This happens during Saturn's equinox, when the sun is directly over Saturn's equator. At this time, the rings, which also orbit directly over the planet's equator, appear edge-on to the sun. During equinox, light from the sun hits the ring particles at very low angles, accenting their topography and giving us a three-dimensional view of the rings.
"The equinox is a very special geometry, where the sun is turned off as far as the rings themselves are concerned, and all energy comes from Saturn," said Dr. Michael Flasar of NASA's Goddard Space Flight Center in Greenbelt, Md.
During Saturn's latest equinox August 11, the rings reached a temperature of 382 degrees below zero Fahrenheit, the coldest yet observed, as seen by the Composite Infrared Spectrometer (CIRS) instrument on board the Cassini spacecraft in orbit around Saturn. CIRS was developed at NASA Goddard, and Flasar is the Principal Investigator for the instrument.
"The whole point of the CIRS observations of Saturn’s rings, other than producing some cool pictures, is to learn something about the physical properties of the ring particles: their spin rates, how sluggish they are in storing and radiating heat (a diagnostic of size and composition), and their vertical distribution in the ring 'plane'," said Flasar.
Although the rings are thousands of miles wide, they are only about 30 feet thick. They are made of particles that are mostly water-ice. Scientists continue to debate the rings' origin and age. Some think they could be remnants of a shattered moon or captured comets, while others think they could have formed along with Saturn from the primordial disk of gas and dust that gave birth to our solar system.
"At first glance, Saturn's rings look broad and bland, but then we got close-up images from the Voyager flybys, and our reaction was: oh, my gosh, there's structure everywhere – what's going on?" said Dr. Linda Spilker, of NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif.
Researchers have discovered that while most of the ring particles are as small as dust and pebbles, there are a few chunks as big as mountains, and even some small moons several miles across embedded in the rings. Instead of orderly orbiting around Saturn, the particles clump together and drift apart, and the rings ripple and warp under the gravitational influence of Saturn's swarm of more than 60 moons.
"The closer we look at the rings, the more complex they get," says Spilker, Deputy Project Scientist for the CASSINI mission and a Co-Investigator on CIRS. She is leading the instrument team's investigation of the rings.
"Because Saturn’s rings are so extended, going out to more than twice Saturn’s radius (from the cloud tops), the furthest rings get less heat from Saturn than the innermost rings, so the ring temperatures at equinox tend to fall off with distance from Saturn’s center," said Flasar.
However, the CIRS team discovered that the A-ring – the outermost of the wide, bright rings – did not cool off as much as expected during the equinox. This might give clues about its structure and evolution. "One possibility is that the gravitational influence of moons outside the A-ring is stirring up waves in it," said Spilker. "These waves could be much higher than the typical thickness of the rings. Since the waves rise above the ring plane, material in the waves would still be exposed to sunlight during the equinox, which would warm up the A-ring more than expected."
"But we have to carefully test this idea with computer models to see if it produces the temperatures we observed with CIRS," adds Spilker. "That's the challenge with CIRS. It's not like seeing a close-up picture of Mars, which can tell you something about its geology right away. We have to look at the CIRS data from different times and sun angles to see how the ring temperatures are changing, then make computer models to test our theories on what those temperatures say about the rings."
The effort to understand the rings could help us understand our origin. "Our solar system formed from a dusty disk, so by understanding the dynamics in a disk like Saturn's rings, we can gain insight into how Earth and the other planets in our solar system were made," said Spilker.
The equators of both Earth and Saturn are tilted compared to their orbit around the sun. This tilt makes the sun appear to rise higher and lower in the sky throughout the year as Earth progresses in its orbit, causing the seasons to change. Likewise, Saturn's tilt makes the sun appear higher and lower in the sky as Saturn moves in its orbit, which takes about 29.5 years to complete.
Saturn experiences two equinoxes per orbit, just as Earth does, when the planet's equator lines up edge-on to its orbital plane, causing the sun to appear directly over the equator. For a viewer on Saturn, the sun would seem to move from south to north around the time of the August 11 equinox.
Technically, the equinox is the instant when the sun appears directly over the equator, but Saturn's situation gives the rings an extended twilight. Saturn is about 10 times farther from the sun than Earth. Since Saturn is farther from the Sun's gravitational pull, it moves relatively slowly in its orbit compared to Earth, which makes it take longer for the sun to noticeably appear higher or lower in the sky. Also, even as far away as Saturn, the sun is large enough to appear as a disk, not a point, according to Spilker.
So, before the August 11 equinox, a viewer embedded in Saturn's rings would have seen sunlight fade as the top edge of the solar disk appeared to touch the rings first. This would be followed by darkness around the equinox as the solar disk slowly crossed the ring plane. Full sunlight would have returned when the sun's bottom edge rose above the ring plane, about four days from when the sunlight first began to fade.
The Cassini-Huygens mission is a cooperative project among NASA and the European and Italian Space Agencies. NASA JPL manages the mission for the Science Mission Directorate at NASA Headquarters in Washington. JPL also designed, developed and assembled the Cassini orbiter and its two onboard cameras. The imaging team is based at the Space Science Institute, Boulder, Colo. The CIRS team is based at NASA Goddard. CIRS was built by Goddard, with significant hardware contributions from England and France.
Bill Steigerwald | EurekAlert!
Significantly more productivity in USP lasers
06.12.2016 | Fraunhofer-Institut für Lasertechnik ILT
Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
07.12.2016 | Health and Medicine
07.12.2016 | Life Sciences
07.12.2016 | Health and Medicine