Flying high

The new study reports on data collected during the 1998 and 1999 Leonid meteor showers.

The annual event, which peaks again this weekend, occurs when Earth moves through a stream of debris left behind by comet Tempel-Tuttle. That comet passes through the inner solar system every 33 years, with its grains of dust zipping along at 160,000 miles per hour (72 kilometers per second) relative to Earth. When they hit our atmosphere, friction vaporizes many of them. From the ground, we see blazes of light commonly called shooting stars.

But studying small meteors from the ground can be frustrating. So Jenniskens and his colleagues at the Aerospace Corporation in Los Angeles, along with other researchers, used two airplanes to create "stereoscopic" images of the meteors. Ground-based instruments were used, as well.

In one striking image (see the click-to-enlarge animation) they followed a meteor that exploded into what scientists call a fireball. The trail left by the fireball contained what the researchers called the "fingerprint of complex organic matter.

Jenniskens and his colleagues caution that more work needs to be done to confirm these findings.

Heat created by the meteors' race through the atmosphere sets up an environment conducive to combining substances to form new compounds, Jenniskens explained in an interview. He suggests, therefore, that comets could have supplied basic chemicals that were lacking on early Earth.

The whole recipe might have gotten mixed in the air, he said, before settling on the planet and getting down to the business of breathing.

Jenniskens and Michael Wilson, of the University of California, San Francisco, also found evidence that the light we see from a meteor comes not from the head of the meteor, but from the wake.

This wake is similar to the one created by a boat. In this analogy, the boat plows the water, but the energy goes into the wake. With a meteor, it means that the heat energy does not destroy the molecules in the dust particle.

"The findings were somewhat surprising because it indicates that the process that gives rise to the light we see from a meteor is more complex than simple heating of the air through collision with the 'head' of the meteor," Wilson said. "The temperature associated with the light is much cooler."

Jenniskens said that the temperature of the wake, 4,300 degrees Kelvin (7,200 degrees Fahrenheit, or 3,982 degrees Celsius), is just right for breaking bonds in carbon monoxide, from which other life-seeding carbon compounds can form.

Wickramasinghe, director of the Cardiff Centre for Astrobiology, described his view of the most likely scenario for how life began on Earth, using the new findings as a springboard for a more controversial view:

"Comets are the breeding sites for cosmic bacteria," he explained. "In the early history of the solar system comets picked up enough viable microbes from interstellar space to incubate them in their warm watery interiors."

A million years later, the bacteria exhausted the comet's heat source, were freeze dried, and became dormant. Then, as the comet approached the Sun, some of its material was blown off into space.

"It is these ready-formed bacterial particles that entered the Earth for the first time 4 billion years ago and established the ancient Kingdom of Archaea, for which we have evidence in the geological record."

Other researchers are warming to the idea of panspermia, but remain cautious.

"But until someone actually finds evidence that life has come from space -- not just evidence that such an event is highly likely -- panspermia is still going to be just a hypothesis, and rightly so," Weiss said.

Jenniskens and his colleagues will not conduct such thorough research of this year's Leonids, but they hope to be back at it in 2001. Meanwhile, NASA will loft a weather balloon toward the stratosphere on Saturday to record the sights and sounds of the 2000 Leonid meteor shower. Video will be broadcast live at LeonidsLive.com.