Meteor activity’s been picking up in recent days as we approach the maximum of the Perseid shower, one of the year’s best. Astrophotographer John Chumack of Ohio has recorded plenty of bright meteors, even fireballs, on his nighttime video camera this past week.
Earth bumped into its first Perseids starting the last week of July with the peak of the shower expected next Saturday night-Sunday morning August 11-12. Expect to see at least one a minute under dark skies.
Lots of other minor showers are active in early August including the Northern Delta Aquarids, Alpha Capricornids, Kappa Cygnids and Iota Aquarids. Individually each amounts to little, but taken together they make the sky busier than normal with shooting stars.
Meteors come from meteoroids, small bits of dust and rock ranging carrot seed size to small pebbles. When a meteoroid strikes Earth’s atmosphere 50-70 miles overhead it burns in a flash to create a meteor. It also leaves behind a trail of minute dust particles or soot called meteoric smoke.
In a recent article published in the Journal of Atmospheric and Solar-Terrestrial Physics, researcher Dr. Mark Hervig used data from NASA’s orbiting AIM spacecraft to discover that meteoric smoke is responsible for seeding noctilucent clouds, those wispy blue curls that appear low in the northern sky during twilight.
AIM or Aeronomy of Ice in the Mesosphere is the first mission dedicated to study noctilucent clouds (also called Polar Mesospheric Clouds) to figure out why they form and whether they might be connected to climate change.
To build a cloud, whether mesospheric or a puffy summertime cumulus, you need dust, soot or some type of particle for water or ice to condense around. The dust forms the nucleus of each raindrop or ice crystal; molecules of water latch onto it and assemble into a crystal in a process called nucleation.
Using data from AIM’s Solar Occultation For Ice Experiment (SOFIE) and comparing it to simulated mixtures of ice and meteoric smoke, Hervig found that up to 3 percent of the material in the ice crystals in noctilucent clouds was dust deposited by meteors. This makes perfect sense when you consider that meteors burn up at the same altitude the cloud form.
AIM found the ice crystals were only 20 to 70 billionths of a meter or 20 to 70 nanometers across. That’s tiny! A sheet of paper is 100,000 nanometers thick, and the ice crystals in a typical cirrus cloud are 250,000 nanometers long. Their small size makes them very good at scattering the short-wavelength blue portion of sunlight back to our eyes. That’s how noctilucent clouds get their distinctive color.
Noctilucents used to be visible only at high northern and southern latitudes. Not only have they been on the increase since the 20th century but they’ve occasionally spread as far south as Colorado and Utah. Scientists think these changes are due to an increase of methane gas from human activities like coal mining, agriculture and natural gas plants. The methane rises into the upper atmosphere, where it’s transformed by chemical reactions into water vapor. The extra water available provides the raw material for creating more noctilucent clouds.
I feel torn. Watching meteors slingshot across the sky this month, we can relish the knowledge that the dust they drop goes to build clouds in part extraterrestrial. At the same time it’s unsettling that their lushness may have much to do with us.