RAS PN 08/20 (NAM 11): Catch a shooting star 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.
Dr Apostolos Christou, who is presenting the results at the RAS National Astronomy Meeting in Belfast on Wednesday 2nd April, said, “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.”
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. 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.
NOTES FOR EDITORS
RAS NATIONAL ASTRONOMY MEETING
The RAS National Astronomy Meeting (NAM 2008) is hosted by Queen’s University Belfast. It is principally sponsored by the RAS and the STFC. NAM 2008 is being held together with the UK Solar Physics (UKSP) and Magnetosphere, Ionosphere and Solar-Terrestrial (MIST) spring meetings.
COMET 79P/DU TOIT-HARTLEY
Comet 79P/du Toit-Hartley was discovered by D. du Toit in April 1945 but then went unobserved during subsequent apparitions for nearly 40 years. In 1982, Malcolm Hartley discovered two comets, 1982b and 1982c, which were later identified as fragments of du Toit’s 1945 discovery. 1982b faded rapidly, but the remaining fragment has been observed in December 1986 and March 2003.
JUPITER FAMILY COMETS
The Jupiter Family Comets (JFCs) 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.
Click here for an animation of a slow, bright fireball passing over Armagh, Northern Ireland in the evening of the 7th of December, 2006. Credit: Apostolos Christou/Armagh Observatory.
Click on images for high resolution versions
Comet 79P/du Toit-Hartley. Credit: Las Cumbres Observatory Global Telescope Network/Faulkes Telescope Project"
Leonid meteor shower. Credit: Shinsuke Abe and Hajime Yano, ISAS
Polar view of the Northern Hemisphere of Mars (actually a topographic map compiled using data another instrument on MGS, MOLA) annotated with the geographical location of the two detections and that of Viking Lander 2 for reference. Credit: MOLA Science Team/Christou
Mars Global Surveyor. Image credit: NASA/JPL-Caltech
Intersection of Comet 79P/du Toit-Hartley with the orbit of Mars in April 2003. Courtesy: NASA JPL/Caltech