NASA’s TESS Mission Reveals the “Puffiest” Planets Ever Found - UNIVERSE

This illustration depicts the Sun-like star TOI-791 and two giant planets that NASA's TESS space telescope discovered in its orbit. These planets, designated TOI-791 b and TOI-791 c, are roughly the size of Jupiter but a tiny fraction of its mass, meaning they have an extraordinarily low density. 

NASA / Daniel Rutter

Data from NASA’s TESS (Transiting Exoplanet Survey Satellite) mission has revealed two new “super-puff” planets, giant worlds so light that their density is comparable to cotton candy. Scientists calculate that these Jupiter-sized planets—named TOI-791 b and TOI-791 c—are the “puffiest” worlds ever found.

The planets orbit a Sun-like star named TOI-791 that is approximately 1,113 light years away from Earth. The TESS mission first detected the planets by watching for repeated dips in TOI-791’s brightness, a telltale sign that a planet is transiting, or passing in front of, a star. Further study revealed two large planets with unusual features.

TOI-791 b is nearly the same size as Jupiter but contains just 3.0 percent of Jupiter’s mass. TOI-791 c is even larger than Jupiter but contains just 5.9 percent of Jupiter’s mass.

“The main reason these planets are interesting to study is that we didn’t expect to see them at all,” said Jon Jenkins, the science lead for the Science Processing Operations Center at NASA’s Ames Research Center in California’s Silicon Valley, which provided the science-ready data from TESS analyzed in this study. “They represent a puzzle for us to solve about how giant planets like Jupiter and the super-puffs form.”

This graphic depicts the two giant planets orbiting the Sun-like star TOI-791 as compared to some of the planets in our solar system. These planets are roughly the size of Jupiter but a very tiny fraction of its mass. NASA's TESS mission detected the shadows of these planets as they passed in front of their star. There is no direct imaging. Therefore, the appearance of the TOI-79 planets in this illustration are an artist’s interpretation.

NASA / Daniel Rutter

The newly found super-puffs also have unusually long orbits, with TOI‑791 b taking 139 days and TOI‑791 c taking 232 days to circle the host star. Such long-orbit planets are rare to find, needing long durations of telescope observation to capture and confirm their attributes. From its vantage point in high Earth orbit, TESS was able to gather 1,122 days of data on this planetary system over the course of seven years, giving the research team a wealth of data about the planetary system.

Further analysis found that TOI-791 b and TOI-791 c are locked in an orbital pattern that allows them to tug on each other gravitationally. As they orbit their host star, the planets alternate pulling on each other, affecting the timing of their transits across the host star. Scientists used that variation in orbital timing to calculate the planets’ masses, cementing their status as low density super-puffs.  

“Only a handful of these super-puffy planets are known, and it is even rarer to find two in the same system,” said lead author George Dransfield of Oxford  University’s Department of Physics in Oxford, England. “Their extremely low densities make them fascinating targets for understanding how planetary systems form and evolve.”

With further study, the super-puffs may have more to tell us about planetary evolution.

“Large planet formation is believed to drive the evolution of a planetary system, so further study of these Jupiter-size, but far less than Jupiter-mass, planets is of high value,” said Steve Howell, a NASA Ames research scientist who was involved in this study.

Scientists hope to learn more about the chemical makeup of the planets’ atmospheres, how their spin affects their shape, and how the tilt of their host star compares to their orbits. Deeper investigation could provide new insight into how TOI-791 b and TOI-791 c migrated through the planetary system during their development, whether their orbits were shaped by interactions with other planets, and how low-density super-puff planets form.

The study, published today in the Monthly Notices of the Royal Astronomical Society, was led by the University of Oxford, in collaboration with Université Côte d’Azur/Observatoire de la Côte d’Azur and the University of Birmingham. 

Jun 24, 2026

Source: NASA's TESS Mission Reveals the “Puffiest” Planets Ever Found - NASA Science 

Greenland meltwater adds to AMOC weakening, but updated model finds no tipping point in sight - Earth - Earth Sciences - Environment

Credit: CC0 Public Domain

The state of the Atlantic Meridional Overturning Circulation (AMOC) has been a hot topic among climate scientists in recent years. The AMOC is crucial for climate regulation because it pulls warm surface water from the tropics north and sends colder, deeper water south, redistributing large amounts of heat, helping to sustain marine ecosystems and keeping global weather patterns steady. However, most standard AMOC-focused climate models may be missing an important piece of the puzzle—they don't include the growing pulse of freshwater from Greenland ice melt, which could further disrupt the AMOC.

