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Collision Course? A Comet Heads for Mars
Presented by Science@NASA
Over the years,
the spacefaring nations of Earth
have sent dozens of probes and rovers to explore Mars.
Today there are three active satellites circling the red planet
while two rovers,
solar-powered Opportunity
and nuclear-powered Curiosity,
wheel across the red sands below.
Mars is dry, barren,
and apparently, hauntingly, lifeless.
Soon, those assets could find themselves
exploring a very different kind of world.
'There is a small
but non-negligible chance
that Comet 2013 A1 will strike Mars next year
in October of 2014,'
says Don Yeomans of NASA's Near-Earth Object Program at JPL.
'Current solutions put the odds of impact at 1 in 2000.'
The nucleus of the comet
is probably 1 to 3 km in diameter,
and it is coming in fast,
around 56 km/s (125,000 mph).
'It if does hit Mars,
it would deliver as much energy
as 35 million megatons of TNT,' estimates Yeomans.
For comparison,
the asteroid strike that ended the dinosaurs on Earth
65 million years ago
was about three times as powerful,
100 million megatons.
Another point of comparison
is the meteor that exploded over Chelyabinsk, Russia,
in February of 2013,
damaging buildings and knocking people down.
The Mars comet is packing 80 million times more energy
than that relatively puny asteroid.
An impact wouldn't necessarily mean the end of NASA's Mars program.
But it would transform the program --
along with Mars itself.
'I think of it as a giant climate experiment,'
says Michael Meyer,
lead scientist for the Mars Exploration Program at NASA headquarters.
'An impact would loft a lot of stuff into the Martian atmosphere--
dust, sand, water and other debris.
The result could be a warmer,
wetter Mars than we're accustomed to today.'
Meyer worries that solar powered Opportunity
might have a hard time surviving
if the atmosphere became opaque.
Nuclear powered Curiosity, though,
would carry on just fine.
He also notes that Mars orbiters
might have trouble seeing the surface,
for a while at least,
until the debris begins to clear.
A direct impact remains unlikely.
Paul Chodas of NASA's Near-Earth Object Program
stresses that a 1 in 2000 chance of impact
means there's a 1999 in 2000 chance of no impact.
'A near-miss is far more likely,' he points out.
Even a near miss is a potentially big event.
The latest orbit solutions
put the comet somewhere within 300,000 km of the red planet
at closest approach.
That means Mars
could find itself inside the comet's gassy, dusty atmosphere.
Visually, the comet would reach 0th magnitude,
that is, a few times brighter than a 1st magnitude star,
as seen from the Red Planet.
'Cameras on ALL of NASA's spacecraft
currently operating at Mars
should be able to take photographs of Comet 2013 A1,'
says Jim Bell, a planetary scientist
and Mars imaging specialist at Arizona State University.
Researchers will be keenly interested to see
how the comet's atmosphere interacts with the atmosphere of Mars.
For one thing,
there could be a meteor shower.
Another possibility is Martian auroras.
Unlike Earth,
which has a global magnetic field
that wraps around our entire planet,
Mars is only magnetized in patches.
Here and there,
magnetic umbrellas sprout out of the ground,
creating a crazy-quilt of magnetic poles
concentrated mainly in the southern hemisphere.
Ionized gases hitting the top of the Martian atmosphere
could spark auroras in the canopies of the magnetic umbrellas.
NASA is sending a new a spacecraft to Mars
to study the dynamics of the Martian atmosphere.
MAVEN is scheduled to launch in November 2013
and would reach Mars just a few weeks before the comet in 2014.
However, MAVEN's principal investigator,
Bruce Jakosky of the University of Colorado, notes
that the spacecraft won't be fully operational
and ready to observe the comet when it reaches Mars.
'It takes a while to get into our science mapping orbit,' he explains.
But he adds
'There are some effects
that I would expect to linger for a relatively long period--
especially if the comet hits Mars--
and we will be able to observe those changes.'
Astronomers around the world are monitoring 2013 A1.
Every day, new data arrive to refine the comet's orbit.
As the error bars shrink,
Yeomans expects a direct hit to be ruled out.
'The odds favor a flyby,
not a collision,' he says.
Either way, this is going to be good.
Stay tuned for updates as the comet approaches,
at science.nasa.gov