Atmospheric Mass-loss through UV Spectroscopy of Exoplanets

Exoplanets are planets that revolve around stars other than our sun. Observations in the last decade in ultraviolet wavelength with Hubble Space Telescope (HST) led to the discovery of materials escaping from the atmosphere of exoplanets orbiting close to its star. Observing this phenomenon will help us understand how planets evolve and how stars interact with planets. But due to limited observations our modelling is limited. This project is aimed at solving this problem by observing almost a dozen of exoplanets with the first NASA ultraviolet CubeSat called CUTE. We will collect data from CUTE and from HST observations for more than a dozen outstanding nearby exoplanet systems, probing a broad range of stellar, planetary, and orbital parameters. These observations will be analysed in a homogenous and systematic manner to provide breakthrough results on the effect of atmospheric escape on planetary evolution and its population distribution. This project will be carried out at the Laboratory for Atmospheric and Space Physics (LASP) of University of Colorado, Boulder, USA and the Space Research Institute of the Austrian Academy of Sciences, Graz, Austria.

Our team has been working with the CUTE (Colorado Ultraviolet Transit Experiment), a smallsat launched in September 2021 to study the upper atmospheres of exoplanets, especially hot Jupiters, i.e. large, gaseous planets orbiting very close to their stars. These extreme environments provide a unique laboratory to explore how planets interact with their host stars and how their atmospheres behave under intense radiation. Since launch, CUTE has completed its initial testing phase and started regular scientific operations. We've built and tested a dedicated pipeline to automatically process the telescope's data. This system has proven effective in handling the observations and correcting for known sources of noise, like small pointing jitters and changes in the satellite's orbit. Our first target was WASP-189b. We analyzed three high-quality datasets and found promising signs of atmospheric escape. These results were verified through independent methods. We also refined how we process and select data, creating new ways to correct for background noise and instrumental effects. Our findings for WASP-189b were published in The Astronomical Journal Letters and shared at major astronomy conferences. We've also analyzed other hot Jupiters including HD 189733b, KELT-9b, KELT-20b, WASP-33b, MASCARA-1b, WASP-178b, and MASCARA-4b, using both CUTE and archival data from the Hubble Space Telescope. These planets, observed in both the near and far ultraviolet, revealed how their atmospheres respond to the radiation from their host stars. To interpret these data, we're also building detailed computer models of planetary atmospheres. One such model for WASP-178b revealed that at high altitudes, the planet's atmosphere is significantly affected by non-standard physical processes. In particular, iron and magnesium atoms play key roles in heating and cooling the upper atmosphere. Our models show that to match observations accurately, especially in ultraviolet wavelengths, we must include these effects. A major outcome from our study so far is the emerging pattern that all hot Jupiters show signs of atmospheric escape. This means their upper atmospheres are being blown away by intense radiation from their stars-a process known as hydrodynamic escape. However, the strength and characteristics of this escape vary from planet to planet depending on their size, temperature, and distance from the host star. In the future, we plan to finalize our analysis of several planets and compare them to better understand how common and diverse these atmospheric escape processes are across different systems. We have fifteen research papers already published, and 3-4 in preparation covering aspects from instrument calibration to in-depth studies of specific planets. This work helps us piece together the broader picture of how planets evolve and survive in extreme environments-insights that are crucial for understanding not only distant worlds but also the future of our own solar system's planets under changing stellar conditions.