Outter planets
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Outer Planets: Discoveries and Insights
Discovery of Outer Planets in Exoplanetary Systems
Kepler-47 System: Multiple Transiting Planets
The Kepler-47 system is unique among the nine confirmed transiting circumbinary planet systems, as it contains more than one planet. The system includes three planets: Kepler-47 b, Kepler-47 c, and the newly discovered Kepler-47 d. The outermost planet, Kepler-47 c, has an orbital period of 303.2 days and a radius of about 4.7 Earth radii (R⊕)3. The discovery of the middle planet, Kepler-47 d, with an orbital period of 187.4 days and a radius of about 7 R⊕, has allowed for better constraints on the masses of all three planets. The outer planets in this system have low bulk densities, suggesting gentle migration in the protoplanetary disk3.
HR 8799 System: Imaging of Giant Planets
High-contrast near-infrared imaging has revealed four giant planets orbiting the nearby star HR 8799. These planets have wide orbits greater than 25 astronomical units (au) and are still hot and bright due to their youth, being less than 100 million years old. The discovery of a fourth planet, similar in mass to the other three, challenges current planet formation models, as none can fully explain the in situ formation of all four planets. This system, with its young giant planets and known cold/warm debris belts, provides a unique laboratory for studying the formation and evolution of giant planets at wide separations4.
Outer Planets in the Solar System
Search for Distant Solar System Objects
Beyond the giant planets of our solar system lies a collection of bodies left over from planet formation. A deep narrow survey using data from the Outer Solar System Origins Survey (OSSOS) aimed to find objects beyond 300 au. Despite the extensive search, no slow-moving solar system objects were found. This null detection allowed researchers to place a 95% upper limit on the number of dwarf planets in the distant solar system, estimating fewer than 1100 such objects5.
Conclusion
The study of outer planets, both in exoplanetary systems and within our own solar system, continues to provide valuable insights into planetary formation and evolution. The discoveries in systems like Kepler-47 and HR 8799 highlight the diversity and complexity of planetary systems, while the search for distant solar system objects helps refine our understanding of the outer reaches of our own planetary neighborhood. These findings underscore the importance of continued observation and exploration to unravel the mysteries of outer planets.
Sources and full results
Most relevant research papers on this topic
A Mini-Neptune and a Radius Valley Planet Orbiting the Nearby M2 Dwarf TOI-1266 in Its Venus Zone: Validation with the Habitable-zone Planet Finder
The TESS mission confirms two planets orbiting the nearby M2 dwarf TOI-1266, with the inner planet being sub-Neptune-sized and the outer planet in the exoplanet radius valley, receiving 2.4 times the insolation of Venus.
A 1.55 R⨁ habitable-zone planet hosted by TOI-715, an M4 star near the ecliptic South Pole
TOI-715 b, a 1.55 R habitable-zone planet orbiting its M4 host, is within the most conservative definitions of the habitable zone for rocky planets.
Discovery of a Third Transiting Planet in the Kepler-47 Circumbinary System
Kepler-47 d, a third planet in the Kepler-47 system, allows for better constraints on the masses of all three planets, suggesting gentle migration in the protoplanetary disk.
Images of a fourth planet orbiting HR 8799
The presence of a fourth planet in the HR 8799 system challenges current planet formation models, offering a unique laboratory for studying the formation and evolution of giant planets at wide distances.
Highly CitedThe search for slow moving planets in the distant solar system
No slow-moving solar system objects were found, but a 95% upper limit on the number of dwarf planets (-3 > H > 2) was established, indicating a 95% probability of 1100 800 dwarf planets beyond several hundred au.
The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf
Three terrestrial-size planets have been discovered orbiting a nearby M dwarf, offering a unique opportunity to study planetary system dynamics and evolution.
Highly CitedEvolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458
Irradiation effects can significantly affect the radius of sub-jovian mass giant planets, but alone cannot explain the large observed radius of HD 209458b.
Highly CitedDirect Imaging of Multiple Planets Orbiting the Star HR 8799
Three planets orbiting the star HR 8799 have been identified, with masses between 5 and 13 times that of Jupiter, indicating a scaled-up version of our solar system.
Highly CitedSYNTHESIZING EXOPLANET DEMOGRAPHICS: A SINGLE POPULATION OF LONG-PERIOD PLANETARY COMPANIONS TO M DWARFS CONSISTENT WITH MICROLENSING, RADIAL VELOCITY, AND DIRECT IMAGING SURVEYS
This study synthesizes results from five different exoplanet surveys, providing a comprehensive picture of large-separation (2 AU) planet demographics consistent with microlensing, radial velocity, and direct imaging surveys.
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