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Japan's Mio Probe to Image Mercury Next Spring

The BepiColombo spacecraft's imaging phase, scheduled after its delayed arrival, would extend the mission's observations of Mercury's sodium atmosphere.

Updated on Nov. 4, 2026 in Space

Gold-foiled spacecraft floating above the grey, cratered surface of Mercury, with a faint amber glow along the planet's horizon.
Japan's Mio probe will take its first images of Mercury next spring as part of the BepiColombo mission, which is still in transit. AI Illustration. Upload story photo >

Japan's Mio probe, part of the Japan-Europe BepiColombo mission to Mercury, is scheduled to take its first images of the planet next spring. The mission is still in the planning-and-transit stage, so the imaging is a forecast rather than a result.

Why it matters

Mio's sodium-imaging camera is designed to show how Mercury's tenuous sodium atmosphere behaves, a question that remains open. BepiColombo is the first mission in which two spacecraft will orbit Mercury simultaneously, which positions it as a major step in planetary observation.

Mio carries a single imaging instrument, the Mercury Sodium Atmospheric Spectral Imager, which detects light emitted by sodium atoms drifting around the planet. The spacecraft reached its target only after roughly eight years and nine gravity-assist maneuvers, following a one-year delay caused by propulsion problems.

The players

JAXA

Japan's national space agency, which developed the Mio probe for the BepiColombo mission.

BepiColombo

The Japan-Europe joint mission to Mercury in which two spacecraft will orbit the planet simultaneously.

The details

Mio launched from Kourou, French Guiana in October 2018 attached to Europe's Mercury Planetary Orbiter and was carried on an Ariane 5 rocket. Its single camera picks up light emitted by sodium atoms that drift around Mercury, a faint atmosphere that the instrument is built to map. Mio will separate from the Mercury Planetary Orbiter in early December and transmit its images through its own antenna.

Timeline

  1. October 2018: Mio launches from Kourou, French Guiana.

  2. December 2025: Original Mercury arrival date, later delayed by one year.

  3. Early December 2026: Mio separates from the Mercury Planetary Orbiter.

  4. March 2027: Test imaging of Mercury is expected.

  5. April 2027: Full-scale scientific observations are scheduled to begin.

The Tech Race

BepiColombo is the first mission in which two spacecraft will orbit Mercury at the same time, giving it a distinct position among planetary missions. Mio's sodium-imaging camera targets a question about Mercury's atmosphere that the mission is designed to address.

The imaging results are a scheduled forecast, with test images expected in March 2027 and full observations in April 2027, so the data will reach researchers and the public only after those dates. For most readers, the practical effect is access to new Mercury imagery and sodium-atmosphere data once the mission completes its observation phase.

The takeaway

Watch for test imaging in March 2027 and the start of full-scale observations in April 2027, which will show whether Mio's camera captures the sodium atmosphere as planned. Early December 2026 marks the separation from the Mercury Planetary Orbiter, after which Mio transmits through its own antenna.

What happens next

Mio separates from the Mercury Planetary Orbiter in early December 2026, and full-scale scientific observations are scheduled to begin in April 2027.

Further reading

For more on the broader field, explore the Space section.