Paris (France) (AFP) – After eight years of traveling to Mercury, the smallest and most unknown of the planets in the Solar System, the double European-Japanese probe BepiColombo began its high-risk approach to its final destination on Thursday.

Published on: 03/09/2026 - 11:55 Modified on: 03/09/2026 - 16:21

Launched in October 2018, the four-ton craft had to complete a journey of more than 10 billion km and nine planetary flybys to adjust its speed and trajectory in order to approach the planet closest to the Sun.

From April 2027, the MPO (Mercury Planet Orbiter) probe of the European Space Agency (ESA) must study it with unequaled precision, grazing it just 480 km from its surface.

The Mio probe (Mercury Magnetospheric Orbiter) from the Japanese space agency (Jaxa) will be interested in its space environment and in particular its magnetic field, by following an elliptical orbit extending up to 11,000 km.

But before that, BepiColombo began a delicate arrival phase lasting several months on Thursday, punctuated by "high-risk" operations, according to Ignacio Tanco, head of operations for missions to the internal solar system at ESA.

The planet's extreme environment - subject to temperatures ranging from –180 to 450°C and intense solar radiation - makes orbital insertion particularly perilous.

On Thursday, as hoped, a first crucial step was taken at 12:00 GMT (2:00 p.m. Paris time), with the separation of the two probes - still attached together - from the transfer module which had propelled them so far.

The vehicle proceeded autonomously to cut the four mechanical legs which connected the orbiters to the transfer module. A spring mechanism then gently pushed the two probes apart.

The separation took place at a rate of "40 cm per second, leaving the two entities relatively close given the immensity of space", commented Geraint Jones, scientific project manager of the mission.

Due to the distance between the probes and Earth, the signal confirming the success of the operation reached the control center located in Darmstadt in Germany almost two hours later, at 1:53 p.m. GMT (3:53 p.m. in Paris), triggering rounds of applause and cries of joy.

“This is the best scenario we could hope for with the telemetry reaching us exactly when we could hope for it,” commented Elsa Montagnon, in charge of operations concerning the module within the ESA.

“This means that the reconfiguration went as planned,” she rejoiced, recalling that this operation resembled a “successful new launch”.

The distance - 200 million km from the Earth - and the proximity to the Sun - 63 million km from the probes - made any real-time operation impossible, increasing the difficulty tenfold.

Mysterious “hollows”

The two probes must now enter the orbit of Mercury on November 21, before a new delicate phase on December 9 and 10 with the separation of the two probes to return to their respective orbits.

With its sixteen instruments for a budget of 1.7 billion euros, the mission will then be able to “offer humanity and the scientific community unprecedented views of Mercury and open a new chapter in our understanding of the Solar System,” enthused Santa Martinez, head of the BepiColombo mission at ESA.

Because the small planet, flown over for the first time in 1974 by the Mariner 10 probe then in 2011 by MESSENGER, remains enigmatic.

BepiColombo will study its very tenuous atmosphere, called the exosphere. And its magnetic field, which it is - apart from Earth - the only rocky planet in the Solar System to possess.

By mapping its entire surface in very high resolution, scientists want to better understand its past volcanic activity, its astonishing density and check whether, as clues suggest, its poles, eternally plunged in shadow, contain water ice.

They also hope to unravel the mystery of Mercury's unique structures called "hollows." Discovered by MESSENGER, "these depressions on the surface of the planet give the impression that it is gradually being eaten away and seem to be linked to the presence of volatile substances which evaporate or sublimate (go from the solid to gaseous state, editor's note) very easily", explained Geraint Jones.

"Basically, we want to understand the origins of this planet and how it became what it is. By studying these celestial bodies further, we also learn how our own planet formed and became what we know it today," the scientist stressed.

© 2026 AFP

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