Cassini Finds Possible Origin of One of Saturn's Rings

Aug 02, 2007
Cassini Finds Possible Origin of One of Saturn's Rings
This image shows the arc orbits at a distance of 167,496 kilometres. It is about 250 kilometres wide in radius and subtends less than 60 degrees of orbital longitude. The classical position of the G ring is about 172,600 kilometres from Saturn, and the arc blends smoothly into this region. Scientists suspect that bodies trapped in this remarkably bright feature may be the source of the G ring material, driven outward from the arc by electromagnetic forces in the Saturn system. The arc itself is likely held in place by gravitational resonances with Mimas of the type that anchor the famed arcs in Neptune's rings. There is an obvious narrow dark gap in the G ring beyond the arc. This feature is close to yet another resonance with Mimas, but no arcs are present at this locale. Credits: NASA - JPL - Space Science Institute

Cassini scientists may have identified the source of one of Saturn's more mysterious rings. Saturn's G ring likely is produced by relatively large, icy particles that reside within a bright arc on the ring's inner edge.

The particles are confined within the arc by gravitational effects from Saturn's moon Mimas. Micrometeoroids collide with the particles, releasing smaller, dust-sized particles that brighten the arc. The plasma in the giant planet's magnetic field sweeps through this arc continually, dragging out the fine particles, which create the G ring.

The finding is evidence of the complex interaction between Saturn's moons, rings and magnetosphere. Studying this interaction is one of Cassini's objectives. The study is in the Aug. 2 issue of the journal Science and was based on observations made by multiple Cassini instruments in 2004 and 2005.

"Distant pictures from the cameras tell us where the arc is and how it moves, while plasma and dust measurements taken near the G ring tell us how much material is there," said Matthew Hedman, a Cassini imaging team associate at Cornell University in Ithaca, N.Y., and lead author on the Science paper.

Saturn's rings are an enormous, complex structure, and their origin is a mystery. The rings are labeled in the order they were discovered. From the planet outward, they are D, C, B, A, F, G and E. The main rings -- A, B and C-from edge-to-edge, would fit neatly in the distance between Earth and the moon. The most transparent rings are D -- interior to C -- and F, E and G, outside the main rings.

Unlike Saturn's other dusty rings, such as the E and F rings, the G ring is not associated closely with moons that either could supply material directly to it -- as Enceladus does for the E ring -- or sculpt and perturb its ring particles -- as Prometheus and Pandora do for the F ring. The location of the G ring continued to defy explanation, until now.

Cassini images show that the bright arc within the G ring extends one-sixth of the way around Saturn and is about 155 miles wide, much narrower than the full 3,700-mile width of the G ring. The arc has been observed several times since Cassini's 2004 arrival at the ringed planet and thus appears to be a long-lived feature. A gravitational disturbance caused by the moon Mimas exists near the arc.

As part of their study, Hedman and colleagues conducted computer simulations that showed the gravitational disturbance of Mimas could indeed produce such a structure in Saturn's G ring. The only other places in the solar system where such disturbances are known to exist are in the ring arcs of Neptune.

Cassini's magnetospheric imaging instrument detected depletions in charged particles near the arc in 2005. According to the scientists, unseen mass in the arc must be absorbing the particles. "The small dust grains that the Cassini camera sees are not enough to absorb energetic electrons," said Elias Roussos of the Max-Planck-Institute for Solar System Research, Germany, and member of the magnetospheric imaging team. "This tells us that a lot more mass is distributed within the arc."

The researchers concluded that there is a population of larger, as-yet-unseen bodies hiding in the arc, ranging in size from that of peas to small boulders. The total mass of all these bodies is equivalent to that of a 328-foot-wide, ice-rich small moon.

Joe Burns, a co-author of the paper from Cornell University and a member of the imaging team, said, "We'll have a super opportunity to spot the G ring's source bodies when Cassini flies about 600 miles from the arc 18 months from now."

Source: NASA

Explore further: Gravitational waves according to Planck

add to favorites email to friend print save as pdf

Related Stories

Strong earthquake hits off eastern Indonesia

Sep 10, 2014

A strong earthquake hit off the coast of eastern Indonesia's Sulawesi island on Wednesday, causing panic among residents, but there were no immediate reports of injuries or damage. Authorities said there was no threat of ...

Cassini Images Ring Arcs Among Saturn's Moons

Sep 05, 2008

( -- NASA's Cassini spacecraft has detected a faint, partial ring orbiting with one small moon of Saturn, and has confirmed the presence of another partial ring orbiting with a second moon. This ...

XMM-Newton reveals cosmic collision in the Bullet Group

Jun 09, 2014

( —Despite the large distances between them, galaxies rarely exist in isolation. They are mostly found in large assemblies known as groups and clusters. Groups are the smallest gatherings, containing ...

Recommended for you

Image: NGC 6872 in the constellation of Pavo

2 hours ago

This picture, taken by the NASA/ESA Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2), shows a galaxy known as NGC 6872 in the constellation of Pavo (The Peacock). Its unusual shape is caused ...

Measuring the proper motion of a galaxy

2 hours ago

The motion of a star relative to us can be determined by measuring two quantities, radial motion and proper motion. Radial motion is the motion of a star along our line of sight. That is, motion directly ...

Gravitational waves according to Planck

19 hours ago

Scientists of the Planck collaboration, and in particular the Trieste team, have conducted a series of in-depth checks on the discovery recently publicized by the Antarctic Observatory, which announced last ...

Infant solar system shows signs of windy weather

19 hours ago

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have observed what may be the first-ever signs of windy weather around a T Tauri star, an infant analog of our own Sun. This may help ...

Finding hints of gravitational waves in the stars

Sep 22, 2014

Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be "seen" by looking at the stars. The new model proposes that ...

How gamma ray telescopes work

Sep 22, 2014

Yesterday I talked about the detection of gamma ray bursts, intense blasts of gamma rays that occasionally appear in distant galaxies. Gamma ray bursts were only detected when gamma ray satellites were put ...

User comments : 0