The first exoplanet detection happened only 30 years ago—but now, thanks to rapid advances in observation and data processing technologies, astronomers are working to not only detect exoplanets, but also to characterize them. This work—enabled by a supercomputer at the University of Cambridge—is providing unprecedented understanding of these extraterrestrial atmospheres.
In the past, exoplanets have typically been characterized using relatively crude metrics like the characteristics of their orbits that were observable using lower-resolution instruments. This team sought to reach beyond those observations, taking a thousand total hours of observations from the Hubble and Spitzer Space Telescopes to study 25 exoplanets. From that data, they were able to analyze eclipses of all 25 exoplanets and transits for 17 of the exoplanets, allowing them to more closely observe their atmospheres.
To crunch this massive amount of data, the researchers needed to run 20 models a quarter of a million times—for each exoplanet. For that, the researchers turned to Cambridge’s Wilkes3 supercomputer. Wilkes3, co-designed by Dell and Nvidia, consists of 80 nodes, each with dual AMD Epyc 7763 CPUs, a terabyte of memory and quadruple Nvidia A100 GPUs (80GB variant). Wilkes3 placed 100th on the June 2021 Top500 list with 4.12 Linpack petaflops of performance, but it also placed third on the June 2021 Green500 list of the world’s most energy-efficient supercomputers.
The planets investigated by the study all belonged to a class known as “hot Jupiters,” which orbit around their stars in ten days or less and have large gaseous atmospheres. Through the modeling, the research team detected thermal inversions—wherein a planet’s atmosphere reverses from cooling to heating at higher altitudes—were signs of particularly hot “hot Jupiters” (over 2000°K, or ~3140°F).
Moreover, they associated these hotter exoplanets with the presence of key elements: H– (a negative ion of hydrogen), as well as titanium oxide (TiO), vanadium oxide (VO) and iron hydride (FeH)—all metals that are able to exist in a stable form in the searing atmospheres of those exoplanets. The researchers hypothesize that those materials might absorb so much stellar light that the upper atmospheres heat up more than usual.
“Our paper marks a turning point for the field: we are now moving from the characterization of individual exoplanet atmospheres to the characterization of atmospheric populations,” said Billy Edwards, co-lead of the study and a research fellow at the University College London.
“This work can help make better models of how the Earth and other planets came to be,” added Ahmed Al-Refaie, co-author of the paper and head of numerical methods at the UCL Centre for Space Exochemistry Data, in an interview with Nvidia’s Rick Merritt. The researchers credit much of their ability to conduct the research to the supercomputer, and specifically to the A100 GPUs, which they said offered significant speedups relative to predecessor GPUs like the V100—let alone CPUs.
Header image: artist’s impression of the 25 hot Jupiters. Image courtesy of ESA/Hubble.