the data for analysis by the end of April.
“We are really looking forward to these new images,” said Javier Peralta, a planetary scientist on the Akatsuki team who first proposed a Parker Solar Probe campaign with Akatsuki, which has been orbiting Venus since 2015. “If WISPR can detect thermal emission from Venus’s surface and nightglow — most likely from oxygen — at the planet’s limb, it can contribute significantly to studies of the Venusian surface.”
The Parker Solar Probe is part of NASA’s Living with a Star program, which aims to investigate aspects of the Sun-Earth system that have a direct impact on life and society. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the Living with a Star program for the Science Mission Directorate in Washington. The spacecraft was designed, built, and is operated by Johns Hopkins APL.