Two more active moons around Saturn

Jun 13, 2007
Two more active moons around Saturn
This is a compound image made from separate images of Saturn's two moons, Tethys (to the left) and Dione (to the right), taken by Cassini. The two moons are flinging great streams of particles into space, according to data from the NASA/ESA/ASI Cassini mission to Saturn. The discovery suggests the possibility of some sort of geological activity, perhaps even volcanic, on these icy worlds. The particles were traced to the two moons because of the dramatic movement of electrically charged gas in the magnetic environs of Saturn. Known as plasma, the gas is composed of negatively charged electrons and positively charged ions, which are atoms with one or more electrons missing. Because they are charged, the electrons and ions can get trapped inside a magnetic field. Credits: NASA/ JPL

Saturn’s moons Tethys and Dione are flinging great streams of particles into space, according to data from the NASA/ESA/ASI Cassini mission to Saturn. The discovery suggests the possibility of some sort of geological activity, perhaps even volcanic, on these icy worlds.

The particles were traced to the two moons because of the dramatic movement of electrically charged gas in the magnetic environs of Saturn. Known as plasma, the gas is composed of negatively charged electrons and positively charged ions, which are atoms with one or more electrons missing. Because they are charged, the electrons and ions can get trapped inside a magnetic field.

Saturn rotates around itself in just 10 hours and 46 minutes. This sweeps the magnetic field and the trapped plasma through space. Just like a child on a fast-spinning merry-go-round, the trapped gas feels a force trying to throw it outwards, away from the centre of rotation.

Soon after Cassini reached Saturn, in June 2004, it revealed that the planet’s hurried rotation squashes the plasma into a disc and that great fingers of gas are indeed being thrown out into space from the disc’s outer edges. Hotter, more tenuous plasma then rushes in to fill the gaps.

Now, Jim Burch of the Southwest Research Institute, USA, and colleagues have made a careful study of these events using the Cassini Plasma Spectrometer (CAPS). They have shown that the direction of the ejected electrons points back towards Tethys and Dione. “It establishes Tethys and Dione as important sources of plasma in Saturn’s magnetosphere,” says Burch.

UUntil this result, among Saturn’s inner moons only Enceladus was known to be an active world, with huge geysers spraying gases hundreds of kilometres above the moon’s surface. “This new result seems to be a strong indication that there is activity on Tethys and Dione as well,” says Andrew Coates from the Mullard Space Science Laboratory, University College London, and a collaborator on this latest work.

Activity is a draw for planetary scientists as it means that the planet has yet to reach equilibrium, or is perhaps being supplied with energy. The activity on Enceladus was detected first by Cassini's Dual Technique Magnetometer (MAG). This led the flight team to schedule a particularly close pass of Enceladus, which revealed a wealth of data about Enceladus’ alien geysers – and spectacular pictures, too.

“The best results arise when we combine a variety of data sets to understand the observations,” says Michele Dougherty, Imperial College, London, and Principal Investigator of MAG.

In the case of Dione and Tethys, more fly-bys are scheduled in the future, which will allow the team and the other instruments a close-up look at the moons. Before that happens, the team has to go back and search for further signs of activity in the data already collected during the Tethys and Dione flybys of 2005.

In addition, Burch says that, having detected the electrons, they will now be on the lookout for the ions, so that the composition of the Tethys and Dione plasmas can be determined.

The findings will appear in the 14 June 2007 issue of the scientific journal Nature. The article, ‘Tethys and Dione as sources of outward-flowing plasma in Saturn’s magnetosphere’, is by J. Burch, J. Goldstein, W. Lewis, D. Young, A. Coates, M Dougherty and N. André.

Source: ESA

Explore further: Next-generation Thirty Meter Telescope begins construction in Hawaii

add to favorites email to friend print save as pdf

Related Stories

Cassini catches Saturn moons in paintball fight

Oct 07, 2010

(PhysOrg.com) -- Scientists using data from NASA's Cassini spacecraft have learned that distinctive, colorful bands and splotches embellish the surfaces of Saturn's inner, mid-size moons. The reddish and bluish ...

Recommended for you

Astronomers measure weight of galaxies, expansion of universe

2 hours ago

Astronomers at the University of British Columbia have collaborated with international researchers to calculate the precise mass of the Milky Way and Andromeda galaxies, dispelling the notion that the two galaxies have similar ...

Mysterious molecules in space

13 hours ago

Over the vast, empty reaches of interstellar space, countless small molecules tumble quietly though the cold vacuum. Forged in the fusion furnaces of ancient stars and ejected into space when those stars ...

Comet Jacques makes a 'questionable' appearance

Jul 28, 2014

What an awesome photo! Italian amateur astronomer Rolando Ligustri nailed it earlier today using a remote telescope in New Mexico and wide-field 4-inch (106 mm) refractor. Currently the brightest comet in ...

Image: Our flocculent neighbour, the spiral galaxy M33

Jul 28, 2014

The spiral galaxy M33, also known as the Triangulum Galaxy, is one of our closest cosmic neighbours, just three million light-years away. Home to some forty billion stars, it is the third largest in the ...

Image: Chandra's view of the Tycho Supernova remnant

Jul 25, 2014

More than four centuries after Danish astronomer Tycho Brahe first observed the supernova that bears his name, the supernova remnant it created is now a bright source of X-rays. The supersonic expansion of ...

User comments : 0