PARIS: A spacecraft carrying Japanese and European probes made an overnight closer approach of Mercury than first scheduled, following engine issues that had caused the mission to explore the little-known, Sun-scorched planet to be postponed.
With a circuitous trajectory, the BepiColombo mission was supposed to launch in 2018 and reach the planet closest to the Sun’s orbit in December 2025. However, in April, a thruster malfunction reduced some of the spacecraft’s power supply, causing ground teams to reroute the craft and postpone its arrival until November 2026.
Due to the altered trajectory, the spacecraft had to make its most recent flyby 35 kilometers closer to the planet than it had originally intended, passing only 165 kilometers over the surface.
The mission’s X account tweeted on Thursday that the European Space Agency’s operations team verified that “everything went well” with the flyby overnight. It also released a brand-new picture of the planet that was captured by the probe and has a mottled surface similar to the Moon.
On the mission’s nine billion-kilometer trip, it was the fourth of six scheduled flybys of Mercury before it could eventually enter the planet’s orbit.
Although expeditions from Earth can reach the red planet in about seven months, Mercury is typically closer to Earth than Mars. According to astronomer Alain Doressoundiram of the Paris Observatory, Mercury is “the most difficult” planet for missions to access.
Because of the planet’s comparatively small mass—it is only marginally larger than the Moon—and consequently weak gravitational attraction in relation to the Sun, satellites find it challenging to remain in its orbit. According to Doressoundiram, “braking and stopping at Mercury requires a lot more energy than traveling to Mars.”
This is when gravitational assists—delicate maneuvers—come into play. Spacecraft can alter their trajectory or speed by slingshotting around celestial bodies. Due to an issue with the electric thrusters, the spacecraft is currently only using 90% of its intended power supply.
The engines will “remain operating below the minimum thrust required for an insertion into orbit around Mercury in Dec 2025,” according to a statement released earlier this week by mission manager Santa Martinez, following months of investigation into the issue. BepiColombo is now scheduled to enter orbit in November 2026 due to the altered, slower path.
“Oddities” in space
Among the four rocky inner planets of our solar system (Mars, Earth, Venus, and Mercury), Mercury is by far the least explored.
In 1974, NASA’s Mariner 10 became the first spacecraft to take a close-up of its surface, which resembled the moon. MESSENGER, a spacecraft, was the first to orbit the planet in 2011.
Doressoundiram, an expert on planet surfaces, stated that the NASA mission verified “some rather bizarre things.” According to Doressoundiram, one of these “oddities” is that Mercury is the only rocky planet with a magnetic field except Earth. It’s unclear exactly how it has such a strong magnetic field this near to the Sun.
Another “oddity” is that just 33% of Earth’s mass is found in its iron core, whereas 60% of Mercury’s mass is found there. “Hollows” are another feature on Mercury’s surface that may indicate relatively recent geologic activity.
