NASA’s Parker Solar Probe captured stunning views of Venus during its close flyby of the planet in July 2020, according to a press release on 24 February 2021. Although the Parker Solar Probe’s focus is the Sun, Venus plays a critical role in the mission: The spacecraft whips by Venus a total of seven times over the course of 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 11 July 2020, the onboard Wide-field Imager for Parker Solar Probe, or WISPR, captured a striking image of the planet’s nightside from 12 381 km away.
When flying past Venus in July 2020, Parker Solar
Probe’s WISPR instrument, short for Wide-field Imager for Parker Solar
Probe, detected a bright rim around the edge of the planet that may be
nightglow, light emitted by oxygen atoms high in the atmosphere that
recombine into molecules in the nightside. The prominent dark feature in
the center of the image is Aphrodite Terra, the largest highland region
on the Venusian surface. Bright streaks in WISPR, such as the ones seen
here, are typically caused by a combination of charged particles,
called cosmic rays, sunlight reflected by grains of space dust, and
particles of material expelled from the spacecraft’s structures after
impact with those dust grains. The number of streaks varies along the
orbit or when the spacecraft is traveling at different speeds, and
scientists are still in discussion about the specific origins of the
streaks here. The dark spot appearing on the lower portion of Venus is
an artifact from the WISPR instrument. Guillermo Stenborg/Brendan Gallagher/Johns Hopkins University Applied Physics Laboratory/Naval Research Laboratory/NASA. WISPR is designed to take images of the solar corona and inner heliosphere in visible light, as well as images of the solar wind and its structures as they approach and fly by the spacecraft. At Venus, the camera detected a bright rim around the edge of the planet that may be nightglow, light emitted by oxygen atoms high in the atmosphere that recombine into molecules in the nightside. The prominent dark feature in the center of the image is Aphrodite Terra, the largest highland region on the Venusian surface. The feature appears dark because of its lower temperature, about 30° C 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 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 surprising observation sent the WISPR team back to the lab to measure the instrument’s sensitivity to infrared light. If WISPR can indeed pick up near-infrared wavelengths of light, the unforeseen capability would provide new opportunities to study dust around the Sun and in the inner solar system. If it can’t pick up extra infrared wavelengths, then these images, showing signatures of features on Venus’ surface, may have revealed a previously unknown 'window' through the Venusian atmosphere.
NASA’s Parker Solar Probe had an up-close view of
Venus when it flew by the planet in July 2020. Some of the features seen
by scientists are labeled in this annotated image. The dark spot
appearing on the lower portion of Venus is an artifact from the WISPR
instrument. Guillermo Stenborg/Brendan Gallagher/Johns Hopkins University Applied Physics Laboratory/Naval Research Laboratory/NASA. 'Either way,' Vourlidas said, 'some exciting science opportunities await us.'
For more insight into the July 2020 images, the WISPR team planned a set of similar observations of the Venusian nightside during Parker Solar Probe’s latest Venus flyby on 20 February 2021. Mission team scientists expect to receive and process that data for analysis by the end of April.
'We are really looking forward to these new images,' said Javier Peralta, a planetary scientist from the Akatsuki team, who first suggested a Parker Solar Probe campaign with Akatsuki, which has been in orbiting Venus since 2015. 'If WISPR can sense the thermal emission from the surface of Venus and nightglow, most likely from oxygen, at the limb of the planet, it can make valuable contributions to studies of the Venusian surface.'
Parker Solar Probe is part of NASA’s Living with a Star program to explore aspects of the Sun-Earth system that directly affect life and society. The Living with a Star program is managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland, for NASA’s Science Mission Directorate in Washington. Johns Hopkins Applied Physics Laboratory designed, built and operates the spacecraft.
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