Space Heist: Chasing Stolen Planets

Title: The Great Planet Heist: Robbery and Capture in Star Forming Regions

Authors.: Emma C. Davern Powell, Richard J. Parker, and Sasha B. Cowans

First Author FoundationDepartment of Physics and Astronomy, University of Sheffield, UK

condition: Accepted by MNRAS [closed access]

a star forming regionIt is a region containing gas and dust with stars appearance Through collapsing small clouds, it can become crowded with stars. Crowded crowds are known to attract petty criminals and pickpockets Target valuables, especially planets. Stars, you better make sure your bags are zipped!

committing a crime

When the star is in the star forming region Encounters Another star that hosts a planet, can maliciously steal the planet. During the confrontation, two stars get close enough gravity affect each other. This gravitational effect can change the planet’s orbit, so that it ends up orbiting the other star. The frequency of encounters within the star-forming region is determined by several factors. One of them is the amount of stars present in the region, which is called stellar density. Another factor is abundance Infrastructure: Gas in star-forming regions is usually not uniformly distributed, but agglomerated and lumpyforming stunning landscapes as shown in Figure 1. How crowded an area or sub-area is in turn determines how often planets can be stolen.

Figure 1: The two star-forming regions of the Milky Way, NGC 3603 (left) and NGC 3576 (right), show amazing infrastructure. Image credit: ESO / G. Beccari

But why should we even care about stealing these planets so far away? The authors of today’s paper answer this question as follows: Stolen planets have different properties than planets still in the system in which they formed. This can help us determine whether or not the planet was stolen.


Use N-body simulationa simulation of tracking gravitational forces between multiple objects, the authors act as investigators by studying Tropical Characteristics of the planets. Tropical features include semi big which determines the distance from the star to the planet, and abnormalityand the Mile as a measure of the orientation of the orbit.

In order to compare characteristics, the authors categorized the planets into three groups: stolen planets, captured planets, and preserved planets. stolen Planets are defined as planets that originally orbited around one star and were transferred directly to another star during an encounter. captured However, planets are planets that have come out of their original star system and have been drifting in space for a while. Then they were caught by another star who randomly found the planet. In the process of drifting, they are summoned floating planets. Although planet-stealing and planet-capturing may seem like the same process, the authors note that they are actually two different mechanisms that may affect the resulting orbital properties differently. last group saved Planets, are planets orbiting their parent star, despite possible gravitational encounters with other stars. Can show some saved planets Variable orbital characteristicsthen they are sub-classified as disabled planets.

With the aim of investigating the influence of initial conditions on the outcome, the authors conducted several simulations. Each simulation contains a thousand stars within a star forming region. 500 planets are randomly assigned to stars, with half of the stars hosting a planet.

crime solving

Figure 2: How the number of stolen (blue) planets captured (yellow), preserved (gray) and free-floating (red) planets change in simulation over time. Each line corresponds to one simulation run. All simulations have the same initial conditions but slightly different results due to the stochastic nature of the setup. The first column of Figure 1 in today’s paper.

What are the characteristics of planets in the end? In their investigation, the authors of today’s paper found that capturing The planets are in much wider orbits than the stolen and preserved planets, and that stolen Planets usually have deviations greater than those conserved. This means that given both the semi-major axis and the eccentricity, we will be able to distinguish the origin of an observed planet. Using their results, they concluded that planets with semi-major axes larger than 500 AU are more likely to be captive planets. Figure 2 shows the amount of each type of planet over time.

The authors further investigate the effect of different initial conditions on the outcome. As one test, they run two nearly identical simulations, with the only difference being in one simulation, all planets are positioned with a semi-major axis of 30 au, while in the other they rotate with an interval of 50 au. The authors found in Figure 3 that the 30 au planets are stolen more than captured. On the other hand, the 50 au planets are more grabbed than stolen. They explain this phenomenon by the fact that planets with larger primary semi-major axes are less bound by gravity and therefore more prone to ejection. Thus, more floating planets occur and therefore more planets can be captured.

Figure 3: the number of stolen Planets greater than number capturing Those for planets initially at 30 au (dark blue), and lower for planets at 50 au (light blue). Figure 2 has been modified in today’s paper.

Further investigation of the initial conditions shows that the results are highly dependent on stellar density and infrastructure. Higher densities of stars lead to more frequent gravitational interactions and thus more planetary expulsion. Simulations with regions with more distinct substructures produce more stolen, liberated, and stolen planets. However, the resulting orbital properties remain similar in simulations regardless of the initial substructures.

There is also an ongoing debate about the ninth planet in our solar system – Planet 9. It hasn’t been proven yet, but it does pointers in favor of from the planet. If present, its semi-major axis is estimated to be 400-600 units. The authors of today’s paper argue with their findings that if there really is a planet, it is most likely a captured planet.

Today’s paper notes that planet theft and capture is very common in the universe. Solving these crimes can shed light on the origin of planets and planetary structures.

Astrobite Edited by Konstantin Gerbig

Featured Image Credit: NOAA and “Carmen Sandiego,” Netflix,

About Lina Kimmig

I am a first year PhD student working at the University of Heidelberg in the exciting field of planet formation. When planets form in protoplanetary disks found around most young stars, I investigate the effects of various physical processes on those disks. To investigate these effects, I run astrophysical simulations. My main interest is the 3D shaped twisted discs (a bit like Pringles chips). Away from searching, I love not only eating Pringles chips, but also dancing, sewing, skating, and elephants.