Planets Discovered on the Verge of Extinction

Planets Discovered on the Verge of Extinction

Astronomers have discovered three Jupiter-like exoplanets that are on the verge of being ‘swallowed up’ by their host stars. The discovery sheds new light on how planetary systems evolve over time, potentially revealing the fate of solar systems such as our own.

Three newly discovered planets have been discovered to be dangerously close to dying stars. These three gas giant planets, discovered by NASA’s TESS (Transiting Exoplanet Survey Satellite) Mission, have some of the shortest-period orbits around subgiant or giant stars among the thousands of extrasolar planets discovered so far. TOI-2337b, one of the planets, will be consumed by its host star in less than a million years, faster than any other planet currently known.

“These discoveries are critical to understanding a new frontier in exoplanet studies: how planetary systems evolve over time,” said lead author Samuel Grunblatt, a postdoctoral fellow at the American Museum of Natural History and the Flatiron Institute in New York City. Grunblatt, who received his PhD from the University of Hawaii Institute for Astronomy (UH IfA), added that “these observations offer new windows into planets nearing the end of their lives, before their host stars swallow them up.”

Grunblatt announced the discovery and confirmation of these planets – TOI-2337b, TOI-4329b, and TOI-2669b – today at an American Astronomical Society press conference; the study has been accepted for publication in the Astronomical Journal.

These discoveries are critical to understanding a new frontier in exoplanet studies: how planetary systems evolve over time, these observations offer new windows into planets nearing the end of their lives, before their host stars swallow them up.

Samuel Grunblatt

The planets’ masses are estimated to be between 0.5 and 1.7 times that of Jupiter, and their sizes range from slightly smaller to more than 1.6 times that of Jupiter. They also have a wide range of densities, from styrofoam-like to three times denser than water, implying a wide range of origins.

These three planets are thought to be just the tip of the iceberg. “We expect to find tens to hundreds of these evolved transiting planet systems with TESS, providing new details on how planets interact with each other, inflate, and migrate around stars like our Sun,” said Nick Saunders, a graduate student at UH IfA and co-author of the study.

The planets were discovered in full-frame image data from NASA’s TESS Mission taken in 2018 and 2019. Grunblatt and his colleagues discovered the candidate planets in TESS data and then confirmed their existence with the W. M. Keck Observatory’s High-Resolution Echelle Spectrometer (HIRES) on Maunakea, Hawaii.

Newly-found planets on the edge of destruction

“The Keck observations of these planetary systems are critical to understanding their origins, helping reveal the fate of solar systems like our own,” said co-author and UH IfA astronomer Daniel Huber.

Current models of planet dynamics suggest that planets should spiral in toward their host stars as the stars evolve over time, particularly in the last 10 percent of the star’s lifetime. This process also heats the planets, potentially causing their atmospheres to inflate. However, this stellar evolution will also cause the orbits of planets around the host star to come closer to one another, increasing the likelihood that some of them will collide, or even destabilize the entire planetary system.

The study’s discovery of a wide range of planet densities suggests that these planetary systems were formed by chaotic planet-to-planet interactions. This could also have resulted in these planets having unpredictable heating rates and timescales, resulting in the wide range of densities we see today.

Observations of one of these systems, TOI-4329, with the recently launched James Webb Space Telescope may reveal evidence for water or carbon dioxide in the planet’s atmosphere in the future. If these molecules are discovered, the data will constrain where these planets formed and what kinds of interactions had to occur to produce the planetary orbits we see today.

The NASA TESS telescope will continue to monitor these systems, limiting the rate at which these planets spiral into their host stars. So far, no clear signal of orbital decay has been observed in any of the systems, but the TESS Extended Missions will provide much tighter constraints on planet in-spiral than are currently possible, revealing how strongly planetary systems are affected by stellar evolution.

The team hopes that this ‘planetary archeology’ will aid in our understanding of the past, present, and future of planetary systems, bringing us one step closer to answering the question, “Are we alone?”