August 8, 2012
Something Strange Is In The Air: Noctilucent Cloud Formation And Meteor Smoke
Watch the Video : [ Meteor Smoke Makes Strange Clouds ]
Lee Rannals for redOrbit.com - Your Universe Online
Noctilucent clouds were first noticed in 1885 about two years after the eruption of Krakatoa. Ash from the volcano caused great sunsets, making it a global past time for people to sit and look up at the sky at dust.
A German named T.W. Backhouse, who is credited with the first discovery of NLCs, noticed something odd while observing the sunsets. He stayed out longer than most people, and once twilight set in, on some nights he saw filaments glowing electric blue against the black sky.
Scientists assumed that what Backhouse was observing back then was some manifestation of volcanic dust. However, once the ash settled from the Indonesian volcano, and the sunsets became less brilliant, the noctilucent clouds did not go away.
Today, the clouds are stronger than ever, and researchers are not sure what role the volcano's ash played in those early sightings. However, one thing they are now sure about, is that the dust behind the clouds that are seen is space dust.
"Using AIM's Solar Occultation for Ice Experiment (SOFIE), we found that about 3% of each ice crystal in a noctilucent cloud is meteoritic," Mark Hervig, who led the team that found the extraterrestrial connection, told Science@NASA recently.
Every day, the Earth scoops up tons of meteoroids of all shapes and sizes, mostly small stuff. Once a meteoroid hits our atmosphere and burns up, it leaves behind a haze of tiny particles suspended 40- to 60-miles above the Earth's surface.
Specks of meteor smoke act as gathering points, allowing water molecules to assemble themselves into ice crystals, a process known as "nucleation."
This process takes place all the time in the lower atmosphere. While ordinary clouds sit, they collect airborne specks of dust, and even living microbes serve as nucleation sites.
The low clouds eventually drop ice crystals, water, and snowflakes to the ground once they become heavy enough.
Nucleating agents are important in the ethereal realm of NLCs. Clouds form at the eye of space where the air pressure is little more than a vacuum. The odds of two water molecules meeting are slim, and the odds of them sticking together is even slimmer.
The new research found that ice crystals grow around meteoritic dust to sizes ranging from 20 to 70 nanometers. The small size of the ice crystals explains the clouds' blue color. Small particles tend to scatter short wavelengths of light, which are blue, more strongly than long wavelengths, which show up red. Once a beam of sunlight hits an NLC, the blue color gets scattered down to Earth.
Scientists believe the NLCs are spreading due to climate change. Methane, a greenhouse gas, has become more abundant in the Earth's atmosphere since the 19th century. This gas forms from landfills, natural gas and petroleum systems.
"When methane makes its way into the upper atmosphere, it is oxidized by a complex series of reactions to form water vapor," James Russell of Hampton University, principal investigator of NASA's AIM mission to study the phenomenon, said in a press release. "This extra water vapor is then available to grow ice crystals for NLCs."
He said that while the clouds look alien to us, they are telling us something very important about our own planet.