Astronomers have recorded two magnificent fireballs that may have come from a nearby comet that made its closest pass by Earth in 24 years this month, prompting speculation on whether the icy cosmic visitor may be offering a meteor shower show.
The fireballs were spotted on Oct. 16, just four days before the close pass by Comet Hartley 2 and a few weeks ahead of a Nov. 4 visit to the comet by a NASA spacecraft. It is possible that the fireballs are related to the comet, but it may also be a coincidence, NASA scientists said. [Photo of the Oct. 16 fireballs]
Before the fireballs were observed, NASA scientists were skeptical of any substantial meteor display from Comet Hartley 2.
"Probably not," said astronomer Bill Cooke, head of NASA's Meteoroid Environment Office, "but the other night we saw something that makes me wonder."
Cooke was speaking, of course, of the twin fireballs. They were spotted five hours apart on the night of Oct. 16 by skywatching cameras in Canada and the United States.
Fireballs from a comet?
The Canadian fireball was first and spotted by all-sky cameras operated by the University of Western Ontario as it streaked over eastern Canada. The fireball over the U.S. was a slow, bright meteor that passed over Alabama and Georgia.
Multiple cameras recorded the displays of each fireball, which allowed astronomers to calculate the orbits of both objects before they struck Earth's atmosphere.
What they found surprised them.
"The orbits of the two fireballs were very similar," Cooke said in a statement. "It's as if they came from a common parent."
The orbits of the two fireballs were roughly similar to the Comet Hartley 2, NASA officials said. That put the comet on the suspect list, but there is still reason for skepticism, Cooke cautioned.
"Thousands of meteoroids hit Earth's atmosphere every night," he said. "Some of them are bound to look like 'Hartley-ids' just by pure chance."
But if there are meteors to be seen from Hartley 2, Cooke will be ready. He plans to keep watching for possible meteors, especially on Nov. 2 and Nov. 3 when the show is expected to be the strongest.
Comet Hartley 2 is a small comet that was discovered in 1986 by astronomer Malcolm Hartley six and a half years and made its closest approach to Earth in 24 years on Oct. 20.
NASA's Deep Impact spacecraft, which has already visited one comet, will fly by Comet Hartley 2 on Nov. 4 to get a good look at the icy object.
"The comet has been sputtering space dust for thousands of years, making a cloud that is much bigger than the comet itself," Cooke said. "Solar radiation pressure and planetary encounters cause the comet and the dust cloud to divergeot a lot, but enough to make the date of the shower different from the date of the comet's closest approach."
Meteors from Comet Hartley 2
Comets are known to be sources for several meteor showers seen throughout the year on Earth. When our planet passes through comet debris streams, the material left behind by the comet can sometimes spawn these meteor displays.
The October Orionid meteor shower and May Aquarid shower, for example, are the remnants of the famed Halley's Comet. The Taurid meteor shower, which peaks between mid-October and mid-November, is caused by the cosmic detritus of Comet Encke.
In an Oct. 22 column, Space.com skywatching columnist Joe Rao wrote that Comet Hartley 2 had the potential of causing at least some meteors, but observers could "hardly call it a meteor shower."
"We currently pass closest to the orbit of Hartley 2 around Nov. 2, but at the moment our respective orbits are too widely separated to produce much more than a few meteors during the course of an entire night watch," Rao wrote.
Any meteors from Comet Hartley 2 would likely appear to emanate from the constellation of Cygnus, the Swan, which is visible directly overhead to skywatchers in the Northern Hemisphere after sunset.
The moon should not outshine the potential sky show since it will be only a slender crescent at the time, NASA officials said. Last week, the moon was nearly full during the peak of the Orionid meteor shower, making observations for that shower a challenge.
"I'll definitely have our cameras turned on," Cooke said of the possible Hartley 2 meteor peak time. "It's probably going to be a non-event. On the other hand, we might discover a whole new meteor shower."