But now, a study published in Science Advances has incorporated the freshwater influx from Greenland's ice melt into a new model. The results show that while the meltwater plays a significant role, it may not push the AMOC over the edge just yet.

To tip or not to tip?

Most climate models agree that the AMOC will continue to weaken this century, but the abrupt collapse that some models suggest remains debated. A recent Intergovernmental Panel on Climate Change (IPCC) model found that none of the Coupled Model Intercomparison Project phase 6 (CMIP6) models show an abrupt AMOC collapse during the 21st century.

Yet another recent study found that the Atlantic "cold blob" indicated a tipping point was nearing if conditions worsen. Earlier work has suggested that the Greenland meltwater contributes to the weakening of the AMOC, but it's been unclear whether that weakening would lead to an abrupt tipping point in which the AMOC collapses completely or is very difficult to reverse.

"However, it currently remains an open question whether these meltwater-induced AMOC changes are associated with tipping point characteristics such as abruptness and irreversibility. In addition, the physical mechanisms of how Greenland meltwater affects the AMOC beyond 2100 have, to our knowledge, not yet been explored," write the authors of the new study. 

AMOC reversibility in EC-Earth3. Credit: Science Advances (2026). DOI: 10.1126/sciadv.aed2633

Greenland's contribution to AMOC weakening

The researchers decided to integrate Greenland meltwater input into future projections with a state-of-the-art climate model to see how it would affect the AMOC as ice continues to melt. They used the CMIP6-class climate model EC-Earth3, run under a very high emissions scenario out to 2300. To isolate the contribution of the Greenland meltwater, they ran paired ensembles with and without added Greenland meltwater.

The model showed that Greenland meltwater does contribute significantly to weakening the AMOC, especially after 2100, but it didn't show an abrupt AMOC crash in the simulated period through 2300. The model indicated that AMOC weakening is roughly linear and scales smoothly with cumulative CO₂ emissions when meltwater is added, arguing against a classic tipping-style jump.

The study authors say, "In contrast to a nonsignificant effect during the historical period, we found a small but significant additional meltwater-induced AMOC weakening of about 1 sverdrup until 2100 (about 10% of the CO₂-induced weakening) and up to 4 sverdrups until 2300 (nearly 40% of the CO₂-induced weakening) under very strong forcing."

The team says that even under strong meltwater forcing, the AMOC persists. It becomes weaker and shallower rather than turning "off" entirely. They also note that the model's added weakening from Greenland meltwater is strongly tied to a future shift in AMOC "source regions" toward the Arctic, where meltwater-driven freshening strengthens stratification and suppresses mixing.

Can a weakened AMOC be reversed?

The researchers also questioned the reversibility of extreme AMOC weakening. They tested this reversibility using two idealized follow-up experiments: one in which CO₂ is ramped down after 2250 and a "meltwater reset," where extra meltwater is turned off. These tests suggested that the meltwater-driven changes are not irreversible on century timescales. Instead, the AMOC recovered in CO₂ ramp-down tests, even after large earlier meltwater input.

The study authors write, "Resetting the meltwater forcing under late-23rd-century conditions leads to a gradual recovery of the AMOC. After 200 years, the meltwater-induced AMOC anomaly at 40°N has decreased from −2.7 to −0.7 sverdrups compared to the reference simulation. The larger recovery rate in the meltwater simulation suggests that both simulations would eventually converge to the same equilibrium.

"The timescale of recovery is (multi)centennial, but it does not take 'significantly longer to recover from than the time it took to reach' in the spirit of the Global Tipping Points Report definition, as meltwater forcing has been applied over more than 200 years."

The team notes that the results are based on a single climate model, and other models may route meltwater differently or have different AMOC stability. They say that similar tipping-focused tests should be repeated across multiple climate models to see whether the non-abrupt and reversible result is robust. 

by Krystal Kasal, Phys.org

edited by Gaby Clark, reviewed by Robert Egan 

Source: Greenland meltwater adds to AMOC weakening, but updated model finds no tipping point in sight