ESA’s Venus Express orbiter has captured an image of a ‘glory’ – a rare rainbow-like optical phenomenon – in the atmosphere of Venus.
This false-color composite image shows the glory phenomenon on Venus. The glory is 1,200 km across, as seen from the Venus Express orbiter, 6,000 km away. Image credit: ESA / MPS / DLR / IDA.
Rainbows and glories occur when sunlight shines on cloud droplets – water particles in the case of Earth.
Glories are only seen when the observer is situated directly between the Sun and the cloud particles that are reflecting sunlight.
On our planet, glories are often seen from aeroplanes, surrounding the shadow of the aircraft on the clouds below, or around the shadow of climbers atop misty mountain peaks.
This phenomenon requires two characteristics: the cloud particles are spherical, and therefore most likely liquid droplets, and they are all of a similar size.
The atmosphere of Venus is thought to contain droplets rich in sulfuric acid.
By imaging the clouds with the Sun directly behind the Venus Express spacecraft, researchers hoped to spot a glory in order to determine important characteristics of the cloud droplets.
These images show the glory at ultraviolet – left, visible – center, and near-infrared wavelengths. Image credit: ESA / MPS / DLR / IDA.
The glory in the images was seen at the Venus cloud tops, 70 km above the planet’s surface, on 24 July 2011. It is 1,200 km wide as seen from the Venus Express, 6,000 km away.
From these observations, the cloud particles are estimated to be 1.2 micrometers across. The fact that the glory is so wide means that the particles at the cloud tops are uniform on this scale at least.
The variations of brightness of the rings of the observed glory is different than that expected from clouds of only sulfuric acid mixed with water, suggesting that other chemistry may be at play.
One idea is that the cause is the so-called UV-absorber – an unknown atmospheric component, possibly ferric chloride or elemental sulfur, responsible for mysterious dark markings seen in the cloud tops of Venus at ultraviolet wavelengths.
The findings appear in a paper published in the journal Icarus.
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Markiewicz WJ et al. Glory on Venus cloud tops and the unknown UV absorber. Icarus, published online February 13, 2014; doi: 10.1016/j.icarus.2014.01.030
