Saturn Moon May Possess Its Own Ring

[FSTargetDrone]

I thought this was kind of cool:

Saturn moon may have its own ring, in a lunar first

5 hours ago

WASHINGTON (AFP) — Saturn's second largest moon Rhea could have at least one ring, the first to be discovered around a planet's satellite, researchers reported in Friday's edition of the journal Science.

A broad debris disk and at least one ring appear to have been detected around Rhea by NASA's Cassini spacecraft, a US-European probe launched in 1997 to explore Saturn, a statement from the US space agency said.

"Until now, only planets were known to have rings, but now Rhea seems to have some family ties to its ringed parent Saturn," said lead researcher Geraint Jones of the Mullard Space Science Laboratory at University College in London, formerly at the Max Planck Institute in Germany.

The discovery was the result of Cassini's close flyby of Rhea in November 2005 when instruments aboard the spacecraft observed the environment around it.

Three Cassini instruments sampled the dust in Rhea's environment. Other instruments showed its interactions with Saturn's magnetosphere and in so doing found it could not have an atmosphere, the NASA statement said.

Rhea is roughly 950 miles (1,502 kilometers) in diameter. The apparent debris disk surrounding it measures several thousand miles (kilometers) from one end to the other.

Particles that make up the disk range in size from small pebbles to boulders, NASA said.

Scientists began to suspect a ring or rings could be embedded in the debris disk because they observed sharp, brief drops in electrons on both sides of the moon, they said.

"Seeing almost the same signatures on either side of Rhea was the clincher," Jones said. "After ruling out many other possibilities, we said these are most likely rings. No one was expecting rings around a moon."

The scientists also carried out numerical simulations to determine if Rhea can maintain rings -- and their models showed that it can.

The four largest planets in the Solar system -- Jupiter, Neptune, Saturn and Uranus -- all have rings, though Saturn's are the post spectacular, and it is likely that Earth had them too at the start of its history, Jones said.

"Like finding planets around other stars, and moons around asteroids, these findings are opening a new field of rings around moons," said Norbert Krupp, a Cassini scientist from the Max Planck Institute for Solar System Research.

In February Cassini scientists said they had found water below the frozen surface of Enceladus, another of Saturn's moons.

On the Net:

* NASA: +http://www.nasa.gov/mission_pages/cassi ... index.html

[Patrick Degan]

How rich to find new surprises and treasures in one's own solar backyard.

[Dark Flame]

I really don't understand the significance of it. To me, the coolness of Saturn's rings is that they are visible and very pleasant to look at. Obviously, this new ring isn't easily visible, so why does it really matter? Is there some other astronomical effect or side effect of the ring?

[Patrick Degan]

I really don't understand the significance of it. To me, the coolness of Saturn's rings is that they are visible and very pleasant to look at. Obviously, this new ring isn't easily visible, so why does it really matter? Is there some other astronomical effect or side effect of the ring?

For a start, it may provide a clue as to what event provided that much material that a gas giant and one of its largest moons could collect ring systems.

[FSTargetDrone]

I really don't understand the significance of it. To me, the coolness of Saturn's rings is that they are visible and very pleasant to look at. Obviously, this new ring isn't easily visible, so why does it really matter? Is there some other astronomical effect or side effect of the ring?

For a start, it may provide a clue as to what event provided that much material that a gas giant and one of its largest moons could collect ring systems.

Not only that, but it is significant merely in that it had never been observed before.

[Dark Flame]

For a start, it may provide a clue as to what event provided that much material that a gas giant and one of its largest moons could collect ring systems.

Gotcha. Scientific purposes and the sake of knowledge and understanding of our solar system. Sorry for being the dumbass that had to ask.

[LadyTevar]

How big is Rhea, compared to Earth?

[Patrick Degan]

A bit more than a tenth the size of our planet.

[GrandMasterTerwynn]

How big is Rhea, compared to Earth?

It is roughly 12% the diameter of Earth. However, as it is principally composed of ice, it is less than 0.05% of Earth's mass. Which is to say it's rather tiny, when compared to Earth.

I really don't understand the significance of it. To me, the coolness of Saturn's rings is that they are visible and very pleasant to look at. Obviously, this new ring isn't easily visible, so why does it really matter? Is there some other astronomical effect or side effect of the ring?

