Lone Wanderers or Evicted Neighbors? New Study Tracks Rogue Planets' Origins

Imagine planets adrift in the vast emptiness of space, untethered to any star. These celestial nomads, called rogue planets or free-floating planets (FFPs), are a captivating enigma for astronomers. Their origins have been shrouded in mystery, but new research is shedding light on where they might come from and how they form.

This article dives into the fascinating world of rogue planets, exploring the two main formation theories and the latest simulations that provide clues to their birthplace.

There are two primary paths for FFP formation:

• Solitary Start: Some FFPs might form in isolation, collapsing from giant clouds of gas and dust without ever encountering a star.

• Ejected Refugees: Alternatively, FFPs could be exiles from established solar systems, flung out due to gravitational interactions with other planets or their host stars.

A recent study by Gavin Coleman from Queen Mary University of London focused on FFPs originating in circumbinary systems – those with two stars. His simulations suggest that these binary systems could be a prolific source of rogue planets.

The study demonstrates that planets within these systems can be ejected with significant velocities, much higher than those observed in lone-star systems. This velocity fingerprint could be a key to differentiating between the two formation pathways.

Coleman's simulations, based on the binary star system TOI 1338, showed that each system could eject an average of 2-7 planets with masses exceeding Earth's. The simulations also revealed that most ejections occur within the first 4 million years of a system's formation, before the surrounding disk dissipates.

The level of turbulence within the system's disk also plays a role. Lower turbulence leads to more frequent ejections, favoring smaller planets (less than 100 Earth masses).

Coleman's work paves the way for further exploration of FFPs. By analyzing their mass distribution, frequency, and velocity dispersion, astronomers can potentially determine whether they originated from single stars or binary systems.

Future telescopes like the Nancy Grace Roman Space Telescope will play a crucial role in this endeavor. This telescope will employ gravitational lensing to detect and characterize a broader range of FFPs, including those with Mars-like masses.

In the next phase of research, Coleman aims to investigate potential chemical composition differences between FFPs. This would provide insights into the types of stars they formed around and their location within the protoplanetary disk. Spectroscopic studies of FFPs will be essential for unraveling this chemical story.