[meteorite-list] Isotopes in Meteorites Suggest that the Sun Formedin a Dense Cluster of Stars

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Mon, 09 Jul 2007 17:16:30 -0400
Message-ID: <BAY141-F3097398DF4F2F4BAB171A8F8060_at_phx.gbl>

>>...latest breakthrough is reported by
Martin Bizzarro...

Does the name "Bizzarro" mean that we really should be thinking opposite to
all these conclusions? ;)
(for those familiar with Superman)

A very interesting article!
Our little rocks continue to be more and more amazing in their history, and
more important to science!

Cheers,
Pete



From: Ron Baalke <baalke at zagami.jpl.nasa.gov>
To: meteorite-list at meteoritecentral.com (Meteorite Mailing List)
Subject: [meteorite-list] Isotopes in Meteorites Suggest that the Sun
Formedin a Dense Cluster of Stars
Date: Mon, 9 Jul 2007 09:13:59 -0700 (PDT)



http://www.psrd.hawaii.edu/July07/iron-60.html

The Sun's Crowded Delivery Room
Planetary Science Research Discoveries
July 6, 2007

--- Isotopes in meteorites suggest that the Sun formed in a dense
cluster of stars.

Written by G. Jeffrey Taylor
Hawai'i Institute of Geophysics and Planetology

Astronomic observations with the latest and greatest telescopes are
leading astronomers to embrace the idea that stars usually form in
clusters, even if they end up, like our Sun, isolated from other stars.
Cosmochemists using optical microscopes, electron microscopes, and mass
spectrometers are finding evidence supporting the idea, along with
important details about the star-forming regions and about the earliest
history of the Solar System. The latest breakthrough is reported by
Martin Bizzarro and his colleagues at the Geological Institute and
Geological Museum in Denmark, at the University of Texas, and at Clemson
University in South Carolina. They made high-precision measurements of
iron and nickel isotopes. The results
show that the oldest planetesimals to form in the solar system did not
contain any iron-60 ( 60Fe), which decays to nickel-60 ( 60Ni) with a
half-life of only 1.5 million years,
yet somewhat younger materials did contain it. In contrast, aluminum-26
( 26Al), with a half-life of 740,000 years, was relatively uniformly
distributed.

This suggests to Bizzarro and his colleagues that 60Fe was added to the
cloud of gas and dust surrounding the primitive Sun (the protoplanetary
disk) about 1 million years after the Solar System formed. This could
happen if the Sun's nursery contained massive stars (perhaps 30 times
the mass of the Sun). Such stars last only about 4 million years. They
are extremely active, blowing away their outer layers in the last
million years of existence. The dispersed material would have included
26Al and might have caused collapse of interstellar gas and dust to
cause formation of the Sun and its protoplanetary disk. A million years
later the massive star exploded, ejecting 60Fe from its interior.
Bizzarro and colleagues argue that this huge event of destruction and
creation is recorded in the meteorites.

Reference:

     * Bizzarro, M., Ulfbeck, D., Trinquier, A., Thrane, K., Connelly, J.
       N., and Meyer, B. S. (2007) Evidence for a later supernova
       injection of 60Fe into the protoplanetary disk. Science, v. 316,
       p. 1178-1181.

PSRDpresents: The Sun's Crowded Delivery Room --Short Slide Summary
<http://www.psrd.hawaii.edu/July07/PSRD-iron-60.ppt> (with accompanying
notes).

------------------------------------------------------------------------

Crowded Star-Forming Regions

There are a lot of stars, including the Sun, sitting by themselves in
the cosmos. Astronomers used to think that stars formed as isolated
objects in vast molecular clouds, but new observations lead many to now
believe that most stars form in clusters containing numerous companions,
large and small. Isolated stars like the Sun may all be derived from
multiple systems. Because massive stars form in such dense clusters,
burn hydrogen and then explode before the cluster has finished producing
new stars, the early lives of stars may be profoundly affected by nearby
siblings. The evidence for the presence of short-lived isotopes like
aluminum-26 ( 26Al) and iron-60 ( 60Fe) in meteorites provides strong
evidence that the Sun probably formed in such a neighborhood and was
peppered with stardust from an exploding star. Cosmochemists like Martin
Bizzarro and his coworkers want to understand the details of events
associated with formation of our Sun. Meteorites contain that record.

IR color composite of RCW38 region

Infrared color image of RCW38, an extremely dusty region of young star
formation in the constellation of Vela. Use of infrared allows
astronomers to see into this very dusty region to observe the numerous
stars making up a cluster. The photograph was taken with the Infrared
Spectrometer and Array Camera on the 8.2-meter Very Large Telescope
(VLT) on the top of Cerro Paranal mountain in the Atacama Desert of
northern Chile.

