08 December 2012

Closest approach of asteroid Toutatis on December 12. 2012
Animation of Asteroid 4179 Toutatis flying by the Earth
between 10:55 and 11:05 UT on September 28, 2004.
Animation courtesy of Scott Sinclair from Automated Patrol
Telescopes Australia. Images taken with a Meade LX200 10" at F/4.5
and consists of 50 x 8 second exposures (15 second separation).
Field of view is FOV 14 x 21 arc minutes.
Toutatis, a potato-shaped asteroid about 4.6 km in its longest extent, will pass within 7,000,000 km of the Earth's center on Wednesday, December 12, 2012. This is roughly 18 times the distance from the Earth to the moon. Toutatis will not pass this closely again for the next 500 years. Because of an extensive set of optical and radar observations, the orbit for Toutatis is one of the best determined of any asteroid and there is no chance that this object will collide with the Earth during this encounter - or any other encounter for at least 5 centuries.
With the help of Toutatis radar observations, a shape and rotation model for this object has been developed. Details on this work by Steve Ostro, R. Scott Hudson and colleagues can be found at:

This particular close approach by Toutatis is extra-special, because Chang'E 2 (China's erstwhile lunar orbiter) is on its way to a flyby, with a close approach on December 13. According to radio astronomer Michael Busch, Chang'E 2 will fly within a few hundred kilometers of Toutatis.
Chang'E 2 produced beautiful photos of the Moon, but it will be a major challenge for it to obtain photos of Toutatis. Chang'E 2's camera, like most mapping cameras on orbiting spacecraft, is a pushbroom-style imager that is designed to take advantage of the spacecraft's predictable, steady orbital speed to sweep an array of pixels along the ground, with the ground a fixed and predictable distance away from the spacecraft. This asteroid encounter bears no resemblance to an orbital mapping mission. Chang'E 2 will be passing Toutatis at a high relative velocity of 11 kilometers per second, which means that the distance to the target will be changing very rapidly. In order for Chang'E 2 to get a photo, it will have to very carefully aim its narrow-angle imager in the correct direction and slew the spacecraft in order to scan the linear camera detector across the asteroid and therefore acquire an image. It's a process that I described when I posted some Mars Express images of Phobos last year.
It helps that the orbit of Toutatis is extremely precisely known (thanks to all those previous radar observations), but still, it will not be easy for Chang'E 2 to succeed. If it does succeed, it will obtain at most two images, one on approach and one on departure, with resolutions of a few tens of meters. This isn't any better than the radar resolution, but images would identify albedo patterns and could help disambiguate radar-derived models of Toutatis' shape. This is an extremely challenging thing for China to attempt, especially given that this is their first deep-space encounter. They only recently brought online a radio telescope of the kind you need to perform the necessary deep-space communication and spacecraft tracking and navigation.

For you people having telescopes, this asteroid is a very challenging object to observe. You will find a good ephemeris chart to get the coordinates of the asteroid for many days HERE. For those who does not have the equipement necessary to observe this asteroid Paul Cox of will be broadcasting live images of Toutatis in a couple of free public shows on the night of the 11th/12th Dec.
Cox will be setting up three of the robotic telescopes to track the asteroid, including the Half Metre telescope. Details and timings of the shows are on the Slooh homepage.

The observatory is in the Canary Islands which is 4-7hrs ahead of USA time so the shows are at an ideal time for those who can't stay up late on a working day. We'll also broadcast a late show at the time of closest approach (2012-12-12T06:40UTC) with live images from Arizona, together with some popular objects using the Half Metre telescope at the Canary Islands Observatory.


No comments:

Post a Comment