The Planet That Shouldn’t Exist

As of this writing, almost 5300 exoplanets spanning approximately 4000 planetary systems have been confirmed to exist in our universe. With each new exoplanet discovery, scientists continue to learn more about planetary formation and evolution that has already shaken our understanding of this process down to its very core. One such example is “Hot Jupiters”, which are Jupiter-sized exoplanets, or larger, that orbit closer to their parents stars than Mercury does to our own. This is in stark contrast to our own Solar System, which has rocky planets closer towards our Sun and the gas giant planets much farther out.

Therefore, it is only right that a recent discovery published in The Astrophysical Journal continues to push our understanding of the cosmos. In this study, an international team of researchers led by the Carnegie Institution for Science confirm the existence of a new Jupiter-sized exoplanet, TOI-5205b, orbiting a young, low-mass, main-sequence red dwarf (M dwarf) star, TOI-5205, located approximately 87 parsecs (284 light-years) from Earth.

What makes this discovery unique is the mass of TOI-5205b is rather large for orbiting such a young and small red dwarf star, thus challenging previous understandings of planetary formation and evolution. This is because gas giant exoplanets have traditionally been observed orbiting older and larger M dwarf stars.

“The host star, TOI-5205, is just about four times the size of Jupiter, yet it has somehow managed to form a Jupiter-sized planet, which is quite surprising!” exclaimed Dr. Shubham Kanodia, who is a postdoctoral fellow in the Carnegie Earth & Planets Lab and an expert in red dwarf stars, and lead author of the study. Dr. Shubham recently discussed the discovery in an in-depth blog post, as well. Using food as an analogy, Jupiter orbiting our Sun is equivalent to a pea orbiting a grapefruit, whereas TOI-5205b orbiting its parent star would be equivalent to a pea orbiting a lemon.

The general theory of planetary formation begins with a massive, rotating disk of gas and dust encircling young stars, with gas planets initially being formed from rocky material comprising approximately 10 Earth masses. Over time, this material forms the core of the giant planet which then accumulates large amounts of gas from the disk to produce the massive gas giants we observe today. As it turns out, the confirmation of TOI-5205b could throw this theory into disarray.

“TOI-5205b’s existence stretches what we know about the disks in which these planets are born,” explained Dr. Kanodia. “In the beginning, if there isn’t enough rocky material in the disk to form the initial core, then one cannot form a gas giant planet.  And at the end, if the disk evaporates away before the massive core is formed, then one cannot form a gas giant planet.  And yet TOI-5205b formed despite these guardrails. Based on our nominal current understanding of planet formation, TOI-5205b should not exist; it is a ‘forbidden’ planet.”

The discovery was initially made using data from NASA’s Transiting Exoplanet Survey Satellite (TESS), which uses the transit detection method for locating exoplanets, and the data indicated that TOI-5205b blocks approximately 7% of its parent star’s light, making TOI-5205b one of the largest transits ever recorded for a confirmed exoplanet in orbit around a main-sequence star.

To confirm the TESS data, follow-up observations were made from an international collaboration of instruments and observatories. These include the Habitable-zone Planet Finder, the ARCTIC camera on the 3.5-m Apache Point Observatory, the NN-Explore Exoplanet Stellar Speckle Imager, the 0.6-m Red Buttes Observatory, and the Three-hundred MilliMeter Telescope.

Given the very large transit that TOI-5205b produced, the researchers demonstrated that this could make this exoplanet an ideal candidate for future atmospheric observations using NASA’s James Webb Space Telescope (JWST), which could help scientists better understand the secrets behind its formation and evolution, as well. This is because JWST has already been successful in observing exoplanet atmospheres in incredible detail, as it recently demonstrated with exoplanet, WASP-39b.

What fascinating new discoveries will scientists make about exoplanets in the coming years and decades, and how much will these discoveries continue to push our knowledge of planetary formation and evolution? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!