Giant Polarized Rings in Venus's Atmosphere: A 2010 Detection That Could Solve the Superrotation Mystery

In a paper published in The Planetary Science Journal, an international team led by Gourav Mahapatra of Delft University of Technology reports the discovery of faint, planet-wide concentric rings in the polarized flux of sunlight reflected by Venus . The data came from a serendipitous 36-minute observing run in 2010 using the Extreme Polarimeter (ExPo) on the William Herschel Telescope in the Canary Islands .

The rings have a contrast of about one part per million (10⁻⁶) and are completely invisible in ordinary total-flux images — they appear only when polarized light is isolated . The researchers who identified the signal more than a decade later spent years trying to rule out an instrumental artifact before concluding the pattern was real .

What Created the Rings?

Numerical radiative transfer simulations by the team show that density variations of 5–10% in the thin gas layer above Venus's cloud tops can produce the observed polarization pattern . The most plausible physical explanation is that the rings are atmospheric gravity waves — rippling density waves that propagate through the upper atmosphere, analogous to ripples spreading on water .

The rings appear centered slightly downwind of the sub-solar point, are visible across different filters in the visible spectrum, and are not obvious in simultaneous total flux observations .

Why It's a Candidate, Not a Confirmed Discovery

The finding is described as a "candidate" detection rather than a confirmed discovery for an important reason: ExPo was dismantled before the rings were identified in the archived data . This single 36-minute dataset is the only observation that exists. There is no way to repeat the measurement with the same instrument, and the signal has not been independently confirmed by any other instrument or spacecraft .

The authors are careful not to claim a definitive detection and instead present the rings as a physically plausible candidate worthy of targeted follow-up observations .

The Superrotation Connection

Venus's upper atmosphere rotates far faster than the planet itself — a phenomenon called superrotation that remains one of the great unsolved puzzles in planetary science . Gravity waves carry momentum in the direction opposite to the superrotation, and when they dissipate at high altitudes, they exert deceleration on the mean flow .

Confirming these planet-wide rings as gravity waves would provide direct evidence of large-scale wave activity in the upper atmosphere, which has long been theorized as a critical mechanism for shaping and regulating Venus's superrotation . Detecting and characterizing such waves could significantly improve models of Venus's atmospheric dynamics and energy balance.

What's Next?

The serendipitous discovery highlights the value of archived data from specialized instruments. Researchers are now calling for targeted polarimetric observations of Venus using existing or future instruments to confirm the ring phenomenon . Confirmation would not only solve a long-standing mystery about Venus's atmosphere but also demonstrate a technique that could be applied to study exoplanet atmospheres, where direct imaging of such waves is impossible .