First evidence of dynamo generation on an asteroid found

Oct 11, 2012 by Jennifer Chu
A mosaic of the Vesta asteroid taken by NASA's Dawn spacecraft. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA

About 4.6 billion years ago, the solar system was little more than a tenuous disk of gas and dust. In the span of merely 10 million years, this soup evolved to form today's massive, complex planets. In the intervening period, however, the solar system contained a mixture of intermediary bodies—small chunks of rock, the remnants of which today are known as asteroids.

Although not much is known about the early composition of asteroids, some scientists suspect that such information may reveal an unexpected diversity of planetary bodies within the early .

Now a new study published this week in Science has found evidence that Vesta, the second-most-massive in the solar system, once harbored a —a molten, swirling mass of conducting fluid generating a magnetic field—resembling that in much larger planets like Earth. Researchers at MIT say the findings suggest that asteroids like Vesta may have been more than icy chunks of .

"We're filling in the story of basically what happened during those first few million years of the solar system, when an entire solar system was dominated by objects like this," says Roger Fu, a graduate student in MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS), and the study's first author. "These bodies are really like miniature planets."

"Vesta becomes now the smallest known planetary object to have generated a dynamo," says co-author Benjamin Weiss, an associate professor of planetary sciences in EAPS. "You can imagine many asteroids in the were doing this."

Measuring a meteorite

Most or all of the planets in the are thought to have generated dynamos at some point in their histories. In a dynamo, molten-hot iron flows within the core, generating a magnetic field that may last for millions of years. As a result, the rocks on the surface of a become magnetized, providing a record of a planet's early history.

Scientists have attempted to characterize the magnetization of meteorites—remnants of asteroids that have fallen to Earth—in order to reconstruct asteroid evolution. But a major challenge has been pinpointing the source of meteorites' magnetization, which may be formed by any number of processes—such as plasmas from a meteoroid impact, or more mundane causes, like passing a magnet over a sample. Determining that a meteorite's magnetic field is the result of an early dynamo is therefore a tricky problem.

To solve the problem, Fu and Weiss collaborated with researchers at the University of California at Berkeley, first to determine the magnetization and the age of a meteorite sample, then to check that the observed magnetic field was, in fact, due to an early dynamo.

The group obtained a meteorite sample from Vesta that was originally discovered in Antarctica in 1981. The 50-gram sample, named ALHA81001, retains exceptional magnetic properties that scientists have been examining for years. Fu and his colleagues managed to acquire a one-gram sample of the rock for analysis.

The team first examined the rock's tiny crystals. When forming in a magnetic field, a rock's ferromagnetic crystals align in the direction of a background field when the rock is heated. The group measured the alignment of these minerals, or the rock's magnetic "moment." The researchers progressively demagnetized the rock until they found the magnetization that they believed to be the oldest remnant of a magnetic field.

The group's next step was to determine the age of the rock. To do that, UC Berkeley researcher David Shuster analyzed the meteorite for evidence of argon. An isotope of argon called argon-40 is produced from the natural decay of potassium-40. A common technique for determining a rock's age is to heat the rock and measure the amount of argon-40 released: The more argon-40, the older a rock may be. Through this technique, the researchers determined that the Vesta meteorite is 3.7 billion years old.

Why a dynamo?

However, because Vesta formed 4.5 billion years ago, any early dynamo must have decayed by the time the meteorite now known as ALHA81001 formed. So what is the origin of the field that magnetized this rock?

Fu and Weiss believe that an early dynamo likely magnetized the surface of Vesta within the first 100 million years of the asteroid's history, magnetizing surface rocks that then persisted over billions of years. When ALHA81001 formed 3.7 billion years ago, it would have also become magnetized due to exposure to fields emanating from the surrounding crust.

Could the magnetization of Vesta's rocks have been caused by anything other than a dynamo? To rule out other scenarios, the group analyzed the crystals in the meteorite sample to determine the rock's cooling history. While large impacts might create a magnetic field, such impact-generated fields would only last a few tens of minutes, according to Fu—and if a rock were to become magnetized in such a short period of time, it would also cool equally quickly.

To determine the cooling history—and therefore the magnetization period—of the meteorite sample, the group examined the tiny crystals on the rock's surface—a technique developed by Timothy Grove, a professor of geology at MIT and a co-author of this week's Science paper. They found that the rock experienced two periods of cooling: an initial rapid cooling, which produced fine crystals with excellent magnetic recording properties, followed by a much longer period of cooling. This longer cooling phase, Fu believes, is proof that the observed in the rock is likely due not to an impact, but to a longer-lived field such as that expected for a dynamo.

The evidence for a dynamo on Vesta lends support to the theory that other small bodies in the solar system may also have harbored similar dynamos, says Christopher Russell, a professor of geophysics and space physics at the University of California at Los Angeles.

