NASA Casini Observes Meteors Colliding With Saturn's Rings

Five images of Saturn's rings, taken by NASA's Cassini spacecraft between 2009 and 2012, show clouds of material ejected from impacts of small objects into the rings. 

Image credit: NASA/JPL-Caltech /Space Science Institute/Cornell

NASA's Cassini spacecraft has provided the first direct evidence of small meteoroids breaking into streams of rubble and crashing into Saturn's rings.

These observations make Saturn's rings the only location besides Earth, the moon and Jupiter where scientists and amateur astronomers have been able to observe impacts as they occur.

Studying the impact rate of meteoroids from outside the Saturnian system helps scientists understand how different planet systems in our solar system formed.

The solar system is full of small, speeding objects. These objects frequently pummel planetary bodies. The meteoroids at Saturn are estimated to range from about one-half inch to several yards (1 centimeter to several meters) in size.

It took scientists years to distinguish tracks left by nine meteoroids in 2005, 2009 and 2012.

Details of the observations appear in a paper in the Thursday, April 25 edition of Science.

Results from Cassini have already shown Saturn's rings act as very effective detectors of many kinds of surrounding phenomena, including the interior structure of the planet and the orbits of its moons.

Linda Spilker

For example, a subtle but extensive corrugation that ripples 12,000 miles (19,000 kilometers) across the innermost rings tells of a very large meteoroid impact in 1983.

"These new results imply the current-day impact rates for small particles at Saturn are about the same as those at Earth -- two very different neighborhoods in our solar system -- and this is exciting to see," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"It took Saturn's rings acting like a giant meteoroid detector -- 100 times the surface area of the Earth -- and Cassini's long-term tour of the Saturn system to address this question."

The Saturnian equinox in summer 2009 was an especially good time to see the debris left by meteoroid impacts.

Matt Tiscareno

The very shallow sun angle on the rings caused the clouds of debris to look bright against the darkened rings in pictures from Cassini's imaging science subsystem.

"We knew these little impacts were constantly occurring, but we didn't know how big or how frequent they might be, and we didn't necessarily expect them to take the form of spectacular shearing clouds," said Matt Tiscareno, lead author of the paper and a Cassini participating scientist at Cornell University in Ithaca, N.Y.

"The sunlight shining edge-on to the rings at the Saturnian equinox acted like an anti-cloaking device, so these usually invisible features became plain to see."

Read the full article here

NASA Casini River Rocks: Titan vs Earth

It appears flash flooding has paved streambeds in the Xanadu region of Saturn’s moon Titan with thousands of sparkling crystal balls of ice, according to scientists with NASA’s Cassini spacecraft.

By analyzing the way the terrain has scattered radar beams, scientists deduce the spheres measure at least a few centimeters (inches) and maybe up to a couple of meters (yards) in diameter. The spheres likely originated as part of water-ice bedrock in higher terrain in Xanadu.

“What we believe happened in this area is a lot like what creates polished river rocks on Earth,” said Alice Le Gall, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and the lead author of the study, which used the Cassini radar instrument. “Bouncing downstream smoothes out the edges of rocks.”

As foothill residents know in southern California and other areas, sudden rains can trigger mudslides and flooding at the mountainous fringes of desert areas. Those flows can pick up boulders and debris and tumble them downstream.

On Titan, the flows appear to have occurred periodically for eons, on a catastrophic scale. The process on Titan, however, involves rain made of liquid methane and ethane, rather than Earth’s water rain.

Titan’s rocks are believed to be made primarily of water ice frozen into a hard mass about minus 180 degrees Celsius (minus 290 degrees Fahrenheit), rather than Earth’s mineral rocks.

For more information go to the Casinin website

Casini Snaps: Eclipse darkens 'Death Star' Moon

The Cassini probe has caught its first glimpse of one Saturn moon eclipsing another, as the moon Enceladus passed silently in front of its neighbour Mimas.

Most of Saturn's moons orbit in the same plane as its rings, along the planet's equator. This arrangement creates frequent alignments, but eclipses are rare because the sun must illuminate this plane almost edge-on in order for moon shadows to be cast in the right direction.

For the first time in almost 15 years, Saturn has reached a spot in its orbit where such events can be seen. The planet's rings, which are tilted by some 27°, will be illuminated perfectly edge-on during Saturn's equinox on 11 August 2009.

The visible moon in this series of images is Mimas, which resembles the Death Star, the planet-destroying space station from the movie Star Wars. It is eclipsed by Enceladus, which spews giant plumes of ice and water vapour from its south pole.

Cassini snapped the eclipse on 13 May, when the probe was roughly 1.3 million kilometres from Mimas.