[meteorite-list] Uncharted Meteors

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:22:43 2004
Message-ID: <200306271955.MAA07477_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2003/27jun_junebootids.htm

Uncharted Meteors
NASA Science News

The solar system is littered with clouds of dust--some of them uncharted.
Earth might encounter one such cloud this Friday, June 27th.

June 27, 2003: In 1967, NASA's Mariner 4 spacecraft was cruising through the
solar system, not far from Earth, when something unexpected happened.

"Mariner 4 ran into a cloud of space dust," says Bill Cooke of the Marshall
Space Flight Center Space Environments Team. "For about 45 minutes the
spacecraft experienced a shower of meteoroids more intense than any Leonid
meteor storm we've ever seen on Earth." The impacts ripped away bits of
insulation and temporarily changed the craft's orientation in space.

Fortunately, the damage was slight and the mission's main objective--a flyby
of Mars--had been completed two years earlier. But it could have been worse.

"There are many uncharted dust clouds in interplanetary space. Some are
probably quite dense," says Cooke. Most of these clouds are left behind by
comets, others are formed when asteroids run into one another. "We only know
about the ones that happen to intersect Earth's orbit and cause meteor
showers such as the Perseids or Leonids." The Mariner 4 cloud was a big
surprise.

"Of all NASA's Mars spacecraft, Mariner 4 was the only one we've sent with a
micrometeoroid detector," he continued. During its journey to Mars and back,
the detector registered occasional impacts from interplanetary dust
grains--as expected. The space between the planets is sprinkled with dust
particles. They're harmless in small numbers. But when Mariner 4 encountered
the cloud "the impact rate soared 10,000 fold," says Cooke.

Mapping these clouds and determining their orbits is important to NASA for
obvious reasons: the more probes we send to Mars and elsewhere, the more
likely they are to encounter uncharted clouds. No one wants their spaceship
to be surprised by a meteor shower hundreds of millions of miles from Earth.

Much of Cooke's work at NASA involves computer-modeling of cometary debris
streams--long rivers of dust shed by comets as they orbit the sun. He
studies how clumps form within the streams and how they are deflected by the
gravity of planets (especially giant Jupiter). He and his colleagues also
watch the sky for meteor outbursts here on Earth. "It's a good way to test
our models and discover new streams," he says.

One such outburst happened on June 27, 1998. Sky watchers were surprised
when hundreds of meteors streamed out of the constellation Bootes over a
few-hour period. Earth had encountered a dust cloud much as Mariner 4 had
done years earlier.

The meteors of 1998 were associated with a well-known meteor shower called
the June Bootids. Normally the shower is weak, displaying only a few meteors
per hour at maximum. But in 1998 it was intense. Similar outbursts had
occurred, with no regular pattern, in 1916, 1921, and perhaps 1927.

The source of the June Bootids is comet 7P/Pons-Winnecke, which orbits the
Sun once every 6.37 years. The comet follows an elliptical path that carries
it from a point near the orbit of Earth to just beyond the orbit of Jupiter.
Pons-Winnecke last visited the inner solar system in 2002. The comet's dusty
trail is evidently clumpy. When our planet passes through a dense spot in
the debris stream, a meteor shower erupts.

Meteor forecasters D.J. Asher and V.V. Emel'yanenko (MNRAS 331, 1998, 126)
have calculated that the meteors seen in 1998 might return in 2003, although
2004 is more likely. "That's why watching for June Bootids this year is
important: any activity now may herald another outburst in 2004," notes
Robert Lunsford, Secretary-General of the International Meteor Organization,
who is encouraging people to monitor the sky this week.

"The shower's peak is expected to occur on Friday, June 27th, near 1930
universal time (3:30 p.m. EDT)," says Lunsford. Although the timing favors
sky watchers in the Middle East and southern Asia, North Americans and
Europeans might see some meteors, too.

Bill Cooke offers this advice: "Step outside after sunset on Friday and look
straight up. The constellation Bootes will be almost directly overhead." If
the shower is active, sky watchers will see one or two meteors flying out of
Bootes every minute.

"You probably won't see a thing other than Bootes itself," Cooke cautions.
On the other hand, you might spot a genuine meteor cloud ... uncharted no
longer.
Received on Fri 27 Jun 2003 03:55:15 PM PDT