The US space agency NASA’s Cassini-Huygens spacecraft that is orbiting Saturn has made its first close dive past the outer rings of the planet giving us an astonishing view of the most beautiful planet of our solar system. As per the schedule, the probe entered in its penultimate mission on November 30 and started grazing Saturn rings on Dec 4.
NASA scientists revealed that the spacecraft crossed through the plane of Saturn’s rings on Dec. 4 at 5:09 a.m. PST (8:09 a.m. EST) at a distance of approximately 57,000 miles (91,000 kilometers) above Saturn’s cloud tops. Two small moons Janus and Epimetheus were also present just 6,800 miles away from the F ring.
The spacecraft performed its last manoeuvre nearly an hour before crossing the ring’s plane. Scientists fired main engines for six seconds which changed the speed and direction of spacecraft. About 30 minutes later, as it approached the ring plane, Cassini closed its canopy-like engine cover as a protective measure.
“With this small adjustment to the the spacecraft’s trajectory, we’re in excellent shape to make the most of this new phase of the mission,” said Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory, Pasadena, California.
“This is the 183rd and last currently planned firing of our main engine. Although we could still decide to use the engine again, the plan is to complete the remaining maneuvers using thrusters,” said Maize.
A few hours after the ring-plane crossing, Cassini began a complete scan across the rings with its radio science experiment to study their structure in great detail.
“It’s taken years of planning, but now that we’re finally here, the whole Cassini team is excited to begin studying the data that come from these ring-grazing orbits,” said Linda Spilker, Cassini project scientist at JPL. “This is a remarkable time in what’s already been a thrilling journey.”
Camera aboard Cassini has captured stunning images of Saturn about two days before crossing through the ring plane. However, the spacecraft did not capture images during the closest approach as scientists were testing the possibilities of closest flyby and engine manoeuvre. The spacecraft will capture images during next dives past the rings and scientists at NASA have assured that those will be the mission’s best images which will feature the outer regions of the rings and small, nearby moons.
Each of Cassini’s orbits for the remainder of the mission will last one week. The next pass by the rings’ outer edges is planned for Dec. 11. The ring-grazing orbits — 20 in all — will continue until April 22, when the last close flyby of Saturn’s moon Titan will reshape Cassini’s flight path. With that encounter, Cassini will leap over the rings, making the first of 22 plunges through the 1,500-mile-wide (2,400-kilometer) gap between Saturn and its innermost ring on April 26.
On Sept. 15, the mission will conclude with a final plunge into Saturn’s atmosphere. During the plunge, Cassini will transmit data on the atmosphere’s composition until its signal is lost.
Previously, NASA scientists said that the Cassini will circle high over and under the poles of Saturn, diving every seven day to explore the unexplored region at the outer edge of the main rings. The process will be repeated for twenty times from November 30 and April 22.
“We’re calling this phase of the mission Cassini’s Ring-Grazing Orbits, because we’ll be skimming past the outer edge of the rings,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. “In addition, we have two instruments that can sample particles and gases as we cross the ringplane, so in a sense Cassini is also ‘grazing’ on the rings.”
On many of these passes, Cassini’s instruments will attempt to directly sample ring particles and molecules of faint gases that are found close to the rings. During the first two orbits, the spacecraft will pass directly through an extremely faint ring produced by tiny meteors striking the two small moons Janus and Epimetheus. Ring crossings in March and April will send the spacecraft through the dusty outer reaches of the F ring.
“Even though we’re flying closer to the F ring than we ever have, we’ll still be more than 4,850 miles (7,800 kilometers) distant. There’s very little concern over dust hazard at that range,” said Earl Maize, Cassini project manager at JPL.
The F ring marks the outer boundary of the main ring system; Saturn has several other, much fainter rings that lie farther from the planet. The F ring is complex and constantly changing: Cassini images have shown structures like bright streamers, wispy filaments and dark channels that appear and develop over mere hours. The ring is also quite narrow — only about 500 miles (800 kilometers) wide. At its core is a denser region about 30 miles (50 kilometers) wide.
Cassini’s ring-grazing orbits offer unprecedented opportunities to observe the menagerie of small moons that orbit in or near the edges of the rings, including best-ever looks at the moons Pandora, Atlas, Pan and Daphnis.
Grazing the edges of the rings also will provide some of the closest-ever studies of the outer portions of Saturn’s main rings (the A, B and F rings). Some of Cassini’s views will have a level of detail not seen since the spacecraft glided just above them during its arrival in 2004. The mission will begin imaging the rings in December along their entire width, resolving details smaller than 0.6 mile (1 kilometer) per pixel and building up Cassini’s highest-quality complete scan of the rings’ intricate structure.