Why is it important to know about exoplanets having their atmospheres stripped while orbiting F-type stars? This is what a recent study submitted to *The Astronomical Journal* hopes to address as an international team of scientists conducted a first-time investigation into atmospheric escape on planets orbiting F-type stars, the latter of which are larger and hotter than our Sun. Atmospheric escape occurs on planets orbiting extremely close to their stars, resulting in the extreme temperature and radiation from the host star slowly stripping away the planet’s atmosphere.
For the study, the researchers analyzed data obtained from ten transits among six exoplanets using the Wide-field Infrared Camera (WIRC) at the Palomar Observatory operated by the California Institute of Technology. The six exoplanets included:
HAT-P-8 b (~750 light-years, 3.08-day orbit) KELT-7 b (~815 light-years, 2.73-day orbit) WASP-93 b (~1,220 light-years, 2.73-day orbit) WASP-103 b (1,250 light-years, 0.925-day orbit) WASP-12 b (~1,400 light-years, 1.09-day orbit) WASP-180 A b (~1,500 light-years, 3.41-day orbit)The goal of the study was to ascertain the amount of atmospheric escape each exoplanet was experiencing as they orbited their respective host stars during their extremely tight orbits. In the end, the researchers found that WASP-12 b and WASP-180 A b were observed to have significant detections of atmospheric escape, with WASP-93 b and HAT-P-8 b observed to have potential detections of atmospheric escape, and WASP-103 b and KELT-7 b were observed to have no detections for atmospheric escape.
After comparing these findings to longstanding computer models, the researchers found that WASP-12 b and WASP-180 A b had atmospheric escape velocities on a logarithmic scale of approximately 12.4 and 11.85 grams per second, respectively. This actually means WASP-12 b and WASP-180 A b are estimated to have atmospheric escape velocities of approximately 1012.4 and 1011.85 grams per second, respectively.
The study notes in its conclusions, “Our mass loss constraints for our other four survey targets (HAT-P-8 b, WASP-93 b, WASP-103 b, and KELT-7 b) are similar to published measurements for WASP-48 b and WASP-94 A b, which also orbit early-type stars, and are broadly in line with measured mass loss rates for gas giants orbiting cooler stars. This suggests that the strong outflows reported in the literature for planets orbiting early-type stars are not representative of all early-type systems.”
As noted, this study conducted a first-time analysis of atmospheric escape for exoplanets orbiting F-type stars, with the researchers noting that studies of atmospheric escape have been limited to exoplanets orbiting K- and M-type stars. While K- and M-type stars are both smaller and cooler than our Sun, it is noted above that F-type stars are larger and hotter than our Sun, meaning exoplanets that orbit close to it like the ones analyzed in this study are subjected to larger amounts of heat and radiation than our Sun and the K- and M-type stars previously studied.
One of the primary motivations for studying exoplanet atmospheric escape is to better understand the long-term evolution of exoplanets, and specifically gas giants that orbit close to their stars, also called “hot” Jupiters and “ultra-hot” Jupiters. It is also an excellent method for gaining insight into star-planet interactions, an exoplanet’s atmosphere composition and detection, habitability potential, and testing planetary models, the last of which was used for this study. Therefore, studies like this demonstrate the importance of using atmospheric escape as a method for learning about exoplanet formation and evolution for several types of stars.
What new insight into atmospheric stripping on planets orbiting F-type stars will researchers make in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
