Current Issues:
   SpaceViews
   SpaceViews Update

Breaking News
Back Issues
Search
Subscriptions
Submissions
Forum
Space Sites of the Week
Home

Comet Hale-Bopp
Top Ten Stories of '96
Life on Mars?
Mars Pathfinder
Space Station Mir

Cassini's Science at Saturn

The objectives for the Cassini mission are split into five distinct areas: studies of the planet itself, its rings, its magnetosphere, its icy satellites, and Titan, Saturn's largest moon. This section looks at what we know about each of those areas and what Cassini may tell us about the Saturnian system.

The Planet Saturn

What We Know: Saturn is the second largest planet in the solar system, behind Jupiter. Its atmosphere consists largely of hydrogen and helium, with distinct cloud bands visible from spacecraft images as well as Earth-based telescopes; the clouds themselves are ammonia ice crystals. Saturn's winds blow at speeds up to 500 meters/second (1100 mph) near the equator, and fall off at higher latitudes in the same way north and south of the equator. The temperature at the cloud tops is about 134 K (-218 F); the atmopshere above the cloud tops is largely isothermal (same temperature) until the uppermost reaches of the atmopshere, when it heats up to several hundred K.

What We Hope to Find Out: Cassini's instruments should give us a better understanding of the composition of the atmosphere, including trace compounds which play a key role in atmospheric chemistry. Cassini's instruments will also give us a better understanding of Saturn's deeper atmosphere, below the cloud deck, as well as temperature and pressure variations at different locations on the planet. Cassini will also look for lightning, which has been seen in Jupiter's atmosphere. Put together, we should gain a better understanding of the composition and structure of Saturn, which should in turn help us understand how the planet was formed in the early days of the solar system.

The Rings

What We Know: The Pioneer 11 and Voyager missions to Saturn showed the rings of Saturn are extraordinarly complex, with fine structure at scales down a few kilometers. Gaps in the rings as seen from Earth, such as the Cassini Division, are actually thinly opulated with ring material. Small ringlets are formed are remain stable thanks to "sheparding moons", pairs of moons in nearly the same orbit with keep ring material between them in a thin band. The rings themselves are made of chunks of water ice and other materials and are very small; the rings overall may be just tens of metes thick!

What We Hope to Find Out: We don't yet have a good idea of what else besides water ice makes up ring material; Cassini should give us a better idea. It will show how the ring systems have evolved in the 20+ years since the Voyager missions, and see how the rungs interact with dust, other ring particles, and Saturn's magnetosphere. Data from Cassini may be able to explain why "spokes", or clumps of materials, form in the rings, and can check to see if the rings are warped in any way (as some Earth-based data recently suggests.)

The Magnetosphere

What We Know: The magnetosphere, or Saturn's magnetic field, is shaped by its interaction with the solar wind. Its magnetic field is closely aligned with the pole of the planet, which is not true for most other planets. Charged particles in the magnetopshere interact with a torus of hydrogen and nitrogen atoms around Titan.

What We Hope to Find Out: Cassini will be able to provide a detailed understanding of the shape and orientation of Saturn's magnetosphere, and measure its strength at various distances from the planet. Cassini will also look in detail at the interaction between Titan's torus of atoms and the magnetopshere.

Titan

What We Know: Titan is a unique world: it is the only moon in the solar system with a thick atmosphere -- denser at the surface than the Earth's atmosphere. The atmosphere of nitrogen, methane, and many other gases, coupled with a dense haze, shields the surface from view; only recently, with infrared images, have we gotten a first, limited look at its surface. There may be lakes of liquid ethane on the surface. The surface temperature is estimated to be 95 K (-288 F).

What We Hope to Find Out: Cassini will drop the European-built Huygens probe into Titan. it will return data on the composition and structure of the atmosphere as it descends. It is designed to survive all the way to the surface and float if it lands in a liquid. Cassini itself has a radar mapper which will be able to peer through Titan's clouds, like the radar on the Magellan spacecraft which studied Venus, and return radar images of portions of the surface. Other instruments will be able to monitor the atmosphere and look for evidence for weather patterns and other changes.

Other Satellites

What We Know: Saturn has up to two dozen other satellites which, unlikle Titan, are icy bodies with no obvious atmopsheres. There are a wide variety of bodies: Mimas has a large crater that dominates one side of the planet (giving it an appearance not dissimilar to the "Death Star" from Star Wars). Iapetus has one hemisphere which reflects far more light than another, making it appear white on one side and balck on another. Hyperion is a small, oddly-shaped asteroid which rotates chaotically. Several small satellites serve as sheparding satellites (see above) keeping thin ring segments together.

What We Hope to Find Out: Cassini will collect images and spectroscopic information on Saturn's icy satellites, which should allow scientists to understand their composition and provide insights into their geology. Cassini may be able to explain the two sides of Iapetus, and may see is Enceladus, another moon, is geologically active, as some believe.

More information about Saturn, its rings, and its moons are available from Views of the Solar System and The Nine Planets.

Articles * Science * Journey * RTG Debate

Return to SpaceViews Home