Steve Desch Nicolas Ouellette Jeff Hester Laurie Leshin Arizona State University

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

2. Outline • Our early Solar System contained 60Fe • 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

3. Early Solar System Contained 60Fe 60Fe/56Fe ~ 5 x 10-7 60Fe/56Fe ~ 2 - 5 x 10-7 Semarkona + Bishunpur pyroxene chondrules (Tachibana et al 2005) 60Fe/56Fe ~ 9 x 10-7 Semarkona troilites + magnetites (Mostefaoui et al 2005) 60Fe/56Fe ~ 7 x 10-7 Semarkona troilites + pyroxenes (Mostefaoui et al 2004) 60Fe/56Fe ~ 3 - 4 x 10-7 Bishunpur + Krymka troilites (Tachibana & Huss 2003) Tachibana & Huss (2003)

4. 60Fe wasn’t created by spallation Shu et al (1996) Irradiation of rocky material at 0.1 AU in principle can produce radionuclides like 60Fe Only 64Ni(p,p)60Fe reaction can happen, but 64Ni is rare and cross section is < 0.1 mbarn Predicted yields: 60Fe/56Fe ~ 10-11 (Lee et al 1998; Leya et al 2003)

5. 60Fe wasn’t inherited from our molecular cloud 129I Supernovae, Wolf-Rayet winds, novae, AGB stars maintain steady-state levels of 60Fe, etc., in the Galaxy Steady-state “average” abundance of 60Fe is 60Fe/56Fe ~ 3 x 10-7 (Harper 1996) or 60Fe/56Fe ~ 3 x 10-8 (Wasserburg et al 1996) But then 129I/127I ~ 10-2, 182Hf/180Hf ~ 10-3, etc. 26Al 60Fe Harper (1996)

6. 60Fe wasn’t inherited from our molecular cloud supernova Our molecular cloud was isolated from sources of radionuclides for >> 107 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 ~108 yr In the meantime, 60Fe completely decays new star-forming molecular clouds M 109

7. 60Fe wasn’t injected by an AGB star AGB outflows do eject 60Fe, 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 10-6 (Kastner & Myers 1994) AGB stars also do not eject appreciable 53Mn, 182Hf (Gallino et al 1998)

8. 60Fe is ejected by supernovae associated with star-forming regions! Live60Fe discovered in ocean crust 3 Myr old (Knie et al 2004) 60Fe Fe Only plausible source is supernovae in Scorpius-Centaurus star-forming region (Maiz-Appelaniz 2001; Fields et al 2004) P. Frisch, U. Chicago

9. 60Fe will be injected into disks associated with those supernovae HST image, Orion Nebula protoplanetary disks ~ 0.2 pc 1 Ori C: 40 M star will supernova in < 1 Myr

10. Sufficient 60Fe 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 10-3 M of dust formed (Colgan et al 1994) Mass of 60Fe ejected by 25 M supernova ~ 8 x 10-6 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 10-8 Mixed with 0.01 M of solar composition material, 60Fe / 56Fe ~ 1 x 10-6

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

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

13. Conclusions 60Fe 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 60Fe 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 60Fe-bearing dust grains into a protoplanetary disk, yielding 60Fe/56Fe ~ 10-6 in the disk material, without destroyingdisk