Fewer than 40 such planets have been identified among the nearly 6,300 confirmed exoplanets.
Astronomers have detected two exoplanets orbiting the star TOI-791, located 1,110 light-years from Earth in the constellation Volans. Both planets are comparable in size to Jupiter but have extremely low densities, classifying them as "super-puffs."
Discovery and Detection
The planets, designated TOI-791b and TOI-791c, were first identified by citizen scientists participating in the Planet Hunters TESS project. The discovery was confirmed using data from NASA's Transiting Exoplanet Survey Satellite (TESS) over a period of 1,122 days. A team led by George Dransfield of the University of Oxford conducted the analysis, which was published in Monthly Notices of the Royal Astronomical Society.
Physical Characteristics
Both planets are Jupiter-sized but have masses significantly smaller than Jupiter's:
- TOI-791b: Nearly the size of Jupiter, with a mass approximately 3% of Jupiter's. Its density is 0.038 grams per cubic centimeter.
- TOI-791c: Larger than Jupiter, with a mass approximately 5.9% of Jupiter's. Its density is 0.047 grams per cubic centimeter.
For comparison, Jupiter has a density of 1.33 grams per cubic centimeter, and Earth has a density of 5.5 grams per cubic centimeter. The planets are between 28 and 35 times less dense than Jupiter, with densities comparable to cotton candy (approximately 0.05 g/cm³) and shaving foam. The planets are likely composed mostly of hydrogen and helium.
"The planets are between 28 and 35 times less dense than Jupiter, with densities comparable to cotton candy and shaving foam."
Orbital Dynamics
The two planets are in a 5:3 mean-motion resonance, meaning that for every five orbits of the inner planet, the outer planet completes nearly three. Their gravitational interaction causes detectable shifts in their transit timing, which allowed scientists to calculate their masses. The planets have longer-than-average orbital periods for exoplanets.
Observational Methods
Density measurements combined observations from telescopes worldwide, including:
- NASA's TESS satellite
- Multiple ground-based telescopes
- The ASTEP telescope in Antarctica, where the austral winter allowed uninterrupted observations of transits lasting over 11 hours.
Future Research
Researchers plan to use the James Webb Space Telescope to study the chemical composition of the planets' atmospheres, including the presence of carbon-, nitrogen-, and oxygen-bearing molecules. Additional research aims to investigate the effect of the planets' spin on their shape and the formation mechanisms of such low-density planets.
Key Researchers
- George Dransfield, University of Oxford (lead author)
- Tristan Guillot, Université Côte d’Azur (co-author)
- Amaury Triaud, University of Birmingham (co-author)
- Steve Howell, NASA Ames Research Center