The interest is scientific. For one thing, it is extremely difficult for a moon to hold onto a ring, because the gravitational interaction between it, its parent planet, and other moons of that planet would tend to steal away the ring material, or force it spiral onto the moon. Which tends to beg the question of how long the ring system has been there, and what caused it. Given that Rhea has no meaningful way to weather, or internally alter its surface, we might actually be able to see traces of the impact or impacts which supplied material for the ring (assuming it was impact-created.) It also suggests that other moons in the solar system might be worth a closer look.

[tim31]

It's great news for NASA; Cassini is doing what it's supposed to: tells us what we didn't already know about Saturn.

[FSTargetDrone]

It's great news for NASA; Cassini is doing what it's supposed to: tells us what we didn't already know about Saturn.

Speaking of Cassini in particular, NASA is hoping it will fly through a plume of water from Saturn's moon Enceladus on Wednesday:

Cassini Spacecraft to Dive Into Water Plume of Saturn Moon
03.10.08

PASADENA, Calif. - NASA's Cassini spacecraft will make an unprecedented "in your face" flyby of Saturn's moon Enceladus on Wed., March 12.

The spacecraft, orchestrating its closest approach to date, will skirt along the edges of huge Old-Faithful-like geysers erupting from giant fractures on the south pole of Enceladus. Cassini will sample scientifically valuable water-ice, dust and gas in the plume.

The source of the geysers is of great interest to scientists who think liquid water, perhaps even an ocean, may exist in the area. While flying through the edge of the plumes, Cassini will be approximately 200 kilometers (120 miles) from the surface. At closest approach to Enceladus, Cassini will be only 50 kilometers (30 miles) from the moon.

"This daring flyby requires exquisite technical finesse, but it has the potential to revolutionize our knowledge of the geysers of Enceladus. The Cassini mission team is eager to see the scientific results, and so am I," said Alan Stern, associate administrator of NASA's Science Mission Directorate, Washington. Scientists and mission personnel studying the anatomy of the plumes have found that flying at these close distances poses little threat to Cassini because, despite the high speed of Cassini, the plume particles are small. The spacecraft routinely crosses regions made up of dust-size particles in its orbit around Saturn.

Cassini's cameras will take a back seat on this flyby as the main focus turns to the spacecraft's particle analyzers that will study the composition of the plumes. The cameras will image Enceladus on the way in and out, between the observations of the particle analyzers.

Images will reveal northern regions of the moon previously not captured by Cassini. The analyzers will "sniff and taste" the plume. Information on the density, size, composition and speed of the gas and the particles will be collected.

"There are two types of particles coming from Enceladus, one pure water-ice, the other water-ice mixed with other stuff," said Sascha Kempf, deputy principal investigator for Cassini's Cosmic Dust Analyzer at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. "We think the clean water-ice particles are being bounced off the surface and the dirty water-ice particles are coming from inside the moon. This flyby will show us whether this concept is right or wrong."

In 2005, Cassini's multiple instruments discovered that this icy outpost is gushing water vapor geysers out to a distance of three times the radius of Enceladus. The moon is only 500 kilometers (310 miles) in diameter, but despite its petite size, it’s one of the most scientifically compelling bodies in our solar system. The icy water particles are roughly one ten-thousandth of an inch, or about the width of a human hair. The particles and gas escape the surface at jet speed at approximately 400 meters per second (800 miles per hour). The eruptions appear to be continuous, refreshing the surface and generating an enormous halo of fine ice dust around Enceladus, which supplies material to one of Saturn's rings, the E-ring.

Several gases, including water vapor, carbon dioxide, methane, perhaps a little ammonia and either carbon monoxide or nitrogen gas make up the gaseous envelope of the plume.

"We want to know if there is a difference in composition of gases coming from the plume versus the material surrounding the moon. This may help answer the question of how the plume formed," said Hunter Waite, principal investigator for Cassini's Ion and Neutral Mass Spectrometer at the Southwest Research Institute, San Antonio.

This is the first of four Cassini flybys of Enceladus this year. In June, Cassini completes its prime mission, a four-year tour of Saturn. Cassini's next flyby of Enceladus is planned for August, well into Cassini's proposed extended mission. Cassini will perform seven Enceladus flybys in its extended mission. If this encounter proves safe, future passes may bring the spacecraft even closer than this one. How close Cassini will be allowed to approach will be determined based on data from this flyby.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL manages the Cassini-Huygens mission for NASA's Science Mission Directorate. The Cassini orbiter was designed, developed and assembled at JPL.

For images, videos and a mission blog on the flyby, visit: +http://www.nasa.gov/cassini . More information on the Cassini mission is also available at +http://saturn.jpl.nasa.gov.

This is some really interesting stuff!