[meteorite-list] First Shooting Star Seen from Mars

[Ron Baalke]

http://www.space.com/scienceastronomy/050601_mars_meteor.html

First Shooting Star Seen from Mars
By Robert Roy Britt 
space.com
01 June 2005

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.