Extinct nuclides in and chronology of the early solar system

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Extinct nuclides in and chronology of the early
solar system

• Can extinct nuclides be used for chronology?
• Were extinct nuclides distributed homogeneously
  in the solar system?
• How were extinct nuclides produced?
• Solar or nucleo-synthetic?
• Al-Mg, Fe-Ni, Ca-K, Be-B and Mn-Cr

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New developments of Al-Mg systematics

• Half life 0.73 Ma
• Canonical value of the initial 26Al/27Al for CAIs
  (Ca-Al-rich Inclusion refractory inclusion) was
  5x10-5.
• SIMS (high spatial resolution)
• Internal isochron for chondrules
• MC-ICPMS (high precision, low spatial resolution)
• Bulk CAIs
• Internal isochron for CAIs
• Bulk chondrules

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Internal isochrons for CAIs, Young et al., 2005
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Internal isochrons for Chondrules, Kita et al.,
2005
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Formation ages of chondrules, Kita et al., 2005
From CAI
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Al-Mg ages of bulk chondrules (Bizzarro et al.,
2004)Ages from CAI are shown.
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Summary of Al-Mg

• CAIs formed with initial 26Al/27Al ratios as
  high as 6.5x10-5.
• The canonical value (5x10-5) is probably due to
  resetting of anorthite. (measured by SIMS)
• High temperatures in CAI forming region continued
  300,000 years.
• Chondrule precursors are as old as CAIs.
• Chondrule formation continued 2 Ma.

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Half life of 60Fe is 1.5 Ma.60Fe is not produced
by solar cosmic ray.60Fe has to be injected from
a nearby supernova.
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Fe-Ni systematics
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60Fe in the early solar system
Decay curve
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summary on 60Fe

• 60Fe is produced by supernova, but not produced
  by solar cosmic ray. Therefore, it is very
  important for understanding origins of
  short-lived nuclides.
• 60Fe seems to be present in the early solar
  system, but the distribution may have been
  heterogeneous.

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41Ca

• Half life of 41Ca is 0.15 Ma.
• Nearly constant initial ratios of 41Ca/40Ca
  1.4x10-8 are observed for CAIs with 26Al.
• If 41Ca is absent, 26Al is also absent.
• FUN (fractionation unknown nuclear component)
  inclusions
• This was explained by a late injection model. But
  now that CAI formation seems to have continued
  for 300,000 years, there seems to be a problem.

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41Ca in CAIs (Sahijpal et al., 1998)
FUN
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What you expect from a late injection model
(Sahijpal Goswami, 1998)
Normal CAI
FUN
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Late injection model41Ca and 26Al
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10Be (half life 1.5 Ma) produced by cosmic ray

• Abundant 10Be in CAIs was initially considered to
  be produced by solar cosmic ray.
• However, it was later shown that it may be GCR
  10Be trapped in cores of molecular clouds.(Desch,
  2003)
• FUN inclusions contain 10Be and do not contain
  26Al.
• Normal CAIs contain both 10Be and 26Al.
• Solar cosmic ray scenario
• Fun inclusions are evaporation residues
  irradiated by solar cosmic ray?
• Normal CAIs are condensates getting the 10Be and
  26Al from the irradiated nebula?
• Galactic cosmic ray scenario
• Fun inclusions are evaporation residues or
  condensates formed before injection of 26Al?
• Normal inclusions are condensates formed after
  injection of 26Al?

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10Be, 26Al and 41Ca in CAIs
Normal inclusions
10Be/9Be
Late injection
FUN inclusions
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53Mn-53Cr, half-life 3.7 Ma

• Suitable for studying planetary processes
• Initial ratios of 53Mn/55Mn in CAIs are not well
  established.
• Recently, comparison with Al-Mg and Pb-Pb ages
  became possible for eucrites and angrites.
• Previously such comparison was made for
  chondrites but was not conclusive.

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High initial Mn ratios for CAIs are inconsistent
with Al-Mg system and could be due to
heterogeneity of the nebula or due to disturbed
Mn-Cr system
Papanastassiou et al., 2005
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Age comparisonAl-Mg, Mn-Cr and Pb-Pb agesCAI,
eucrite and angrites
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Summary on Mn-Cr and comparison

• Al-Mg and Mn-Cr systems can be used as
  chronometers.
• Absolute ages of CAIs are probably 4568Ma.

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conclusions

• Can extinct nuclides be used for chronology?
• Probably yes 10Be, 26Al (excluding FUN), 53Mn
  (excluding CAIs)
• Not sure 41Ca, 60Fe
• How were extinct nuclides produced?
• Because of 60Fe, nucleo-synthetic origin seems
  more likely than SCR origin.
• But, the late injection model need closer
  examination.

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Initial 53Mn/55Mn in CAIs (Nyquist et al., 2001)
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Mn-Cr age of chondrules (Nyquist et al., 2001)
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Al-Mg system of a CAI measured with ICPMS (Young
et al., 2002)
Internal isochron
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Al-Mg ages of CAIs (Bizzarro et al., 2004)
MC-ICP-MS of bulk CAIs The initial 26Al/27Al
ratio is 6.0x10-5 if equilibrium fractionation
law is used.
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Angrite (S99555)
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Eucrite (Juvinus) with impact melt
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Solar nebula before exposed to supernova ejecta.
Hester et al., 2004
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Tachibana et al., 2005
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Angrite (error bars are one sigma.)
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More on 10Be

• So far, internal isochron for the first 13 Ma is
  made only with Al-Mg system.Thus, cannot be
  cross-calibrated.
• e.g.dating of chondrules.
• Mn-Cr cannot be used because the initial in CAIs
  are strange.
• 10Be seems to be hopeful.

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10Be in FUN
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