On the evening
of January 3, 2008, NASA Ames Research Center and SETI Institute hosted an
airborne observing campaign that took an international team of 14 researchers above
the Arctic Circle and back in a privately owned Gulfstream V aircraft for an
unprecedented view of a mysterious meteor shower called the "Quadrantids."
The first impressions, images, and predictions are posted at the Quadrantid
Multi Instrument Aircraft Campaign (Quadrantid MAC) mission website.
For eight
hours, six visual observers scanned the video output of four intensified
cameras that were aimed low above the crystal-clear horizon. We counted meteors
and the tally provided our first solid glimpse at the fascinating origin and
history of the Quadrantid meteor shower. We found the highest rates occurred
around 8h UT. This is later than all of our advance predictions (02:00 UT to
07:37 UT), which has caused some head scratching among the modelers in our
team.
We observed
these natural New Year
fireworks from a lofty altitude of 47,000 ft. during a peculiar roundtrip
from the Bay Area to the Bay Area, via the Arctic Circle. The mission departed during
one of the strongest rainstorms to hit the area in two years. When the aircraft
emerged from the cloud deck, the sky was brilliantly clear and remained so
throughout the mission. The view over the horizon provided a large surface area
for spotting Quadrantid meteors, little dimmed by the low atmospheric extinction
at altitude.
The mission
path was designed to compensate for the rotation of the Earth and kept the
shower in view throughout the mission. Observers on the ground are plagued by
the fact that the Quadrantids are mostly a daytime shower, disappearing from
view around midnight when the radiant of the shower sinks below the horizon,
only to appear again in the early morning hours. The Quadrantid shower is only
about 8 hours wide at half the peak rate. The shower is impressive only when
the peak happens to occur in the early morning hours at your local site. At
that time, it can outshine other strong annual showers including the Perseids
and Geminids.
By flying
north when the radiant was about to set, and returning south when the radiant
was again rising, we kept the radiant at an elevation between 15 and 30 degrees
throughout the mission. This meant that the Quadrantids were entering the
atmosphere at a shallow angle and created long-lasting and slow-moving meteors.
We counted some 846 of these shooting stars during the flight. This was the
very first time that the Quadrantid shower was observed under nearly constant conditions
for the entire period during which the peak might occur.
The
Quadrantid shower is caused by a steeply inclined sheet of meteoroids that
stretches from Earth's orbit to the orbit of Jupiter, where the heavy planet
frequently scatters the meteoroid orbits in and out of Earth's path. Potentially,
this can lead to large variations in peak activity and in peak time. Our goal
for the mission was to start disentangling those effects from the reported
variations caused by the difficult and changing observing conditions on the
ground.
How much
influence Jupiter has depends on how much dispersion the Quadrantid orbits have
accumulated over time. The dispersion depends on the age of the shower and how
the stream was created. Like most of our meteor showers, the stream appears to
have been created in a breakup of a comet,
instead of from a slow and gradual oozing out of water vapor. Likely, the
massive stream is younger than 500 years. About 500 years ago, in A.D. 1490-91,
Chinese observers reported a comet moving in the same plane as that of the
Quadrantids. We are now investigating whether or not this comet C/1490 Y1
represents the moment in time that the Quadrantid parent body broke and created
the massive stream. In 2003, we discovered that a minor planet called
"2003 EH1" moves among the meteoroids. This now-dormant remnant of
the breakup provides an anchor to investigate the origin and evolution of the
stream, but the current models that predict how the stream manifests 500 years later
are clearly insufficient.
Our team
collected other evidence about the origin of the stream. The 2008 Quadrantid MAC
mission deployed a total of 25 cameras of various sorts and purposes. We
measured spectra for main element composition of the dust, light curves to
investigate how the grains break upon entering the atmosphere, and meteoroid
size distributions to understand the fragmentation processes during formation
of the stream.
We thank
all the individuals and organizations that made this mission possible. Once we understand
what happened in 2008, we all hope to verify that with another Quadrantid MAC
mission some time in the future.
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