A stellar occultation by the transneptunian object (50000) Quaoar observed by CHEOPS

Stellar occultation is a powerful technique that allows the determination of
some physical parameters of the occulting object. The result depends on the
photometric accuracy, the temporal resolution, and the number of chords
obtained. Space telescopes can achieve high photometric accuracy as they are
not affected by atmospheric scintillation. Using ESA's CHEOPS space telescope,
we observed a stellar occultation by the Transneptunian object (50000) Quaoar.
We compare the obtained chord with previous occultations by this object and
determine its astrometry with sub-milliarcsecond precision. Also, we determine
upper limits to the presence of a global methane atmosphere on the occulting
body. We predicted and observed a stellar occultation by Quaoar using the
CHEOPS space telescope. We measured the occultation light curve from this
data-set and determined the dis- and re-appearance of the star behind the
occulting body. Furthermore, a ground-based telescope in Australia was used to
constrain Quaoar's limb. Combined with results from previous works, these
measurements allow us to obtain a precise position of Quaoar at the occultation
time. We present results obtained from the first stellar occultation by a
Transneptunian object (TNO) using space telescope orbiting Earth. It was the
occultation by Quaoar observed on 2020 June 11. We used the CHEOPS light curve
to obtain a surface pressure upper limit of 85 nbar for the detection of a
global methane atmosphere. Also, combining this observation with a ground-based
observation we fit Quaoar's limb to determine its astrometric position with an
uncertainty below 1.0 mas. This observation is a first of its kind, and it
shall be considered as a proof of concept of stellar occultation observations
of Transneptunian objects with space telescopes orbiting Earth. Moreover, it
shows significant prospects for the James Webb Space Telescope.