Space Station Meteor Shower
NASA Science News
The crew of the International Space Station enjoyed a unique view of the
2001 Leonid meteor storm.
May 17, 2002: "It looked like we were seeing UFOs approaching the earth
flying in formation, three or four at a time," recalls astronaut Frank
Culbertson. "There were hundreds per minute going beneath us, really
spectacular!"
That was last November, and Culbertson, then the commander of the
International Space Station (ISS), was watching the 2001 Leonid meteor
storm. No UFOs, just lots and lots of "shooting stars."
News reports had warned sky watchers in advance: On Nov. 18, 2001, Earth was
due to plow through a minefield of debris shed by Comet Tempel-Tuttle.
Innumerable bits of comet dust would become meteors when they hit Earth's
atmosphere at 144,000 mph. Experts predicted an unforgettable display ...
and it came.
Millions of people saw the show, but only three of them -- the ones on board
the space station -- saw it from above. "We had to look down to see the
meteors," says Culbertson. "That's because the atmosphere (where comet dust
burns up) is below the station."
"A typical Leonid disintegrates about 100 km above Earth's surface,"
explains NASA scientist Rob Suggs. "The ISS is much higher than that. The
station (like the space shuttle) orbits our planet at an altitude of about
350 km." Suggs is the leader of the Space Environments group at the Marshall
Space Flight Center; he helped organize the crew's observations of the
Leonids.
"I had seen [meteors] on shuttle flights before," continued Culbertson, "but
when the Leonids happened it was supposed to be one of the best showers in a
long time, so we stayed up late to see them. Mikhail Tyurin and I were
inside the Pirs docking compartment, which had the darkest windows." (Pirs
is one of the Russian-built parts of the ISS; it serves as a docking port
for visiting Progress supply ships and Soyuz crew capsules.)
Gazing at the nightside of the earth below, they spotted so many meteors
that they soon lost count of all the flashes. Culbertson used a handheld
video camera to film parts of the storm, but it wasn't designed for
low-light photography. The best images were the ones Culbertson saw using
nothing but his eyes: "The storm was pretty spectacular," he said again.
Leonid meteors come from the direction of the constellation Leo -- hence the
name Leonids. At one point during the storm, the space station passed almost
directly between Leo (above) and the Earth (below). Peering out the window,
Culbertson could see meteoroids disintegrating directly underneath the
station. "Then's when you start thinking," he recalled, "they're coming
right by us! It's like being in the middle of a hailstorm."
"We didn't have any damage, but Vladamir (Dezhurov) said he heard some
little pings on the outside of the module," Culbertson said with a smile.
"I'm not sure if he really did ... he jokes a lot."
In fact, the station was in little danger. "There are several hundred
different shields protecting the crew and critical hardware," says Eric
Christiansen, the station's Shielding Subsystem Manager at the Johnson Space
Center. "The heavier shielding typically includes meteoroid/debris blankets.
These are made of a ceramic fabric (NextelTM) backed by KevlarTM -- the same
material found in bullet-proof vests."
The station's windows are sturdy, too. Each one consists of at least two
panes -- "always with primary and redundant pressure panes," says
Christiansen. "In some cases, the windows include transparent 'debris panes'
specifically designed to protect them from meteoroid impacts." Others are
shielded (when not in use) by metal shutters and debris blankets.
Although Leonid meteoroids travel much faster than bullets, the vast
majority of them are microscopic and fragile. They make pretty lights when
they hit Earth's atmosphere -- but that's all. They are not tough enough to
penetrate the station's defenses.
Culbertson was grateful for the protection. "We literally did see thousands
of Leonids all at once. It makes you think how crowded it is in space
sometimes, why it's so important to have those shields on the outside."
Another Leonid meteor storm is due on Nov. 19, 2002, and forecasters say it
could be even more intense than the one last year. Unfortunately, a glaring
full Moon will diminish the show -- as much for the crew of the ISS as for
sky watchers on the ground below.
Air molecules and aerosols -- that is, water droplets, dust and smoke --
scatter bright moonlight. Earth's atmosphere literally glows when the Moon
is full. Sky watchers looking up at the Leonids will see them through a
100-km thick layer of glowing air. Astronauts looking down at the Leonids
will see them streaking on top of that same glowing layer.
Moonlight will reduce the number of visible Leonids by some factor between 2
and 5. Even so, that's not necessarily enough to wipe out a full-fledged
Leonid meteor storm. If predictions are correct, sky watchers -- on Earth
and in space -- could see hundreds or thousands of shooting stars in spite
of the glare.
Rob Suggs notes that astronauts have two advantages: "They see a lot more of
the sky than we do from the ground, and they can't be clouded out!" The crew
can probably look forward to another good show.
Culbertson won't be one of them, though. He's back on the ground. "I was
fortunate to have that perspective," he says of the 2001 Leonids from space.
After all, it's not every day you can look down ... and see meteors beneath
your feet. |
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