Analysis of Pluto’s atmosphere during 2020 stellar occultation.
Stellar occultation is a phenomenon in which a body (e.g.planet or moon) passes in front of a Star intervening its light from reaching the observer. This light now passes through the object’s(herein planet’s) atmosphere if any, before reaching the observer and hence, stellar occultations are often used to study, indirectly a planet’s atmosphere by evaluating the effect it has on the Star’s light.
Since the conformation of Pluto’s atmosphere during the stellar occultation of 1988, its atmosphere has been studied by both ground and space-based telescopes. This study was conducted during the occultation on 06 June 2020 by a ground-based observatory in Iran.
It is based on a model to calculate Pluto’s atmospheric pressure based on the thermal gradient indicated as a light curve.
The structure of Pluto’s atmosphere was determined in areas investigated during occultation. Research conducted during recent decades has indicated that the change in Pluto’s atmospheric pressure is due to its seasonal cycle of Pluto’s surface cycle.
Observations
On 06 June 2020, the occultation of the star Gaia was observed by an observatory in Iran, with a 24" Schmidt-Cassegrain as the main telescope. The observation was undertaken using a clear filter and using two CCDs. The CCDs took images at the same time and afterward all the images were merged into pairs to get an integrated image.
Since the main component of Pluto’s atmosphere is nitrogen (N₂), the atmospheric deviations have been caused by the sublimation/condensation of N₂.
To obtain the pressure of Pluto, they fitted the occultation light curve to a spherical and transparent atmospheric model of Pluto.
By assuming a spherically symmetric planet and an N₂ pure atmosphere in the DO15
model, they satisfactorily fit the light curve.
The Laboratoire de Météorologie Dynamique (LMD) model shows that high thermal inertia leads to more formation of seasonal N₂ ice and an increase in atmospheric pressure. Over the next few years, the subsolar point will move to higher latitudes. Thus, a decrease in pressure is predicted.
Conclusion
The occultation light curve with the DO15 atmospheric model taking a spherically symmetric planet and pure N₂ atmosphere into account was successfully fitted allowing the analysis of the Planet’s atmosphere.
The analysis of photometric data gives the value of atmospheric pressure at 1215 km radius as 6.72 ± 0.48 µbar.
This throws light on the fact that there is a pressure decrease of 3% from the highest ever pressure estimate in 2015. The Pluto volatile transport model predicts a decrease in surface pressure over the next few years due to the orbital decline in solar insolation and more condensation of N₂ ice.
This study’s consistency with past studies indicates that the sublimation and condensation rate of N₂ ice in Sputnik Planitia’s glacier is continuing to increase because of maximum insolation over this area. ice in Sputnik Planitia’s glacier is continuing to increase because of maximum insolation over this area.
Reference: The article “Study of Pluto’s atmosphere based on 2020 stellar occultation light curve results” was published in the Journal Astronomy & Astrophysics on 21 September 2021.
