Comet ISON鈥檚 visit to Earth was a bit of a disappointment 鈥� but next year Mars is getting a cometary visitor that looks like it will be anything but. Calculations suggest that the Red Planet鈥檚 鈥渃omet of the century鈥� will come closer to its surface than any comet has come to Earth鈥檚 in recorded history 鈥� causing a meteor shower so epic that it may pose a danger to the spacecraft that orbit Mars.
Comet C/2013 A1, also known as comet Siding Spring after the , where it was discovered, is due to cross Mars鈥檚 orbit on 19 October 2014.
Early estimates of its path made it look as though the comet could smack into the Red Planet.
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A more recent study rules out a collision 鈥� but only just 鈥� and raises the alarm for the fleet of orbiters overhead.
Trouble for MAVEN
The comet will come within 173,000 kilometres of Mars鈥� surface, according to the study, and could even get as close as 89,000 kilometres. For comparison, the closest a comet has come to Earth in recorded history was 3.5 million kilometres, and that was in 1770, says Bill Cooke of NASA鈥檚 Marshall Space Flight Center in Huntsville, Alabama.
At that distance, the comet鈥檚 coma 鈥� the halo of gas and rocks that surrounds it and can stretch to hundreds of thousands of times the width of the comet鈥檚 nucleus 鈥� could engulf the entire planet and its natural and human-made satellites.
Cooke and his colleagues used data from past measurements of cometary comas to estimate that during the 2 hours of the comet鈥檚 closest approach, the Martian atmosphere will contain between 1000 and 10,000 times the density of space rocks that are normally present in low Earth orbit.
That could spell trouble for Mars鈥檚 cadre of satellites, including India鈥檚 Mars Orbiter Mission and NASA鈥檚 MAVEN orbiter, both of which are on their way and due to arrive before the comet.
Brilliant show
鈥淎ny large particle travelling at the velocity at which the comet is passing Mars can be a threat to MAVEN,鈥� says the orbiter mission鈥檚 principal investigator of the University of Colorado at Boulder.
Although MAVEN is designed to be robust, Jakosky says the team is still taking this specific threat seriously. 鈥淲e are in the process of defining the risk and the potential operational mitigations that can be taken to minimise the risk.鈥�
Spacecraft on the Martian ground, such as NASA鈥檚 Curiosity rover, may be in for a brilliant show. Dust from the comet and its coma should burn up in the Martian atmosphere, creating a meteor shower with potentially millions of meteors per hour, which should be visible to rovers on the surface.
of Texas A&M University in College Station says that the Curiosity and Opportunity rovers should be able to see bright meteors. He also hopes orbiters will be able to use radio waves produced in the storm to probe Mars鈥檚 ionosphere.
鈥淭he joint experiment of using radio waves to probe the ionosphere and cameras to document how active the meteor shower is 鈥� that is something to look forward to,鈥� he says.
鈥淚f I could have my druthers, I鈥檇 love to be on the surface of Mars for this event,鈥� says Cooke. 鈥淚t will probably be the most intense meteor storm on record.鈥�
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