Webb detects infrared emission from methane coming from brown dwarf, 47 light-years from Earth

Astronomers using NASA's James Webb Space Telescope have found infrared emission from methane coming from W1935 - a brown dwarf located about 47 light-years from Earth.

This discovery came as a surprise because the dwarf is cold and doesn't have a host star, which means there is no apparent source of energy to warm its upper atmosphere and cause the methane to glow. The methane emission could be due to processes that produce aurorae, according to the researchers.

The team observed 12 cold brown dwarfs using Webb and two of them - W1935 and W2220 - appeared to be almost identical in composition, brightness, and temperature. However, methane emission was observed in W1935, instead of the expected absorption feature seen in W2220.

To decode this emission mystery, the team turned to our solar system. Methane emissions are a common feature in gas giant planets such as Jupiter and Saturn. This emission is linked to aurorae, which are caused by heating in the upper atmosphere.

On Earth, aurorae are created when energetic particles blown into space from the Sun are captured by Earth's magnetic field. These particles interact with gases in our atmosphere, which results in beautiful displays of light in the sky. Aurorae on Jupiter and Saturn occur similarly and involve interacting with the solar wind, but they also get auroral contributions from their nearby active moons like Io (for Jupiter) and Enceladus (for Saturn).

In the case of isolated brown dwarfs like W1935, the absence of a stellar wind to contribute to the auroral process and explanation of the extra energy in the upper atmosphere required for methane emission is a mystery.

The research team has concluded that either unaccounted internal processes similar to the atmospheric phenomena of Jupiter and Saturn, or external interactions with interstellar plasma or a nearby active moon, may help explain the methane emission.