The occultation of a star by the asteroid Polymele has been observed from Kaolack, Senegal.
During the night of 23rd to 24th September 2020, an international scientific cooperation, mobilising Senegalese, Belgian and French researchers, made it possible to observe for the first time a star occultation by the asteroid (15094) Polymele. This observation campaign is part of the preparations for NASA's Lucy space mission.
Formation of the solar system
Coordinated by NASA, the Lucy space mission will start in October 2021 for 12 years. Its objective: to fly by an asteroid in the main belt and six Trojan asteroids of Jupiter, small rocky bodies that follow (or precede) the planet at a stable distance on the same orbit around the Sun. The aim is to improve our knowledge of the origin of the planets and the formation of the solar system.
A preparatory step for the flyby is for astronomers to determine the size and shape of the asteroids. Since they reflect very little sunlight, direct observation is difficult: measurements are made by observing the shadows they form as they pass in front of a distant star, a phenomenon called stellar occultation.
Second mission
Already in 2018, 50 American, 7 French and 21 Senegalese researchers had observed from Senegal the last occultation of the asteroid Arrokoth, before its overflight in January 2019 by the New Horizons probe. On the strength of this success, Marc Buie of the Southwest Research Institute, who is contributing to the preparation of the Lucy mission, convinced NASA to entrust a new mission to the Senegalese Association for the Promotion of Astronomy (ASPA).
Senegal was indeed, according to forecasts, ideally placed for the observation of the occultation of a star by (15094) Polymele, the smallest of the six Trojan asteroids, which will be flown by the Lucy mission in 2027. The data collected would be used to learn more about the asteroid before launching the probe.
Intensive training
On the night of 23rd to 24th September, the international team assembled in Senegal effectively observed this stellar occultation by Polymele. About forty researchers were mobilised, with the support of IRD and CNRS.
Fourteen mobile telescopes measuring 20 centimetres in diameter were deployed at different observation sites in the Fatick and Kaolack regions of Senegal. The intensive training of researchers in the installation and use of these telescopes and their acquisition systems, sent by NASA to Senegal, took place during the three days preceding the occultation at Fatick.
Successful observation
Despite the development of a large storm cell over the Kaolack region on the night of the observation, the deployment strategy of the telescopes proved to be effective in observing the stellar occultation. The data collected will enable a first estimate of the size of the Polymele asteroid to be obtained, while the shape of the object will be specified by future observation campaigns.
This successful observation campaign, carried out overwhelmingly by Senegalese astronomers, marks an important step in the development of astronomical research in Senegal. These actions illustrate a coordinated effort to promote astronomical and space sciences in Africa, led since 2017 by an international consortium of researchers: the African Planet and Space Science Initiative.
Watch more about the preparation and training of the teams before the observation in this slideshow.
The video of the Polymele occultation, observed in Senegal on 24th September 2020, shows the brevity of the phenomenon, and the performance achieved by the researchers.
This article comes form a release published by IRD. It has been translated and adapted by Afriscitech.