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PostPosted: Tue Jan 22, 2013 12:00 am 
Broken Crown Panelist
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View from Titan

Broken Crown: Escape Titan takes place, well, on Titan. Titan is an extremely important moon (or satellite) because it is the only one in the solar system with a known dense atmosphere. In this post, we will discuss details about Titan’s atmosphere. Following that, we will briefly touch on what someone might see from the surface of Titan.

Discovering the Atmosphere

An atmosphere is layer of gases that surrounds a massive body such as a planet or moon. The origin of the atmosphere on Earth and Titan comes from the original cloud of gas that these bodies formed from in the early days of the solar system. Gas is made up of individual molecules, each of which is moving around at its own speed; a gas’s temperature is defined by how fast the molecules are moving around. The Earth’s atmosphere is made up mostly of nitrogen and oxygen. Even though much of the gas that Earth formed from was hydrogen and helium, there is only a trace of hydrogen in the Earth’s atmosphere. This is because Earth’s gravity is not strong enough to hold such a light molecule in place; at the Earth’s temperature, hydrogen gas moves so quickly that, over time, it escapes Earth’s atmosphere and leaks into space. In the meantime, other gasses such as nitrogen build up from biological and geological processes.

While the atmosphere on Earth and Titan is mostly nitrogen (80% and 98% respectively). In contrast, the atmosphere of the heaviest planets (Jupiter and Saturn) is mostly hydrogen and there is little nitrogen on Venus or Mars. There are many guesses why the atmospheres on different planets are so different, but there is no definitive theory.
Titan is one of the largest satellites in the solar system, with a diameter about 50% larger than that of the Moon and slightly smaller than Ganymede, a satellite of Jupiter. Titan’s size clearly contributes to the existence of its atmosphere, but it is not clear why Titan has an atmosphere, but Ganymede does not. Titan’s atmosphere is over 98% nitrogen. The atmosphere also contains about 1.4% methane, which is a big puzzle because methane converts to other materials over time. This implies that the methane is being replenished, either by volcanoes or possibly by biological organisms.

How do we know Titan has an atmosphere? As early as 1907, astronomers suspected that the dark edges around Titan corresponded to an atmosphere. In 1944, Kuiper showed that light passing through Titan’s atmosphere shows “absorption bands” consistent with the presence of methane. Different materials absorb different wavelengths or “colors” of light, and the light reaching Titan was missing the like absorbed by methane. However, it was only when Voyager 1 flew by Titan in 1980 that it was realized that Titan’s atmosphere is mostly nitrogen just how thick the atmosphere was- thicker than Earth’s by about 50%.

View from Titan

Does the atmosphere yield cloud cover and color? Voyager tried to take pictures of Titan, but could only see the dense haze pictured below.

Image

This means that the surface of Titan is almost invisible from space, and that there is a constant haze on Titan’s surface. What would the view from Titan’s surface be like? Here is an actual picture:

Image

There is haze in the sky which is caused by trace organic compounds in Titan’s atmosphere. The haze is so thick that when the Huygen’s probe descended in 2004, it could not detect the direction of the sun. Standing on the surface of Titan, someone would see a sky of a hazy brownish or dark orange color. Because of its distance and thick atmosphere, Titan only receives about .03% of the light that Earth does, making it look like a bright twilight at its brightest. Saturn would be invisible and the sun would likely be barely visible as a lighter patch in the sky. Since Titan experiences climate and likely methane rain, rainbows could form, the only place besides for Earth where this is possible. On this matter, see Jacob Haqq-Misra’s recent post on methane rains on Titan.

Titan's Sky

Because Titan is about 10 times as far from the Sun as Earth is, its apparent diameter is one-tenth the size that the Sun appears on Earth. This means that the size of the disk is about 1% of the size of the Sun on Earth. While Saturn is probably completely obscured by the haze on Titan, it would be about 100 times bigger than the Sun appears on Earth. Below is a partial view of Saturn snapped by the Cassini mission. The Cassini mission was in space above Titan, so the top part of Saturn was visible above Titan’s atmosphere. The lower half of Saturn was not visible, obscured by Titan’s haze.

Image


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