Saturn’s E-ring

E-ring Saturn

The mote hoop lies about 13 million km (eight million miles) from the planet, some 50 times more distant than the other rings and in a different plane. Scientists think that the tenuous ring is probably made up of debris kicked off Saturn’s moon Phoebe by small impacts. They believe this dust migrates towards the planet where it is picked up by another Saturnian moon, Iapetus.

The discovery would appear to resolve a longstanding mystery in planetary science: why the walnut-shaped Iapetus has a two-tone complexion, with one side of the moon significantly darker than the other. “It has essentially a head-on collision. The particles smack Iapetus like bugs on a windshield,” said Anne Verbiscer from the University of Virginia, US.

Observations of the material coating the dark face of Iapetus indicate it has a similar composition to the surface material on Phoebe. The scale of the new ring feature is astonishing. Nothing like it has been seen elsewhere in the Solar System. The more easily visible outlier in Saturn’s famous bands of ice and dust is its E-ring, which encompasses the orbit of the moon Enceladus. This circles the planet at a distance of just 240,000 km.

The newly identified torus is not only much broader and further out, it is also tilted at an angle of 27 degrees to the plane on which the more traditional rings sit. This in itself strongly links the ring’s origin to Phoebe, which also takes a highly inclined path around Saturn. Scientists suspected the ring might be present and had the perfect tool in the Spitzer space telescope to confirm it.

The US space agency observatory is well suited to picking up the infrared signal expected from cold grains of dust about 10 microns (millionths of a metre) in size. The ring would probably have a range of particle sizes – some bigger than this, and some smaller.

Modelling indicates the pressure of sunlight would push the smallest of these grains towards the orbit of Iapetus, which is circling Saturn at a distance of 3.5 million km. The particles are very, very tiny, so the ring is very, very tenuous. Actually if anyone were standing in the ring itself, he or she wouldn’t even know it. In a cubic km of space, there are all of 10-20 particles.

Indeed, so feeble is the ring that scientists have calculated that if all the material were gathered up, it would fill a crater on Phoebe no more than a kilometer across. The moon is certainly a credible source for the dust. It is heavily pockmarked. It is clear that throughout its history, Phoebe has been hit many, many times by space rocks and clumps of ice.

Christiaan Huygens, mathematician

One of the greatest scientists of all time was Christiaan Huygens. He was born on  April 14th, 1629 in Den Haag, Holland. His Father was Constantijn Huygens (1596-1687), a Dutch statesman, diplomat, and artist. At his home famous poets, painter, and philosopher of his time were guests, besides others Rubens, Rembrandt, and Descartes. Raised in this worldly-open family with many childrens Christiaan Huygens studied like Pierre de Fermat (1601-1665) jurisprudence first, then mathematics and natural sciences.

He was in relationship with Antony van Leeuwenhoek (1632-1723), who was known as the best microscope builder of his time and who not only grinded his lenses out of glass, but also out of rock crystal and diamond. Huygens was involved at the examination of small life forms and microscopic objects like sperms and blood cells. He grinded his own lenses for astronomical telescopes. His biggest refractor had a length of five meter. With his theory of the wave form of light he was able to calculate the refraction within the lenses and was able to make refractors with lesser chromatic and spherical aberration. He also invented a type of ocular/eyepiece named according to him, where the image pojected by the objective is placed between two different ocular lenses on a visual plate, consisting of two planoconvex lenses.

With his advanced telescopes Huygens discovered 1655 the Saturnian moon Titan, which was thought to be the biggest moon within the solar system for a long time. Today its known that the real diameter of Titan with ca. 5200 kilometer is somewhat smaller than the diameter of the Jovian moon Ganymede with ca. 5400 kilometer. After the discovery of the Galileian moons around Jupiter Titan was the second discovery of satellites around a planet. It has a dense atmosphere of methane and ammonia, which is responsible for an apparently larger size and for the reddish color.

At that same time Huygens was examining the Saturnian rings, which were an open phenomenon out of the time of the discovery by Galilei. Huygens presented the correct explanation for the rings in 1656. They are angled by 27 degrees to the Saturnian orbit, and therefore from Earth they are seen half a Saturnian year with their North side and half a Saturnian year with their South side, while the additional angle of the Saturnian orbit to the ecliptic makes some complex transitions possible. At the time around a transition the rings seem to dissapear, because in correlation to their huge diameter of ca. 280,000 kilometer—without G- and E-ring—they are extremely thin: the thickness of the rings varies from ten to fourhundred meter.

The rings are no solid objects. This fact is a deduction of the Keplerian laws. To be stable for decades and centuries the rings had to rotate and therefore stationary gas or liquids are not the material of them. At the outer edge the rotation speed of the rings are 16 and at the inner edge 21 kilometer per second(!). A solid object would chatter because of the speed differences, calculatable with the Keplerian laws. Huygens also discovered that the rings have no connections to the Saturnian body. He recorded his observations about Saturn in 1659 in his work “Systema Saturnium.”

Like Galilei before, Huygens was pointing his telescopes to nearly anything the sky presented him. He discovered the difference of polar and equatorial diameter of Jupiter, made a first map of Mars, calculated the Martian day to ca. 24 hours because of the movement of surface marks on the red planet, he proposed that Venus is covered by clouds, and he resolved the inner region of the Orion nebula and mapped the stars within. This brightest part of the nebula therefor is called Huygens region after him. He also discovered several other interstellar nebular and many double stars.

While his mathematical studies Huygens created a complete theory about the game of dice, which was published by his mathematics teacher Frans van Schooten (1615-1660) in 1657 as “De ludo aleae.” With this Huygens is known as the founder of the theory of probabilistics. Although principially the pendulum clock was invented by Galilei and da Vinci already, Huygens was the first who worked out the practical problems of such a chronometer and let build many different clocks of that type. He also invented the clock with spiral spring or cycloid pendulum, which enables a more precise time measurement and helped to determine the longitude on sea. His inventions on chronometer he wrote down until 1673 in his book “Horologium oscillatorium”.

In 1660 Huygens travelled to England. And in 1663 he was admitted as a member of honor at the British Royal Society. Toward 1666 he travelled to Paris, where he was teaching at the university since 1681. Here he also made observations together with Giovanni Domenico Cassini at the 1672 finished observatory of Paris. After a serious illness he returned to Den Haag to the families house of Hofwijck. Briefly before his dead he wrote the book “The Discovery of Celestial Worlds: Theories about Inhabitants, Plants, and Products of Planetary Worlds” where he speculated about life not only on planets of the Sun, but also about life on worlds of other stars. Huygens died on June 8th, 1695 at the early age of 66 years-old in Den Haag. A life worth living as his was has to be known.