1 The story of asteroid 2008 TC3 Peter Jenniskens ( SETI Institute) 07/14/09

2 Meteorites are great, but from which asteroid do they come?

3 Earth is in a shooting gallery, lots of asteroids passing close...

October 6, 6:39 UT Discovery of a small asteroid, soon called 2008 TC3 Catalina Sky Survey (Richard Kowalski) Discovery Image

October 6, 14:59 UT Minor Planet Center: It’s coming right at us! MPEC 2008-T50: “The nominal orbit given above has 2008 TC3 coming to within one earth radius around Oct The absolute magnitude indicates that the object will not survive passage through the atmosphere.” “ Steve Chesley (JPL) reports that atmospheric entry will occur on 2008 Oct UTC over northern Sudan.”

October 6, about 18h UT Unusual: Meteor community (a.o. Dr. Jenniskens) is alerted. Small asteroid = Big meteoroid!

7 Over the course of 20 hours, the asteroid’s position relative to the stars is measured some 570 times... La Sagra Sky Survey - S. Sanchez et al., Mallorca

8 Orbit in space determined 10,000 times better than typical orbit derived from few seconds long bolide Orbital elements (Steven R. Chesley): a = ± AU q = ± AU i = ± º  = ± º  = ± º J2000

9 Astronomical reflectance spectrum: color of the asteroid is gray A. Fitzsimmons and collaborators (La Palma / U.K.)

10 Asteroid flickering: tumbling and shape R. Dantowitz and M. Kozubal, Clay Center Observatory, USA

11

12 Impact point in Nubian Desert of northern Sudan Meteosat 8 In Kenya: Distant rumble (Infrasound) P. Brown, UWO

13 End of the story…? 37-km explosion: Apparently, object will not survive passage through the atmosphere, no fragments survived. Never before have meteorites been recovered from such a high explosion. But was this really the end of the meteor?

14 October - early November 2008: Jenniskens established contact with Dr. Muawia Shaddad (University of Khartoum) to gather eye witness accounts. Shaddad forwards images of train taken by cell phone. M. Elhassan

15 Cell phone images of train: APOD Nov 8

Dec. 4: Visit location of APOD train image Mohamed Elhassan, Wadi Halfa

17 Train drift due to winds Wadi Halfa Calculations by Jim Albers

18 Sinking feeling... Fireball had abrupt ending: No big fragments emerged from the explosion below about 32 km –Search for small pieces…? –These should have fallen close to explosion (deep into desert) If anything small survived, it would be spread over huge area because, at this high altitude, the asteroid had not significantly slowed down.

19 Back at “Station 6”: Busload of students from U. of Khartoum!

20 Next day: take bus along freshly created ~30-km long ‘Asteroid Track’

21 Start search just down range of explosion

22 Foot search required: gravel plain, hard to see small things far away...

23 Very end of day #1: They can be found! “Incredible” - M. H. Shaddad Mohammed Alameen

24 #4: 2nd day more scruffy black looking meteorites

25 3rd day they finally got bigger as they should, but 29 km down track... #15

Feb 27 - Mar 02 (back to Sudan): Peter’s first find!

27 Almahata Sitta Consortium Peter Jenniskens, SETI Institute Muawia Shaddad, U. of Khartoum Mike Zolensky, JSC Doug Rumble, Carnegie Institute Jon Friedman, Univ. Fordham, NY Andrew Steele, Carnegie Institute Scott Sandford, NASA Ames Kees Welten, Berkeley Rainer Weiler, Switzerland Carla Taricco, Turin, Italy Noriko Kita, Univ. Wisconsin-Madison S.V.S. Murty, Navrangpura, India U. Ott, MPI fuer Chemie, Mainz Takahiro Hiroi, Brown Univ. …. Reflection spectroscopy Mass, type, density, XRF SEM, EPMA, petrography Oxygen isotopes Bulk chemistry Raman spectroscopy Mid-IR transmission spectroscopy Cosmic radio nucleides Nobel gasses Gamma-ray spectroscopy SEM, EPMA, SIMS Nobel gasses Reflection spectroscopy ….

28 Lucky #7: first one analysed

29 #7 broken along white layer: tensile strength 56 ± 26 MPa strength of asteroid (explosion) ~ MPa!

30 Meteorite spectrum = asteroid spectrum (no dust/sand on the surface)

31 Astronomical spectrum: F Average asteroid spectra by Takahiro Hiroi

32 Size: 3-4 meter object From brightness asteroid + albedo > size: –Kinetic energy = 6.4 x 10^12 J (Albedo = 0.046: 4.1m, assume density 2.3 g/cm3) From acoustic signal: –Kinetic energy = 6.7 ± 2.1 x 10^12 J Bolide light curve (Meteosat 8): –Kinetic energy ~ 4 x 10^12 J

33 Petrography: anomalous Data: Mike Zolensky, NASA JSC

34 Pores are lined with olivine crystals

35 Find out what type of meteorite this is from oxygen isotopes O/ O O/ O

36 anomalous polymict Ureilite (an achondrite)! (Data: Doug Rumble, Carnegie Institution of Washington) O/ O O/ O

37 Rare Earth Element abundances: residue of partial melt (Data: Jon Friedman, Fordham University, NY) < chondrite < everything molten and sunk

38 Asteroid formation: growing by collisions

39 Ureilites: a brief history in the origin of differentiated planets like Earth - on the cusp of complete melting Chondrite Basaltic achondrite Iron meteorite Ureilites

40 Asteroid evolution: collisions, decay

41 Trail of crumbs: trace F-class asteroids back to their region of origin in the asteroid belt Orbital period (semi-major axis) Elongation of orbit (eccentricity)

42 The moral of the story... As far as asteroids are concerned: smaller can be better (but not easier). As far as meteorite falls are concerned: whole new game in town by following up on high explosions. As far as meteorites are concerned: Ureilites may finally be understood. As far as impact location (Sudan) is concerned: We couldn’t have been more lucky with this one! University of Khartoum staff and students: Well done!

43 The impact and recovery of asteroid 2008 TC3 P. Jenniskens et al., May 26 issue of Nature