BepiColombo's Mercury Arrival: Four Key Milestones, with Orbit Insertion Scheduled for 21 November 2026

ESA's arrival updates page summarises the arrival in four dates. The arrival phase began with separation of the Mercury Transfer Module on 3 September 2026. The composite spacecraft is scheduled to enter orbit around Mercury on 21 November 2026, MPO and Mio to separate from each other on 9-10 December 2026, and the science phase to begin in April 2027. ESA's detailed timeline lists further steps — release of Mio's sunshield (MOSIF) on 16 December 2026 and MPO reaching its final orbit on 10 March 2027 — and notes that exact dates may change for operational reasons.^[1][4]

The start of the arrival phase should not be confused with Mercury orbit insertion. After separation ESA described the two orbiters as on their way towards orbit insertion, still more than three million kilometres from Mercury. On 24 September MPO fired its thrusters for 8 minutes 42 seconds, a push of 11.4 m/s that ESA calls the first planned trajectory correction since separation; more small correction slots are planned before insertion in November.^[1][2]

The Mercury Transfer Module is the propulsion element that carried the stack through the inner Solar System. The remaining stack includes two science orbiters flown by different agencies — ESA's Mercury Planetary Orbiter and JAXA's Mercury Magnetospheric Orbiter, known as Mio — and Mio's sunshield and interface structure, MOSIF. ESA says BepiColombo will be the first mission to orbit Mercury with two spacecraft at the same time.^[1][3][4]

The two orbiters are still joined. MPO powers the spacecraft stack until Mio separates on 9-10 December 2026, and steering passed to MPO's thrusters after the transfer module left. So between September and December there is one composite vehicle with one orbiter supplying power, not two independent spacecraft.^[1][4]

ESA describes the separation as a critical event executed more than 200 million kilometres from Earth, demanding precise planning, navigation and commanding, with no opportunity for real-time intervention.^[1]

Confirmation therefore arrived in stages rather than at once. Controllers first detected a preliminary Doppler signal — a variation in the radio frequency between Earth and the spacecraft when its velocity changes, the same principle as the changing pitch of a passing siren — which ESA said was consistent with the planned separation sequence. Full confirmation came with acquisition of signal through two Estrack deep space antennas at Cebreros in Spain and Malargüe in Argentina. A preliminary indication and a confirmed separation are not the same statement.^[1][2]

ESA’s account of the separation says this is the first in a sequence of manoeuvres that "will ultimately see BepiColombo become the first mission to place two spacecraft in orbit around Mercury, in December 2026." ESA’s own factsheet, meanwhile, lists "MPO+Mio enter Mercury orbit: 21 November 2026." Read quickly, those look like two different arrival dates.^[2][3]

The December wording may refer to the deployment of the two orbiters into their separate orbits, but ESA does not explicitly explain it. Its detailed timeline distinguishes the November capture of the still-stacked spacecraft into a polar orbit from the 9-10 December release of Mio onto her final orbit.^[2][3][4]

Linking the December phrase to the separation is this page's reading, not a statement by ESA. A reader quoting only one of the two sentences will state the arrival date differently, which is the practical risk here.^[2][3]

According to ESA's retrospective account, the team gave the official "GO" for separation at 12:00 CEST, the expected separation time arrived at 14:00 CEST, and the team "would have to wait nearly two hours for confirmation to arrive from 200 million kilometres away." (The live updates page carries its own posting times, such as 12:03 CEST for the GO post, which are not the event times.)^[1][2]

In the same account, confirmation came in two stages. At 14:20 CEST a preliminary Doppler signal gave the first indication that separation had occurred, and only at 15:49 CEST did mission control receive "the long-awaited acquisition of signal" — 109 minutes after the expected separation time (this page's calculation). Between those two moments the outcome was indicated but not confirmed.^[2]

What the stack did in between is also on the record: ESA says that following separation "the remaining spacecraft stack entered safe mode, readjusted its attitude and reconfigured itself before transmitting its status back to Earth." The article does not describe this as a malfunction.^[2]

ESA quotes Spacecraft Operations Manager Ignacio "Nacho" Clerigo saying "Separating two spacecraft from 200 million kilometres away is not something we do every day... we are really pleased to have had a perfect separation," and B-shift Spacecraft Operations Manager Emmanuela Bordoni describing the Doppler moment. Both are ESA staff describing ESA’s own operation, and no outside assessment is cited on this page.^[2]

The transfer module is not recovered and not operated further. ESA says that "with no antenna or onboard computer of its own, the now inoperable module will remain in a stable orbit around the Sun."^[2]

Its contribution is quantified in the same account: "Over the last eight years, BepiColombo has travelled 9.9 billion kilometres through the inner Solar System and completed nine planetary flybys," with the module providing power and the solar electric propulsion for that journey. The factsheet lists those flybys individually — Earth (10 April 2020), Venus twice (15 October 2020, 11 August 2021) and Mercury six times between 1 October 2021 and 8 January 2025.^[2][3]

The module also carried three monitoring cameras that ESA says documented the voyage, with a "full collection of these images ... available in the ESA Planetary Science Archive." Nothing on this page rests on the images themselves.^[2]

A note on sourcing. The detailed dates, the confirmation timeline and the description of the module's fate come from ESA. JAXA's ISAS mission page, from the other mission partner, independently states that Mio launched on 20 October 2018 together with MPO and is scheduled to arrive at Mercury in November 2026. Both are mission partners describing their own mission, not outside assessments.^[2][3][5]