------------------------------------------------------------------------

Measuring Short-Lived Isotopes

Short-lived isotopes no longer actually exist in meteorites, except for
a few produced by cosmic ray interactions. They formed in other stars
(and perhaps close to the Sun in our Solar System), were incorporated
into solids such as meteorite parent bodies and the planetesimals that
accreted to form the planets, and decayed away with half lives ranging
from 0.1 to 100 million years. Fortunately, their decay products remain
behind, including 60Ni from decay of 60Fe and 26Mg from decay of 26Al.

A real trick is to measure the abundances of the isotopes accurately and
precisely enough to determine the ratio of a decay product (for example,
60Ni) to a common nickel isotope (for example, 58Ni). This is where
laboratory chemistry and high-tech gear come into play. Bizzarro and his
colleagues used acids and ion exchange columns to separate nickel from
other elements from metallic iron minerals and from silicate (rocky)
minerals. The metallic samples were dissolved in hydrochloric acid, and
then sent through an ion exchange column. Ion exchange is a technique
used to separate ions from a solution. A common use is to purify water
in a water-softening system, where calcium and magnesium are removed by
passing water through a column filled with granules (usually of a resin)
that latch on to certain ions. Bizzarro and his lab mates ran the
meteoritic iron through two separate types of columns to get rid of all
elements except nickel. They followed a similar procedure for extracting
nickel from silicate minerals. They also ran "blanks," a common chemical
procedure in which all the procedures are followed, but no sample is
used. This tells the chemist how much contamination there is in the
chemical system and how good their separation techniques are. They found
insignificant levels of nickel in their blanks.

Once Bazzarro had a solution containing nickel only, he and his
colleagues analyzed them in an inductively-coupled plasma mass
spectrometer. This technique uses a hot flame coupled to a radio
frequency generator to create a plasma from the solution. A plasma is a
gas in which many of its atoms and molecules are ionized (that is,
charged). The ions in the plasma are sent through a mass spectrometer
and the abundance of each nickel isotope is measured. The system is
equipped with multiple detectors, which allow the investigators to
measure all nickel isotopes at once. This produces a more accurate
analysis than older techniques that required each ion mass to be
selected by varying the magnetic field strength in the mass
spectrometer, which introduces errors largely because of small
variations in the plasma with time.

icp-ms multi-collector system

The photo above shows the Inductively-Coupled Plasma Mass Spectrometer
(ICP-MS) multi-collector system used in the Geological Institute in
Copenhagen. The glowing area is where the plasma is produced (see
close-up insert). At the far left is a set of collectors to count the
number of ions of a specific mass traveling through the mass
spectrometer (central area). Courtesy of Martin Bazzarro.

------------------------------------------------------------------------

Planets and Chondrites

Bazzarro and his team studied terrestrial samples, meteorites from Mars,
chondritic meteorites, and differentiated meteorites (hence from
asteroids that melted early in their histories). Other studies have
shown that the formation ages of the meteorites studied range from the
start of the Solar System to about 3 million years later. The beginning
of the Solar System is defined by the ages of calcium-aluminum-rich
inclusions, CAIs, 4.5672 billion years ago [see PSRD article: Dating the
Earliest Solids in the Solar System
<http://www.psrd.hawaii.edu/Sept02/isotopicAges.html>].

Eight samples from Earth, a Martian meteorite, and chondritic meteorites
have essentially the same abundance of 60Ni (see diagram below). This
gives them a value of epsilon-60Ni of 0.0 on the diagram. (The epsilon
notation (??) is simply the deviation from the terrestrial value in parts
per 10,000.) This uniformity indicates that inner Solar System objects
that formed after 60Fe had decayed away (Earth and Mars) or have solar
iron/nickel ratios (chondrites) must have formed from materials in which
60Fe had been uniformly distributed. In contrast, differentiated
meteorites have no evidence for 60Fe (low epsilon-60Ni); see figure and
discussion below.

graph of epsilon-60Ni values for meteorites

??60Ni values for differentiated meteorites (irons, pallasites,
ureilites, and one angrite, SAH9955, are systematically lower than the
values for the inner planets (Earth and Mars) and chondritic meteorites.
This indicates that when the differentiated meteorites formed, they did
not contain 60Fe. That was added about a million years later, mixing
with the raw materials for chondrites and subsequently the planets.
Because differentiated meteorites and chondrites both contain evidence
for the presence of now-extinct 26Al, it appears that the 60Fe addition
to the Solar System was decoupled from that of 26Al.

------------------------------------------------------------------------

Melted Planetesimals

The differentiated meteorites formed in asteroids that melted. Some are
cores (irons), others seems to represent the boundary between a core and
rocky mantle (pallasites), still others are residues left behind when
magma formed inside and migrated to the surface (ureilites), and yet
others are lava flows (angrites). It used to be thought that
differentiated meteorites were somewhat younger than chondrites, but
recent age dating shows that in fact, they are 1-2 million years older
than most chondritic components. CAIs are the oldest, about 1 million
years older than differentiated meteorites. [See PSRD article:
Cosmochemistry from Nanometers to Light Years
<http://www.psrd.hawaii.edu/Jan06/protoplanetary.html>.]

