Science.-Saturn and its rings, captured from the Moon by the LRO mission

Saturn and its rings, captured from the Moon by the LRO mission

From a vantage point 90 kilometers from the lunar surface, the camera aboard NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft captured images of Saturn.

In this view, the Lunar Reconnaissance Orbiter Camera (LROC) was looking toward the north face of the rings, and from this perspective, the rings facing Saturn appear below its equator.

LROC’s Narrow Angle Cameras (NACs) are line scan cameras, presenting a challenge to image anything other than the Moon. This is because they were designed to acquire images by taking advantage of the movement of the spacecraft on the surface (LRO travels at more than 1,600 meters per second on the Moon), to build a line-by-line image with very short exposure times.

To image Saturn, the spacecraft moves the NACs across Saturn, building the image by mimicking our orbital motion of the earth. The spin through Saturn was accomplished by pointing the NACs to one side of Saturn and then pointing to the other side.

LRO responded to the updated target by turning towards it at a specific speed across the planet. This rate is programmed to optimize LRO speed and stability and resulted in a NAC exposure time of 3.82 milliseconds, NASA reports.

Since Saturn is much dimmer than the Moon (and Jupiter) and the exposure time is in effect set by the speed of rotation, the moons of Saturn could not be detected as it was done with the Galilean moons of Jupiter, simply because they are too faint.

Fortunately, NACs can image Saturn’s astonishing rings, which are probably only 10 to 100 million years old, 10 meters thick, and made up almost entirely of water ice. The main rings visible here have a diameter of 270,000 kilometers, about 70% of the average distance between the Earth and the Moon.

Launched on June 18, 2009, LRO has compiled a treasure trove of data with its seven powerful instruments, making an invaluable contribution to our knowledge of the Moon.

Ben Oakley
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