Tuesday 27 May 2014

The orbit of Linus.

22 Kalliope is a 166.2 km Main Belt Asteroid with an 1814 day orbit that takes it from 2.62 AU from the Sun (2.62 times the distance at which the Earth orbits the Sun) to 3.20 AU. Unusually, but not exclusively, it has a small Moon, Linus, thought to be about 28 km in diameter. While other asteroids with Moons have been discovered, the positioning of 22 Kaliope within the Main Asteroid Belt makes regular observations easier than is the case with most such bodies, with the result that it has received considerable scientific interest in recent years.

The calculated orbit of 22 Kalliope. JPL Small Body Database Browser.

In a paper published on the arXiv Database at Cornell University Library on 5 May 2014, a team of scientists led by Iraida Sokova of the Pulkovo Astronomical Observatory in St. Petersburg detail the results of a study which aimed to determine the orbital parameters of Linus using speckle interferometry.

Speckle interferometry is a method developed to make accurate observations of very small or distance astronomical objects from ground-based observatories, where distortions due to atmospheric disturbances would otherwise be a problem. It essentially relies on taking a large number of short exposure images of the target, then combining these to remove any atmospheric turbulence effects.

(a) The example of power spectrum of the binary asteroid 22 Kalliope obtained with the use speckle interferometer at the 6-m BTA telescope. (b) The reconstructed image of satellite Linus and its main component 22 Kalliope. Angular distance between the components and apparent magnitude differences are given. Sokova et al. (2014).

Sokova et al. observed the 22 Kaliope/Linus system on 10-16 December 2011 using the 6-m BTA telescope at the Special Astrophysical Observatory at Nizhnij Arkhyz in the Zelenchukskiy Region of the Karachai-Cherkessian Republic of Russia. Having created a series of images of the system, they then used these to build a model of the orbit of Linus.

The approximate location of the Special Astrophysical Observatory. Google Maps.

Sokova et al. estimate that Linus orbited 22 Kaliope at a distance of 1109 km every 3.6 days. This is closer to the parent body than previously calculated by Descamps et al. in 2008 (1099 km) and Vachier et al. in 2012 (1082 km). However Sokova et al. do not dispute the accuracy of either of the previous studies, instead observing that it is likely that the week gravity and probable irregular shape of 22 Kaliope results in Linus having a highly unstable orbit, with the potential for sudden shifts in orbital parameters.

See also…

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