"The moon's ancient dynamo is given added credibility by this measurement," Russell says. "Another small body, Jupiter's moon Ganymede, today appears to have an active dynamo in its core. This measurement makes that interpretation more credible as well."

"Vesta is so interesting, because it's one of these building blocks that eventually formed the planets, and this is a remnant that's still preserved and didn't end up forming a planet," Fu says. "It's only 500 kilometers across, but it actually had many of the same global processes that the Earth has."

Explore further: Observing the onset of a magnetic substorm

More information: An Ancient Core Dynamo in Asteroid Vesta, Science, 12 October 2012: Vol. 338 no. 6104 pp. 238-241 DOI: 10.1126/science.1225648. www.sciencemag.org/content/338/6104/238.abstract

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User comments : 16

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cantdrive85
1.3 / 5 (14) Oct 11, 2012
Or, one other hypothesis could be that Vesta at one time had an electric charge that was different than the solar wind, and a magnetic field would be a natural response to the charged body protecting itself within a larger electric field. Simple!

Either that, or an asteroid the size of Colorado somehow possessed this mythical "dynamo" effect. BTW, Earth's plasmasphere is created the exact same way as described above, dynamos are no more than a farce of modern science.
jibbles
5 / 5 (4) Oct 11, 2012
how did they ascertain that alha81001 came from vesta?
PhotonX
5 / 5 (2) Oct 11, 2012
how did they ascertain that alha81001 came from vesta?
Apparently the oxygen isotope ratio of the meteorite matches that seen spectroscopically on Vesta, but I don't think that's 100% definitive.
LED Guy
5 / 5 (3) Oct 12, 2012
Canrdrive - so the dynamos in hydroelectric plants that provide power all over the world are a farce?????
alfie_null
4.4 / 5 (7) Oct 12, 2012
Until electric universe proponents start taking on the trappings of legitimacy, the rest of us will continue to regard you as nothing more than cranks.

Get yourselves a Wikipedia entry for starters. Invite critical discourse and defend your ideas convincingly.

Cite supporting material, if you choose to proselytize here. If your content is yours alone, don't hide behind monikers like "cantdrive85", let us know who you are. We need to verify your credentials, your CV. Good science isn't done under a cloak of anonymity; it requires strong scrutiny.
Shinobiwan Kenobi
1 / 5 (3) Oct 12, 2012
Cite supporting material, if you choose to proselytize here. If your content is yours alone, don't hide behind monikers like "cantdrive85", let us know who you are. We need to verify your credentials, your CV. Good science isn't done under a cloak of anonymity; it requires strong scrutiny.


Nail-head, meet hammer. inb4 EU supporter's ad hominem retort.
HannesAlfven
2 / 5 (4) Oct 12, 2012
Re: "Until electric universe proponents start taking on the trappings of legitimacy, the rest of us will continue to regard you as nothing more than cranks."

The IEEE -- the world's largest scientific institution -- has a working group studying Plasma Cosmology. IEEE informs its membership of the status of that group, just as it does for all other working groups within the IEEE. To be clear, these people do in fact consider the EU to be a valid course of inquiry within that framework.

So, although the Thunderbolts group (the Electric Universe) is in fact an independent organization which is not directly funded, their research is occasionally published and reviewed by the same people who brought you things like the semiconductor and the computer.

You might want to seriously consider that plasma physics is simply a highly controversial subject: Not only are plasmas incredibly difficult to simulate, but the government uses plasma physics to model nuclear explosions.
cantdrive85
1 / 5 (4) Oct 12, 2012
The "dynamos" in hydroelectric plants require a mechanical force to create it, it is not self sustaining.

However, as Kristian Birkeland discovered nearly a hundred years ago, a magnetic field is a natural response of a charged body immersed within an electric field.

Cranks, heretics, call me what you will, I could really careless. The idea of a magnetic field without the need for electric currents is downright imbecilic.
HannesAlfven
1.7 / 5 (6) Oct 12, 2012
Re: "Get yourselves a Wikipedia entry for starters. Invite critical discourse and defend your ideas convincingly."

Wikipedia is an encyclopedia. Encyclopedias have *never* been the place to go to understand controversial issues. Despite the fact that the EU is based most fundamentally on the work of established or published scientists -- Hannes Alfven, Ralph Juergens and Kristian Birkeland, for instance -- Wikipedia editors have refused to accept an entry for the Electric Universe. Accordingly, Ian Tresman created his own wiki interface at ...

http://www.plasma-universe.com

There is also an incredibly important archive at http://www.catastrophism.com (a subscription site), which includes many of the source materials which the EU uses to infer a plasma-mythology link. Attempts to understand the mythological archetypes have dramatically slowed over the past century, but before that, it was an incredibly active field of study.
HannesAlfven
2 / 5 (4) Oct 12, 2012
Re: "We need to verify your credentials, your CV. Good science isn't done under a cloak of anonymity; it requires strong scrutiny."

