Collision course? A comet heads for Mars

March 28, 2013 by Dr. Tony Phillips, NASA
Collision course? A comet heads for Mars
Opportunity might have trouble observing the aftermath of a comet impact if dust in the air cuts sunlight to the rover's solar panels.

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, Opportunity and Curiosity, wheel across the red sands below. Mars is dry, barren, and apparently lifeless.

Soon, those assets could find themselves exploring a very different kind of world.

"There is a small but non-negligible chance that 2013 A1 will strike next year in October of 2014," says Don Yeomans of '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 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.

Collision course? A comet heads for Mars
Orbit of Comet 2013 A1.
"I think of it as a giant ," says Michael Meyer, lead scientist for the 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 or "coma." Visually, the comet would reach 0th magnitude, that is, a few times brighter than a 1st magnitude star, as seen from the .

"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. "The issue with Mars Odyssey and the Mars Reconnaissance Orbiter will be the ability to point them in the right direction; they are used to looking down, not up. Mission designers will have to figure out if that is possible."

"The issue with the Opportunity and Curiosity rovers will be power for imaging at night," he continues. "Opportunity is solar powered and so would need to dip into reserve battery power to operate the cameras at night. Whether or not we will be able to do this will depend on how much power the rover is getting from dusty solar panels in the daytime. On the other hand, Curiosity is nuclear powered, so it could have better odds at night-time imaging."

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. "Analyzing the spectrum of disintegrating meteors could tell us something interesting about the chemistry of the upper atmosphere," notes Meyer.

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.

Even before the comet flyby was known, NASA had already decided to send a spacecraft to Mars to study the dynamics of the . If the probe, named MAVEN (short for "Mars Atmosphere and Volatile Evolution"), is launched on time in November 2013, it would reach Mars just a few weeks before the comet in 2014.

However, notes MAVEN's principal investigator Bruce Jakosky of the University of Colorado, the spacecraft won't be ready to observe the comet when it reaches Mars. "It takes a while to get into our science mapping orbit, deploy the booms, turn on and test the science instruments—and so on," he explains. "MAVEN won't be fully operational until perhaps two weeks after the comet passes. 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.

Explore further: Is a comet on a collision course with Mars?

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5 / 5 (6) Mar 28, 2013
"I think of it as a giant climate experiment."
Why such a narrow focus? If it happens, this is a unique opportunity in planetary physics, tectonics, astronomy, and geology (or would it be 'areology' on Mars?). The effects on the Martian atmosphere will be minor compared to the effects on the condensed matter of Mars.
Even if it doesn't happen, it will be a unique opportunity in celestial mechanics - the orbits of Mars, Comet 2013 A1 and possibly Phobos and Deimos will be measurably affected.
1 / 5 (3) Mar 28, 2013
Comet = 1-3 km diameter, How about a Really Big climate experiment and crash Phobos (22.2 km) and Deimos (12.6 km) into Mars, its bound to happen anyway in the coarse of a few million years, just help it a hand with ie. ion engines/mass drivers and cover the surface of both satellites (as they are a bit porous) with ceramic heat tiles, as to give mars surface the full impact. Now we are talking Apocalyptic proportions, preferably crash them into a once vulcanicly active area, see if we can wake up some vulcanic magma activity (think subsurface water vapour!) as well.
1.7 / 5 (3) Mar 28, 2013
within the next 2 months of observation there is a near 99% chance that the information gained about this comets directional path will help us refine our predictions by 10 fold.

right now there's a less than 1/3 of 1% chance this thing will hit mars.
by the end of two months, that will probably drop to 1 in 100,000. within half a year. there will be a 1 in a million chance this thing will hit mars and it will be forgotten.

if it hit mars at its projected speed (even faster than it is going now due to mars' gravity well) this thing would be the most amazing astronomical event in our solar system in thousands of years. the estimated mass and speed of this comet would ensure that our astronomers and skyviewers would have the show of the millenia.

that kind of impact would be biblical in proportion particularly because mars is so close to us.
4 / 5 (4) Mar 28, 2013
"It if does hit Mars, it would deliver as much energy as 35 million megatons of TNT,"

