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Wednesday, April 26, 2017

Cassini begins its final dive - in & out of Saturn's rings !!

If you live away from a City or visit a village, the great opportunity is ‘star gazing’ in the night – away from city light refractions, you can easily spot more stars !!

The second largest planet in our solar system, adorned with thousands of beautiful ringlets, Saturn is unique among the planets. It is not the only planet to have rings -- made of chunks of ice and rock -- but none are as spectacular or as complicated as Saturn's. Like fellow gas giant Jupiter, Saturn is a massive ball of mostly hydrogen and helium. Surrounding by 53 confirmed and nine provisional moons, Saturn is home to some of the most fascinating landscapes in our solar system. From the jets of Enceladus to the methane lakes on smoggy Titan, the Saturn system is a rich source of scientific discovery and still holds many mysteries.

The farthest planet from Earth observable by the unaided human eye, Saturn has been known since ancient times and is named for the Roman god of agriculture and wealth. The Greek equivalent was Cronos, the father of Zeus/Jupiter. This is all about an  ambitious 20-year mission to gain a better understanding of Saturn, its rings, its magnetosphere and its icy moons. It is  Cassini – a sophisticated robotic spacecraft – sent to orbit the ringed planet and study the Saturnian system in detail.  It was to have 4 phases :
1.       initial four-year mission (2004-2008)
2.       first extension, called the Cassini Equinox Mission (2008-2010)
3.       second extension, called the Cassini Solstice Mission (2010-2017)
4.       conclusion – to  carry out a daring set of orbits called the Grand Finale (2017)

Cassini-Huygens was a joint project between Nasa, the European Space Agency and the Italian Space Agency when the probe first launched in 1997. After seven years it arrived at Saturn on July 1, 2004 and it has been orbiting it ever since. The Huygens probe attached to the spacecraft and travelled with Cassini until 2005, when it detached and landed on Titan in 2005. Both have beamed back invaluable images about Saturn and its moons.

Today, Nasa's Cassini spacecraft will boldly go where no probe has gone before as it begins its descent to the region between Saturn and its innermost ring. The spacecraft's "Grand Finale" will see it dip in and out of the planet's rings 22 times over the coming months before it enters the planet's atmosphere, burning up in the process.  Cassini, which launched two decades ago, has been circling the planet for 13 years but it has finally begun to run low on the propellant used to adjust its course, and scientists fear it damaging one of the moons it was sent to space to study for signs of life.

NASA's Cassini spacecraft has had its last close brush with Saturn's hazy moon Titan and is now beginning its final set of 22 orbits around the ringed planet. The spacecraft made its 127th  and final close approach to Titan on April 21 at 11:08 p.m. PDT (2:08 a.m. EDT on April 22), passing at an altitude of about 608 miles (979 kilometers) above the moon's surface.

Cassini transmitted its images and other data to Earth following the encounter. Scientists with Cassini's radar investigation will be looking this week at their final set of new radar images of the hydrocarbon seas and lakes that spread across Titan's north polar region. The planned imaging coverage includes a region previously seen by Cassini's imaging cameras, but not by radar. The radar team also plans to use the new data to probe the depths and compositions of some of Titan's small lakes for the first (and last) time, and look for further evidence of the evolving feature researchers have dubbed the "magic island."  "Cassini's up-close exploration of Titan is now behind us, but the rich volume of data the spacecraft has collected will fuel scientific study for decades to come," said Linda Spilker, the mission's project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.

The flyby also put Cassini on course for its dramatic last act, known as the Grand Finale. As the spacecraft passed over Titan, the moon's gravity bent its path, reshaping the robotic probe's orbit slightly so that instead of passing just outside Saturn's main rings, Cassini will begin a series of 22 dives between the rings and the planet on April 26. The mission will conclude with a science-rich plunge into Saturn's atmosphere on Sept. 15.

After the spacecraft's first finale on April 26 at 2 a.m. PDT (5 a.m. EDT). (Pacific Daylight time and Eastern daylight time) – the  spacecraft will be out of contact during the dive and for about a day afterward while it makes science observations from close to the planet. Cassini may be beginning its journey to destruction, but the process will take several months. It will dip in and out of Saturn's rings 22 times over the next 142 days before its mission finally ends on September 15, reaching a top speed of 76,806 miles per hour. The mission has been extended by Nasa three times, but with Cassini finally running out of fuel, scientists fear that it could crash into one of the planets that may support life. While unlikely, Nasa wants to avoid any microbes from earth that might remain on the probe contaminating the surface.

Giovanni Domenico Cassini (1625 – 1712) was an Italian mathematician, astronomer, astrologer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the County of Nice, part of the Duchy of Savoy. Cassini is known for his work in the fields of astronomy and engineering. Cassini discovered four satellites of the planet Saturn and noted the division of the rings of Saturn; the Cassini Division was named after him. Giovanni Domenico Cassini was also the first of his family to begin work on the project of creating a topographic map of France. The Cassini spaceprobe, launched in 1997, was named after him and became the fourth to visit Saturn and the first to orbit the planet.

With regards – S. Sampathkumar
26th apr 2017

Pic credit : News source : NASA

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