Saturn
Cassini

Cassini successfully dives between Saturn and its rings

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The veteran Cassini spacecraft has pulled off an impressive high speed manoeuvre: passing between the narrow gap between Saturn’s upper atmosphere and the planet’s rings, traveling at speeds of around 77,000mph.

Colliding with the rings’ particles at such speeds could potentially have disabled the craft — but the first (ever) ring-crossing was executed successfully. It’s the closest a spacecraft has ever been to Saturn, the Solar System’s sixth planet.

The current set of planned passes are shown below in blue, with Cassini’s earlier ring-grazing orbits shown in gray:

Credit: NASA / Jet Propulsion Laboratory – Caltech

The scientists running the Cassini mission had to hold their breath for a while yesterday while they waited to see if the craft had successfully navigated the gap — as an extra precaution they had oriented its dish-shaped antenna in the direction of the oncoming ring particles to act as a shield, meaning the spacecraft was out of contact with Earth during the ring-plane crossing.

“We could only rely on predictions, based on our experience with Saturn’s other rings, of what we thought this gap between the rings and Saturn would be like,” said Cassini project manager Earl Maize of NASA’s Jet Propulsion Laboratory, in a statement. “I am delighted to report that Cassini shot through the gap just as we planned and has come out the other side in excellent shape.”

The veteran, 20-year-old spacecraft is now sending back fresh science and engineering data collected during the passage and while it was close to the planet. The scientists will also be using data gathered during the first dive to figure out if they need to take the shielding precaution next time around.

NASA says that Cassini came within around 1,900 miles of Saturn’s cloud tops and within about 200 miles of the innermost visible edge of the rings as it made the manoeuvre. The gap between the rings and the top of Saturn’s atmosphere is about 1,500 miles wide.

What are the scientists hoping to learn from this component of the Cassini mission? They’re using the close encounters with Saturn and its rings to take what they describe as “unprecedented measurements” of its atmospheric composition and interior structure.

Given the craft is passing closer than ever to Saturn it’s able to send back high resolution views of the innermost rings and the planet’s atmospheric features — which could lead to new observations.

NASA is already showing a trio of unprocessed images from the first dive:

Credit: NASA/JPL-Caltech/Space Science Institute

The ring-crossing Cassini data will also enable mission scientists to measure Saturn’s gravity and magnetic fields to study its interior structure; reveal its internal rotation rate; and provide a basic understanding of how giant planets form and how they work.

Another specific aim is to determine the mass of the rings — and estimate ring system age and longevity. Determining the mass of the rings could in turn shed light on how rings form, and potentially also how all planets form, they say.

Cassini will be taking direct samples of ring particles, as well as samples of Saturn’s innermost radiation belts and upper atmosphere.

A second dive between Saturn and its rings is scheduled for May 2. They’re aiming to make 22 ring dives in all — before the mission concludes (hence the “grand finale” moniker).

Cassini’s final, terminal plunge is illustrated above, on the second image in this post, as the single orange line.

Cassini arrived at Saturn back in 2004, and has been sending back data on the planet and its myriad moons ever since. Earlier this month, for example, mission scientists reported finding evidence of what they think is hydrogen gas coming from sub-sea vents on one of Saturn’s ice-covered moons, Enceladus, which has liquid water under its icy surface, that they say could provide the energy required to support life forms such as microbes.

The spacecraft’s long days of data gathering are finally numbered because its fuel is running out. Cassini is programmed on a trajectory that will plunge it on a last, one-way mission into Saturn’s atmosphere on September 15 this year. The idea being to “safely dispose” of the spacecraft in the planet’s upper atmosphere, rather than let it blindly drift out of the Solar System. It also, of course, makes for a dramatic finale to the mission’s two decades of data gathering.

Featured Image: NASA/JPL-Caltech