[meteorite-list] Fiercest Meteor Shower on Record to Hit Mars Via Comet C/2013 A1 (Siding Spring)

[Ron Baalke]

http://www.newscientist.com/article/dn24715-fiercest-meteor-shower-on-record-to-hit-mars-via-comet.html 

Fiercest meteor shower on record to hit Mars via comet
by Lisa Grossman
New Scientist
06 December 2013

Comet ISON's visit to Earth was a bit of a disappointment - but next year 
Mars is getting a cometary visitor that looks like it will be anything 
but. Calculations suggest that the Red Planet's "comet of the century" 
will come closer to its surface than any comet has come to Earth's in 
recorded history - 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 observatory 
in New South Wales, Australia, where it was discovered, is due to cross 
Mars's orbit on 19 October 2014.

Early estimates of its path made it look as though the comet could smack 
into the Red Planet.

A more recent study rules out a collision - but only just - and raises 
the alarm for the fleet of orbiters overhead.

Trouble for MAVEN

The comet will come within 173,000 kilometres of Mars' 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's Marshall Space 
Flight Center in Huntsville, Alabama.

At that distance, the comet's coma - the halo of gas and rocks that surrounds 
it and can stretch to hundreds of thousands of times the width of the 
comet's nucleus - 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's 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's cadre of satellites, including India's 
Mars Orbiter Mission and NASA's MAVEN orbiter, both of which are on their 
way and due to arrive before the comet.

Brilliant show

"Any large particle travelling at the velocity at which the comet is passing 
Mars can be a threat to MAVEN," says the orbiter mission's principal investigator 
Bruce Jakosky 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. "We are in the process of defining 
the risk and the potential operational mitigations that can be taken to 
minimise the risk."

Spacecraft on the Martian ground, such as NASA's 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.

Mark Lemmon 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's ionosphere.

"The joint experiment of using radio waves to probe the ionosphere and 
cameras to document how active the meteor shower is - that is something 
to look forward to," he says.

"If I could have my druthers, I'd love to be on the surface of Mars for 
this event," says Cooke. "It will probably be the most intense meteor 
storm on record."

Journal reference: Icarus, DOI: 10.1016/j.icarus.2013.11.028