Which moons have atmospheres

The innermost layer is a core of rock specifically, water-bearing silicate rock about 2, miles 4, kilometers in diameter. Surrounding the core is a shell of water ice—a special type called ice-VI that is only found at extremely high-pressures. The high-pressure ice is surrounded by a layer of salty liquid water, on top of which sits an outer crust of water ice. This surface is coated with organic molecules that have rained or otherwise settled out of the atmosphere in the form of sands and liquids.

The surface is hugged by a dense atmosphere. However, its atmosphere provides a clue. The surface of Titan is one of the most Earthlike places in the solar system, albeit at vastly colder temperatures and with different chemistry.

Here it is so cold degrees Fahrenheit or degrees Celsius that water ice plays the role of rock. No other world in the solar system, aside from Earth, has that kind of liquid activity on its surface.

The "sand" in these dunes is composed of dark hydrocarbon grains thought to look something like coffee grounds. In appearance, the tall, linear dunes are not unlike those seen in the desert of Namibia in Africa. Titan has few visible impact craters, meaning its surface must be relatively young and some combination of processes erases evidence of impacts over time. Earth is similar in that respect as well; craters on our planet are erased by the relentless forces of flowing liquid water, in Earth's case , wind, and the recycling of the crust via plate tectonics.

These forces are present on Titan as well, in modified forms. In particular, tectonic forces—the movement of the ground due to pressures from beneath—appear to be at work on the icy moon, although scientists do not see evidence of plates like on Earth. Oxygen probably forms at Callisto when water ice molecules at the surface are split into hydrogen and oxygen atoms; some of the lightweight hydrogen escapes from the atmosphere entirely, leaving the heavier oxygen behind.

John Spencer who was second author on the paper helped me convert from atmospheric column abundances to surface pressures. Cunningham and coauthors' work suggests that Callisto's leading hemisphere has a surface atmospheric pressure of 26 picobars -- that is, it is 40 billion times less dense than Earth's -- but that the air over its trailing hemisphere may be 10 times denser. A dynamic atmosphere, even though very thin, slightly shifts our view of Callisto.

Callisto is the outermost of the Galilean satellites and also, to use a highly technical term, the deadest. Its gravity field suggests that, unlike the other Galilean moons, it never got warm enough to differentiate into a rocky core and icy mantle, remaining instead a primitive mixture of ice and rock all the way down.

A couple of years ago, Jeff Moore postulated that Titan might not have internal geological activity and may just be " Callisto with weather. Callisto's atmosphere is more than dense enough for its molecules to collide with each other. Oxygen atmospheres form at Europa and Ganymede for the same reason that they form at Callisto. But their oxygen atmospheres are a factor of a few less dense than Callisto's, making theirs exospheres, not collisional atmospheres.

No wind, and no weather. At least not at present. So here you go: the unlikely set of four solar system moons known to have atmospheres dense enough for weather. One final remark. I think that the discovery of a collisonal atmosphere at Callisto is an incredibly cool result, the kind of thing you'd see on all the space blogs. Liberated carbon and oxygen could combine, forming carbon dioxide.

Micrometeorite bombardment could also be delivering the carbon for such reactions, according to the researchers. It's also possible that carbon dioxide is escaping from Rhea's interior fully formed. The gas could be primordial? Researchers may get their chance to do so very soon. Cassini is scheduled to make an even closer flyby of Rhea in January, coming to within about 47 miles 75 km of the moon's south polar region, Teolis said.

The new study suggests that oxygen atmospheres? The implications of this pattern are intriguing, according to the researchers. Oxygen is extremely reactive, so big, frozen moons could host more complex chemistry at or near their surfaces than previously imagined. This chemistry could get even more interesting if the oxygen goes underground and mixes with a liquid-water sea.

The smaller, inner planets probably got their atmospheres from the outgassing that occurred as they cooled down volcanoes. Some scientists think that much of the Earth's atmosphere came late in Earth's formation history and was brought in by the last of the impacts that formed the planet comets and wet asteroids. In the case of Venus, it had what is called a runaway greenhouse. It got so hot that the surface water if it ever had any evaporated and more greenhouse gasses went into the atmosphere.

As the atmopshere got even hotter, the surface rocks that contained carbonates heated up and put more carbon dioxide into the atmosphere, another greenhouse gas. The exosphere is the top of the atmosphere the outer atmosphere where molecules can move around with little chance of hitting other molecules. If they are moving fast enough, they can escape the atmosphere and go off into space. It starts at about to 1, kilometers above the surface and extends out into space.