SHOWER METEOROID ENVIRONMENT
The Earth, and spacecraft near it, encounters
quasi-periodic meteoritic enhancements caused by streams of
material ejected from mainly short period comets that pass
near the Earth's orbit. These streams of debris produce meteor
showers observed here on Earth, and normally represent only a
modest enhancement over the background (a few percent). The
density of material in a stream, however, can be increased by
a recent entry of the parent comet into the inner Solar
System, thereby resulting in an enhanced shower (meteor rates
of several hundred per hour) or a meteor storm (rates in
excess of 1000 meteors per hour). As might be expected, an
enhanced shower or storm presents a time of increased risk for
spacecraft. Mitigating the meteoroid risks from such events
can be accomplished by operational procedures, such as
reorienting a vehicle to point sensitive equipment away from
the radiant, slewing solar panels edge-on to minimize the
cross sectional area presented, and closing shutters to
protect sensitive optics.
The Meteoroid Environment Office (MEO) has developed the
MSFC Meteoroid Stream Model to forecast meteor showers for
Earth and Earth orbiting spacecraft.
MSFC Meteoroid Stream Model
The MSFC Meteoroid Stream Model simulates particle ejection
and subsequent evolution from comets in order to provide
meteor shower forecasts to spacecraft operators for hazard
mitigation and mission planning purposes. Custom forecasts are
available from the MEO by
request.
A 15th order RADAU integrator is used to integrate
meteoroid position and velocity forward in time, accounting
for the effects of radiation pressure, Poynting-Robertson
drag, and the gravitational forces of the planets. General
relativistic effects have also been taken into account. The
number of particles simulated depends on the particular comet
in question.
See Moser & Cooke (2004) for more details.
Meteor Shower History
Streams that are notorious for producing enhanced showers
or storms at Earth are the Perseids, the Draconids (also
called the Giacobinids) and the Leonids. The Leonids are
especially famous for producing spectacular meteor storms at
33-year intervals. The table below presents information on
those meteor streams that are known to have the potential for
causing outbursts at Earth and the Earth-Sun L1 and L2 points.
| |
Radiant |
|
Time of max
activity |
| Stream |
RA |
Declination |
Speed (km/s) |
| Quadrantids |
230º |
+49º |
41 |
Jan 03 |
| Cygnids |
286º |
+59º |
25 |
Aug. 18 |
| Lyrids |
271º |
+34º |
49 |
Apr. 22 |
| Draconids |
262º |
+54º |
20 |
Oct. 09 |
| Perseids |
46º |
+58º |
59 |
Aug 13 |
| Leonids |
152º |
+22º |
71 |
Nov. 17-18 |
At least one satellite has been damaged and one effectively
killed by encounters with meteor streams. In mid-September of
1967, the Mariner IV spacecraft was located midway between the
orbits of Earth and Mars when it encountered an unknown meteor
stream. The onboard meteor counter registered a thousand-fold
increase in flux for about 45 minutes, during which time the
spacecraft was slightly torqued about its roll axis and had
some of its thermal insulation ripped away. Mariner IV was
lucky in that it suffered no major damage; this was not the
case for Olympus, a European communications satellite. During
an enhanced shower in August of 1993, Olympus was struck by a
Perseid somewhere near its electronics bay. The resulting
plasma discharge generated enough current to disable a gyro,
causing the satellite to tumble. By the time control was
restored some days later, the spacecraft had used practically
all of its fuel and was effectively dead as far as its mission
was concerned.
2009 Meteor Shower Forecast -- Brief
2009 looks to be a normal year with regard to meteor flux, with most major showers projected to exhibit usual activity. The 2009 Leonids are the exception, however. The unexpected minor outburst of the 2008 Leonids (peak ZHR of ~100) has led to a recalibration of stream models using the 2008 visual observations. The 2009 outburst will be caused by meteoroids from the 1102, 1466, and 1533 streams, and all models are consistent in predicting a peak between 21:40 and 22:00 UT on November 17. There is some ambiguity on the estimated ZHR/flux levels, with peak ZHR estimates ranging from as low as 160 to as high as 500, depending on the model used. The MSFC Meteoroid Stream Model puts the peak at 21:44 UT on November 17, with a peak ZHR around 300 ± 100.
2009 Leonids Peak Visibility
The five most active showers in 2009, with regards to flux, are the Quadrantids, Arietids, Perseids, Leonids, and Geminids.
