Atmosphere
The presence of carbon dioxide on the surface suggests that Titania may have a tenuous seasonal atmosphere of CO2, much like that of the Jovian moon Callisto. Other gases, like nitrogen or methane, are unlikely to be present, because the moon's weak gravity could not prevent them from escaping into space. At the maximum temperature attainable during Titania's summer solstice (89 K), the vapor pressure of carbon dioxide is about 3 nbar.
On September 8, 2001, Titania occulted a bright star (HIP106829) with a visible magnitude of 7.2; this was an opportunity to both refine the moon's diameter and ephemeris, and to detect any extant atmosphere. The data revealed no atmosphere to a surface pressure of 10–20 nanobars; if it exists, it would have to be far thinner than that of Triton or Pluto. This upper limit is still several times higher than the maximum possible surface pressure of the carbon dioxide, meaning that the measurements place essentially no constraints on parameters of the atmosphere.
The peculiar geometry of the Uranian system causes the moons' poles to receive more solar energy than their equatorial regions. Since the vapor pressure of CO2 is a steep function of temperature, this may lead to the accumulation of carbon dioxide in the low-latitude regions of Titania, where it can stably exist on high albedo patches and shaded regions of the surface in the form of ice. During the summer, when the polar temperatures reach as high as 85–90 K, carbon dioxide sublimates and migrates to the opposite pole and to the equatorial regions, giving rise to a type of carbon cycle. The accumulated carbon dioxide ice can be removed from cold traps by magnetospheric particles, which sputter it from the surface. Titania is thought to have lost a significant amount of carbon dioxide since its formation 4.6 billion years ago.
Read more about this topic: Titania (moon)
Famous quotes containing the word atmosphere:
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—Ralph Waldo Emerson (1803–1882)
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—Charles Baudelaire (1821–1867)