This year’s Leonid meteor shower may well be one to remember. Astronomers
are predicting a storm of meteors, or shooting stars, perhaps up to 15000
per hour on the night of 18-19 November, and spacecraft operators are
standing by. Unfortunately, for those of us in Europe the Leonids will be
below the horizon at that time. ESA scientists have gone ‘down under’ to
catch the light show.

Shooting stars

Every 33 years, Comet Tempel-Tuttle travels through the inner Solar
System. As it approaches the Sun, the comet’s ices begin to vapourize and
the embedded dust particles fall away and trail the comet in its orbit.
Every year, the Earth passes through the trail of debris left behind by
the comet, and the comet’s dust particles plunge into Earth’s atmosphere
at some 71 kilometres per second — fast enough to travel from Amsterdam
to Moscow and back in about one minute. Comet Temple-Tuttle last passed
close to the Sun and was visible from Earth in March 1998.

On Sunday 18 November, Earth will once again pass through Comet Temple-
Tuttle’s dust tail. As the dust particles — tiny meteoroids — burn up
in Earth’s atmosphere, they give rise to ‘shooting stars’. This display,
known as the Leonid meteor shower because the meteors emanate from the
constellation Leo (The Lion), may be most visible over both North
America and Asia. This is because two separate maxima are predicted —
one on Sunday 18 November around 10:00 UT which favours American
observers and again on the same day around 18:00 UT favouring observers
in Australia and Asia.

Observing campaigns

Since Europe will not be a suitable location for Leonid observations
this year, a group of ESA scientists have travelled half-way around the
world to ensure that they get the best possible view of this visually
spectacular but also scientifically interesting natural event. In
addition to their studies of the meteor shower, the team, from the
Research and Scientific Support Department of ESA, intend to test a new
prototype of an instrument that is being developed for future planetary
missions to Mars, Mercury and the Moon.

Their campaign to observe the Leonid shower will take place between 15
and 19 November. “The primary objective of our campaign is to count the
meteor trails and measure their brightness,” said Detlef Koschny, one
of the team members. “With our cameras, we can record many more meteors
than are visible to the naked eye.”

“This will eventually enable us to calculate the changing numbers of
meteors over the five-day observing period,” he said. “We can then use
this information to improve existing computer models of the many dust
streams that are associated with Comet Tempel-Tuttle.”

“We will also learn a lot about the size and type of material that is
being incinerated by studying its speed and light curve — how each
meteor trail brightens and dims as it burns up in the atmosphere,” he

They will also be attempting to record tiny changes in the electric
field caused by the glowing meteor trails using a prototype of a
sensitive electric field sensor that is very difficult to test in
laboratory conditions. The isolated region of Australia where the team
are based is suitable for testing such a sensitive instrument.

Some of the team will also be busy testing another instrument, the
Mutual Impedance probe. Similar to an instrument on the Rosetta lander,
this probe is designed to measure how easily electrical current flows
through the ground. This is a particularly useful technique for
detecting subsurface water or ice, and so has potential for future
applications on the Moon, Mars or Mercury.

Across the world other observing campaigns, mostly land-based
observations and a few airborne missions, will also be taking place.
Historically, there has not yet been a large observing campaign covering
the world’s oceans. This year, however, the Dutch Meteorological Office
KNMI has initiated a large marine meteor observing campaign. The combined
‘meteor-counts’, from both land and marine-based locations could lead to
a detailed analysis of the dust-distribution in the Leonid meteor shower
thereby contributing to a better understanding of the formation of the
comet-tail of Comet Temple-Tuttle.

Satellites at risk?

Satellite operators will be keeping a close eye on their Earth-orbiting
spacecraft during the meteor shower. ESA’s operations centre in Germany
has already issued guidelines and will be providing real-time data for
spacecraft operators.

Though the risk of damage from a stray speck of dust is greater than
normal, officials are confident there will be no natural disasters in
space. The International Space Station, where the current Expedition
Three crew of Frank Culbertson, Vladimir Dezhurov and Mikhail Turin are
wrapping up a four-month stay in space, has armour to protect itself
against impacts from space debris as much as a few centimetres across.
Most Leonids are much tinier specks of dust.

Nevertheless, if a Leonid meteoroid does hit a satellite, the small
grain could destroy an imaging mirror or plow through fragile parts
such as an electricity-generating solar panel, possibly creating
electrical shorts that could disable the craft. The demise of ESA’s
Olympus spacecraft is thought to have been caused by the Perseid
meteoroid stream.

Last chance?

The year 2001 may be the last chance to get a clear understanding of the
activity levels of these showers as Earth encounters various Leonid dust
trails. Although the year 2002 has the potential to produce an even
larger display than in 2001, a nearly full moon will wipe out the
fainter meteors and hinder observations.

After 2002, encounters with Leonid dust trails will decline. Models
predict little activity for three years followed by ‘normal’ Leonid rates
of 10 to 15 per hour. The models then indicate another peak of over 100
Leonids per hour in 2006 and a possible similar peak in 2007. Thereafter,
it appears that the 33-year cycle of intense displays will end for nearly
100 years, as Jupiter will deflect the whole system of trails just enough
to prevent further encounters with Earth.

Related links

* ESA Science: Leonids 2001

* ESOC Leonids real-time data tracking

* World Meteorological Organization

* Astronomical and Geophysical Observatory (AGO)

* Astronet: Leonids 2001


[Image 1:]
Photo of the Leonids taken in 1998 by the Astronomical and Geophysical
Observatory (AGO) in Modra, Slovakia. Taken with a fish-eye lens, the
photo shows the whole sky. (Photo: Juraj Toth, Comenius University,

[Image 2:]
The constellation Leo rises at 23:30 CET (22:30 GMT). It can be seen
above the south southwestern horizon just before dawn (Illustration:

[Image 3:]
Satellite photo showing the positions of observation stations and ships
taking part in the land and marine-based observing campaign. (Photo:

[Image 4:]
Earth orbiting spacecraft are not only at risk of being hit by Earth
orbiting debris but to some extent also by meteorites (Illustration:
Leonid Storm Fluence Calculator)