Tag: moon - Spacevolve

Saturn Moon Enceladus

Peering from the shadows, the Saturn-facing hemisphere of tantalizing inner moon Enceladus poses in this Cassini spacecraft image. North is up in the dramatic scene captured during November 2016 as Cassini’s camera was pointed in a nearly sunward direction about 130,000 kilometers from the moon’s bright crescent.

In fact, the distant world reflects over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as fresh snow. A mere 500 kilometers in diameter, Enceladus is a surprisingly active moon. Data collected during Cassini’s flybys and years of images have revealed the presence of remarkable south polar geysers and a possible global ocean of liquid water beneath an icy crust.

Saturn’s moon Iapetus

What has happened to Saturn’s moon Iapetus?

Vast sections of this strange world are dark as coal, while others are as bright as ice. The composition of the dark material is unknown, but infrared spectra indicate that it possibly contains some dark form of carbon. Iapetus also has an unusual equatorial ridge that makes it appear like a walnut.

To help better understand this seemingly painted moon, NASA directed the robotic Cassini spacecraft orbiting Saturn to swoop within 2,000 kilometers in 2007. Pictured here, from about 75,000 kilometers out, Cassini’s trajectory allowed unprecedented imaging of the hemisphere of Iapetus that is always trailing.

A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an older crater of similar size. The dark material is seen increasingly coating the easternmost part of Iapetus, darkening craters and highlands alike.

Close inspection indicates that the dark coating typically faces the moon’s equator and is less than a meter thick. A leading hypothesis is that the dark material is mostly dirt leftover when relatively warm but dirty ice sublimates.

An initial coating of dark material may have been effectively painted on by the accretion of meteor-liberated debris from other moons.

Moon Halo over Stone Circle in Wales, UK

Have you ever seen a halo around the Moon? This fairly common sight occurs when high thin clouds containing millions of tiny ice crystals cover much of the sky.

Each ice crystal acts like a miniature lens. Because most of the crystals have a similar elongated hexagonal shape, light entering one crystal face and exiting through the opposing face refracts 22 degrees, which corresponds to the radius of the Moon Halo.

A similar Sun Halo may be visible during the day. Exactly how ice-crystals form in clouds remains under investigation.

In the featured image, the ice circle in the sky is mirrored by a stone circle on the ground. Taken just over a month ago in Pontypridd Common, Wales, UK, the central Rocking Stone survives from the last ice age, while the surrounding stones in the circles were placed much more recently — during the 1800s.