All the differentiated meteorites analyzed by Bizzarro and his
colleagues have significantly lower epsilon-60Ni values. This indicates
that they did not contain measurable 60Fe when they formed and melted.
Thus, because the younger objects (chondrites and the inner planets) did
contain it, 60Fe must have been added after the differentiated
planetesimals formed. On the other hand, 26Al was present in the
differentiated meteorites. The 60Fe must have come in later. Bizzarro
and colleagues estimate that 60Fe was added about 1 million years after
Solar System formation began.

Bizzarro and coworkers think they have an explanation for the difference
in arrival times of 26Al and 60Fe. Formation of the Sun might have
involved the formation and rapid life span (only 4 million years) of a
massive star, 30 times more massive than the Sun. Astronomical
observations indicate that such stars pass through a stage in which they
lose mass--up to an Earth mass per day!-- rapidly by blowing it into
space at a couple of thousand kilometers per hour. These stellar winds
contain 26Al, but 60Fe is still ensconced in the interior. At some point
the star blows up, sending the products of nuclear fusion into
interstellar space, including 60Fe. Note the sequence here: 26Al leaves
with the strong stellar winds, which possibly triggered the collapse of
a cloud of gas and dust to form a new star, our Sun. There is good
evidence that 26Al was uniformly distributed throughout the Solar System
[see PSRD article: Using Aluminum-26 as a Clock for Early Solar System
Events <http://www.psrd.hawaii.edu/Sept02/Al26clock.html>]. The 60Fe comes
about a million years
later when the star explodes, but also after many planetesimals
differentiated. They did not contain any 60Fe, but had their full
complement of 26Al. In fact, they had enough 26Al to heat up internally
and melt.

The 60Fe cannot have come from a source too far from the infant Sun. If
too far away it would decay before arriving or be so diluted that we
could not measure it. The exploding star had to be in the Sun's general
vicinity. It was a cluster mate of the Sun.

One type of massive star is called a Wolf-Rayet star (named after the
discoverers). In these large objects, elements formed inside by nuclear
fusion, such as oxygen and aluminum, migrate toward the surface. This
concentration of material begins to adsorb light from inside, eventually
resulting in strong winds blowing off the surface and into interstellar
space. The winds are shown in the image, below, taken in the infrared.
Astronomers believe that most massive stars (those >20 times the mass of
the Sun) go through a Wolf-Rayet phase, which ends when they explode as
supernova.

click for more information about Wolf-Rayet star in nebula
<http://apod.nasa.gov/apod/ap970102.html>

Stellar winds blowing from a massive Wolf-Rayet star (brightest star
near center). Courtesy of P. Berlind & P. Challis, Harvard-Smithsonian
Center for Astrophysics.

------------------------------------------------------------------------

Testing the Observations

Cosmochemists welcome the results reported by Martin Bizzarro and his
colleagues. It is going to start a new round of meteorite analyses to
test the measurements. Scientists spend a lot of time testing each
other's results, and these results are so important that it is essential
that they be tested. In fact, previous results have not observed the
deficiency in 60Fe that Bizzarro reports. Besides replicating the
measurements, there are other tests to perform, such as searching for
60Fe in a greater range of meteorites and in specific components in
meteorites (for example, individual chondrules). This research is just
beginning.

------------------------------------------------------------------------

ADDITIONAL RESOURCES

     * PSRDpresents: The Sun's Crowded Delivery Room --Short Slide
       Summary <http://www.psrd.hawaii.edu/July07/PSRD-iron-60.ppt>
       (with accompanying notes).

     * Bizzarro, M., Ulfbeck, D., Trinquier, A., Thrane, K., Connelly, J.
       N., and Meyer, B. S. (2007) Evidence for a later supernova
       injection of 60Fe into the protoplanetary disk. Science, v. 316,
       p. 1178-1181.

     * Taylor, G. J. (January, 2006) Cosmochemistry from Nanometers to
       Light Years. Planetary Science Research Discoveries.
       http://www.psrd.hawaii.edu/Jan06/protoplanetary.html

     * Taylor, G. J. (May, 2003) Triggering the Formation of the Solar
       System. Planetary Science Research Discoveries.
       http://www.psrd.hawaii.edu/May03/SolarSystemTrigger.html

     * Taylor, G. J. (September, 2002) Using Aluminum-26 as a Clock for
       Early Solar System Events. Planetary Science Research Discoveries.
       http://www.psrd.hawaii.edu/Sept02/Al26clock.html

     * Taylor, G. J. (September, 2002) Dating the Earliest Solids in our
       Solar System. Planetary Science Research Discoveries.
       http://www.psrd.hawaii.edu/Sept02/isotopicAges.html
______________________________________________
Meteorite-list mailing list
Meteorite-list at meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list

_________________________________________________________________
See Fireworks On Live Image Search
http://search.live.com/images/results.aspx?q=Fireworks&mkt=en-ca&FORM=SERNEP
Received on Mon 09 Jul 2007 05:16:30 PM PDT