rendering of Cassini above Saturn
August 15, 2017

Cassini dips into Saturn’s atmosphere

The Cassini probe has officially entered the final phase of its 13-year mission studying Saturn, as it executed the first of five planned ultra-close passes of the gas giant this past weekend – a series of dives that will allow it to travel through the top portion of the planet’s atmosphere.

According to BBC News, the NASA spacecraft is currently encircling Saturn along a pattern that will see it travel along the gap between its rings and its atmosphere – a course which will allow it to collect vast amounts of data on the chemical composition of both the planet and its rings.

“As it makes these five dips into Saturn... Cassini will become the first Saturn atmospheric probe,” Dr. Linda Spilker, a project scientist from NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, explained in a statement. “It's long been a goal in planetary exploration to send a dedicated probe into the atmosphere of Saturn, and we're laying the groundwork for future exploration with this first foray.”

On Sunday, Cassini came to within just 1,000 miles (1,600 kilometers) of Saturn’s cloud tops at 9:22 pm PDT on Sunday (12:22 am EDT/04:22 GMT on Monday). This flyby enabled Cassini to directly samples the gases of the planet’s upper atmosphere, which is believed to be roughly 75% hydrogen and 25% helium and trace gases.

“It's expected that the heavier helium is sinking down,” European Space Agency (ESA) Cassini project scientist Nicolas Altobelli stated in an interview with BBC News. “Saturn radiates more energy than it's absorbing from the Sun, meaning there's gravitational energy which is being lost. And so getting a precise measure of the hydrogen and helium in the upper layers sets a constraint on the overall distribution of the material in the interior.”

NASA hoping to determine precise length of Saturn’s day

Cassini was launched in 1997 and arrived in the Saturn system seven years later, according to CNN. For the past 13 years, it has been studying the gas giant and its moons, but as the mission winds down, the spacecraft is completing final maneuvers before plunging into the atmosphere, where it is expected to burn up on September 15.

Before that can happen, however, the spacecraft has one final phase of its mission to complete – a phase which started on Sunday and will continue over the next month. Data from the first pass through Saturn’s atmosphere is expected to be sent back to Earth when Cassini once again makes contact with ground control on Tuesday, according to BBC News.

Among the information NASA is hoping to ascertain as a result of these final flybys is the actual length of a day on Saturn. While they know it is approximately 10.5 hours long, NASA scientists are hopeful that they will be able to  come up with a more precise figure by looking for an offset between the planet’s magnetic field at its rotational axis. While such an offset should exist, so far scientists thus far have not been able to detect one.

“All magnetic field theory as we know it requires an offset. To generate a field, you need to keep the currents in the metallic hydrogen layer inside Saturn flowing, and without the offset the thinking is that the field would simply go away,” Dr. Spilker told BBC News. “What's going on? Is something shielding our ability to see the offset, or do we simply need a new theory?”

“Without the tilt, without being able to see the tiny wobble, we cannot be more precise about the length of a day,” she said, adding that her team would keep working on the issue. In addition, the researchers hope to be able to use Cassini’s ion and neutral mass spectrometer (INMS) to collect atmospheric data from the region around Saturn’s cloud tops, NASA said in a statement.

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Image credit: NASA/JPL-Caltech