Meteoritic Constraints on Astrophysical Models of

Star and Planet Formation

Steve Desch, Arizona State University

Star Formation

Chondrites: Leftover crumbs from solar system formation

Cross section of Carraweena (L3.9) CAIsMATRIX GRAINS CHONDRULES

CAIs: The first minerals formed in the solar system CAIs contain many minerals that are the first to condense out of a solar nebula gas (Grossman 1972):

•melilite: Ca(Al,Mg)(Si,Al)2O7,

•hibonite: Ca2(AlTi)24O35,

•anorthite: CaAl2Si2O8,

•pyroxene: (FeMg)SiO3

McSween 1999

CAIsFluffy Type A:

•Not as large as other CAIs (< 1 mm)

•Most abundant (about 1% of all CCs and OCs, 2% of Allende)

•aggregations of small, zoned spheroids with spinel at their cores and mantles of melilite (Wark & Lovering 1977)

•Group II Rare Earth Element patterns show ultrarefractory component depleted (Tanaka & Masuda 1973); that component apparently concentrated in nuggets like those recently found (Hiyagon et al 2003)

•Formed (condensed?) in hot environment: 1400 K < T < 1800 K

Compact Type A:

•Same compositions as fluffy type A, but were melted

CAIs Types B and C:•Larger (up to cm-size)

•Very abundant in CVs (6-10% of volume), nonexistent in others

•Clearly melted after formation

•Type B CAI cooling rates constrained from chemical zoning in melilite: 0.5 - 50 K/hr (Stolper & Paque 1986; Jones et al 2000)

•At one time contained 26Al, 41Ca, 10Be, etc.

CAIsFUN inclusions:

•“Fractionation and Unknown Nuclear effects”

•Very rare (only 6)

•Large mass-dependent fractionations in O, Mg, Si: apparently were severely heated and evaporated

•Are anomalous in certain neutron-rich nuclei: 48Ca, 50Ti

•Contain evidence they once contained 10Be

•Contain no evidence they ever contained 26Al, 41Ca, etc.

Short-Lived Radionuclides• CAIs contained live short-lived radionuclides: 41Ca (t1/2 = 0.1 Myr) (Srinivasan et al. 1994) 36Cl (t1/2 = 0.3 Myr) (Murty et al. 1997) 26Al (t1/2 = 0.7 Myr) (Lee et al. 1976) 60Fe (t1/2 = 1.5 Myr) (Tachibana & Huss 2003) 10Be (t1/2 = 1.5 Myr) (McKeegan et al. 2000) 53Mn (t1/2 = 3.7 Myr) (Birck & Allegre 1985)

• These half-lives are so short, the radionuclides must have been created shortly before, or during, solar system formation

• CAIs with evidence for 26Al all have remarkably uniform ratio 26Al/27Al = 5 x 10-5: they all formed within ~105 years of each other

10Be/9Be Ratios

Excess 10B correlates with amount of Be: this 10B is from the decay of 10Be

McKeegan et al. (2000)

Natural 10B/11B level

CAIs formed with10Be/9Be = 9 x 10-4

Slope gives initial 10Be/9Be ratio

10Be decays to 10B with t1/2=1.5 Myr

10Be/9Be Ratios

• 10Be has been found in every CAI looked at, at levels consistent with 10Be/9Be = 9 x 10-4

• 10Be is present even if other radionuclides such as 26Al, 41Ca are not, in FUN inclusions and hibonites (Marhas et al. 2002; MacPherson et al. 2003)

10Be has a different origin than 26Al, 41Ca, etc. (Marhas et al. 2002): Could it be Galactic Cosmic Rays?

Table from Desch et al. (2004)

Collapse of Cloud Cores: Observations• Stars form in parts of molecular

clouds that have gravitationally collapsed, dragged in magnetic field lines

• Even the Orion Nebula must have gone through this stage (Schleuning 1998)

• 10Be GCRs follow magnetic field lines, are trapped when column densities first exceed ~ 10-2 g cm-2 (before first stars)

Schleuning (1998)

1.3 pc

Side view:

Collapse of Cloud Cores: Calculations• Numerical simulations show how

magnetic fields and gas densities vary with time in collapsing molecular cloud core (Desch & Mouschovias 2001)

• We calculate rates at which 10Be GCRs are trapped, and 10Be is produced by spallation

• First stars form << 1 Myr after t=0

Desch & Mouschovias (2001)

1.5 pc

10Be in a Collapsing Cloud Core

• 10Be/9Be ratio = CAI ratio as first stars form!

