2024-09-27 09:45:35
An international team of astronomers has discovered the “Neptune ridge”, a new structure in the distribution of exoplanets. This result shows the complex processes that take place in the “Neptune desert” (a region with a scarcity of Neptune-like exoplanets close to its stars) and the “Neptune savannah” (a more distant region where these planets are found more often). frequency). This research provides valuable information on the dynamical and atmospheric processes that govern the evolution of Neptunian exoplanets in close orbits.
This study was led by the Center for Astrobiology (CAB), a joint entity of the High Council for Scientific Research (CSIC) and the National Institute of Aerospace Technology (INTA), in Spain. The universities of Geneva in Switzerland, Warwick in the United Kingdom, Coimbra in Portugal and Paris in France also collaborated.
To study the vast population of exoplanet systems, researchers analyze the distribution of known planets based on, for example, their radius and orbital period. As the number of detections increases, this distribution shows new patterns and peculiarities that astronomers are trying to understand and whose origins are closely related to the processes of formation and evolution of the planets. One of the most barren regions is the “Neptune desert”, where there are few Neptune-sized planets orbiting close to other stars. This scarcity of hot exoplanets is believed to be the result of intense stellar radiation, which would erode their atmospheres to the point of complete elimination, turning these planets into iron spheres and planetary rocks. Beyond this inhospitable wilderness lies the “Neptunian Savannah,” a region further away from the intense stellar radiation where Neptunian planets are most often found. In this region, environmental conditions are more favorable and allow the planets to maintain their original gaseous cover for millions of years.
One of the most relevant questions in exoplanet research is how and when these exoplanets reached the close orbit where they are found today, since theories of planetary formation suggest that these giant planets formed much longer, over the desert and Savannah, in an orbit similar to that of Jupiter and Saturn in relation to the Sun.
Therefore, understanding how the desert and Savanna were populated is a critical question in explant research.
Neptune, photographed by the Voyager 2 space probe (Photo: NASA JPL)
The exoneptunian mountain range
The new study focuses on the transition between Neptune’s desert and savanna. The authors of this work found an unexpected concentration of planets on the edge of the desert, which creates a sharp separation between the two realms, a feature they called the “Neptunian mountain range”.
“We found that a large number of Neptunian planets orbit their stars with orbital periods between 3.2 and 5.7 days. We estimate that the probability of finding a planet in this region is about 8 times greater than finding it at shorter distances (in the desert), and about 3 times more than finding it at longer distances ( in the savanna), which “suggests that these planets were subject to specific processes that brought them to this orbital region,” explains Amadeo Castro-González, INTA pre-doctoral fellow at the Center for Astrobiology (CAB), INTA-CSIC , and lead author of this study.
Discovery of the Cordillera: Methods and Tools
The discovery was made thanks to the analysis of data from NASA’s Kepler space mission that was corrected for observational biases using advanced statistical techniques. The researchers carefully mapped the relationship between the radius and period of these exoplanets, revealing distinct regions that define the new Neptune landscape. This comprehensive mapping shows the complex processes of atmospheric migration and evaporation on these planets.
“The quality and systematicity of the observations of the Kepler mission were decisive in being able to carry out this study, as well as the efforts to monitor its planets from the ground, to which the Center for Astrobiology has dedicated significant efforts to in recent years, ” comments Jorge Lillo-Box, co-author of the study.
Implications for planetary formation and evolution
The authors of the study have presented the results in the context of the theories regarding the formation and evolution of the planets and they conclude that the accumulation of the planets in the mountain range of Neptune could be interpreted by the existence of two migration mechanisms that would put the mountain range and savanna on a different way.
“Current observational evidence suggests that a significant fraction of the planets in the mountain range may have come from their birthplace through a mechanism called high-escape tidal migration, which can bring planets closer to their stars at any stage of their lives. “On the contrary, the planets in the savanna could have been brought mainly by another type of migration, called disk-driven migration, which occurs immediately after the formation of the planets,” explains Vincent Bourrier, researcher at the University of Geneva and co-author of the study.
“It is likely that these migration processes, together with the evaporation of the planetary atmospheres, shape the various features observed in the Neptunian landscape,” concludes Vincent Bourrier.
Ambitious Observation Programmes
To further unravel the mysteries of Neptune’s landscape, various observing programs are underway. The HARPS-NOMADS collaboration, an observing program led by David J. Armstrong — a researcher at the University of Warwick and co-author of this study — is using the European Southern Observatory’s (ESO) HARPS high-resolution spectrophotograph to search for new planets in the desert, in the mountain range and in the Neptune Savannah with the final objective of making statistical studies of their properties. Some of these new planets will be monitored with the ESPRESSO high-resolution spectrograph, also from ESO, in the context of the ATREIDES collaboration, led by Vincent Bourrier. The aim of this program is to make a comprehensive census of the orbital orientation of the planets, which depends on the migration process, and will therefore provide relevant information regarding the formation and evolution of the Neptune planets as a whole.
“These future observation programs will be completed by new mass searches of planetary systems, such as those carried out by the European Space Agency’s PLATO space telescope, and in which Spain and the CAB have invested a large amount of resources,” explains David Barrado, co-author the study too.
“The discovery of the Neptunian mountain range is a paradigm shift in the understanding of one of the most relevant questions in current exoplanet exploration,” said Jorge Lillo-Box; and “opens a new door to our understanding of the origin and formation of planets like our Neptune,” concludes Amadeo Castro-González.
The title of the study is “Mapping the exo-Neptunian landscape.” And it has been published in the academic journal Astronomy & Astrophysics. (Source: CAB)
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