* Astronomy

Uranus's Orbit Inclination Precession, Last Million Years

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Uranus has no diamonds after all
Hunting for diamonds on Uranus or Neptune would be a lost cause, say the authors of a new study. Contrary to previous suggestions, these two planets do not have enough carbon to make diamonds.
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An international team of astronomers led by Apostolos Christou at Armagh Observatory has made the first ever observation of one of the satellites of the planet Uranus passing in front of another. The observation was made on the night of 4th May by Marton Hidas and Tim Brown, of the Las Cumbres Observatory Global Telescope, Santa Barbara, California, using the robotic Faulkes Telescope South at Siding Spring Observatory, Australia. This work involves a collaboration between scientists at Siding Spring, Las Cumbres, Armagh and Cardiff University.

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Title: Light curves and colours of the faint Uranian irregular satellites Sycorax, Prospero, Stephano, Setebos and Trinculo
Authors: Michele Maris, Giovanni Carraro, M. Gabriela Parisi

After the work of Gladman et al. (1998), it is now assessed that many irregular satellites are orbiting around Uranus. Despite many studies have been performed in past years, very few is know for the light-curves of these objects and inconsistencies are present between colours derived by different authors. This situation motivated our effort to improve both the knowledge of colours and light curves. We present and discuss time series observations of Sycorax, Prospero, Stephano, Setebos and Trinculo, five faint irregular satellites of Uranus, carried out at VLT, ESO Paranal (Chile) in the nights between 29 and 30 July, 2005 and 25 and 30 November, 2005. We derive light curves for Sycorax and Prospero and colours for all of these these bodies. For Sycorax we obtain colours B-V =0.839 ±0.014, V-R = 0.531 ±0.005 and a light curve which is suggestive of a periodical variation with period about 3.6 hours and amplitude about 0.067 ±0.004 mag. The periods and colours we derive for Sycorax are in agreement with our previous determination in 1999 using NTT. We derive also a light-curve for Prospero which suggests an amplitude of about 0.2 mag and a periodicity of about 4 hours. However, the sparseness of our data, prevents a more precise characterisation of the light-curves, and we can not determine whether they are one-peaked or two-peaked. Hence, these periods and amplitudes have to be considered preliminary estimates. As for Setebos, Stephano and Trinculo the present data do not allow to derive any unambiguous periodicity, despite Setebos displays a significant variability with amplitude about as large as that of Prospero. Colours for Prospero, Setebos, Stephano and Trinculo are in marginal agreement with the literature.



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Light curves in R for Sycorax.
Data are for the nights of 2005, July 29th (left) and 30th (right). Squares in gray represents measurements of magnitudes for a common field star of similar magnitude. To avoid confusion error bars for the field star are not reported and the averaged magnitude is shifted.

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