• All of the 10Be in CAIs is attributable to GCRs:

80% from 10Be GCRs trapped in cloud core

20% produced by spallation reactions

• 10Be/9Be ratio does indeed peak when column densities exceed ~ 10-2 g cm-2

CAI ratio

Trapped 10Be GCRs Total

10Be produced by GCR protons spalling CNO nuclei in gas

9.5 x 10-4

Supernova Injection of Radionuclides• We attribute 10Be to trapped 10Be Galactic cosmic rays• A type II supernova is the most likely source of all the other

radionuclides: 41Ca, 36Cl, 26Al, 60Fe produced in proportions seen in meteorites (Meyer & Clayton 2000; Meyer et al. 2003)

• We do not claim that a supernova triggered the collapse of the solar system’s cloud core

• We claim the solar nebula already existed and CAIs were forming when the supernova ejecta entered the solar system (Sahijpal & Goswami 1998): “Late injection”

• FUN inclusions are CAIs that formed before 26Al, 41Ca, 60Fe, and anomalous 48Ca and 50Ti were injected by supernova

The Sun’s Star-Formation Environment• 80% of Sunlike stars

form near a star massive enough to supernova (Adams & Laughlin 2001)

• Before massive star goes supernova it ionizes, heats, and “photoevaporates” surrounding gas Evaporating

gaseous globules: new solar systems

Hester et al (1996)

•Ionization fronts probably triggered star formation in Eagle Nebula

The Sun’s Star-Formation Environment• After EGG stage, solar

system emerges into H II region as a “proplyd”

• Disk resides in H II region for ~105 yr until O star(s) supernova

• Disk intercepts supernova ejecta with radionuclides

• Proplyds in Orion will acquire 26Al/27Al ~ 5 x 10-5 when 1 Ori C supernovas

Protoplanetary Disks

QuickTime™ and aGIF decompressor

are needed to see this picture.

HH30: Watson, Stapelfeldt, Krist & Burrows (2000)

outflow

Mass accretes onto star through disk

•Protoplanetary disks are accretion disks

•Angular momentum is transported outward, mass moves inward

•Angular momentum transport probably due to magnetohydrodynamic turbulence (Desch 2004)

PPDs:

•As mass moves inward, gravitational energy is released, mostly at midplane

•Temperatures highest at midplane, lowest at surfaces

•Heat flux drives convection (Bell et al 1997)

•Gas rises, cools in convection cells, rocks condense

PPDs:

Evidence for Condensation

T = 1770 K

T = 1370 K

All vapor

Metallic Fe condenses

FeMg silicates

Refractory minerals condense as rising gas cools

Z

T = 1270 K

Simon et al (2002)

QuickTime™ and aGIF decompressor

are needed to see this picture.

More Evidence for Condensation

Meibom et al (1999, 2000)

•FeNi metal condenses as gas moves from T=1370 K to 1270 K

•Ni zoning reproduced if condensation takes a few weeks, as in a convection cell model (Meibom, Desch et al 2000)

•Convection repeatedly moves material through hot midplane, evaporates most silicates

•Only most refractory minerals grow (CAIs)

•Convection and turbulence disperse CAIs widely (Cuzzi et al 2003a,b, 2004)

•This stage requires dM/dt > 10-6 Msol/yr, ends after ~105 yr (Bell et al 2000)

PPDs:

•After few x 105 years, magnetohydrodynamic turbulence occurs only in surface layers•Temperatures are everywhere much cooler, FeMg silicates form at midplane (chondrules)•Accretion is unsteady with time, leads to shocks•Shocks melt CAIs and chondrules, cool at rates ~ 50 K/hr (Desch & Connolly 2002)

PPDs:

ConclusionsCAI radionuclides constrain setting of solar system formation:

• 10Be attributable to trapped 10Be Galactic cosmic rays

• Other radionuclides (26Al, 41Ca, esp. 60Fe) injected by supernova

• Injection occurred after first CAIs (FUN inclusions) formed

• Implicates formation in H II region like Orion or Eagle Nebula

CAIs constrain disk temperatures, dynamics, timescales…

• CAI mineralogy implicates hot (> 1400 K) protoplanetary disk

• Condensates implicate convection

• Requires high mass accretion rates through disk > 10-6 Msol/yr, attainable only for ~ 105 yr

• Convection, turbulence will then widely disperse CAIs