Discoveries on Saturn

dudara

Cassini-Huygens has shown that Saturn's rings have their won atmosphere of molecular oxygen, and that the rotation of the planet appears to have slown down by 7 minutes from previous measurements in the 70's and 80's. Link

Saturn rings have own atmosphere
By Paul Rincon
BBC News science reporter

Saturn's vast and majestic ring system has its own atmosphere - separate from that of the planet itself, according to data from the Cassini spacecraft.

And Saturn is rotating seven minutes more slowly than when probes measured its spin in the 70s and 80s - an observation experts cannot yet explain.

Cassini-Huygens mission scientists are celebrating the spacecraft's first year in orbit around the ringed planet.

Details were unveiled at the British Festival of Space 2005 in Birmingham.

By making close flybys of the ring system, Cassini has been able to determine that the atmosphere around the rings is composed principally of molecular oxygen (O2).

The finding was made by two experiments on Cassini: the Ion and Neutral Mass Spectrometer (INMS) and Cassini Plasma Science (Caps) instrument.

"The INMS sees the neutral oxygen gas, Caps sees the ionised products of that oxygen and the electrons associated with it. There is an enhancement over the rings," said Dr Andrew Coates, co-investigator for the Caps instrument, told the BBC News website.

Dr Coates, from the Mullard Space Science Laboratory (MSSL) at University College London, said the atmosphere was very similar to that of Jupiter's moons Europa and Ganymede.

"As water comes off the rings, the hydrogen is lost from it, leaving the oxygen," he explained.

Saturn's rings consist largely of water ice mixed with smaller amounts of rocky matter. Dr Coates said the ring atmosphere was probably kept in check by gravitational forces and a balance between loss of material from the ring system and a resupply of material from elsewhere.

Scientists admitted they were surprised by the finding that Saturn's rotation is slowing.

"The rotation seems to have slowed down by about seven minutes compared to what was inferred from the Pioneer and Voyager data, but we don't actually understand why," said Professor Michele Dougherty, principal investigator for Cassini's magnetometer instrument.

Data from the magnetometer and Cassini's Radio and Plasma Wave Science (RPWS) instrument both seem to show the slow down in Saturn's rotation.

"You would expect the rotation of the planet to slow down if its internal dynamo had stopped, but that does not seem to be the case with Saturn," Professor Dougherty, from Imperial College London, told the BBC News website.

The internal dynamo is the source of a planet's magnetic field and requires rotation and a fluid core. Professor Dougherty said it was possible the instruments were observing "rotational regions" closer to the surface of Saturn rather than anything to do with the dynamo itself.

"If you sit down and think about it, it's very difficult to come up with a scenario where the interior of the planet is slowing down," she said.

UK science and innovation minister Lord Sainsbury, who was at the briefing in Birmingham, praised UK scientists involved in Cassini-Huygens as the orbiter celebrated its first year in orbit around Saturn.

"The scientists and engineers in this country have played an integral role, making it the biggest British success story in space of the last 12 months," Lord Sainsbury said.

Cassini performed its Saturn Orbit Insertion (SOI) on 1 July 2004 after a six-year, three billion-kilometre trek.

In December 2004, it released its piggybacked Huygens probe, which performed a successful touchdown on Saturn's moon Titan in January this year.

The mission is a co-operative mission between the US space agency Nasa, the European Space Agency (Esa) and the Italian Space Agency (Asi).

Sparks

It's not quite a breathable atmosphere though, more a thin mist caused by offboiling from the ice. And it's a lot more likely that the original pioneer data had a larger error margin than we thought, than that saturn is actually shedding that much kinetic energy that fast. I mean, seriously folks, work it out. Rotational kinetic energy is given by this formula:

Where I is the moment of inertia. Assuming saturn's a solid sphere (yes, I know, but this is back-of-an-envelope stuff), I=2/5MR^2 = 2/5*5.6851e+26*60,268,000^2=2.36e+41
The rotational speed is a bit trickier in reality as saturn's mostly gas, but assuming it's a solid for now, the length of the day is 10 hrs, 13.8 minutes. So dropping 7 minutes leads to a change in omega of 1.15%, which means that you've lost about 2.27% of your rotational kinetic energy, which comes to approximately 5.36e+39 Joules, or in more manageable units, 12,804,015,296,367,100,000,000,000,000 megatons of TNT over what, 30 years or so? Which would be 4,268,005,098 megatons per year.

Y'know, I'd think we'd have noticed that much energy being emitted from the general vicinity of saturn

dudara

When I first read the article, the immediate thought than came to mind is that one of the measurements, whether the older, or the newer, is wrong somehow.

A planet really can't lose that much rotational energy without it being noticed. It's more likely that the error is human.