Pluto's Atmosphere Warmer Than Thought
Artist’s impression of how the surface of Pluto might look. The image shows patches of pure methane on the surface.
Credit: ESO/L. Calçada

Pluto, the runt of the solar system, is still a mystery to astronomers in many ways. But thanks to a new study of the dwarf planet?s atmosphere, this misunderstood place is a little more known to us now.

Using the European Southern Observatory?s (ESO) Very Large Telescope in Chile, researchers made the first ever quantitative measurement of the chemical composition of the atmosphere around Pluto. The study revealed that the dwarf planet?s air is warmer, and contains more methane, than previously thought.

The astronomers discovered that Pluto?s atmosphere is warmer than its surface ? though not by much. The air is a frigid -292 degrees Fahrenheit (-180 degrees Celsius), while the dwarf planet?s face is -364 degrees Fahrenheit (-220 degrees Celsius). The researchers think some patches of pure methane in the atmosphere, or perhaps a methane-rich layer covering the surface, create this warming effect.

?Pluto is pretty far out there, so to me it was amazing that we got this data at all,? ESO researcher Hans-Ulrich K?ufl told ?It was well known that Pluto had an atmosphere, but it?s really the very first quantitative measurement of it. We were surprised that it is that warm.?

Pluto?s atmosphere is very different from Earth?s: It is a tenuous layer of nitrogen, methane, and carbon monoxide that is only present for part of Pluto?s 248-year-long, elongated orbit. When the tiny world gets very far away from the sun, the gaseous atmosphere freezes and falls to the ground. The pressure of Pluto?s atmosphere is only about one hundred-thousandth of that on Earth.

?It might look like a vacuum, like on the moon,? K?ufl said. ?At this point we cannot really say if there is haze, but you might see some kind of cirrus clouds. They would be white and gray.?

Because of the atmosphere?s thin substance, and Pluto?s small size and extreme distance, gathering data about the atmosphere before now has been difficult. Previous studies noticed the unique seasonal changes in Pluto's atmosphere as the dwarf planet moves closer and farther away from the Sun.

The team harnessed the Very Large Telescope (VLT)?s strong observing power, adaptive optics technology to reduce blurriness caused by turbulence in Earth?s atmosphere, and a high-resolution instrument called a spectrograph to make their measurements.

The CRyogenic InfraRed Echelle Spectrograph (CRIRES) on the VLT separated light from Pluto?s atmosphere into its constituent colors, enabling the researchers to tell what elements in the air the light passed through. The new data, which was significantly more detailed than any previous measurements, allowed the researchers to compare their findings to sophisticated computer simulations to understand how different chemicals in the atmosphere affect temperatures.

"The combination of CRIRES and the VLT is almost like having an advanced atmospheric research satellite orbiting Pluto,? K?ufl said.

Kaufl, with a team led by Emmanuel Lellouch of France?s Observatoire de Paris, reported the findings in a paper to be published in the journal Astronomy & Astrophysics.

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