BepiColombo Mercury Mission to Make First Venus Flyby Tonight

The Mercury-bound BepiColombo spacecraft will observe Venus during tonight’s pass, on the hunt for phosphine and sulfur-dioxide.

The joint Japanese/European Space Agency’s BepiColombo spacecraft makes a scheduled pass near Venus tonight, while the cloud-shrouded planet has been very much in the news.

The flyby it part of a complex series of passes that the spacecraft must make to arrive in orbit around Mercury on Christmas Day, December 25th, 2025. Launched on an Ariane-5 rocket from Guyana Space Center on October 20, 2018, BepiColombo made a solitary Earth flyby earlier this year on April 10th, 2020.

Update: Last night’s Venus flyby was successful, and mission controllers at Darmstadt, Germany report that BepiColombo is on track. The spacecraft even posed for a brief selfie with Venus in the background:

Venus, during the October 15th flyby. ESA/BepiColombo/MTM

The closest approach tonight is set for 11:58 PM EDT/3:58 UT at ~6,700 miles (10,800 kilometers) from the surface of Venus. BepiColombo will then make a much closer 400 mile (630 kilometers) pass by Venus next year on August 11th, 2021. After that, BepiColombo will make six passes near Mercury prior to orbital insertion in late 2025. BepiColombo will be only the second spacecraft (after NASA’s Mercury MESSENGER) to orbit the innermost world.

ESA Operations will live tweet the flyby tonight, starting at 3:30 UT/11:30 PM EDT.

Tonight’s Venus Flyby… Credit: ESA

BepiColombo is actually two spacecraft on one platform: the Mercury Planetary Orbiter (MPO), and the Mercury Magnetospheric Orbiter (MMO). The spacecraft is named after 20th century scientist Giuseppe ‘Bepi’ Colombo, who first proposed using gravitational assists during planetary missions, now standard practice.

Observations made during the brief flyby will serve to calibrate instruments and complement measurements made by Earth-based observatories and Japan’s Akatsuki spacecraft, currently the only active mission on station around Venus.

“Overlapped or complementary viewing geometries from the three locations of BepiColombo, Akatsuki, and Earth will result in complete global (day and nightside) views of the atmosphere, across multiple atmospheric levels simultaneously,” Johannes Benkhoff (ESA) told Universe Today. “MERTIS observations will contribute to studies of Venus’ radiative balance, atmospheric structure, cloud level chemical processes, and the impact of global-scale atmospheric waves on Venus weather patterns.”

The BepiColombo stack getting prepared for launch. Credit: ESA/CNES/Arianespace

The flyby comes just a month after astronomers announced the detection of phosphine in the Venusian atmosphere. What’s ironic is that researchers were initially using Venus as a baseline measurement as an example of a sterile world, when the detection was made. On Earth, phosphine is reactive and is only replenished by volcanic activity and life… but Venus would require higher levels of volcanic activity than we know of to produce the amounts of phosphine seen in the study.

An artist’s impression of volcanism on Venus. NASA/JPL-Caltech/Peter Rubin

BepiColombo does have a detector capable of measuring phosphine levels: the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS). Though MERTIS may not reach the 20 parts per billion threshold needed during tonight’s distant pass, it could serve as a test run for next year’s close pass of Venus, providing much better prospects.

MERTIS may, however, make detections of another chemical compound capable of shedding light on another aspect of the puzzle: sulfur dioxide, which could hint at recent volcanic activity on Venus.

“At the levels (of phosphine) that have been observed, our chances for tonight’s flyby are quite low.” says Jörn Helbert (German Aerospace Center Institute of Planetary Research). “It would have to be significantly more than previously reported to be observable by MERTIS. During the second flyby we have a bit better situation.”

“We will be able to measure sulfur dioxide.” Helbert continued. “The levels of this gas have strongly varied in the atmosphere of Venus over the past decades, and it might indicate active volcanism.”

The Planetary Virtual Observatory Laboratory (PVOL) is also calling for amateur observations to back up science observations made during tonight’s flyby.

Modern amateurs can tease out actual detail in the Venusian cloud-tops, using ultraviolet filters. Credit: Roger Hutchinson

Venus may become the target of future missions in the coming decade. First up may well be Rocket Labs’ proposed Venus mission incorporating a modified version of its small Photon spacecraft, set to head to Venus in 2023. Other proposed missions include NASA’s proposed Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy (VERITAS) mission, the Deep Atmosphere Venus Investigation of Noble Gasses, Chemistry Investigation (DAVINCI+) and the Bio-Inspired Ray for Extreme Environments and Zonal Exploration (BREEZE) mission. Another interesting concept, ESA’s Venus orbiter EnVision, may launch in the 2030s.

You can currently see Venus and wave to BepiColombo low in the dawn sky. As a plus, Venus is joined by the mission’s ultimate target Mercury low in the dawn in late October… and if you have binoculars (and it doesn’t disintegrate) be sure to hunt for +8th magnitude comet C/2020 P1 NEOWISE low to the east.

Looking east on the morning of October 31st. Credit: Stellarium

Be sure to follow the BepiColombo tonight for a brief glimpse of Venus, a planet that’s sure to be the target of scientific scrutiny in the decade to come.

Lead image credit: An artist’s impression of BepiColombo passing Venus. Credit: ESA/ATG MediaLab

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