2012 Goldstone Radar Observations of (4179) Toutatis4179 Toutatis was discovered by C. Pollas at Caussols (France) in January of 1989. Toutatis
has been making close approaches to Earth at four-year intervals since its discovery, and
as a result, it was studied extensively with radar in 1992, 1996, 2000, 2004, and 2008, and also
at a variety of optical and infrared wavelengths in 1992-1993. Toutatis is an irregular and very
elongated object. It's also a very slow, non-principal axis rotator characterized by 5.4-day
rotation about the long axis and 7.3-day precession of the long axis about the
angular momentum vector. A summary of earlier observations of Toutatis is available online
at:
http://echo.jpl.nasa.gov/asteroids/4179_Toutatis/toutatis.htmlToutatis will approach within 0.0463 AU of Earth on December 12, 2012 when it will be
a very strong radar target at Goldstone and Arecibo. We are planning an extensive campaign
of radar observations at both telescopes between December 4 - 22. We are also planning
radar speckle tracking observations using the antennas in the Very Long Baseline Array
(VLBA) as receivers. The radar speckle observations should provide particularly tight
constraints on the spin vector and help improve the shape model.
Previous radar images of Toutatis achieved range resolutions as fine as 7.5 m/pixel
at Arecibo and 18.75 m/pixel at Goldstone. In 2012, we will observe Toutatis with the
new 4-meter-resolution chirp imaging system at Goldstone, which could reveal finer
detail than has previously been visible.
In addition, Toutatis will be the target of a flyby by the Chinese Chang'e 2 spacecraft on
December 13, 2012 (Previous reports that the flyby would occur on January 6, 2013 are
apparently incorrect). Chang'e 2 was originally launched to study the Moon but was diverted
in April, 2012 for the asteroid encounter. We hope to use new radar images obtained in
late 2012 to predict the orientation of Toutatis during the Chang'e 2 flyby. Evidently the
spacecraft flyby will occur at a distance of about 300 km on the sunward side of Toutatis.
The next opportunity for radar imaging of Toutatis will occur in late 2016 and early 2017
during an encounter within 0.251 AU when it should be possible to get radar
images at Arecibo with resolutions of about 150 meters per pixel.
The next time Toutatis will approach at least this close to Earth is in November of 2069
when the asteroid will flby at a distance of only 0.0198 AU (7.7 lunar distances).
Five Toutatis tracks occur on the same day as tracks with Europa/Ganymede and are indicated
below. On Dec. 11 and 15, we hope to have enough time to start with Toutatis, do Europa/Ganymede, and
then return to Toutatis. On Dec. 18 and 22, we will start with Europa and Ganymede and then finish
with Toutatis.
On Dec. 21 and 22 we also intend to devote a fraction of our time to observing 99942 Apophis.
Other days are scheduled for observations of Apophis in January.
