"Gather ye rosebuds while ye may" is the opening line of a poem by English poet Robert Herrick, first published in 1648. Its cautionary message is a sublime reminder of the fleeting nature of beauty and it admonishes us to be mindful to appreciate it for the short time it exists.
While we do not generally think of astronomical phenomena as short-lived, new NASA research has found that one of the most breathtakingly beautiful features of our solar system may well be surprisingly ephemeral: Saturn's rings.
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In 1977, NASA launched two intrepid space probes named Voyager 1 and 2 to take advantage of a unique alignment of the planets that allowed them to visit all four of the outer gas giants of the solar system. While only Voyager 2 made the grand tour, both spacecraft passed close by Saturn in the early 1980s.
Images taken by the spacecraft revealed dark bands in the mid-latitudes in Saturn's northern and southern hemispheres. The origin of these bands was traced to water from the planet's majestic rings raining down onto its surface. Astronomers of the time were astounded by the rate at which this rain occurred. It was so large and constant that some thought that the measurement must have somehow been an error.
However, a recent measurement published in the research journal Icarus confirms the earlier result. Using the special instruments attached to the Keck telescope in Mauna Kea, Hawaii, a team of scientists was able to image infrared light emitted by a form of hydrogen that originated from the inflowing water. They found that the amount of water flowing from the rings to the planet would fill two Olympic-size swimming pools every hour. That's 1.3 million gallons (5 million liters).
The water's journey from Saturn's rings to the surface of the planet begins with chunks of ice ranging in size from microscopic grains to boulders perhaps ten feet across, which make up the rings of the planet. This ice experiences bombardment of ultraviolet light from the Sun, which causes it to get a small electrical charge. When a charged object moves and encounters a magnetic field, it experiences a force. Saturn's magnetic field is the second strongest in the solar system, and the resulting force sends the charged ice crystals down to the planet's surface. Most of this rain occurs into the southern hemisphere.
If you compare this magnetically-generated flow rate to the finite amount of ice in the rings of Saturn, you find that the rings will be completely gone in just a very short amount of time, astronomically-speaking. On the basis of this measurement alone, the rings of Saturn will last only about 300 million years. There was an independent measurement of ring material falling directly onto Saturn's equator by the Cassini spacecraft during its thirteen-year mission observing the planet. When these two effects are added together, it looks like the Saturn rings will be gone in a "mere" 100 million years.
While a hundred million years is a long time, it pales in comparison to the lifetime of Saturn, which is about 4.5 billion years.
But a question still remains: Where did the rings come from?
While there have been many theories proposed for the origin of the rings of Saturn, this observation of their short-lived nature suggests that they were created relatively recently. Most likely, some small and icy moons in Saturn's orbit collided and the debris spread out into the rings.
If that explanation is true, it's likely that a long time ago the other gas giants -- Jupiter, Uranus, and Neptune -- also had spectacular rings. The rather small rings they now host would then simply be shadows of their ancient glory.
This recent measurement on Saturn also revealed another band on the planet's surface that emits infrared light. This band is at a higher latitude than the two that were previously known. It exists in the southern hemisphere where Saturn's magnetic field intersects the orbit of Enceladus, one of the planet's geologically active moons, which means that its interior is substantially liquid. Because of radioactivity found in Enceladus' core, along with strong tidal forces from Saturn, its interior is warm and it is surrounded by a liquid ocean.
This liquid water is occasionally emitted by geysers -- essentially "water volcanoes," if one interprets Enceladus' geology with an Earthly mindset. That water then falls onto the surface of Saturn.
Astronomers have long known of the measurements by the Voyager probes and have been aware that the rings of Saturn were likely to be a short-lived phenomenon, but this observation clinches it.
So maybe it's time to dig out that old telescope and take another look at Saturn and its beautiful rings before they're gone.
And it wouldn't hurt to gather a rosebud or two...
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