* Astronomy

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Martian "Cepheids"

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RE: Mars Meteor

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Title: The dust trail complex of comet 79P/du Toit-Hartley and meteor outbursts at Mars
Authors: A. A. Christou1, J. Vaubaillon2, and P. Withers3

Aims. Meteoroid trails ejected during past perihelion passages of the Mars-orbit-intersecting comet 79P/du Toit-Hartley have the potential of generating meteor outbursts in the Martian atmosphere. Depending on timing and intensity, the effects of these outbursts may be detectable by instrumentation operating in the vicinity of Mars. We aim to generate predictions for meteor activity in the martian atmosphere related to that comet; to search for evidence, in planetary mission data, that such activity took place; and to make predictions for potentially detectable future activity.
Methods. We have modelled the stream by integrating numerically the states of particle ensembles, each ensemble representing a trail of meteoroids ejected from the comet during 39 perihelion passages from 1803, and propagated them forward in time, concentrating on those particles that physically approach Mars in the recent past and near future.
Results. We find several instances where meteor outbursts of low to moderate intensity may have taken place at Mars since 1997. A search through Mars Global Surveyor (MGS) radio science data during two periods in 2003 and 2005 when data coverage was available showed that a plasma layer did indeed form in the martian ionosphere for a period of a few hours in April 2003 as a direct consequence of the predicted outburst. The apparent failure to identify such an event in 2005 could be due to those meteoroids ablating lower in the atmosphere or that the cometary dust follows a different particle size distribution than what was assumed. Our study highlights the need for further theoretical modelling of the response of the martian ionosphere to a time-variable meteoroid flux, observations of the comet itself and, most importantly, regular monitoring of the martian ionosphere during future outbursts predicted by our model.

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A team of scientists led by Armagh Observatory have, for the first time, detected a storm of shooting stars on Mars. The detections were made using predictions of when meteor showers should occur as the orbit of Mars intersects with debris from comet 79P/du Toit-Hartley. These predictions were cross-referenced with observations of activity in the Martian ionosphere by NASA's Mars Global Surveyor (MGS) satellite.

"Just as we can predict meteor outbursts at Earth, such as the Leonids, we can also predict when meteor showers are going to occur at Mars and Venus. We believe that shooting stars should appear at Venus and Mars with a similar brightness to those we see at Earth. However, as we are not in a position to watch them in the Martian sky directly, we have to sift through satellite data to look for evidence of particles burning up in the upper atmosphere" - Dr Apostolos Christou, who presented the results at the RAS National Astronomy Meeting in Belfast on Wednesday 2nd April.

Observations of meteor showers, caused when a planet passes through the dusty trail left by a comet as it moves along its orbital path, give insights into the age, size and composition of particles ejected from the comet's nucleus, the ejection velocity, as well as general information about the structure and history of the comet itself. Roughly four times more comets approach the orbit of Mars than the Earth's and a high proportion of these are Jupiter Family Comets. Mars therefore offers a significant opportunity to improve our understanding of meteor showers and Jupiter Family Comets.
When meteor particles burn up in a planet's atmosphere, metals contained within them are ionised to form a layer of plasma. On Earth, this layer has an altitude of approximately 95-100 kilometres and on Mars the layer is predicted to be around 80-95 kilometres above the Martian surface. Meteor showers leave a narrow layer of plasma superimposed on top of the main plasma layer, caused by meteors that are general debris from the Solar System.
Christou and his colleagues developed a model to predict meteor showers caused by the intersection of Mars with dust trails from comet 79P/du Toit-Hartley. From the model, the team identified six predicted meteor showers since the MGS satellite entered into orbit around Mars in 1997. Although the metallic ions cannot be observed directly by MGS instruments, evidence for the plasma layer can be inferred by monitoring electron density in the Martian atmosphere using the spacecraft's radio communication system.
Out of the six predicted showers, ionospheric data from MGS was only available for the outbursts in April 2003 and March 2005.
In the April 2003 data, the team found that an ionospheric disturbance appeared at the exact time of the predicted meteor outburst. The height of the disturbance corresponded with the predicted altitude for the formation of the metallic ion layer and its width and multi-peaked shape were similar to structures observed in the Earth's ionosphere linked to the Perseid meteor shower.
For the 2005 data, no features were observed near or immediately after the predicted meteor shower.

"We speculate that we don't see anything in the 2005 data because the meteors burned up deeper in the atmosphere where their ionisation is less efficient. If we are going to get a clear picture of what is going on, we need more optical and ionospheric observations of meteor showers at both the Earth and Mars so we can establish a definitive link between cause and effect. Equally importantly, we need further observations of Martian meteor showers, either from orbit or from the planet's surface, to confirm our predictions. Finally, we need to improve our prediction model by tracking more comets that might cause meteor showers on Mars" - Dr Apostolos Christou.

Dr Christou is now investigating the possibilities of making observations with Europe's ExoMars mission, which is due to land on Mars in 2015.

Source: Royal Astronomical Society

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Blobrana · L

The streak of light that the Spirit rover photographed on Mars 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.

Sky watchers 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.

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 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.
"On Earth for instance, Leonids emerge from the constellation Leo and the Perseids from Perseus." - Franck Selsis.

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," - Franck Selsis.

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 (About 14.2 degrees above 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 200-300 kilometres 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.

"Our findings indicate that Martian meteor showers may now be predictable events. Detailed simulations show that we can expect an intense Cepheid shower on Mars, on Dec. 20, 2007." - Franck Selsis

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.