|Comparison of noctilucent cloud coverage in 1880 versus 1990. They have increased over time. Credit: NASA|
|Astronauts on board the ISS took this picture of noctilucent clouds near the top of Earth's atmosphere on July 13, 2012. Credit: NASA|
Specks of meteor smoke act as gathering points where water molecules can assemble themselves into ice crystals. The process is called "nucleation."
|This graphic shows how methane, a greenhouse gas, boosts the abundance of water at the top of Earth's atmosphere. This water freezes around "meteor smoke" to form icy noctilucent clouds. Graphic courtesy of Prof. James Russell of Hampton University|
Russell explains: "When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor. This extra water vapor is then available to grow ice crystals for NLCs."
Tweets by @Threelas