Another image from Cassini this week. Here’s Titan as the intrepid space probe passes behind the moon yesterday from the sun’s view. Titan’s ample atmosphere bends sunlight to give the false appearance of an eclipse. As viewed from Saturn, the sun is quite small.
You can see the north polar “hood,” plus a distinct layer of high haze above it. Saturn’s rotational axis (therefore its rings and main orbiting moons) are tilted 29 degrees (compared to Earth’s 23.5) so there are seasonal changes easily detected on the planet and on Titan.
These mystifying clouds are called Polar Mesospheric Clouds, or PMCs, when they are viewed from space and referred to as “night-shining” clouds, or noctilucent clouds, when viewed by observers on Earth. The clouds form during the Northern Hemisphere’s summer season that begins in mid-May and extends through the end of August. They are being seen by AIM’s instruments more frequently as the season progresses. The clouds also are seen in the high latitudes of the Southern Hemisphere during the summer months. Very little is known about how these clouds form over the poles, why they are being seen more frequently and at lower latitudes than ever before, or why they have been growing brighter. AIM will observe two complete polar mesospheric cloud seasons over both poles, documenting for the first time the entire, complex life cycle of PMCs.
“It is clear that PMCs are changing, a sign that a distant and rarified part of our atmosphere is being altered, and we do not understand how, why or what it means,” stated AIM principal investigator James Russell III, Hampton University, Hampton, Va. “These observations suggest a connection with global change in the lower atmosphere and could represent an early warning that our Earth’s environment is being altered.”
It will be interesting to see if Titan’s and Earth’s polar clouds have any connection.