OSIRIS-REx Status Report (and What We’ve Learned

about Bennu)

Carl Hergenrother Asteroid Astronomy Lead SBAG – 2013 July 11

NASA Headquarters – April 30, 2013 1 Recent Accomplishments

. TAGSAM microgravity tesng @ JSC . Mission “upgraded” to Category 1 . 2012 DA14 flyby and Chelyabinsk media events . OLA authorizaon received for Phase B2/C . Successful Mission Preliminary Design Review . ‘Name That Asteroid’ winner announced – we are going to Bennu . NFPO directed Project to remove all “STEM educaon” acvies and eliminate E/ PO element . APMC KDP-C Confirmaon Review – Confirmed! • Start of Phase C – 6/3/2013

NASA Headquarters – April 30, 2013 2 OSIRIS-REx Science Team Meeng #4 – June 18-20, 2013 2 Asteroid (101955) 1999 RQ36 is now . . .

. Bennu . Bennu is an Egypan mythological bird that was born from the heart of Osiris . It is associated with the Sun, creaon, and renewal Image credit: . The name was selected hp://www.touregypt.net in an internaonal contest run by the Planetary Society

NASA Headquarters – April 30, 2013 3 INITIAL CHARACTERIZATION: 1999

Bennu 10 Discovery: Sept 11, 1999 by the LINEAR survey 12 Follow-up: ~200 astrometric observaons between Sept 12 – 24, 1999 14 Radar: Arecibo and Goldstone observaons from 16 Sept 21 – 25, 1999

18 Visible Spectroscopy: McDonald Observatory for 5 nights in September 1999 20 LINEAR Detecon limit

22 Visual Magnitude 24

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Date

NASA Headquarters – April 30, 2013 4 REACQUISITION AND PHYSICAL CHARACTERIZATION: 2005

Bennu 10 Reacquision: 71 observaons between Aug 8 – Sept 17, 2005 12 Vis-IR Spectroscopy: NASA IRTF observaons on Sept 4, 2005 14 Photometry: Lightcurve and ECAS colors on Sept 14 – 17, 2005 16 Radar: observaons from 18 Sept 16 – Oct 2, 2005

20 Catalina Sky Survey 22 Detecon limit Visual Magnitude (Mt. Lemmon) 24

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Date

NASA Headquarters – April 30, 2013 5 FINAL CAMPAIGN: 2007 - 2012

Bennu 10 Thermal IR: Spitzer observaons on May, 2007 and Aug., 2012 12 Radar: Further Arecibo observaons in Sept, 2011 14 Phase funcon: Photometric measurements through May, 2012 16 Light Curve: Hubble-WFC3 observaons in Sept. and 18 Dec., 2012 20

22 Visual Magnitude 24

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 Date

NASA Headquarters – April 30, 2013 6 A QUALITY ORBIT REQUIRES EXTENSIVE OBSERVATION

1.E+08 Reacquision 1.E+07 ∆a = 4 km 1.E+06 Second Radar 1.E+05 ∆a = 100 m

1.E+04 Obs. at opposion ∆a = 15 m 1.E+03

1.E+02 Unceranty in Semi-major Axis (km)

1.E+01 1.E+01 9/10/99 9/15/99 9/20/99 9/25/99 9/30/99 10/5/99 Date Discovery 1.E+00 ∆a = 376,000 km Follow-up 1.E-01 ∆a = 20,500 km 1.E-02 First Radar

∆a = 43 km 1.E-03 Jun-05 Jul-05 Sep-05 Oct-05 Dec-05 Feb-06 Mar-06 May-06 Jul-06 NASA Headquarters – April 30, 2013 7 Date RADAR AND PHOTOMETRY ARE POWERFUL SOURCES OF INFORMATION ABOUT ASTEROID PHYSICAL PROPERTIES

. Measurements of the distribuon of range and radial velocity provided two-dimensional images with spaal resoluon of 7.5 m . Images used to construct a geologically detailed three- dimensional model and define the rotaon state • Size = 492-m (±20 m, mean diameter) • Shape = spheroidal “spinning top” • Rotaon state = 4.29 hr period, 180º obliquity . Radar also probed the near- surface bulk density (1.7 g cm-3) and structural scales larger than a

few cenmeters ! NASA Headquarters – April 30, 2013 8 FINDING THE RIGHT ASTEROID MEANS KNOWING WHAT IT IS MADE OF

• OSIRIS-REx seeks to return samples from a Carbonaceous Asteroid • Visible, near-infrared spectroscopy and ECAS photometry show that Bennu is a B- type asteroid • Linear, featureless spectrum with bluish to neutral slope • Near-IR thermal emission starng at 2 µm suggest an albedo of 3-5% • The hydrated CI and CM carbonaceous chondrite meteorites are the most likely analogs

!

NASA Headquarters – April 30, 2013 9 AN OSIRIS-REX FIRST: MEASURING A PLANETARY MASS USING RADAR AND INFRARED ASTRONOMY

• The three precise series of radar ranging posion measurements over two synodic periods allows us to measure the Yarkovsky acceleraon • The asteroid has deviated from its gravity-ruled orbit by 160 kilometers in just 12 years • This result, when combined with the thermal inera and the shape model, constrains the mass to 6.278 (-0.942/+1.883) x 1010 kg • Mass and shape constrain the bulk density to 0.980 ± 0.147 g/cm3 • Spitzer observaons yield a very low albedo – 4.5 ± 1.5%

NASA Headquarters – April 30, 2013 10 SURFACE PROPERTIES ARE CONSISTENT WITH ABUNDANT LOOSE REGOLITH AVAILABLE FOR SAMPLING

• Radar polarizaon shows transion to a “rough” surface at a scale smaller than the shortest (3.5-cm) wavelength • The thermal inera is substanally below the bedrock value – regolith grains are significantly smaller than the scale of the skin depth (~1 cm) • The asteroid’s shape, dynamic state, and geomorphology provide addional evidence for the presence of loose parculate regolith • There is one ~10–m boulder apparent on the surface

NASA Headquarters – April 30, 2013 11