Nereid from space: Rotation, size and shape analysis from Kepler/K2, Herschel and Spitzer observations

Abstract

In this paper we present an analysis of Kepler K2 mission Campaign 3 observations of the irregular Neptune satellite, Nereid. We determined a rotation period of P=11.594(+/-)0.017 h and amplitude of dm=0.0328(+/-)00018, confirming previous short rotation periods obtained in ground based observations. The similarities of light curve amplitudes between 2001 and 2015 show that Nereid is in a low-amplitude rotation state nowadays and it could have been in a high-amplitude rotation state in the mid 1960's. Another high-amplitude period is expected in about 30 years. Based on the light curve amplitudes observed in the last 15 years we could constrain the shape of Nereid and obtained a maximum a:c axis ratio of 1.3:1. This excludes the previously suggested very elongated shape of a:c=1.9:1 and clearly shows that Nereid's spin axis cannot be in forced precession due to tidal forces. Thermal emission data from the Spitzer Space Telescope and the Herschel Space Observatory indicate that Nereid's shape is actually close to the a:c axis ratio limit of 1.3:1 we obtained, and it has a very rough, highly cratered surface

arXiv commentAccepted for publication in MNRAS

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• Small Bodies Near and Far (SBNAF): a benchmark study on physical and thermal properties of small bodies in the Solar System
• 101 Trojans: a tale of period bimodality, binaries, and extremely slow rotators from K2 photometry
• Properties of the irregular satellite system around Uranus inferred from K2, Herschel and Spitzer observations
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• TESS in the Solar System
• Rotational properties of Hilda asteroids observed by the K2 mission
• Light curves of transneptunian objects from the K2 mission of the Kepler Space Telescope
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• TNOs are Cool! A Survey of the transneptunian Region XV. Physical characteristics of 23 resonant transneptunian and scattered disk objects
• Nereid as a Regular Satellite of Neptune