Cassini prepares for a death dive into Saturn



26, Nov 2016

All great missions come to an end. NASA’s Cassini mission is set to begin on November 30 a daring set of “ring-grazing” orbits, during which it will fly closest to Saturn’s rings since its 2004 arrival. If it survives this phase, in April 2017, the spacecraft will begin its “Grand Finale”. After nearly 20 years in space, the mission is drawing near its end because the spacecraft is running low on fuel.

What is the daring stunt Cassini is about to perform?

NASA's Cassini spacecraft begins a series of daring dives through Saturn's rings Nov. 30, the first step in the probe's "grand finale" investigation of the gas giant planet.

  • From Nov. 30 to April 22, Cassini will dive through the outer edge of Saturn's rings 20 times, once every seven days. The spacecraft will be entering uncharted territory, getting the closest look ever at Saturn's outer rings and its moons.
  • Cassini will pass through a faint outer ring for a few orbits, and then probe the outer reaches of Saturn's F ring, which marks the boundary of the main ring system. The F ring is about 500 miles (800 kilometers) wide — narrow compared to other rings — and features constantly changing streamers, filaments and dark channels that change over the course of hours, NASA researchers said in the statement.
  • "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 km) distant." Earl Maize, Cassini project manager at JPL, said in the statement.
  • While there, Cassini will explore the many small moons orbiting within and near the rings (including Pandora, Atlas, Pan and Daphnis), scoop up ring particles and gas to analyze, and build an in-depth scan of the rings' structure.
  • "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," Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory (JPL) in California, said in a statement." In addition, we have two instruments that can sample particles and gases as we cross the ring plane, so in a sense, Cassini is also 'grazing' on the rings."

Note: There are seven broad classifications among the rings: A, B, C, D, E, F, G, each receiving its name in the order it was discovered. The main rings most visible from Earth are A, B and C. Each ring is really just a collection of thousands of smaller rings packed very closely together. Furthermore, between each ring there are gaps.

Why does Cassini need to die?

In this groundbreaking mission Cassini will be closest to the planet’s rings than any spacecraft before. After the mission phase ends in April, Cassini will begin the "Grand Finale" proper, slinging around the moon Titan to begin 20 dives between Saturn and its rings, and finally turning to dive into the planet's atmosphere on Sept. 15.

  • At its closest, Cassini will get about 1,012 miles (1,628 km) above the clouds, before it ends its 20 year space mission.
  • That final dive will not only keep the spacecraft, that is running out of fuel, from contaminating Saturn's potentially habitable moons, but it will also provide an unprecedented view of the planet's gravity, composition and atmosphere.
  • The mission is also expected to offer unprecedented views of the moons that orbit near Saturn’s rings including Pandora, Daphins, Pan and Atlas, give scientists an insight into other possible moons in the area and observe any meteor impacts on the rings.
  • Researchers will use observations of the planet during this ring-grazing phase of to calculate how close the spacecraft can safely go during its dives before the final plunge, the scientists said.

Sept. 15, 2017, Cassini will dive down into Saturn's atmosphere and send back one-of-a-kind data about the gas giant's chemistry. Soon after the probe's plunge, engineers will lose contact with the craft, researchers said in the statement.Soon after that, the spacecraft will burn up like a meteor due to friction with the planet's atmosphere. Nothing can survive upon coming in contact with Saturn; even Indian astrologers can vouch for this.

  • Cassini was designed to die in order to enrich us with critical information on Saturn.

When was Cassini launched?

Cassini left for Saturn in 1997, taking a complicated path past Venus twice, Earth and then Jupiter to build up speed before reaching the ringed planet's system in 2004.

  • The Cassini spacecraft has studied Saturn for 12 years, and the probe has just one more year to go before its final dive into the planet itself.
  • For the past 12 years, Cassini has explored Saturn's system, sending the Huygens lander to touch down on Titan; discovering huge plumes of water and a subsurface ocean on another Saturn moon, Enceladus; and cataloging the planet's many other moons and ever-changing ring system.

The Jet Propulsion Lab of NASA hosts a countdown to the end of Cassini's mission on September 30 next year, at which point the probe will have also made detailed maps of Saturn's gravity and magnetic fields, analyzing samples from the planet's rings and capturing spectacular images up close to the ringed world.

Where have Cassini's revelations been helpful?

Before Cassini, there had been only brief glimpses of the discoveries waiting at Saturn.Pioneer 11 and Voyagers 1 and 2 conducted flybys decades ago, taking pictures, measurements and observations as they zoomed past. These missions shed new light on Saturn’s complicated ring system, discovered new moons and made the first measurements of Saturn’s magnetosphere.But these quick encounters didn’t allow time for more extensive scientific research.

