Was Mars' Magnetic Field Blasted Away?
Written by Nancy Atkinson
Map from the Mars Global Surveyor of the current magnetic fields on Mars. Credit: NASA/JPL
Spacecraft orbiting Mars have found only weak magnetic fields present in various regions of the Red Planet. These fields are probably remnants of an earlier global field that has since disappeared. But how and why did the global field vanish? Recent studies have proposed that giant asteroids slamming into Mars may have wiped out the planetary magnetic field. But scientists are still trying to determine if the magnetic field was suddenly blasted out of existence or if it slowly withered away.
Mars early magnetic field was likely driven by a dynamo formed from the convection of material in the core as molten iron rises, cools and sinks, much like the Earth core works today. In a new study, Robert Lillis and Michael Manga, from the University of California, Berkeley along with James Roberts of John Hopkins University Applied Physics lab suggest that energy released by massive collisions upset the heat flow in Mars' iron core that produced the magnetic field.
Magnetic analysis of the Martian surface indicates that when Mars was just 500 million years old, its global magnetic field disappeared. Without this shield, streams of ionizing particles spewing from the sun strip away a planet's atmosphere, vaporizing any water on the surface, and killing any life that may have emerged, or perhaps, forcing it underground.
A massive asteroid collision would have warmed Mars's mantle, disrupting core convection. That's because the cooling action of the mantle draws heat from the core, keeping it churning. Without that flow, core convection grinds to a halt.
This theory fits with the observation that only the oldest impact craters on Mars are magnetized. Newer impact regions like Hellas basin are show no traces of magnetism, and must have been formed when the magnetic field of Mars had ceased to exist.
Last year Lillis and Manga linked age estimates of impact basins with magnetic field strength to show that the previously established date of heavy bombardment, about 3.9 billion years ago, corresponds to the death of Mars's dynamo.
Now, Lillis, Manga, and Roberts have modeled the effects of heat produced by impacts. When they added the heat release from the biggest asteroids to models of mantle convection, they found that the mantle became a heating blanket rather than an ice pack. The extra heat was enough to stop core convection, the team reports in the current issue of the Journal of Geophysical Research – Planets.
Mars was hit by at least five particularly large asteroids during the bombardment. "Any one of the super-giant impacts could have shut off [the dynamo]," says Roberts. Earth likely suffered the same onslaught, but at twice the radius of Mars, it probably had a strong enough dynamo to withstand or recover from huge impacts.
But according to an article in ScienceNow, some scientists are not convinced the collisions released enough energy to influence the dynamo, which may have stopped working on its own. "The dynamo does not need to have an external influence to stop functioning," said David Stevenson, a planetary scientist at the California Institute of Technology, adding that without enough core convection, "it may simply die of its own accord."
Source: ScienceNow
Filed under: Mars
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May 6th, 2009 at 2:19 pm
theoreticly , is it possible to restart the plants dynamo ??
what consequences would this have?
May 6th, 2009 at 5:17 pm
I'm sure given enough energy you could get it going, but there would probably be earthquakes for quite a while as the interior settled down into a pattern.
May 6th, 2009 at 8:11 pm
If Mars magnetic field was stopped when Mars was only 500 million years old, does that preclude water running on its surface? It seems at odds with evidence that water was once there. I wonder if that also means that life would have had a tought time evolving there.
May 7th, 2009 at 12:42 am
The magnetic map of Mars, from the equator to the south pole at 180 deg. latitude, is very similar to the thermal map of Enceladus south pole 'stripes':
http://www.esa.int/images/PIA10361_annotated_H.jpg
Is there a common cause to these similarities?
May 7th, 2009 at 3:53 am
I would have thought that the earths molten core, and hence its magnetic field are sustained (in part, at least) by the action of the moons constant gravitational influence perhaps helping to keep the core moving, fluid and molten far below the surface.
I'm not suggesting that the moon warps the earth enough to cause the earths core to become molten – but that it might help to keep it that way. Does the core have 'tides' like the oceans?
May 7th, 2009 at 5:51 am
@ solrey:
I doubt it – they are too far away from each other.
The warmer stripes on the south pole of Enceladus follow very deep cracks in the surface, which are the source of (relatively) warm geysers…. which in turn "feed" one of Saturn's rings.
