Giant Concentric Rings in Venus's Atmosphere: A Candidate Detection from 2010 Polarimetry Data

In 2010, during a serendipitous 36-minute observation of Venus with the Extreme Polarimeter (ExPo) on the William Herschel Telescope in the Canary Islands, researchers captured something unexpected. More than a decade later, a team led by Gourav Mahapatra at Delft University of Technology analyzed that data and detected faint, planet-wide concentric rings in the polarized flux of sunlight reflected by Venus — structures invisible in ordinary total-flux images . The rings appear centered slightly downwind of the sub-solar point and are visible across different filters in the visible spectrum .

The team published their findings in The Planetary Science Journal in July 2026, describing the rings as a candidate detection of planet-wide, concentric density waves in Venus's upper atmosphere .

What Did the Polarimetric Data Reveal?

The rings were detected using ExPo, a highly sensitive experimental instrument designed to measure polarized light. ExPo's dual-beam exchange and double-differencing design strongly suppresses first-order instrumental polarization, allowing it to detect signals as faint as 10⁻⁶ of the total flux . When the researchers compared ordinary images with polarized-light images, the concentric rings appeared only in the polarized data — a pattern that persisted through multiple tests designed to rule out instrumental artifacts .

The team spent years trying to prove the observation wrong, but the signal withstood every check they performed . Lead author Gourav Mahapatra, an atmospheric physicist at Delft University of Technology, noted that the rings were not expected and that rigorous testing was essential before publishing .

What Causes the Concentric Rings?

The researchers believe the rings are caused by planet-scale gravity waves — ripples in the upper-atmosphere gas layer. Numerical radiative-transfer simulations show that gas-density variations of about 5–10% above the cloud tops can produce the observed polarization pattern . Such subtle density changes would not show up in total-flux observations, which is why the rings remained hidden until polarimetric analysis was applied .

The waves may be linked to Venus's atmospheric superrotation, a phenomenon in which the planet's upper atmosphere rotates far faster than the surface below . However, the exact mechanism that generates these large-scale waves remains unclear.

Why Is This a Candidate Detection, Not a Confirmed Discovery?

The researchers describe their finding as a candidate detection rather than a confirmed discovery for two main reasons :

1. Single, unrepeatable dataset — ExPo was dismantled before the rings were identified in the archived data, so no follow-up observations with the same instrument are possible. The team cannot return to the exact configuration that captured the original signal.

2. Lack of independent corroboration — Because only one brief observation exists, the team cannot rule out unknown instrumental artifacts or verify that the pattern is a persistent atmospheric phenomenon. The rings could be a transient event or a rare coincidence of viewing geometry.

The authors present their observations and simulations not as a final answer but as a motivation for future targeted polarimetric campaigns that could confirm or refute the existence of such planet-wide waves .

What Comes Next?

The discovery highlights the value of polarimetric observations for studying planetary atmospheres. The same technique used to detect these rings on Venus could also be applied to exoplanet observations, where polarimetry may reveal atmospheric structures invisible to traditional imaging .

The researchers have called on the scientific community to design new polarimetric instruments or repurpose existing ones to observe Venus and look for the rings again . Until such observations are made, the giant concentric rings in Venus's upper atmosphere will remain a compelling candidate detection — a signal that passed every test its discoverers could devise, yet still awaits independent confirmation.