Solar Orbiter spacecraft sends postcard from Venus in flyby video

The sun-exploring spacecraft Solar Orbiter has captured this video of a glowing crescent of Venus as it flew past the planet during an orbit adjustment maneuver on Aug 9.

The video was taken by Solar Orbiter's Heliospheric Imager, or SoloHI, as the joint European Space Agency (ESA)/NASA satellite zipped by the hot and cloudy planet at a distance of 4,967 miles (7,995 kilometers).

The Monday flyby took place only a day before another inner-solar-system explorer visited Venus. On Tuesday (Aug 10), the Mercury-bound BepiColombo, a joint mission of ESA and the Japan Aerospace Exploration Agency (JAXA), passed Venus at a distance of only 340 miles (550 kilometers).

Related: Here's every successful Venus mission humanity has ever launched

As both spacecraft are in their cruise phase, not all of their instruments were available to take a close look at Venus. The available cameras on both spacecraft struggled to capture details of the planet's surface because of its extreme glow caused by its high albedo, or reflectivity.

"Ideally, we would have been able to resolve some features on the nightside of the planet, but there was just too much signal from the dayside," Phillip Hess, astrophysicist at the Naval Research Laboratory in Washington, D.C., said in a statement. "Only a sliver of the dayside appears in the images, but it reflects enough sunlight to cause the bright crescent and the diffracted rays that seem to come from the surface."

Early in the sequence, the stars Omicron Tauri (on the right) and Xi Tauri (on the left), both part of the Taurus constellation, pass through SoloHI's view.

ESA BepiColombo project scientist Johannes Benkhoff told Space.com that having both spacecraft fly so close to the planet almost at the same time provides interesting opportunities to study its environment from multiple points.

"We could for the first time obtain multi-dimensional measurements of the environment around Venus," Benkhoff said. "That could enable us to see, for example, how the solar wind interacts with the planet and how fast these processes are."

The Japanese mission Akatsuki, the only spacecraft currently orbiting Venus, also provided additional measurements.

The Monday flyby was already the second at Venus for Solar Orbiter. During these flybys, spacecraft traveling through the solar system take advantage of the gravity of planets and other celestial bodies to adjust their trajectory. Solar Orbiter, which will commence its nominal science phase later this year, will keep revisiting Venus regularly between 2022 and 2030. Its operators plan to use the planet's gravity to tilt the spacecraft's orbit out of the ecliptic plane (in which planets orbit), to enable the mission to achieve one of its main science goals - to provide the first ever up close views of the star's poles.

Solar Orbiter doesn't get as close to the sun as NASA's Parker Solar Probe. However, it is equipped with high-resolution telescopes that will enable it to capture the closest ever images of the star at the center of the solar system. It's first close approach to the sun will take place in March 2022, when the spacecraft will get as close as 42 million kilometers to the sun's surface (about a quarter of the sun-Earth distance and within the orbit of Mercury). 

The Parker Solar Probe can dive much closer to the sun's surface, within a few million miles. However, the temperature this close to the sun is so hot that the probe cannot carry a camera that would face the sun directly.

Even though Solar Orbiter's nominal science phase has not yet commenced, it has already made some fascinating discoveries. Its first test imaging campaign in late spring 2020 discovered new phenomena on the surface of the sun, miniature eruptions, since dubbed the campfires. These tiny flares could be behind one of the greatest mysteries of the sun, the extremely high temperature of its outer atmosphere, the corona. 

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