Leonids Meteor Shower Peaks
As this week’s 2002 Leonids meteor shower peaks, the astrobiology community is watching closely for what may be more intriguing signs of biochemistry.
A team of 42 astrobiologists from seven countries departed on November 15 from southern California’s Edwards Air Force Base on a mission to Spain to observe this year’s two Leonid storm peaks. The DC-8 Airborne Laboratory, operated by NASA’s Dryden Flight Research Center, Edwards, Calif., will carry high-speed cameras; a radio receiver to listen to upper atmosphere molecules; and a team of meteor observers, who will keep track of the meteor activity for satellite operators concerned about impact hazards.
"This final deployment of the Leonid Multi-instrument Airborne Campaign program promises an important and unique database for the development of instruments targeted at in situ sampling of cometary materials and for the future definition of comet missions," said Dr. John Hillman, lead scientist for planetary astronomy at NASA Headquarters. "It is hoped that these scientific data will provide new insights for the comparative studies of comets," he said.
The Leonids are grains of dust from comet Tempel-Tuttle colliding into the Earth’s atmosphere. Most Leonid particles are tiny and will vaporize very high in the atmosphere due to their extreme speed (about 44 miles per second, or almost 71 km/sec), so they present no threat to people on the ground or even in airplanes. As it progresses in its 33-year orbit, the comet releases dust particles every time it comes near the Sun. Earth intersects the comet’s debris trail every year in mid-November, but the intensity of each year’s Leonid meteor shower depends on whether Earth ploughs through a particularly concentrated stream of dust within the broader debris trail.
"Even with the full moon, this year’s Leonids will probably be better than any other for the next hundred years," said Dr. Don Yeomans, an astronomer at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. "If you’re ever going to see them, this might be the year to try," he said.
"Last year’s Leonid meteor storm yielded rich research results for NASA astrobiologists," said Dr. Peter Jenniskens, a NASA astronomer based at Ames Research Center and principal investigator for the airborne research mission. "Findings to date indicate that the chemical precursors to life — found in comet dust — may well have survived a plunge into early Earth’s atmosphere."
"Observers in good locations away from city lights might see a few hundred per hour. You’ll only get to see the bright ones because the moonlight will wash out the ones that aren’t as bright," said Yeomans. Last year, observers did not have to contend with the Moon and saw meteors at a pace of several hundred per hour.
|A composite of Leonid meteor images recorded by a CCD camera onboard the MSX satellite|
Jenniskens and his international cadre of researchers think that much of the organic matter in comet dust somehow survived the rapid heating of Earth’s atmospheric entry. "Organic molecules in the meteoroid didn’t seem to burn up in the atmosphere," he explained. They may have cooled rapidly before breaking apart, he concluded.
Another finding with potentially important implications for astrobiology is that meteors are not as hot as researchers had previously believed. "We discovered that most of the visible light of meteors comes from a warm wake just behind the meteor, not from the hot meteoroid’s head," said Jenniskens. This warm wake has just the right temperature for the creation of life’s chemical precursors, he said.
Utah State University researchers found that, during the meteors’ demise in the atmosphere, their rapid spinning caused small fragments to be ejected in all directions, quite far from the meteoroid’s head. This is an important finding for astrobiology, because it means that meteors may be able to chemically alter large amounts of atmosphere.
The Leonids get their name from the constellation where they appear to originate; the meteors will be radiating from the Sickle pattern in the constellation Leo the Lion, which will be rising out of the east-northeast sky. Don’t look directly at the constellation, but at the area above and around it. And, though you don’t need them to see the Leonids, a pair of binoculars could come in handy.
Public observers of this year’s meteor shower and fireballs are invited to report their results online with various astronomical organizations.
"We are looking for clues about the diversity of comets and their impact on the chemistry of life’s origin on Earth," Jenniskens said.
"We are eager to get another chance to find clues to two puzzling questions: What material from space rains down on Earth, and what happens to the (meteor’s) organic matter when it interacts with the atmosphere?" said Dr. Michael Meyer, senior scientist for astrobiology at NASA Headquarters in Washington.