The rings around Saturn may be two or three times as massive as previously thought, according to new observations by the Cassini spacecraft.
Previous estimates of the rings鈥� mass were based on observations by the Voyager spacecraft in 1981. Now, those estimates have been revised upwards with new Cassini measurements of the B ring, one of the planet鈥檚 two brightest rings.
They reveal that the ring is quite clumpy and filled with gaps, which Voyager was not able to see.
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鈥淲e originally thought we would see a uniform cloud of particles. Instead we find that the particles are clumped together with empty spaces in between,鈥� says Larry Esposito, principal investigator for Cassini鈥檚 Ultraviolet Imaging Spectrograph (UVIS), which made the observations.
鈥淚f you were flying under Saturn鈥檚 rings in an airplane,鈥� he continues, 鈥測ou would see these flashes of sunlight come through the gaps, followed by dark and so forth.鈥�
To make the observations, UVIS watched as the rings appeared to cross in front of a background star. Cassini saw this happen 11 times with stars and twice with the Sun.
Stretch like taffy
This dimming of the starlight or sunlight told researchers how much material was between Cassini and the star. Clumps of ring material blocked more of the light and nearly transparent gaps in the ring blocked less.
These clumps, known as self-gravity wakes, are created by the gravitational attraction of the ring particles to one another. If Saturn was smaller or the rings were farther away from Saturn, these clumps might be able to aggregate and form a moon.
Instead, Saturn鈥檚 gravity keeps the particles from clumping together further once they reach about 30 to 50 metres in diameter. At that point, the clumps are stretched apart like taffy because different parts of the clumps are accelerated at different speeds around Saturn. Then the particles move on to form new clumps and repeat the cycle.
鈥淎t any given time, most particles are going to be in one of the clumps, but the particles keep moving from clump to clump as clumps are destroyed and new ones are formed,鈥� says team member Joshua Colwell of the University of Central Florida in Orlando, US.
Sheet-like clumps
Similar clumps had been known to exist in Saturn鈥檚 outer bright A ring, but this is the first time the clumps were observed in the B ring. In the A ring, the spaces between the clumps are greater, making them easier to spot. In the B ring, the clumps are tightly packed and are just a few metres thick.
鈥淚t鈥檚 not shocking that these clumps exist in the rings,鈥� Colwell told 快猫短视频. 鈥淲hat we鈥檝e done is measured just how flat they are and how prevalent they are in the B ring.鈥�
The newly observed clumps suggest the rings contain two or three times as much mass as previous estimates, which were based on Voyager spacecraft observations of a star passing behind the rings in 1981.
Previously, Cassini, the Hubble Space Telescope and Voyager had spotted 鈥渟pokes鈥� in the B ring (see Mystery of Saturn鈥檚 vanishing 鈥榮pokes鈥� illuminated).
快猫短视频s believe spokes are produced when micron-sized dust grains on the surface of boulders in the ring become charged and float above the ring plane. But they do not agree on how the dust particles become charged in the first place.
Journal reference: Icarus (doi:10.1016/j.icarus.2007.03.018)
Cassini: Mission to Saturn 鈥� Learn more in our continually updated .
