Home Sciences The universe is the scene of great planetary heists

The universe is the scene of great planetary heists


Planet hijacking and theft is common in star-forming clusters and explains the orbital eccentricities of many celestial bodies. The hypothetical Planet Nine was surely abducted and brought into our solar system.

Astronomers have found, through complex computer simulations, that the theft of planets from other stars, or their capture from the interstellar medium, are common processes in star-forming regions or clusters.

They even believe that many of the known exoplanets in wide orbits, such as the hypothetical planet nine of our solar system, were orphaned planets long ago that were captured by their current systems. The results of this research have been published in the journal Monthly Notices of the Royal Astronomical Society.

To date, scientists know of many exoplanets whose orbits cannot be fully explained within the framework of current theories of star and planet formation.

In particular, dozens of planetary-mass candidate bodies with unusually large eccentricities and large orbital semi-axes have been discovered, some of them located as far as 2500 AU from their stars.

orphan planets

In addition, scientists know of orphan planets located in interstellar space and devoid of parent stars. They think that, in the case of the solar system in its outer part, it may be the case of the hypothetical Planet Nine, whose orbit is estimated to be very wide and is characterized by a great eccentricity and inclination with respect to the plane of other planets.

All these celestial objects could have arisen as a result of dynamic interaction with external bodies, during which some planets changed their orbit and others were expelled from the system: they would have either been captured by one planetary system after being ejected from another, or else they would have been displaced from one star to another, a situation which is known as planet heist.

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These dynamic interactions occur easily in environments with a high density of star systems, such as star-forming regions where many stars and planets originate. It is believed that our solar system could have formed in a relatively dense cluster containing between 100 and 1,000 stars.

Clarifying simulations

To delve into all these processes, a team of astronomers led by Emma C. Daffern-Powellfrom the University of Sheffield, has developed simulations of these planetary dynamics in star-forming regions.

The team used a simulation method used in physics and astronomy called N-bodywhich computationally replicates the behavior of a dynamic system of objects, usually under the influence of physical forces, such as gravity.

The researchers applied this method to replicate the dynamics of dense understructured star-forming regions, numbering 1,000 luminaries or suns, where half of the stars have Jupiter-mass planets located 30 to 50 km away. astronomical units of their respective stars, during a time period of 10 million years.

The objective of the work was to estimate the proportion of exoplanets that are abducted or stolen by other suns, moving them away from their parent stars, or captured by another planetary system from outside.

Common astronomical crime

The simulation revealed that the theft of planets by stars, or their capture by other planetary systems, is a relatively common occurrence: in this simulation, about two percent of the planets were stolen by other stars, while the same amount it was captured by other planetary systems.

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Scientists emphasize in this regard that the theft and capture of planets must be considered as two different mechanisms, although the majority of the thefts and seizures occur in the first periods of the evolution of the star-forming cluster, when the density of objects is maximum.

They found that small initial lengths of the planets’ orbital semi-major axes after 10 million years lead to more planets stolen than captured, while longer initial semi-axes lead to more planets captured than stolen.

Planet Nine, abducted

The scientists also concluded that the results of the simulations indicate that many of the planets found by direct imaging were captured in their current systems, but were previously orphaned planets.

In particular, if the length of the semi-major axis of the planet’s orbit is about 500 astronomical units, regardless of the initial conditions, it will be a captured planet.

Scientists suggest that the same conclusion extends to the Ninth Planet: if it exists, it was most likely captured, not stolen. That is, it would come from another planetary system from which it was abducted and taken to its current position in the confines of our solar system.


The great planetary heist: Theft and capture in star-forming regions Get access Arrow. Emma C Daffern-Powell et al. Monthly Notices of the Royal Astronomical Society, stac1392. DOI:https://doi.org/10.1093/mnras/stac1392

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