  • Cassini began the first in-depth, up-close study of Saturn and its system of rings and moons in 2004. The Saturnian system proved to be rich ground for exploration and discoveries, and Cassini's science findings changed the course of future planetary exploration.
  • Cassini's observations of Saturn's largest moon, Titan, have given scientists a glimpse of what Earth might have been like before life evolved. It has now been believed that Titan possesses many parallels to Earth, including lakes, rivers, channels, dunes, rain, clouds, mountains and possibly volcanoes.
  • Saturn’s smaller moon, Enceladus, also proved to be a rich source of discovery. The spray of icy particles from the surface jets forms a towering plume three times taller than the width of Enceladus itself.Cassini confirmed that the plume feeds particles into Saturn's most expansive ring, the E ring.

Who can possibly benefit from a study of Saturn?

Scientists have used the National Science Foundation's Very Long Baseline Array (VLBA) radio-telescope system and NASA's Cassini spacecraft to measure the position of Saturn and its family of moons to within about a mile — at a range of nearly a billion miles. This feat improves astronomers' knowledge of the dynamics of our Solar System and also benefits interplanetary spacecraft navigation and research on fundamental physics.

  • Combined with information about Cassini's orbit from NASA's Deep Space Network, the VLBA observations allowed the scientists to make the most accurate determinations yet of the position of the center of mass, called the barycenter, of Saturn and its numerous moons.
  • The improved positional information will directly benefit scientists' ability to precisely navigate interplanetary spacecraft. In addition, it will help refine measurements of the masses of other Solar System objects.
  • Also, the positional precision will improve predictions of when Saturn or its rings will pass in front of background stars, events that provide a variety of research opportunities.
  • Other benefits will come to studies of several aspects of fundamental physics. The new positional information will help researchers improve their precision when timing the radio pulses from pulsars — spinning superdense neutron stars. Such timing will help answer unsolved questions about particle physics and the exact nature of the highly-compressed material inside a neutron star.
  • Ongoing projects that time the pulses from multiple pulsars spread across our Milky Way Galaxy in an attempt to detect the effects of passing gravitational waves also will benefit from the improved Saturn ephemeris, which also improves the overall Solar System ephemeris.

Note: Ephermeris is a table or data file giving the calculated positions of a celestial object at regular intervals throughout a period.

Just how unique is Saturn?

Saturn, the sixth planet from the sun, was discovered by Galileo in the early 1600s. Since its discovery, Saturn continues to fascinate astronomers from all over the world. The second-largest planet in the solar system, it is unlike Earth and is sometimes referred to as the "Jewel of the Solar System."

  • Saturn is one of five planets that can be seen with the naked eye. It is also the fifth brightest object in the solar system.
  • Saturn is the least dense planet in the solar system. It is made mostly of hydrogen and has a density which is less than water – which technically means that Saturn would float in water. The layers of hydrogen get denser further into the planet, eventually becoming metallic and leading to a hot interior core.
  • Its beautiful rings are not solid. They are made up of bits of ice, dust and rock. Some of these bits are as small as grains of sand. Some are much larger than tall buildings. Some are up to a kilometer (more than half-a-mile) across.
  • The rings are huge but thin. The main rings could almost go from Earth to the moon. Yet, they are less than a kilometer thick. Other planets have rings. Saturn's rings are the only ones that can be seen from Earth. All you need is a small telescope.
  • Saturn gives off more energy than it receives from the Sun. This unusual quality is believed to be generated from the gravitational compression of the planet combined with the friction from large amount of helium found within its atmosphere.
  • Saturn has the fastest winds of any other planet in our solar system. These winds have been measured at approximately 1,800 km per hour (1,100 miles per hour).
  • With a polar diameter that is 90% of its equatorial diameter, Saturn is the flattest of all the planets. This is because of the planet’s low density and fast rotation speed – it takes Saturn 10 hours and 34 minutes to turn on its axis.

Note: Gravitational compression is a phenomenon in which gravity, acting on the mass of an object, compresses it, reducing its size and increases the object's density. At the center of a planet or star, gravitational compression produces heat by the Kelvin–Helmholtz mechanism. The Kelvin–Helmholtz mechanism is an astronomical process that occurs when the surface of a star or a planet cools. The cooling causes the pressure to drop, and the star or planet shrinks as a result. This compression, in turn, heats the core of the star/planet.

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Tags | Cassini Cassini mission NASA Saturn rings Space mission

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