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

New developments of Al-Mg systematics Half life =0.73 Ma Canonical value of the initial 26 Al/ 27 Al for CAIs (Ca-Al-rich Inclusion = refractory inclusion) was 5x SIMS (high spatial resolution) –Internal isochron for chondrules MC-ICPMS (high precision, low spatial resolution) –Bulk CAIs –Internal isochron for CAIs –Bulk chondrules

Internal isochrons for CAIs, Young et al., 2005

Internal isochrons for Chondrules, Kita et al., 2005

Formation ages of chondrules, Kita et al., 2005 From CAI

Al-Mg ages of bulk chondrules (Bizzarro et al., 2004) Ages from CAI are shown.

Summary of Al-Mg CAIs formed with initial 26 Al/ 27 Al ratios as high as 6.5x 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.

Half life of 60 Fe is 1.5 Ma. 60 Fe is not produced by solar cosmic ray. 60 Fe has to be injected from a nearby supernova.

Fe-Ni systematics

60 Fe in the early solar system Decay curve

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

41 Ca Half life of 41 Ca is 0.15 Ma. Nearly constant initial ratios of 41 Ca/ 40 Ca ~1.4x10 -8 are observed for CAIs with 26 Al. If 41 Ca is absent, 26 Al 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.

41Ca in CAIs (Sahijpal et al., 1998) FUN

What you expect from a late injection model (Sahijpal & Goswami, 1998) FUN Normal CAI

Late injection model: 41 Ca and 26 Al

10 Be (half life =1.5 Ma) produced by cosmic ray Abundant 10 Be in CAIs was initially considered to be produced by solar cosmic ray. However, it was later shown that it may be GCR 10 Be trapped in cores of molecular clouds.(Desch, 2003) FUN inclusions contain 10 Be and do not contain 26 Al. Normal CAIs contain both 10 Be and 26 Al. –Solar cosmic ray scenario Fun inclusions are evaporation residues irradiated by solar cosmic ray? Normal CAIs are condensates getting the 10 Be and 26 Al from the irradiated nebula? –Galactic cosmic ray scenario Fun inclusions are evaporation residues or condensates formed before injection of 26 Al? Normal inclusions are condensates formed after injection of 26 Al?

１０ Be, 26 Al and 41 Ca in CAIs 10 Be/ 9 Be FUN inclusions Normal inclusions Late injection

53 Mn- 53 Cr, half-life = 3.7 Ma Suitable for studying planetary processes Initial ratios of 53 Mn/ 55 Mn 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.

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

Age comparison Al-Mg, Mn-Cr and Pb-Pb ages CAI, eucrite and angrites

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

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

Initial 53 Mn/ 55 Mn in CAIs (Nyquist et al., 2001)

Mn-Cr age of chondrules (Nyquist et al., 2001)

Al-Mg system of a CAI measured with ICPMS (Young et al., 2002) Internal isochron

Al-Mg ages of CAIs (Bizzarro et al., 2004) MC-ICP-MS of bulk CAIs The initial 26 Al/ 27 Al ratio is 6.0x10 -5 if equilibrium fractionation law is used.

Angrite (S99555)

Eucrite (Juvinus) with impact melt

Solar nebula before exposed to supernova ejecta. Hester et al., 2004

Tachibana et al., 2005

Angrite (error bars are one sigma.)

More on 10Be So far, internal isochron for the first 1~3 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. 10 Be seems to be hopeful.

10 Be in FUN