Occultation by the Ice Giants at the time of Gaia: the largest ground observational campaigns in over 30 years

The powerful method of stellar occultations is an unbeatable technique uniquely approaching, in some aspects, the performances of planetary space missions. It allows km-level accuracies on the determination of shapes and sizes of objects, and permits the discovery and study of rings, comæ, atmospheres, and satellites around planets and some small bodies. Stellar occultations allowed for instance the discovery of the incomplete rings (arcs) around Neptune in 1984 [1, 2, 3, 4]. Recently, a stellar occultation in 2017 provided invaluable constraints on the structure and seasonal variations of Triton [5].

We present, here, the Oct. 7th, 2021 stellar occultation of a Kmag=13 star by Neptune and its surroundings. We organised at this occasion the largest, post-Voyager, ground observational campaign, involving most large and medium size telescopes across the Americas and in Hawaii. Additional AO images from Keck were obtained in the hours before and after the occultation. The preliminary findings will be presented here.

Furthermore, we present our long-term efforts for the upcoming occultation campaigns by both Uranus and Neptune in a context where the Ice Giants have captured the attention of the decadal survey, and where occultation data can complement that of JWST.

As both Uranus and Neptune were receding from the galactic plane since the 1980s, occultations by these planets were rare. Furthermore, the precision of the Gaia stellar catalogues [6, 7, 8, 9] has marked the beginning of a new era in predicting stellar occultation. We will conclude by presenting the September 2022 occultation by Uranus.

References

[1] Roques, F., et al., 1984, BAAS.

[2] Sicardy, et al.,: 1985, BAAS.

[3] Hubbard, W.B., et al., 1986, Nat 319, 636.

[4] Covault, C.E., et al.,: 1986, Icarus 67, 126.

[5] Marques Oliveira, J., et al.: 2022, A&A 659, A136.

[6] Gaia Collaboration, Brown, A.G.A., et al., A&A 595, A2.

[7] Gaia Collaboration, Brown, A.G.A., et al., 2018, A&A 616, A1.

[8] Gaia Collaboration, Brown, A.G.A., et al. 2021, A&A 650, C3.

[9] Gaia Collaboration, Vallenari, A., et al., 2022, arXiv:2208.00211.