Spitzer Space Telescope - Directors Discretionary Time Proposal #468

Using IRAC to Measure the Yarkovsky Effect for 1862 Apollo

Principal Investigator: Amanda Mainzer
           Institution: JPL

Technical Contact: Amanda Mainzer, JPL

Co-Investigators:
David Vokrouhlicky, Charles University
Bill Bottke, SWRI
David Nesvorny, SWRI
Russ Walker, MIRA
Steve Chesley, JPL
Ned Wright, UCLA
Peter Eisenhardt, JPL

Science Category: asteroids
Observing Modes: IracMap
Hours Approved: 4.2

Abstract:
The Yarkovsky force, first postulated in 1900, is now recognized as  an extremely
important mechanism for transporting small bodies throughout the  Solar System.
Bottke et al. (2007) recently computed that the Yarkovsky force is  partially
responsible for putting the D~10 km K/T impactor on a collison course  with Earth.
Recent, unpublished work has detected the Yarkovsky force for the  asteroid (1862)
Apollo. It is possible to use Spitzer to make an independent  measurement of the
Yarkovsky force by measuring the differences in an asteroid's thermal  fluxes and
colors at two epochs separated by several months, corresponding to  viewing it
at its local morning and evening. Apollo is an ideal candidate for  validating
this technique, since its spin state, shape, orbit, and Yarkovsky  force are all
well-established, and it is easily observed by Spitzer. If this  technique can be
validated on Apollo, it can be used to measure the Yarkovsky force  directly for
large numbers of asteroids using thermal IR data alone. This will be of
considerable use to future infrared asteroid surveys. However, Apollo  has
only two remaining visibility windows during Spitzer's cryogenic  mission, both
over before Summer 2008 and the start of Cycle 5. We request time to  conduct
the dual epoch IRAC observations necessary to validate this valuable  method of
measuring the Yarkovsky force.