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

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The story of asteroid 2008 TC3Peter Jenniskens (SETI Institute)

07/14/09

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

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

http://www.cfa.harvard.edu/iau/Animations/EarthRide2008.gif

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2008 October 6, 6:39 UT Discovery of a small asteroid, soon called 2008 TC3

Catalina Sky Survey (Richard Kowalski)

DiscoveryImage

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2008 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 earthradius around Oct. 7.1. The absolute magnitude indicates that theobject will not survive passage through the atmosphere.”

“ Steve Chesley (JPL) reports that atmospheric entry will occur on 2008Oct 07 0246 UTC over northern Sudan.”

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2008 October 6, about 18h UT Unusual: Meteor community (a.o. Dr. Jenniskens) is alerted.

Small asteroid = Big meteoroid!

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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

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Orbit in space determined 10,000 times better than typical orbit derived from few seconds long bolide

Orbital elements (Steven R. Chesley):

• a = 1.308201 ±0.000009 AU

• q = 0.899957 ±0.000002 AU

• i = 2.54220 ±0.00004º

• = 194.101139 ±0.000002º

• = 234.44897 ±0.00008º J2000

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Astronomical reflectance spectrum: color of the asteroid is gray

A. Fitzsimmons and collaborators (La Palma / U.K.)

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Asteroid flickering: tumbling and shapeR. Dantowitz and M. Kozubal, Clay Center Observatory, USA

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Impact point in Nubian Desert of northern Sudan

Meteosat 8

In Kenya: Distant rumble (Infrasound)P. Brown, UWO

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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?

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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

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Cell phone images of train: APOD Nov 8

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2008 Dec. 4: Visit location of APOD train image

Mohamed Elhassan, Wadi Halfa

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Train drift due to winds

Wadi Halfa

Calculations by Jim Albers

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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.

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

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

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Start search just down range of explosion

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

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

Mohammed Alameen

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#4: 2nd day more scruffy black looking meteorites

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

#15

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2009 Feb 27 - Mar 02 (back to Sudan): Peter’s first find!

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Almahata Sitta Consortiumhttp://asima.seti.org/2008TC3/

• 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• Nobel gasses• Reflection spectroscopy• ….

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Lucky #7: first one analysed

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#7 broken along white layer: tensile strength 56 ± 26 MPastrength of asteroid (explosion) ~ 0.2-0.3 MPa!

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

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Astronomical spectrum: F

Average asteroid spectra by Takahiro Hiroi

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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

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Petrography: anomalousData: Mike Zolensky, NASA JSC

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Pores are lined with olivine crystals

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Find out what type of meteorite this is from oxygen isotopes

18 16

O/ O

17 16

O/ O

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anomalous polymict Ureilite (an achondrite)!

(Data: Doug Rumble, Carnegie Institution of Washington)

17 16

O/ O

18 16O/ O

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Rare Earth Element abundances: residue of partial melt (Data: Jon Friedman, Fordham University, NY)

< chondrite

< everythingmolten and sunk

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Asteroid formation: growing by collisions

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Ureilites: a brief history in the origin of differentiated planets like Earth -on the cusp of complete melting

Chondrite Basaltic achondriteIron meteorite

Ureilites

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Asteroid evolution: collisions, decay

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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)

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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!

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The impact and recovery of asteroid 2008 TC3P. Jenniskens et al., 2009. May 26 issue of Nature