Scientists Discover Ultra-Light Giant Planets Weighing Less Than Cotton Candy

NASA astronomers have discovered two exoplanets with densities as low as cotton candy, defying conventional models of gas giant formation. The findings, published June 27, 2026, describe worlds orbiting a distant star where their mass-to-volume ratios suggest porous, fluffy interiors—unlike any known planet in our solar system or prior exoplanet surveys.

Their densities, measured at approximately 0.05 grams per cubic centimeter, are comparable to that of cotton candy, a substance so light it would float on water. For comparison, Saturn, the least dense planet in our solar system, has a density of 0.687 grams per cubic centimeter—more than ten times denser.

The discovery challenges existing theories of planetary formation. Most gas giants, including Jupiter and Saturn, are believed to form from dense cores that gravitationally attract surrounding gas. However, the newly identified planets appear to have retained far less mass relative to their size, indicating a formation process that may involve unusual conditions, such as rapid gas dissipation or collisions with other celestial bodies.

Indonesian news outlets including detikInet and Kompas.com highlighted the rarity of such findings, noting that only a handful of ultra-low-density exoplanets have been documented since the first exoplanet was confirmed in 1992. The planets were initially flagged by citizen scientists participating in the Planet Hunters TESS project before being verified through follow-up observations by NASA’s Spitzer Space Telescope.

While the discovery raises intriguing questions about planetary evolution, astronomers caution that further study is needed to confirm their exact compositions. “These planets might be the remnants of a violent past,” suggested Shreyas Vissapragada, a research scientist at JPL. “Their low density could imply they were once much larger but lost significant mass due to tidal forces or collisions.”

The findings also prompt comparisons to other recent exoplanet discoveries, such as WASP-107b, another low-density gas giant whose atmosphere was found to contain water vapor and other molecules. However, TOI-4603.01 and TOI-4603.02 stand out due to their even lower densities, pushing the boundaries of what scientists previously thought possible for planetary structures.

For now, the discovery underscores the diversity of planetary systems beyond our own. As NASA continues to analyze data from TESS and upcoming missions like the James Webb Space Telescope, these “cotton candy” planets may offer new insights into how worlds form and evolve across the universe.

Why do these planets defy conventional models of gas giant formation? The two newly discovered exoplanets, TOI-4603.01 and TOI-4603.02, have densities as low as 0.05 grams per cubic centimeter—far lighter than any known planet, including Saturn. Unlike traditional gas giants, which form from dense cores that attract surrounding gas, these planets appear to have retained minimal mass relative to their size, challenging existing theories of planetary evolution.

How were these planets discovered, and what makes them unique?
The planets were identified using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and later verified through observations by the Spitzer Space Telescope. Their discovery was initially flagged by citizen scientists in the Planet Hunters TESS project. What sets them apart is their extreme low density—comparable to cotton candy—which suggests a composition unlike any other known exoplanet. Their mass-to-volume ratios imply they may be filled with hydrogen and helium, with a significant fraction of their volume occupied by a porous core, possibly made of rock or ice.

What remains uncertain about these “cotton candy” planets?
While the discovery is groundbreaking, astronomers emphasize that further study is needed to confirm their exact compositions and formation histories. Questions remain about whether their low density is due to rapid gas dissipation, tidal forces, or past collisions. NASA’s upcoming James Webb Space Telescope may provide deeper insights by analyzing their atmospheres and internal structures. For now, these planets serve as a reminder of the vast diversity of planetary systems beyond our solar system.

Comparing the new discoveries to other low-density exoplanets
While TOI-4603.01 and TOI-4603.02 are among the lightest known exoplanets, they join a small but growing category of ultra-low-density worlds. For example:

• WASP-107b: Discovered in 2017, this exoplanet has a density similar to that of styrofoam, with a significant fraction of its mass in a diffuse atmosphere.
• Kepler-51b, c, and d: These “super-puff” planets, found in 2012, have densities comparable to marshmallows, though they are less extreme than the newly identified TOI-4603 planets.
• HAT-P-1: Another low-density gas giant, though its density is closer to that of Saturn rather than the newly discovered worlds.

The TOI-4603 planets push these records further, suggesting that the universe may host even more exotic planetary structures than previously imagined.

What comes next for studying these planets?
NASA and international astronomers plan to use the James Webb Space Telescope to analyze the atmospheres of TOI-4603.01 and TOI-4603.02 in greater detail. Key questions include:

• Are their atmospheres primarily composed of hydrogen and helium, with traces of heavier elements?
• Do they have solid cores, or are they entirely gaseous with a porous structure?
• Could their formation process provide clues about planetary evolution in other star systems?

The findings also highlight the importance of citizen science in exoplanet discovery. The initial identification of these planets by volunteers in the Planet Hunters TESS project demonstrates how public participation can accelerate scientific breakthroughs.

As research progresses, these “cotton candy” planets may redefine our understanding of how worlds form—and how diverse they can be across the cosmos.