Here come the Trojans (asteroids, that is)

The 74” telescope in Sutherland was employed at the end of February 2016 to observe faint, small bodies in our Solar System. SAAO Astronomer Dr. Amanda Sickafoose,  visiting planetary astronomer Dr. Andrew Rivkin (Johns Hopkins University Applied Physics Laboratory), and SAAO postdoctoral researcher Dr. Nicolas Erasmus spent time on the 74” telescope, using the SHOC instrument to study Jovian Trojan asteroids. These small, rocky objects share an orbit with Jupiter and are located in stable regions that lead and trail the gas giant by 60 deg. It is not known whether these objects were formed in their current locations or were gravitationally captured. The colors of large Trojan asteroids have been observed to fall into two color groupings: red or gray. The 74″ observations were specifically looking at small Jovian Trojans and will be used to determine whether the color trend extends to all sizes. Colors can be indicators of formation location; therefore, the ultimate aim is to gain insight into how the Trojan asteroids reached their current stable orbits.

An example of the excellent 74” data is shown in Fig. 1. Asteroid 2008GU141 has R magnitude 21.0. It is located in the cloud of Trojans that trail Jupiter (aka L5), which is 4.5 AU from the Earth (AU = astronomical unit, or roughly 150 million km). For scale, a map of the Cape Town area is shown in Fig. 2 with a representation of 2008GU141.

After taking these images, the observers discovered a second object in the frame: main-belt asteroid 2010VY30. This second asteroid is even fainter, at 22.1 R magnitude. 2010VY30 is located approximately 2.2 AU from the Earth and is a mere 1-2 km in size.

These observations take advantage of Sutherland’s geographic location and demonstrate the capability of the 74” + SHOC to observe faint targets. We expect many more observations as part of South Africa’s growing planetary science presence!

Fig. 1. Animated GIF showing Trojan asteroid 2008GU141 (yellow circle) and the unexpected main-belt asteroid 2010VY30 (red circle). The images are 420-sec exposures taken in the R filter. There are two larger jumps in position because images were taken in sequences of two, with other filters interspersed.

Fig. 1. Animated GIF showing Trojan asteroid 2008GU141 (yellow circle) and the unexpected main-belt asteroid 2010VY30 (red circle). The images are 420-sec exposures taken in the R filter. There are two larger jumps in position because images were taken in sequences of two, with other filters interspersed.

Fig. 2. Representation of the size of Trojan asteroid 2008GU141, shown here to scale with Cape Town, South Africa. The asteroid is located approximately 675 million km away and is approximately 12.5 km in diameter.

Fig. 2. Representation of the size of Trojan asteroid 2008GU141, shown here to scale with Cape Town, South Africa. The asteroid is located approximately 675 million km away and is approximately 12.5 km in diameter.

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