NASA’s Cassini spacecraft conducted one last flyby of Saturn’s moon, Hyperion. Yesterday morning, the spacecraft flew past the strange moon at a distance of around 21,000 miles. Images from this flyby are expected to reach Earth sometime today or tomorrow.

The unusual features of Hyperion

Hyperion isn’t your typical moon. It looks more like an asteroid thanks to its irregular shape. Plus, it’s the only moon in the Solar System that has a chaotic rotation. Instead of rotating on a set axis, it tumbles through space.

Hyperion is best known for its sponge-like appearance. Scientists say this is due to the extremely low density of such a large object. NASA says the moon’s density is half that of water, and it has weak surface gravity.

These features combine to help preserve Hyperion’s craters. Most of Hyperion’s asteroid impacts create craters by compressing the surface material, not blasting it away. There are very few, if any, secondary craters from asteroid impacts. Any ejected material produced by an impact usually goes back to space due to Hyperion’s weak surface gravity.

Cassini’s mission team are crossing their fingers for a different look at Hyperion’s terrain. The moon’s tumbling orbit makes this difficult. Scientists can’t predict what part of the surface Cassini will see. They will just have to wait for the images to reach Earth.

What’s next for Cassini?

As Cassini says so long to Hyperion, it continues its exploration of Saturn and its moons. The next date to keep an eye on is June 16 as it passes within 321 miles of the moon Dione.

Mars’ Water Puzzle Persists

I can’t wait for October. Cassini will fly by Enceladus twice as it studies the moon and its jet plumes. Scientists have uncovered evidence of a large ocean beneath Enceladus’ icy exterior. In 2014, gravity measurements suggested a vast, regional ocean about 6 miles deep beneath an ice layer of around 19 to 25 miles thick.

Enceladus ocean

Scientists are also excited about the possibility of microbial life on Enceladus.

“Material from Enceladus’ south polar jets contains salty water and organic molecules, the basic chemical ingredients for life,” said Linda Spilker, Cassini’s project scientist at JPL. “Their discovery expanded our view of the ‘habitable zone’ within our solar system and in planetary systems of other stars. This new validation that an ocean of water underlies the jets furthers understanding about this intriguing environment.”

During its final pass, Cassini will be just 30 miles above Enceladus.

Towards the end of this year, Cassini will prep for the final phase of its mission, and it’s going out with a bang. Cassini will soar between Saturn and its rings during its last year. Can you imagine the images of Saturn’s rings we will get see?

Image credit: NASA (taken during Cassini’s closest flyby in 2005)

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