I'm fairly confident that the theorists are not spending much time on forums like this one. The reason is almost surely the widespread refusal amongst people who frequent such venues to actually read any theory which questions fundamental assumptions in cosmology or astrophysics. Against-the-mainstream theorists are forced to make a choice in this modern world: Spend all of their time defending their work to pseudoskeptics, to the detriment of that work, or instead culture relationships with those who do in fact read and appreciate their work, sufficient to intelligently review or critique it. It remains a fairly small group, but Wal Thornhill, David Talbott and Don Scott, among others, have cultivated numerous important contacts at prestigious institutions which you are already familiar with. You might try YouTube'ing "Don Scott NASA" ...
HannesAlfven
2 / 5 (4) Oct 12, 2012
You know, I spend a lot of my time every day correcting misconceptions about the Electric Universe online. I try to be extremely patient with people and refuse to become emotional about it. I am not a subject of this worldview. This new way of looking at the universe is simply the *object* of my thoughts. And I highly encourage everybody to perform this subject-to-object transition when discussing cosmology and astrophysics. It's really the *only* way to have a rational discussion about a controversial subject matter.

But, I just wanted to point out -- to those who are following along -- the sheer number of misstatements which occur on this subject matter every day, in every online scientific forum. Plasma physics is a tricky discipline, and plasmas dramatically diverge from the behavior of gases and condensed matter. Considering that plasma is the universe's preferred state for observable matter, we'd be wise to consider the impact which these misconceptions are having.
HannesAlfven
1.8 / 5 (5) Oct 12, 2012
I'd also like to note how incredible it is to observe how such a speculative press release and paper somehow does not elicit the howls it deserves. Wal Thornhill has gone to great lengths to explain that the only significant difference between asteroids and comets is their orbits: Comets exhibit elliptical orbits, whereas asteroids are on circular orbits. This raises the distinct possibility that the cometary displays exhibited by comets result from an electrical discharge with the Sun's local environment, as laboratory work with plasmas suggests that cosmic plasmas might exhibit sufficient electrical resistance to sustain heliospheric-scale electric fields (After all, what accelerates the solar wind?). When the comet is far away from the Sun, it takes on a different charge density. Thus, as it approaches the Sun, it then discharges. Remnant magnetism could clearly result from this discharge. These views are supported by the observation of two distinct flashes w/ Deep Impact.
Torbjorn_Larsson_OM
5 / 5 (3) Oct 12, 2012
The original dynamo strength is akin to what has been predicted as the initial field strength for the Moon dynamo (~ 1 uT).

In fact, since the Moon formed from impact debris so near Earth and with such a strong field, it has consequences for modeling the atmosphere and its loss on primordial Earth. "Field Wars", as it were. ["Thermal core-mantle coupling in an early lunar dynamo: Implications for a global magnetic field and magnetosphere of the early Moon", Takahashi et al, Geophys. Res. Lttrs, 2009.]

EU/PC believers shouldn't comment on science. It is hilarious to see. The geodynamo is the remaining fact and theory that has withstood the test of time, precisely as plate tectonics did. It does so by quantitative predictions, something crackpots never manage to make besides their pattern search as we can not yet again.
cantdrive85
1.8 / 5 (5) Oct 12, 2012
The original dynamo strength is akin to what has been predicted as the initial field strength for the Moon dynamo (~ 1 uT).

In fact, since the Moon formed from impact debris so near Earth and with such a strong field, it has consequences for modeling the atmosphere and its loss on primordial Earth. "Field Wars", as it were. ["Thermal core-mantle coupling in an early lunar dynamo: Implications for a global magnetic field and magnetosphere of the early Moon", Takahashi et al, Geophys. Res. Lttrs, 2009.]

EU/PC believers shouldn't comment on science. It is hilarious to see. The geodynamo is the remaining fact and theory that has withstood the test of time, precisely as plate tectonics did. It does so by quantitative predictions, something crackpots never manage to make besides their pattern search as we can not yet again.

Remaining fact? Somebody has seen this phenomenon within Earth's core? Once again, the delusions of the dogmatic dictate what "facts" are.
Allex
5 / 5 (1) Oct 13, 2012
The idea of a magnetic field without the need for electric currents is downright imbecilic.

By this post you have shown you have no idea about the conditions required for a geodynamo to form/exist nor the necessary knowledge of Earth core geophysics to understand on how many levels you are wrong.

Also magnets - how do they work? Cantdrive85 can't explain that $hit.
cantdrive85
1 / 5 (4) Oct 13, 2012
The idea of a magnetic field without the need for electric currents is downright imbecilic.

By this post you have shown you have no idea about the conditions required for a geodynamo to form/exist nor the necessary knowledge of Earth core geophysics to understand on how many levels you are wrong.

Also magnets - how do they work? Cantdrive85 can't explain that $hit.

Here is a peer reviewed paper that explains the folly of ignoring the necessary electric currents/field to create magnetism.

http://www.bentha...OAAJ.pdf