Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2022 January 4
The featured image shows the Moons Rhea and Janus
being the rings of Saturn as captured by the robotic 
Cassini mission in 2010.
Please see the explanation for more detailed information.

Moons Beyond Rings at Saturn
Image Credit: NASA, ESA, JPL, Cassini Imaging Team

Explanation: What's happened to that moon of Saturn? Nothing -- Saturn's moon Rhea is just partly hidden behind Saturn's rings. In 2010, the robotic Cassini spacecraft then orbiting Saturn took this narrow-angle view looking across the Solar System's most famous rings. Rings visible in the foreground include the thin F ring on the outside and the much wider A and B rings just interior to it. Although it seems to be hovering over the rings, Saturn's moon Janus is actually far behind them. Janus is one of Saturn's smaller moons and measures only about 180 kilometers across. Farther out from the camera is the heavily cratered Rhea, a much larger moon measuring 1,500 kilometers across. The top of Rhea is visible only through gaps in the rings. After more than a decade of exploration and discovery, the Cassini spacecraft ran low on fuel in 2017 and was directed to enter Saturn's atmosphere, where it surely melted.

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