Would be interesting if it actually happened, as it would give opportunity to study large terrestrial planet impacts for real, instead of just theory crafting or modeling.
3 / 5 (4) Mar 28, 2013
I vote for giving it a hand too but I doubt NASA would have the guts to take responsibility for such an action even though this would be such a grand learning experience. With only about a year to prepare for takeoff I doubt it anyway.
not rated yet Mar 28, 2013
We may lose our rovers if it hits Mars but the knowledge we learn from them is of little value if we can't learn how to detect ,calculate objects headed to earth and figure out ways to manipulate and miss us. This is just a wake up call !!
1 / 5 (5) Mar 28, 2013
the asteroid strike that ended the dinosaurs on Earth 65 million years ago was about three times as powerful, 100 million megatons.
Dr. Tony Phillips, you don't know how to use a comma!
5 / 5 (5) Mar 28, 2013
Something not yet mentioned: How will the comet's orbit be changed by the close approach? That could speak volumes about the density of Mars...and the eventual path of the comet.
1 / 5 (2) Mar 28, 2013
The worst impact is one which essentially has the meteor fail just short of skimming it, but passing right through and dislodging considerable numbers of space debris, some of which might be as large as small moon sized. That kind of event could affect every planet in the inner circle, if it strikes just wrong.
3.7 / 5 (3) Mar 28, 2013
Would it not create a sizable hot spot were it to impact Mars? If so, it would seem a natural focus for any future base/colony plans.

Their calculated value is about 150,000 times the energy of the 1883 Krakatoa eruption.

If it were to happen, it would be the biggest event in the inner solar system since humans have existed.

It even makes Toba or Yellowstone look like a joke.
3.2 / 5 (5) Mar 28, 2013
The effects of Krakatoa were noticed by Edward Munch, after which he painted the Scream, with the orange sky in the background. The Western hemisphere's sunsets were tinted red for months. Multiply that by 150,000? The recent Russian one last February, 2013, was about 500,000 tons of TNT equivalent.

If we assume that the upper atmosphere of Mars where it mixes with space is about 200 miles up, then it would take about 6 seconds for the meteor to hit the surface from space, which at 125,000 mph might not be enough time for it explode. It would do that when it collided with the surface, and that would be a colossal event that would change the topography of that planet considerably. Earth would be affected.
5 / 5 (2) Mar 28, 2013
Even if it doesn't happen, it will be a unique opportunity in celestial mechanics - the orbits of Mars, Comet 2013 A1 and possibly Phobos and Deimos will be measurably affected.
An object the size of this comet (only 5% of the mass of Halley's Comet) does not have nearly enough mass to gravitationally affect the orbits of Phobos or Deimos, much less Mars. Its mass is no more than 1% of Deimos, 0.1% of Phobos, 10^-8 % of Mars.

…space debris, some of which might be as large as small moon sized. That kind of event could affect every planet in the inner circle, if it strikes just wrong.
How big is a "small moon"? This would considerably affect expectations of damage to the inner planets.
...a colossal event that would change the topography of that planet considerably. Earth would be affected.
Earth might be affected in a minor way, but remember that the ejecta would scatter through a large volume of space. In such terms, Earth is a small target.
1 / 5 (4) Mar 29, 2013
a comet this size would end civilization as we know it. of 7 billion people on earth, likely 70 million or less would survive the devastating global crop failure, and ensuing famine, that would result from such an atmosphere altering event.

the world would decline into multi year winter, immediate mini ice ages would destroy enormous crop quantities, let alone the petroleum fertilizer distribution sytems, and if 1% of humanity survived ( 70 million people) those who were left would necessarily have to broaden their diet to include all sorts of detritus (possibly some canniablism of course too)

at the end of the day, only those with the strongest stomachs would survive. all those bunkered down survivalists could live for a few years on their food storage scraps, but what then? i propose we prevent this from happening:

4 / 5 (2) Mar 30, 2013
NASA should absolutely help this comet hit Mars. Not only would it help with any future colonization plans, it would also confirm their ability to alter the paths of comets and asteriods.
1 / 5 (2) Apr 01, 2013
I've long wondered what would happen if a 'dirty snowball' comet, say 50 km or 100 km diameter, were to hit Mars. I have gone over this as a thought-experiment several times, but I haven't been able to get anyone to model such an impact.
One thing I would like to get an estimate for is... how long will it rain on Mars after such a collision?
Long enough to cut obviously water-worn features in the landscape?

As you can guess by this, I'm rooting for the big Mars smack-down....

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