Janus tagged posts

In a first for white dwarfs, the burnt-out cores of dead stars, astronomers have discovered that at least one member of this cosmic family is two faced. One side of the white dwarf is composed of hydrogen, while the other is made up of helium.

“The surface of the white dwarf completely changes from one side to the other,” says Ilaria Caiazzo, a postdoctoral scholar at Caltech who leads a new study on the findings in the journal Nature. “When I show the observations to people, they are blown away.”

White dwarfs are the scalding remains of stars that were once like our sun. As the stars age, they puff up into red giants; eventually, their outer fluffy material is blown away and their cores contract into dense, fiery-hot white dwarfs...

This image from NASA’s Cassini mission clearly show the ring’s density waves created by the small moons. The waves look like the grooves in a vinyl record. Credit: NASA

For 3 decades, astronomers thought that only Saturn’s moon Janus confined the planet’s A ring – the largest and farthest of the visible rings. But after poring over NASA’s Cassini mission data, Cornell astronomers now conclude that the teamwork of seven moons keeps this ring corralled. Without forces to hold the A ring in check, the ring would keep spreading out and ultimately disappear...

This view looks toward the sunlit side of the rings from about 1 degree above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Nov. 23, 2015. The view was acquired at a distance of approximately 28,000 miles (44,000 kilometers) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 54 degrees. Image scale is 1.8 miles (3 kilometers) per pixel. Image Credit: NASA/JPL-Caltech/Space Science

Their contrasts are related, in large part, to their sizes. Tethys (660 miles across) is large enough to be spherical and to have varied geology, like chasms and smooth plains, along with some puzzling arc-shaped features (see PIA19637 http://photojournal.jpl.nasa.gov/catalog/PIA19637) ...