The Mercury-bound BepiColombo spacecraft will fly by Venus on October 15th, and the mission is asking amateurs for their help.
BepiColombo, a joint mission of the European and Japanese space agencies, is headed for Mercury, due to arrive at the baked planet in late 2025. But Mercury isn’t the only planet it will observe.
The spacecraft will pass by Venus twice, first on October 15th and then again on August 11, 2021, using the planet’s gravity to boost its journey into the inner part of the solar system. The flybys present the perfect opportunity to observe our intriguing sister planet in conjunction not only with Japan’s Akatsuki spacecraft, in orbit since 2015, but also with Earth-based observers.
BepiColombo and Akatsuki will have similar views of Venus, seeing the planet half in daylight and half in night. Earth, on the other hand, will see an almost entirely daylit Venus, providing complementary observations that provide context for what both spacecraft see.
At closest approach, BepiColombo will come about 11,000 kilometers (6,800 miles) from the Venusian cloudtops. Akatsuki will be a bit farther out in its orbit, seeing the planet from some 324,000 km. Earth will be much farther still, 175 million km (or 1.17 astronomical units) away. Despite the distance, Earth-based observations are perfectly capable of spotting cloud features and even peering through to Venus’s surface.
BepiColombo will have 11 instruments operating during the flyby (although not every instrument will be looking down at the planet), and the mission will be coordinating with Akatsuki to take ultraviolet and infrared images. Amateurs can help by observing at ultraviolet wavelengths, imaging the upper cloud layer on the dayside, as well as near-infrared wavelengths (800 nanometers or longer), which penetrate to intermediate cloud layers.
“Amateurs today are able to observe all the interesting altitudes in the Venus atmosphere,” says Itziar Garate Lopez (University of the Basque Country, Spain). “The scientific potential for these observations is high.”
“BepiColombo will be able to observe fine details, but from the Earth we can have the global context at that very moment and thus investigate whether large and small-scale structures are related to each other,” she adds. “We are always on the lookout for new structures or waves at any level of the atmosphere.”
As an example, amateur observations combined with Akatsuki images were instrumental in detecting shifting patterns in Venus's middle cloud layers, a result Javier Peralta (then at JAXA) and colleagues published in the Geophysical Research Letters in 2019.
If you’re interested in taking part in the campaign, the missions are looking for observations a couple days before and after the flyby as well as during the flyby itself, currently set for 3:57 UT on October 15th. Visit the Planetary Virtual Observatory & Laboratory to find more information on how to participate.
Other Venus Visits
The BepiColombo flyby follows another recent flyby by NASA’s Parker Solar Probe last July. It was the spacecraft’s third flyby, and the first time the mission went past the planet’s nightside. While Earth-based observers had a trickier time of it then, as the planet was not so large on the sky as it is now, they were still able to capture meaningful observations.
During the campaign, Parker’s WISPR camera captured the planet’s nightside, imaging the infrared-bright clouds as well as parts of the dark surface below. “It’s an interesting image but difficult to interpret, the team still working on it,” Garate Lopez said at the Europlanet Science Congress, running virtually from September 21st until October 9th. Angelos Vourlidas (Johns Hopkins APL) confirmed that the Parker team is still working on analyzing the instrument's response to infrared radiation.
At the same time, Akatsuki observed Venus’s dayside, imaging clouds and determining daytime temperatures. Both atmospheric waves and a polar vortex can be seen in the images. Meanwhile, back on Earth, the Infrared Telescope Facility in Hawai‘i, the Nordic Optical Telescope in La Palma, Spain, and the Pic du Midi Observatory in France probed deeper clouds on Venus’s nightside. And amateur astronomers observed upper and middle clouds in ultraviolet, violet, and near-infrared wavelengths.
“The campaign has resulted in multiple, multi-level observations right from the surface to the cloudtops and airglow phenomena,” says Ricardo Hueso (University of the Basque Country, Spain), who coordinated amateur participation.
Although Akatsuki is the lone Venus orbiter (for now), there will be several more close passes in the near future, including the August 21, 2021, flyby of the BepiColombo mission, as well as several additional flybys by the Parker Solar Probe, including two in 2021.