NASA Considers Precautions For Upcoming Mars Comet Encounter

Comet C/2013 A1 Siding Spring photographed on Jan. 14, 2014. It’s currently a faint magnitude 14 object visible from the southern U.S. traveling through the constellations Eridanus and Fornax. Eridanus. Credit: Roland Ligustri

When the dandelions raise their heads to the sun this spring, NASA will be paying close attention a little comet that could raise a mess at Mars. Comet C/2013 A1 Siding Spring will pass just 86,000 miles (138,000 km) from the planet on October 19 this year, raising the possibility that dust sputtering from its nucleus could pepper the three orbiting spacecraft there and two additional probes expected to arrive about three weeks before the comet’s closest approach. That’s a close shave!

NASA’s taking precautions starting with an intensive observing campaign already underway using the Hubble Space Telescope and the NEOWISE probe. Scientists hope to characterize the comet, carefully monitor the size (and production rate) of dust particles that are released when the comet’s ices vaporize and also refine its orbit. As A1 Siding Spring moves closer to Mars, NASA’s Mars Reconnaissance Orbiter could provide pictures with enough resolution to image the actual nucleus.

No one knows exactly how big the nucleus is yet but already NEOWISE has revealed that A1 Siding Spring is active and dusty even though it’s still three-quarters as far from the sun as Jupiter.

Graphic depicting the orbit of comet A1 Siding Spring as it swings around the sun in 2014. On Oct. 19, the comet will have a very close pass at Mars. Although the nucleus will miss the planet, the comet’s coma of dust particles might envelop the planet. Credit: NASA/JPL-Caltech

While it’s too early to know whether dust could pose a threat to the orbiters, the two rovers are protected by Mars’ atmosphere, which is thick enough to burn up any dusty meteors released from vaporizing chunks of comet ice. Cameras on the rovers might be used to photograph what could be a spectacular meteor shower, though it appears for the moment that the geometry of the flyby would put the best of the shower in the daylight sky.

Simuated view of a comet passing close to the planet Mars. Credit: Michael Jaeger (comet image)

“During April and May, the comet will cross the range of distances from the sun at which water ice on a comet’s surface typically becomes active – vaporizing and letting dust particles loose. Dust ejected then could get far enough from the nucleus by October to swarm around Mars,” according to a NASA press release.

Dust shed by the comet is traveling faster than the typical dust that causes meteors – about 35 miles (56 kilometers) per second, relative to the Mars orbiters – because the comet is orbiting in almost the opposite direction as Mars and the other planets. It’s the difference between a car hitting you head-on versus from the side or behind. The two velocities – comet and Mars – add up to a significantly higher speed for dust particle impact.

NASA’s NEOWISE mission captured this image of the comet on Jan. 16, 2014 when it was 355 million miles (571 million km) from the sun. The infrared pictures reveal a comet that’s active and very dusty. The orbiters that could be affected by comet dust during the close flyby are NASA’s Mars Reconnaissance Orbiter, Mars Odyssey and MAVEN,  Europe’s Mars Express and India’s Mars Orbiter Mission. Credit: NASA/JPL-Caltech

If NASA decides evasive maneuvers are necessary for the five orbiting probes, plans are being discussed to position them on the backside of the planet away from the brunt of the meteor storm and orient their “delicate” sides away from the comet’s direction to avoid impacts.

Comet 2013 A1 Siding Spring was discovered on Jan. 3, 2013 from Siding Spring Observatory in Australia. Although it will pass 10 times closer than any identified comet has ever flown past Earth, it won’t come anywhere near as close to our planet. That said, it should still be fun to see it involved with Mars in binoculars and telescopes around Oct. 19 when the comet’s expected to glow around magnitude 8.

7 Responses

  1. Michael Blasi

    Bob, will this comet be seen by us northern hemisphere dwellers? I am a little anxious after comet Isons demise, to see another great one like Hale-Bopp.

    1. astrobob

      Hi Michael,
      Yes, we will see it in the northern hemisphere but it will be low in the southwestern sky in Sagittarius in October. When it’s near Mars it could be around 8th magnitude and visible in binoculars from a dark sky site.

  2. Kevin

    This is quite an event – it will be interesting to see how the thin atmosphere reacts to the onslaught of new gases and material. If the atmosphere of Mars gets even the slightest, miniscule addition of gases like hydrogen, oxygen, or ammonia, there will be great scientific finds that will come with this comet. There has been mention in science fiction novels over how to build Mars an atmosphere, and crashing comets into the planet has been thought of a messy way to terraform.

    Obviously, this is science fiction and far off from ever happening in real life, but it is interesting to see a planetary “close call” like this just to see what scenarios play out in case we ever have a comet approach like this on Earth. The distance this comet is coming to Mars is equivalent to a comet passing by Earth at 1/3 the distance to the Moon. Considering a comet’s coma can grow to the size of the Sun, it is very likely Mars might be ‘lost in fog’ for a brief time. I’ll be crossing my fingers that the satellites can capture some incredible information without getting buckshot with debris.

  3. Bob, guys – lets do the trig! There are other images of this pair. One is from the Siding Spring Observatory. The breadth of the visible comet – coma and tail is about the same as this galaxy – NGC 1291, that is, 9 arc minutes or about 500,000 km wide as viewed from our present perspective. But it is the denser coma of the comet that will really effect Mars’ atmosphere and possibly the orbiting constellation of NASA and ESA satellites. It is about 4 arc minutes in breadth and is essentially spherical in shape. So 4 arc minutes at its present distance from Earth of 197 Million Kilometers (JPL/Horizons) is equal to a breadth of 228,000 Kilometers. The comet will come within 138,000 km of Mars’ surface. This is why NASA and ESA are taking precautions! Siding Spring is going to be a very interesting event. It is possible that the space probes at Mars could be effected and an auroral or meteoritic show could take place and be viewed by the Rovers. Furthermore, Siding Spring is not done yet. The coma should grow even larger and denser in the next 75 days. This could be really really cool apparition but I hope the spacecrafts are spared damage.

    1. astrobob

      Hi Tim,
      Thanks for the calcs! I think with the precautions NASA’s taking, the probes should be OK. The window for possibly getting hit by particles in the comet’s tail is very narrow because of the speeds involved.

      1. Yeah, probably safe but it will be dicy. Depends, as has been said, whether Siding Spring becomes especially active or fragments. Has to happen soon though to provide time to disperse a Mars distance from the body. The density distribution of the coma must be roughly a normal distribution. So the density should be pretty low at a Mars distance; maybe at 2 or 3 sigma. The orbiters will take about 50 minutes to make a half orbit and I guess ground controllers are setting the orbits to step into the planet’s wake so that they get nearly a full 50 minutes of cover. It is probably 30 minutes of time when the coma will cover the planet but it depends on whether S-Spring has a sudden outburst in the next few days. Given this is a first-time comet with fresh volatiles, I lean towards something cool happening – a significant interaction between the two.

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