Based on observations made with the James Webb Space Telescope of one of the best-known star-forming regions closest to Earth, a research group from the European Space Agency (ESA) has identified dozens of wandering planets, not linked to any star, and that form double systems.
Although the existence of orphan planets was already known, and is contemplated in theoretical models of planetary formation, the finding that these worlds can form pairs is surprising since there is currently no sufficiently satisfactory explanation for this. The study is pending publication in the journal Nature.
The Orion Nebula is an enormous birthplace of stars that, in relatively recent times, has given birth to a large number of suns of all types, including very massive stars, stars similar to our Sun and red dwarfs.
In this nebula, especially in its central area (called the Trapezium), numerous non-stellar objects have also been detected, among which are brown dwarfs (bodies with masses greater than 13 times that of Jupiter but not enough to initiate the nuclear fusion of hydrogen and becoming stars) and other minor ones, compatible with planets not linked to any star.
Rogue planets appear to be very abundant in the universe. In fact, a study carried out by NASA and Osaka University in Japan suggests that free planets could even be more numerous in our galaxy than those linked to star systems.
But detecting these solitary planets is very complex. They emit light simply because they are hot and not because they are illuminated by any sun, and their luminosity, already low, is reduced even more with the passage of time and progressive cooling. Furthermore, objects with masses less than about 3 planets of Jupiter emit even weaker and essentially in the infrared light range.
Therefore, the use of the capabilities of the James Webb, with its instruments sensitive precisely to these radiation frequencies, is essential for the study and characterization of these bodies. On the other hand, the Orion Nebula is a perfect laboratory thanks to the extensive population of young objects formed in the last two million years.
The study, focused on observations made by James Webb between September 26 and October 2, 2022 and which have totaled 34.9 hours of data collection from the Trapezium area of ??the Orion Nebula, has found 540 wanderer planet candidates. By analyzing the light emitted by these bodies (specifically, from the analysis of the light spectrum and its comparison with theoretical models) it has been possible to deduce their approximate masses, which cover a very diverse range that reaches up to the observed minimum of 0, 6 times the Jovian mass (equivalent to 2 times that of Saturn).
In general, when astronomers arrange celestial bodies that form multiple systems (composed of two or more objects linked by gravity and orbiting the common center of mass), they conclude that the probability of existence of these systems decreases with mass. of the objects. Thus, for massive stars it is found that the majority of them form pairs, while the proportion of binary systems is reduced to 50% for solar-type stars, and to only 8% for brown dwarfs. Based on this trend, smaller objects would be expected to have a very low probability of forming multiple systems.
However, among the population of 540 wandering planets detected in the Trapezium of the Orion Nebula, 40 binary and 2 triple systems have been found, a surprisingly high result that cannot be explained with existing theoretical models.
The multiple planetary systems discovered by the study span a wide range of separation between the two components of the system, distances ranging from 25 to 390 astronomical units (one astronomical unit is equivalent to the average distance between the Earth and the Sun). Although these values ??are clearly higher than those observed for binary systems formed by brown dwarfs (which show separations centered on the 4 astronomical units), the authors of the study warn that the sensitivity of the observations made with the James Webb does not allow the detection of separations less than 25 astronomical units.
Regarding the masses of the components of the binary systems analyzed, a clear similarity is observed between the two planets that form each pair. Specifically, the study indicates that a large proportion of these systems are made up of planets of almost identical mass.
To explain the existence of wandering planets, astronomers turn to two possible scenarios. The first of them is based on the operation of processes very similar to those that form complete star systems. That is, the fragmentation and gravitational collapse of disks of material. But this mechanism, according to current theoretical models, can generate planets at least 3 times the mass of Jupiter although not lighter.
The alternative scenario is based on the possibility that some planets, formed in star systems, are expelled into interstellar space due to gravitational interactions with other planets or even with neighboring stars. This assumption would be perfectly plausible in the Trapezium area of ??the Orion Nebula because of the high density of stars in the region.
However, the probability that one of these ejected planets would find a companion in similar conditions and form a linked system is minimal. Likewise, the mechanism that would make it possible for two planets to be ejected at the same time and remain linked is not clear, as the authors point out in their study.
The conclusion of the publication is that new models and simulations will be required to understand how large populations of linked wanderer planets can form in multiple systems.
