Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have a "tenuous surface-bounded exosphere" containing hydrogen, helium, oxygen, sodium, calcium, potassium and others.
"Studying Mercury's surface, tenuous atmosphere and magnetic field are a key to understanding the evolution of the inner solar system, including Earth," said Dr. Daniel N. Baker of the University of Colorado, a lead investigator for one of Messenger's seven scientific instruments.
For a Romantic viewer, the tenuous, unpolished, wavering, dappled surface was far more evocative than the veneered and polished surface.
Triton moves in a retrograde orbit around Neptune that is, opposite to the direction of the planet's orbit around the Sun and features plumes of material rising through its tenuous atmosphere from a surface whose temperature is only 37 kelvins (K; −393 °F, −236 °C).
"Maybe they are not really surface structures, but tenuous clouds of hot gas at a certain altitude," he says.
This final down-selection removes data points over the strongest magnetic anomalies without a measurable loss cone, times with tenuous magnetic connection to the surface, and poor/noisy data.
And the way in which the light of the occulted star faded and reappeared suggests that Quaoar may have an extremely tenuous methane atmosphere, with a surface pressure 10 million times smaller than Earth's.
The heliopause, a surface separating the tenuous hot heliosheath flow and the dense, strongly magnetized interstellar flow, is subject to instabilities of the Rayleigh–Taylor and Kelvin–Helmholtz types.
Researchers had previously suggested that a substantial fraction of the tenuous shroud, which has a surface pressure about one-billionth that of Earth's atmosphere at sea level, turns to frost for the 2 hours that Io lies in Jupiter's shadow.
In addition to the predominant water ice, solid carbon dioxide is present on the surface, and an extremely tenuous carbon dioxide atmosphere is slowly escaping into space.
Many atoms in Mercury's surface rocks and in its tenuous atmosphere become ionized when struck by energetic particles in the solar wind and in Mercury's magnetosphere.
