That's an excellent article for better a understanding of the
pallasites plus reference to pallasites we all know - Esquel, Imilac
and Brenham.
Thanks!
John
Here is the editor's summary from Nature.
Shortly after the birth of the Solar System, small planetary bodies
became hot enough to segregate into a liquid metal core surrounded by
rocky mantle. As the core cooled and froze, swirling motions of liquid
metal, driven by the expulsion of sulphur from the growing inner core,
generated a magnetic field. A class of meteorites known as pallasites
preserves this phase of Solar System history as in the form of
gem-quality crystals of the silicate mineral olivine embedded in a
metallic matrix of iron–nickel alloy. James Bryson et al. use
high-resolution magnetic imaging of the iron–nickel matrix of the
Imilac and Esquel pallasite meteorites to derive a time-series record
of magnetic activity on the pallasite parent body, encoded within
nanoscale intergrowths of iron-rich and nickel-rich phases. This
record captures the dying moments of the magnetic field generated as
the liquid core solidified, providing evidence for a long-lasting
magnetic dynamo driven by compositional convection.
On Wed, Jan 21, 2015 at 8:26 PM, Robin Whittle via Meteorite-list
meteorite-list@meteoritecentral.com wrote:
Here is a write-up of some interesting research.
- Robin
http://phys.org/news/2015-01-death-dynamo-hard-space.html
The researchers' magnetic measurements, supported by computer
simulations, demonstrate that the magnetic fields of these
asteroids were created by compositional, rather than thermal,
convection - meaning that the field was long-lasting, intense and
widespread. The results change our perspective on the way magnetic
fields were generated during the early life of the solar system.
These meteorites came from asteroids formed in the first few
million years after the formation of the Solar System. At that
time, planetary bodies were heated by radioactive decay to
temperatures hot enough to cause them to melt and segregate into a
liquid metal core surrounded by a rocky mantle. As their cores
cooled and began to freeze, the swirling motions of liquid metal,
driven by the expulsion of sulphur from the growing inner core,
generated a magnetic field, just as the Earth does today.
It's funny that we study other bodies in order to learn more
about the Earth, said Bryson. Since asteroids are much smaller
than the Earth, they cooled much more quickly, so these processes
occur on shorter timescales, enabling us to study the whole
process of core solidification.
Scientists now think that the Earth's core only began to freeze
relatively recently in geological terms, maybe less than a
billion years ago. How this freezing has affected the Earth's
magnetic field is not known. In our meteorites we've been able to
capture both the beginning and the end of core freezing, which
will help us understand how these processes affected the Earth in
the past and provide a possible glimpse of what might happen in
the future, said Harrison.
However, the Earth's core is freezing rather slowly. The solid
inner core is getting bigger, and eventually the liquid outer core
will disappear, killing the Earth's magnetic field, which protects
us from the Sun's radiation. There's no need to panic just yet,
however, said Harrison. The core won't completely freeze for
billions of years, and chances are, the Sun will get us first.
The article itself is behind a paywall:
http://www.nature.com/nature/journal/v517/n7535/full/nature14114.html
Long-lived magnetism from solidification-driven convection on the
pallasite parent body
James F. J. Bryson et al.
Nature 517, 472–475 (22 January 2015)
doi:10.1038/nature14114
Palaeomagnetic measurements of meteorites suggest that,
shortly after the birth of the Solar System, the molten
metallic cores of many small planetary bodies convected
vigorously and were capable of generating magnetic fields.
Convection on these bodies is currently thought to have
been thermally driven, implying that magnetic activity
would have been short-lived. Here we report a
time-series palaeomagnetic record derived from nanomagnetic
imaging of the Imilac and Esquel pallasite meteorites, a
group of meteorites consisting of centimetre-sized metallic
and silicate phases. We find a history of long-lived magnetic
activity on the pallasite parent body, capturing the decay
and eventual shutdown of the magnetic field as core
solidification completed. We demonstrate that magnetic
activity driven by progressive solidification of an inner
core, is consistent with our measured magnetic field
characteristics and
