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A 2026 CHEOPS highlight: AU Mic c’s transit timing reversed

Timings from 2024 moved AU Mic c back toward its predicted schedule; the size and cause of the variation remain uncertain.

By GreenSpacealien Editorial1 min read
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AU Microscopii appears at two nearby positions in a wide star field, showing its motion between differently filtered exposures.
AU Microscopii appears twice because the coloured-filter exposures were made years apart while the same star moved across the sky.ESO/Digitized Sky Survey 2 · Wide-field view of the sky around the nearby star AU MicroscopiiLicense terms · CC BY 4.0. Resized and converted for web.View full image

A changed transit schedule

The 2026 CHEOPS study of AU Mic’s 2024 observations found planet c’s transits moving toward the predicted schedule after late offsets in 2023.[1]

CHEOPS observes the small dip in starlight as a planet crosses its star, with frequent measurements that help locate the transit’s beginning, end, and midpoint. Comparing the midpoint with a predicted time can expose timing variations; ESA describes such changes as one way to detect the gravitational influence of another planet.[3]

From late to early

An earlier CHEOPS analysis of 2022–23 observations found AU Mic c arriving progressively later than predicted. It explored whether a third body could explain the pattern, but said the available timings could not establish a unique configuration. That was a proposed model, not a confirmed additional planet.[2]

On the updated schedule, two 2023 transits were about 49 and 57 minutes late; 2024 transits were roughly 38 to 8 minutes early. The tentative fit gave c an amplitude of 46 ± 26 minutes and a characteristic modulation timescale of 2,150 ± 110 days—not an orbital period or TTV superperiod.[1]

A timing pattern, not an explanation

The authors did not reanalyze the 2023 light curves; stellar activity, dynamics, transit-shape changes, coverage gaps, and systematics remain possible contributors.[1]

Further transit monitoring could test whether this reversal persists; its physical cause remains unresolved.[1]

Sources & further reading

  1. CHEOPS photometry from 2024 reveals a timing reversalGarai et al. / arXivPublished August 2, 2026Accessed November 3, 2026

    Paper: 2024 timings, tentative fits, and possible causes.

  2. Transit-timing variations in AU Mic observed with CHEOPSGarai et al. / arXivPublished January 23, 2025Accessed November 3, 2026

    Earlier paper: timing trend and uncertain third-body model.

  3. How to characterise an exoplanetEuropean Space AgencyAccessed November 3, 2026

    ESA explains transit photometry and timing measurements.

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