The Meaning of 60 Fe: A Nearby Supernova Injected Short-Lived Radionuclides into our Protoplanetary Disk Steve Desch Nicolas Ouellette Jeff Hester Laurie Leshin Arizona State University

Outline Our early Solar System contained 60 Fe It wasn’t created by in-situ spallation... It wasn’t inherited from our molecular cloud... It wasn’t injected by an AGB star... It had to come from a supernova... It was probably injected directly into our protoplanetary disk

Early Solar System Contained 60 Fe 60 Fe/ 56 Fe ~ x Semarkona + Bishunpur pyroxene chondrules (Tachibana et al 2005) 60 Fe/ 56 Fe ~ 9 x Semarkona troilites + magnetites (Mostefaoui et al 2005) 60 Fe/ 56 Fe ~ 7 x Semarkona troilites + pyroxenes (Mostefaoui et al 2004) 60 Fe/ 56 Fe ~ x Bishunpur + Krymka troilites (Tachibana & Huss 2003) Tachibana & Huss (2003) 60 Fe/ 56 Fe ~ 5 x 10 -7

60 Fe wasn’t created by spallation Irradiation of rocky material at 0.1 AU in principle can produce radionuclides like 60 Fe Only 64 Ni(p,p  ) 60 Fe reaction can happen, but 64 Ni is rare and cross section is < 0.1 mbarn Predicted yields: 60 Fe/ 56 Fe ~ (Lee et al 1998; Leya et al 2003) Shu et al (1996)

60 Fe wasn’t inherited from our molecular cloud Harper (1996) Supernovae, Wolf-Rayet winds, novae, AGB stars maintain steady-state levels of 60 Fe, etc., in the Galaxy 60 Fe 26 Al 129 I Steady-state “average” abundance of 60 Fe is 60 Fe/ 56 Fe ~ 3 x (Harper 1996) or 60 Fe/ 56 Fe ~ 3 x (Wasserburg et al 1996) But then 129 I/ 127 I ~ 10 -2, 182 Hf/ 180 Hf ~ 10 -3, etc.

60 Fe wasn’t inherited from our molecular cloud Our molecular cloud was isolated from sources of radionuclides for >> 10 7 yr (Wasserburg et al 1996; Harper 1996) Much of the radionuclides produced by supernovae go into hot phase, and don’t enter molecular clouds for ~10 8 yr M 109 supernova new star-forming molecular clouds In the meantime, 60 Fe completely decays

60 Fe wasn’t injected by an AGB star AGB outflows do eject 60 Fe, but only for ~ 1 Myr, after star has evolved for > 2 Gyr AGB stars randomly distributed in Galaxy: no reason to associate them with star-forming regions Odds per 1 Myr that a parcel of gas in a molecular cloud will be contaminated with AGB material: < 3 x (Kastner & Myers 1994) AGB stars also do not eject appreciable 53 Mn, 182 Hf (Gallino et al 1998)

60 Fe is ejected by supernovae associated with star-forming regions! Live 60 Fe discovered in ocean crust 3 Myr old (Knie et al 2004) Only plausible source is supernovae in Scorpius-Centaurus star-forming region (Maiz-Appelaniz 2001; Fields et al 2004) P. Frisch, U. Chicago 60 Fe Fe

60 Fe will be injected into disks associated with those supernovae ~ 0.2 pc  1 Ori C: 40 M  star will supernova in < 1 Myr protoplanetary disks HST image, Orion Nebula

Sufficient 60 Fe can be injected without destroying disk Iron likely in form of dust grains: gas-phase Fe disappeared from SN 1987A ejecta at same time (1-2 years post-explosion) that M  of dust formed (Colgan et al 1994) Mass of 60 Fe ejected by 25 M  supernova ~ 8 x M  (Woosley & Weaver 1995) Fraction intercepted by 30 AU radius disk at 0.3 pc away ~  (30 AU) 2 / 4  (0.3 pc) 2 ~ 6 x Mixed with 0.01 M  of solar composition material, 60 Fe / 56 Fe ~ 1 x 10 -6

Sufficient 60 Fe can be injected without destroying disk Worst-case scenario: fast cooling Ouellette et al (2005), in prep

Sufficient 60 Fe can be injected without destroying disk Ouellette et al (2005), in prep With realistic cooling

Conclusions 60 Fe in early solar system could not be inherited, could not be produced by spallation, almost certainly was not from AGB star Only plausible source of the 60 Fe is a nearby supernova Protoplanetary disks are observed near (~ 0.3 pc) massive stars that will soon go supernova Supernova ~0.3 pc away can inject 60 Fe-bearing dust grains into a protoplanetary disk, yielding 60 Fe/ 56 Fe ~ in the disk material, without destroying disk