Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Moon’s early history may have been interrupted by big burp, geophysicists claim


Using a state-of-the-art computer model of the lunar interior, geophysicists at the University of California, Berkeley, have shown that a mighty burp early in the moon’s history could account for some of its geologic mysteries.

The burp of hot rock, like a blob rising to the top of a lava lamp, would have lifted a blanket covering the moon’s core, allowing the core to cool quickly enough to produce a magnetic field.

The moon has long since cooled off and the global magnetic field disappeared, but the brief burp nearly 4 billion years ago would explain the old, magnetized rocks picked up from the moon’s surface during the Apollo missions 30 years ago.

"This 3-D convection model produces an elegant explanation for the magnetic field astronauts discovered on the moon," said UC Berkeley graduate student Dave Stegman, who developed the lunar model based on earlier and more general computer models simulating the dynamics of planetary interiors. "If this model is correct, this would be the first full understanding of the thermal history of any planet, including the Earth, and would be a cornerstone for understanding the histories of all the other planets, such as Mars and Earth."

The theoretical burp predicted by the computer model would also explain the lunar mare - seas of metal-rich volcanic rock, or basalt, that cover much of the near side of the moon but little of the far side.

Stegman; Mark Jellinek, a Miller postdoctoral fellow at UC Berkeley; Mark Richards, UC Berkeley professor of earth and planetary science; and John R. Baumgardner, of Los Alamos National Laboratory, report results of their modeling in the Jan. 9 issue of Nature. The late Stephen A. Zatman, a former post-doctoral fellow at UC Berkeley and most recently of the Department of Earth and Planetary Sciences at Washington University in St. Louis, also contributed significantly to the work.

"Unlike many previous models of planetary evolution, this one starts from a ball of goo and looks at how a likely magma ocean solidifies around a metallic core," said Jellinek, who will be joining the Department of Physics at the University of Toronto in April as an assistant professor. "One message from this research is that, if you want to look at planetary evolution properly, it’s important to consider the initial conditions carefully."

A global magnetic field like the Earth’s, strong enough to wrench a magnetized needle into north-south alignment, requires active convection within a molten iron core, akin to the convection in a boiling pot of water. The slowly cycling molten metal carries charged particles with it that, like any electric current, generate a magnetic field.

Convection, however, can only be sustained if heat flows out of the core at a high enough rate. The Earth’s large core, for example, has presumably remained convective since its formation more than 4.5 billion years, thanks, in part, to the planet’s active surface. Through volcanic eruptions and plate subduction, the Earth’s tectonic surface efficiently cools the mantle and underlying core to maintain a high heat flux.

The problem with smaller bodies like the moon and Mars is that their cores may not be big enough and hot enough, and the cooling processes in the mantle efficient enough, to maintain a heat flux high enough to allow core convection. The solid crust of these single-plate planets seems to act as a blanket to keep heat from escaping the mantle, damping the heat flux in the core and quenching any convection. If the core heat flux drops below the level needed to sustain convection, any magnetic field disappears, usually leaving the only record of its existence in volcanic rocks erupted during that time.

How, then, could the moon have had a magnetic field from 3.9 to 3.6 billion years ago, as suggested by dating of lunar rocks? Some scientists have proposed that meteor impacts may have magnetized the surface briefly, creating the small fields we see today. Stegman hit upon the idea of a blanket of dense material that would briefly insulate and even heat the core before bobbing to the surface to allow a brief period of rapid heat flux and core convection. Others had proposed such a buoyant thermal blanket to explain the uneven distribution of dense basalts that covers the Earth-facing half of the moon, though support for this has come only from two-dimensional models of the moon’s interior.

Stegman had at his disposal a three-dimensional, spherical convective model of planetary interiors originally developed by Baumgardner. Stegman, however, added a crucial component - the ability to account for different chemical elements in the interior. Since different chemicals heat and cool differently and have different densities, this makes a critical difference in what the model can predict.

"Modeling two-component fluid flow, what we call thermochemical convection, is much more difficult than modeling thermal convection alone," Richards said. "This was a technical challenge that Dave Stegman has solved by significant improvements to the computer model developed for the Earth."

Based on his model, Stegman proposes that, after the birth of the moon 4.5 billion years ago from the debris of a cataclysmic collision between the Earth and a Mars-sized object, the moon began to cool and solidify, with material separating into layers of different density. Iron intermixed with sulfur settled to the core, while less dense matter formed a thick mantle above the core. As the mantle solidified, however, the last liquid to freeze was at the top, producing a titanium and thorium-rich layer of rock. Because of the layer’s density, however, it was unstable, and some of it eventually dripped through the mantle to form a blanket at the core-mantle boundary.

"Without this sinking, the moon would have cooled off very slowly," Stegman said. "This one event determined whether or not the moon had convection and thus allowed the planet to have an interesting life."

This layer, rich in radioactive elements, eventually heated up and became buoyant, rising to the top in one or more burps, or superplumes. This removed the thermal blanket surrounding the core, allowing, for a brief time - about 300 million years - sufficiently rapid heat flux to start convection and generate a magnetic field. The lunar model shows that this scenario would create a lunar dynamo and a resultant surface magnetic field of about one-tenth of a Gauss - one-fifth the Earth’s current field of one-half Gauss.

The burp would break through the surface over one hemisphere, not the whole surface, Stegman said, possibly explaining the mare of thorium-rich basalts - the dark feature we see as the "man on the moon."

Perhaps the most controversial aspect of the model is whether the early magnetism reported from the moon, based on analysis of moon rocks, is real.

"The paleomagnetism done on moon rocks is sketchy," Richards noted. "Dave’s work is really motivating people to go back and reanalyze the samples from the Apollo missions."

This model of the moon’s three-dimensional interior could also apply to the Earth, which appears to have a layer of dense material sitting at the core-mantle boundary. The model also could help explain the evolution of other planetary bodies, such as Mars, that have only one crustal plate. Stegman’s next projects are to model the Martian interior as well as the dense rock layer at the base of Earth’s mantle.

"We are inspired by this work on the moon to think that some similar kind of catastrophic overturn event may have occurred on Mars as well," Richards said.

The research was funded by the Los Alamos National Laboratory, the National Aeronautics and Space Administration, the National Science Foundation and the Miller Institute for Basic Research in Science.

A color graphic showing a rising superplume in the moon’s mantle is at

Robert Sanders | EurekAlert!
Further information:

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>



Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

More VideoLinks >>>