Pluto's atmosphere has an extended reach. Data collected by NASA's New Horizons spacecraft reveals that the gas surrounding the dwarf planet extends as far as 1,000 miles outward into space. That's more than 13 times farther than Earth's atmosphere, which tapers off at around 75 miles above our planet's surface. Previous observations from Earth have only been able to record Pluto's atmosphere reaching 170 miles out into space.
Pluto's atmosphere has an extended reach
About an hour after its flyby of Pluto, New Horizons used its Alice imaging spectrograph to gather information about the atmosphere. The data had to be collected during a special time when New Horizons passed through Pluto's shadow and the Sun backlit the dwarf planet. It's an event known as solar occultation, and it allows the spectrograph to measure the wavelengths of the Sun's light filtered through Pluto's atmosphere. Changes in wavelengths help researchers figure out what gases make up the atmosphere.
At the highest altitudes, the atmosphere is comprised mostly of molecular nitrogen. Closer to the planet, methane mixes in with the nitrogen, followed by hydrocarbons at the lowest altitudes.
A significant portion of this gaseous mixture is also escaping out into space — around 500 tons of material per hour. NASA New Horizons team member Fran Bagenal noted that the atmospheric gases are escaping thanks in part to the weaker gravity on Pluto. But she also said it's possible solar wind is colliding with the escaping atmosphere and carrying it outward into space. The New Horizons SWAP (Solar Wind Around Pluto) instrument found evidence of an ionized tail behind Pluto — a result of ionized particles from the Sun mixing with the atmosphere and pushing it beyond the edge of the Solar System.
Right now New Horizons is 2 million miles past Pluto, and the spacecraft has sent back only 1 to 2 percent of its data back to Earth. Bagenal says they'll be able to discern more about Pluto's atmosphere as they receive more data from New Horizons other instruments. By next week, we should have about 5 percent of the spacecraft's data, and we'll get the full 100 percent over the next 16 months.
Correction: Pluto's atmosphere is more than 13 times farther out into space than Earth's. A previous version of this story suggested it was much farther than that.