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Close-Up Imaging and Study of Planets
Importance of Close-Up Imaging in Planetary Exploration
Close-up imaging has proven to be an essential tool in the exploration of outer planets and their satellites. This method allows for the discovery of atmospheric phenomena that are beyond the reach of terrestrial laboratories and intuition. For instance, photography of Jupiter from terrestrial telescopes has revealed unexpected features, and close-up imaging from fly-bys and orbiters has the potential to uncover even more1. The study of cloud structures, both horizontal and vertical, as well as their motions and time changes, is crucial for understanding atmospheric circulation. Additionally, the size and composition of cloud particles can be determined through imaging and photo-polarimeter experiments1.
Orbital Obliquity of Close-In Planets
The orbital obliquity of close-in planets, particularly massive ones, is a significant parameter for understanding the architecture of planetary systems. Studies have shown that the Rossiter-McLaughlin effect can be used to measure the orbital obliquity of transiting exoplanets. For example, the GAPS project has provided new insights into the orbital obliquity of three close-in giant planets: WASP-43 b, HAT-P-20 b, and Qatar-2 b. These planets orbit dwarf K-type stars and exhibit varying degrees of alignment and obliquity2. Such measurements are crucial for distinguishing between different scenarios proposed to explain the existence of close-in giant planets.
Occurrence and Mass Distribution of Close-In Planets
Recent studies have focused on the occurrence and mass distribution of close-in planets, including super-Earths, Neptunes, and Jupiters. Observations suggest that about 23% of Sun-like stars may harbor a close-in terrestrial-mass planet. Contrary to theoretical models, there is no shortage of planets with masses between 5 to 30 times that of Earth, indicating that these models may need revision3. This finding is essential for understanding how planets form and evolve.
Formation Mechanisms of Close-In Planets
The formation of close-in planets, such as hot Jupiters, can occur through various mechanisms, including mutual scattering, the Kozai effect, and tidal circularization. N-body simulations have shown that about 30% of close-in planets form through these processes, with some retaining non-negligible eccentricities and high inclinations4. Additionally, different models for forming hot Earths, such as in situ accretion and inward migration, produce unique observable signatures that can be distinguished through current and upcoming missions5.
Characteristics of Close-In Giant Planets
The discovery of transiting close-in giant planets, such as HD 209458b, has provided valuable data on their radii and masses. These planets are typically hydrogen-rich gas giants, and their large radii are not due to atmospheric thermal expansion but rather to high residual entropy from their early proximity to a luminous primary star. This suggests that such planets either formed near their current orbital distances or migrated inward shortly after their formation6.
Conclusion
Close-up imaging and the study of close-in planets have significantly advanced our understanding of planetary systems. From revealing atmospheric phenomena on outer planets to determining the orbital obliquity and mass distribution of close-in planets, these methods provide critical insights into planet formation and evolution. As technology and observational techniques continue to improve, we can expect even more discoveries that will further our knowledge of the cosmos.
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Most relevant research papers on this topic
Imaging of the outer planets and satellites
Imaging is the most effective method for exploring the outer planets and their satellites, offering opportunities for discovery of atmospheric phenomena beyond terrestrial laboratories and intuition.
The GAPS Programme with HARPS-N at TNG XIII. The orbital obliquity of three close-in massive planets hosted by dwarf K-type stars: WASP-43, HAT-P-20 and Qatar-2
The orbital obliquity of WASP-43 b and HAT-P-20 b is aligned with their host stars, while Qatar-2 shows a small but significant obliquity.
The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters
23% of Sun-like stars harbor a close-in Earth-mass planet, indicating that planet formation models need revision, and suggesting that the predicted deficit of planets with masses 5 to 30 times that of Earth is well populated.
Highly CitedORBITAL DISTRIBUTIONS OF CLOSE-IN PLANETS AND DISTANT PLANETS FORMED BY SCATTERING AND DYNAMICAL TIDES
Close-in planets can form by a combination of mutual scattering, Kozai effect, and tidal circularization, with up to 29% having retrograde orbits and small eccentricities.
Highly CitedObservable consequences of planet formation models in systems with close-in terrestrial planets
Tidal circularization and photoevaporation can form hot Earths in close-in systems, with unique observable signatures in planetary system architecture and bulk composition.
Highly CitedOn the Radii of Close-in Giant Planets
Close-in gas giant planets have large radii due to high residual entropy from early proximity to a luminous primary, not thermal expansion of their atmospheres.
Highly CitedA space telescope for infrared spectroscopy of Earth-like planets
A 16m diameter space telescope could image and measure oxygen in thermal infrared spectra of Earth-like planets up to 4pc away, potentially detecting life on nearby stars.
Highly CitedGround-based imaging of extrasolar planets using adaptive optics
Adaptive optics in large ground-based telescopes can potentially detect extrasolar planets orbiting nearby stars, overcoming the technical challenge of detecting them against background light from nearby stars.
Highly CitedThe HARPS-N Rocky Planet Search. I. HD 219134 b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun
HD219134b, the nearest known transiting planet, is a rocky planet in a multi-planet system at 6.5 pc from the Sun, with a mean density of 5.89 g/cc.
Highly CitedThe Stability of Multi-Planet Systems
Multi-planet systems with 10 planets are unstable due to energy and angular momentum conservation being disrupted by additional planet(s).
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