Meteor Shower… On Mars!

What’s that? Another meteor shower we can’t possibly see? Of course you can. All you need to view this meteor shower is a backyard on Mars! A team of scientists led by Armagh Observatory have, for the first time, detected a storm of shooting stars on Red Planet.

What happens when the orbit of Mars intersects with debris from comet 79P/du Toit-Hartley? Scientists were hard at work making predictions. The detections were then cross-referenced with observations of activity in the Martian ionosphere by NASA’s Mars Global Surveyor (MGS) satellite. Says Dr. Apostolos Christou:

“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.”

We’re all familiar with the cause of most meteor showers. They happen when a planet (and not always ours!) passes through the debris trail left by a comet as it moves along its orbital path. The material lets us glimpse into the age, size and composition of particles ejected from the comet’s nucleus, the speed at which it was thrown off, as well as general information about the structure and history of the comet itself. Oh, to be a comet watcher on Mars! About four times as many comets approach the orbit of Mars than the Earth’s and the greatest majority of these are Jupiter Family Comets.

Studying Martian meteor showers can definitely improve our understanding of meteor showers and the Jupiter Family Comets as well. JFC are short period comets with an orbital period of less than 20 years. Their orbits are controlled by Jupiter and many are believed to originate from the Edgeworth-Kuiper Belt, a vast population of small icy bodies that orbit just beyond Neptune. Famous JFCs include Comet 81P/Wild 2, which was encountered by the Stardust spacecraft in January 2004 and Comet Shoemaker-Levy 9, which broke up and collided with Jupiter in July 1994.

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. Dr. 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.

Just like earthly meteor showers, we can predict all we want – but sometimes we draw a blank. In this instance only one of the six predictions came true. 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. Dr Christou says, “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 Christou is now investigating the possibilities of making observations with Europe’s ExoMars mission, which is due to land on Mars in 2015.