May 7th, 2009 at 6:49 am
@solrey: I cannot see the similarities, in the maps, at all; would you be kind enough to point them out?
There is a similarity in the patterns (they both have a number of more or less parallel coloured stripes), but that's a quite different thing than similarities in the maps, as I'm sure you'd be the first to agree.
May 7th, 2009 at 9:59 am
@nereid
Yes, it's the pattern. Mostly parallel and evenly spaced lines.
On Mercury, a 'magnetic tornado' was detected ripping neutral atoms from the surface. Lower energy, surface 'sputtering' is an ongoing process, a complex EM environment and a filamentary tail were discovered.
On Enceladus there are the stripes at the south pole. That image I linked to on another article looks like an etching of a tornado, imo. (folks either see it or they don't, I suppose) It's actively jetting material into space. I think most folks (especially scientists) agree that the terrain on Enceladus is quite unique.
On Mars the pattern of magnetic fields is very similar to the infrared signature of the stripes on Enceladus. The common cause that I mentioned is the same one that produces ongoing 'sputtering' on Mercury and Enceladus, and 'flux transfer events' (magnetic tornadoes) on Mercury (even stronger than those detected around Earth). Only the 'flux transfer event' that reconfigured Mars magnetic field was of immense power. A super-massive planet wrecking CME, for example. Picture Mars as a comet, with discharge jets forming a filamentary tail. Based on that Map, the planet wide 'flux transfer event' would have entered Mars centered somewhere along 0 deg. longitude, while Mars axis was angled at around 40 – 45 deg in relation to the incoming particle stream. The discharge on the other side, around 180 deg. lon. appears to be centered around 40-45 deg. latitude, based on the oblong area where the magnetic field is strongest. The pattern of current flow is mapped out in the uneven bands of magnetic fields stretching ENE and WNW from that coordinate, merging on the other side. It looks like there was a strong northern polar auroral ring that was instigated at the time. That tells me that Mars did have a uniform magnetic field prior to this event, strong enough to direct a significant portion of the incoming stream into the northern region and deflect/distribute the incoming stream somewhat. We see polar rings on Saturn, Jupiter, Venus and even Earth.
May 7th, 2009 at 10:23 am
Just a random thought, is it possible that an ancient asteriod collision on earth may have intiated a process where our magenic field flips every so often?
I am under the impression that the reason for polarity reversal is not well understood- please someone correct me if I'm wrong about that!
May 7th, 2009 at 10:42 am
There's a pretty nifty movie called "Core" that deals with exactly that topic, SweenyTodd. It is based on the idea that Earth's core is shutting down, and that the dynamo will shortly cease to exist. The movie is rather unrealistic in its timeframes, implying that the dynamo will shut down almost instantly and that the effects will be seen quickly, in the form of storms, electro-bombardment, radiation, and "regular" weather on an extreme scale. They decide to build a giant "Drill" type of ship that will burrow to the core and restart the Dynamo through a runaway nuclear reaction. I won't spoil the story of the material and logistics involved in building said drill. Not an outstanding movie, but as far as a Sci-Fi/Geological/Astro-evolutionary type of thing goes, it's pretty entertaining. You can read a bit more about it here:
http://www.imdb.com/title/tt0298814/
May 7th, 2009 at 11:18 am
@BeckyWS and @TiltDogg78…
the Earths magnetic field is actually quite fickle. Both poles wander about quite a bit, and at intervals which seem completely random, like thousands or tens of thousands of years, it winds down completely and starts up again, eventually, with reversed polarity.
I've seen no sensible attempts at explaining this erratic process. It flies in the face of some theories which propose permanent currents connecting stars and planets. It appears to be totally isolated from everything else going on in the solar system.
May 7th, 2009 at 12:20 pm
Do you want to hear my opinion? I think the movie is quite bad and dull!
May 7th, 2009 at 12:44 pm
If what solrey tosses out as fact about Mercurian magnetic tornadoes blasting chunks of the planet or huge streams of ionized material into space (above the streaming calcium atoms found on an earlier flyby), MESSENGER sounds like it is in danger of being blasted once it achieves orbit. I wonder if NASA will change MESSENGER's planned orbit as a result of the 'magnetic tornadoes' (darn NASA hyperbole in its' Press Releases)?