A forward-looking infrared camera aboard a USAF platform filmed an apparent object transiting the super-heated ash plume during Etna's 1 December 2018 eruption. Atmospheric refraction elongated and brightened the signature, simulating high-speed passage through the plume. Interagency modelling placed the target roughly 170 km from the crater, co-moving with upper-level winds, and AARO concluded it was a standard meteorological balloon.1
AARO reconstruction
AARO's pixel-level reconstruction placed the luminous target twenty-seven nautical miles south-west of the sensor, at roughly 15 000 ft mean sea level and well outside the ash column. The model matched later frames when the object was no longer visible, confirming that its course aligned with the 260°/21 kt wind field sampled by regional radiosondes.2
Motion parallax and perceived velocity
Relative motion between the unmanned aircraft and a slow-moving balloon produced a strong parallax cue that made the target appear to race eastward near 345 mph. After subtracting the platform vector, the residual ground track yields an airspeed near 24 mph, consistent with passive drift in the prevailing flow.
Spectral signature
Short-wave infrared systems register reflected solar irradiance from cool objects rather than self-emission. Thermal gradients above an erupting volcano triggered automatic contrast-stretching, generating flicker and pulsation artefacts that operators misinterpreted as deliberate manoeuvre or shape change.
Shape and scale
Magnified frames reveal a circular silhouette with negligible limb darkening, matching a spherical target of roughly 0.3 m diameter. No appendages, control surfaces, or panel structure appear after deconvolution.
Alternate explanations
Initial partner assessments suggested a bird or a craft transiting the plume. Subsequent multisensor review removed wingbeat artefacts and corrected parallax, eliminating avian and high-speed hypotheses. The remaining explanation compatible with kinematics, reflectance, and regional launch logs is a free-floating balloon.
Assessment
Given sensor range uncertainty, AARO assigns moderate confidence to the balloon attribution and high confidence that the object displayed no flight performance beyond weather-driven drift.