NASA's Spirit rover photographed
a streak of light that was likely part of a martian meteor shower, scientists
announced today.
The picture is the first
of a shooting star above Mars. Further, the flash has been traced back to its
parent comet. And now astronomers figure they should be able to forecast martian
meteor showers.
Meteor showers on Earth
are typically caused by streams of debris that boils off comets when they pass
through the inner solar system on their orbits around the Sun. The bits, from
the size of sand grains to peas, vaporize as they plunge through the atmosphere.
Skywatchers on Earth are
sometimes dazzled by the annual displays of the winter Leonid meteor shower
and the summer Perseids, among others.
Similar meteor showers ought
to occur on Mars, even though the red planet has a very thin atmosphere compared
to Earth.
As predicted ...
On March 7, 2004, Spirit's
panoramic camera photographed a bright streak in the sky. Scientists released
the image a few days later, but at the time they were not sure if it was
a meteor or the Viking Orbiter 2, still circling Mars after its 1970s mission.
Now the scientists have
analyzed the path of the object and considered meteor showers that were predicted
to have occurred on Mars around that time.
The meteor was likely once
a tiny chunk of a comet called Wiseman-Skiff, according to a team led by Franck
Selsis of Centre de Recherche Astronomique de Lyon in France.
The analysis is presented
in the June 2 issue of the journal Nature.
The result is somewhat speculative,
but no other known comet debris stream (or spacecraft) fits the data.
Because of perspective, all meteors from a comet seem to emerge from a single
point in the sky, called the radiant, Selsis explained. "On Earth for instance,
Leonids emerge from the constellation Leo and the Perseids from Perseus."
So the researchers checked to see if the streak was aligned with the theoretical
radiant of comet Wiseman-Skiff.
"We found a very good agreement," Selsis told SPACE.com.
The view from Mars
The shooting star was low
in the sky and ran across the horizon, creating a relatively long spectacle.
If you were on Mars and held a fist at arm's length, resting it on the horizon,
the meteor would have soared barely above your fist. In astronomers' terms,
it was 14.2 degrees off the horizon.
If you could trace the meteor
back and below the horizon, it would have appeared to emanate from the constellation
Cepheus, and so the scientists have dubbed the apparent meteor shower the Cepheids.
The streak of light was
about 125 to 185 miles (200-300 kilometers) away from the rover.
Other researchers have catalogued
debris streams from various comets. The streams are made up of many strands,
each representing previous passages of the comet. A meteor shower in any given
year can vary in intensity depending on the density of the portion of the stream
a planet passes through that year. All this knowledge allows astronomers to
roughly predict the intensity of future showers.
Upcoming event
Avid meteor watchers might want to
begin planning a trip to Mars for 2007.
"Our findings indicate that
martian meteor showers may now be predictable events," Selsis said. "Detailed
simulations show that we can expect an intense Cepheid shower on Mars, on Dec.
20, 2007."
The word meteor
is applied to any object that streaks through a planet's atmosphere. If one
reaches the ground, it is called a meteorite. Earlier this year, Spirits twin
rover, Opportunity, stumbled upon a basketball-sized rock that turned out to
be the
first known Mars meteorite.
Ancient asteroid impacts
have also carved chunks of rock from Mars, launching them into space. Some of
these have arrived at Earth millions of years later, becoming meteors and, in
some cases, meteorites. Scientists study these rocks
from Mars for clues about the history of the red planet.
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