A three-year research project funded by the National Science Foundation is underway to uncover the origins of eccentric warm Jupiters, massive gas giants with elongated orbits around their stars. Led by an astronomer at Northern Arizona University, the study aims to explain why these planets align precisely with their stars' equators despite their unusual paths. The findings could reshape understanding of planet formation, including our own solar system.
Eccentric warm Jupiters are a puzzling class of exoplanets: massive gas giants that orbit their stars in stretched, unexpected paths, unlike the closer-orbiting hot Jupiters. For years, scientists assumed warm Jupiters formed similarly to hot Jupiters, but improved telescope data has revealed key differences. Warm Jupiters nearly always align with their stars' equators, and the more elongated their orbits, the more precise the alignment—a pattern no current theory explains.
Daniel Muñoz, an astronomer at Northern Arizona University's Department of Astronomy and Planetary Science, is leading the investigation with collaborators at Indiana University Bloomington. The project, funded by the National Science Foundation, will run until 2028 and includes building a new catalog of these planets using data from NASA's Transiting Exoplanet Survey Satellite (TESS).
"The variability of extrasolar planets is just enormous," Muñoz said. "Extrasolar systems can look like our solar system, but in some cases, they look entirely different and exotic. We're very interested in seeing how the solar system forms in context by understanding systems that look like ours and ones that look completely different. We can get a sense of what the extremes are, how average our planet formation history is and how average our solar system is."
Muñoz is exploring multiple hypotheses for these orbits. One involves companion planets that alter paths without causing misalignment. Another points to interactions with the gaseous nebulas where planets form. His favored theory suggests internal waves in fluid stars could extract energy from orbits, enforcing alignment.
"The data tells us that warm Jupiters are not just the tail end of hot Jupiters," Muñoz said. "It tells us they may have a different history. We need to understand if this is just a quirk—if these are pathological cases that happen maybe once every million cases—or if there is an additional physical process that we have ignored in the past that we might be able to unveil."
As a theorist, Muñoz uses computer models and calculations to test ideas. "I'm a theorist, so I work on models using heavy-duty computers, pencil-and-paper calculations and anything in between," he said. "We don't have a model that predicted this to begin with, so we're going to go crazy and dive into the most creative ways we can think about this problem. But once you have a mathematical model, that is just the beginning."
Next year, Muñoz plans to hire a graduate student to assist. His work on the stellar waves hypothesis shows promise, with publications expected soon. Understanding these processes could reveal hidden aspects of solar system evolution.