Meteors are unpredictable. You never know, not exactly, when one will streak
across the sky.
Not so on Wednesday, Sept. 8. At precisely 8:52:46 a.m. Pacific Daylight Time
(PDT), northwest of Bend, Oregon, a fireball will appear: a white-hot dot of
light, brighter than the planet Venus, gliding across the blue morning sky.
This is no ordinary meteor. It's a space capsule jettisoned by NASA's Genesis
spacecraft, returning to Earth with precious samples of the Sun, and we know
exactly where it will go:
From Bend, traveling 25,000 mph (11 km/s), the fireball will streak across
eastern Oregon, brightening as it descends into denser parts of Earth's atmosphere.
At 8:53:35 a.m. PDT it crosses the southwestern corner of Idaho and, moments
later, northern Nevada not far from the tiny town of Elko. Finally, at 8:54
a.m. PDT, slowed to a near-halt by the capsule's drogue parachute, the fireball
will fade over Utah.
Sky watchers as far away as 100 miles from the reentry path could see the capsule
glowing "10 to 100 times brighter than Venus," says meteor expert Peter Jenniskens
of NASA's Ames Research Center. For comparison, that's about as bright as a
fat crescent Moon. Jenniskens expects the fireball to be most luminous (visual
magnitude -9) when it is over Nevada.
To people within viewing range, he offers this advice: "Unless you're directly
beneath the reentry path, the fireball will be low in the sky, so pay attention
to the horizon. Try using binoculars to increase the contrast between the bright
blue sky and the fireball. But do not look toward the Sun." Focused sunlight
can blind you--permanently.
Jenniskens will be watching the reentry himself from the air, along with 20
other scientists, inside an Air Force NKC-135 aircraft. The plane is equipped
with a battery of telescopes and spectrometers pointing out of 20 upward-looking
windows. In years past, the NKC-135 has flown to study Leonid meteor showers.
This time "we plan to study the hot shock wave in front of the capsule," explains
Jenniskens.
Astrobiologists are interested because meter-sized asteroids--coincidentally,
about the same size and velocity as the Genesis capsule--hit Earth several times
a year, bringing organic materials from space to our planet. Do these molecules
survive reentry? Could they react with atmospheric gases in the hot cauldron
of their own shock wave to create new materials of biological importance?
"We don't know," he says. "It's so hard to catch a genuine asteroid in the
act of re-entering." Genesis is a rare "meteor on cue."
Watching the reentry, exciting and fruitful as that may be, is merely a prelude
to the main event:
Once the fireball is spent, a parafoil will pop out and the capsule will glide
gently toward the US Air Force's Utah Test and Training Range, southwest of
Salt Lake City. If all goes as planned, Hollywood stunt pilots -- no kidding!
-- will pluck the capsule from mid-air using a long hook extended from a helicopter's
belly. This prevents delicate sample holders from breaking on the ground below.
The samples are bits of the Sun -- the solar wind, actually -- which Genesis
has spent the last 27 months collecting. Scientists believe the solar wind is
almost identical in composition to the primeval solar nebula, the cloud from
which the Sun and planets condensed 4.5 billion years ago. Examining pristine
bits of the solar wind amount to examining the "stuff" of our origins--hence
the name "Genesis."
"The excitement really begins when scientists around the world get hold of
these samples for their research," says Genesis principal investigator Don Burnett
of the California Institute of Technology.
A star-spangled entrance. A Hollywood ending. And that's just the beginning?
Stay tuned.
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