Free-floating planets (FFPs) are a fascinating and relatively new field of study in astronomy. These objects are essentially orphaned planets, unattached to any star, that are thought to have been ejected from their original planetary systems. In this blog post, we will delve into the latest research on FFPs, including their origin, how they are detected, and what the future holds for studying them.
Firstly, it is important to understand the context in which FFPs are formed. Stars, brown dwarfs, and planets are all thought to form in groups that share the same properties as their parent molecular clouds. These objects can be identified and studied using techniques such as spectroscopy and age tagging. FFPs are the lightest products of star formation and carry important information on the initial conditions of the environment in which they were formed.
The origin of FFPs is still not fully understood, but recent research has shed some light on the subject. One theory is that they are formed in planetary systems that are later abandoned. Several studies indicate that the observed fraction of FFPs outnumbers the prediction of turbulent fragmentation, which is the driving mechanism for star formation. This suggests that many FFPs may have been ejected from planetary systems due to dynamical instabilities in the system, caused by interactions with other bodies in the same system or due to the close passage of an external star.
The detection of FFPs is a challenging task, but recent advances in technology have made it possible to identify these objects. The James Webb Space Telescope (JWST), set to launch later this year, is expected to make a significant contribution to our understanding of FFPs and the early stages of their formation. However, even with the help of the JWST, detecting and characterizing FFPs will still be a difficult task. Spectroscopy is a commonly used technique to confirm the existence of FFPs. By comparing their spectra to young and field M and L-dwarf standards, astronomers can confirm their identity as young ultracool objects.
Recent studies have identified 70-170 FFPs in the Upper Scorpius and Ophiuchus star-forming regions, 16 of which have been confirmed with spectroscopy. This has helped to measure a very low contamination rate of less than 6% on the initial sample. However, discrepancies of up to 50% in age tagging techniques can cause inaccuracies in the identification of FFPs. Therefore, precise ages for nearby star-forming regions in which they were formed will be necessary to accurately interpret new observations.
Comparing the observational mass function in Upper Scorpius and Ophiuchus with the mass function from different sets of simulations, researchers found an excess of observed FFPs by a factor of up to seven. This suggests that not all FFPs form as low-mass stars and brown dwarfs, but a significant fraction may have been ejected from planetary systems. This excess of observed FFPs indicates that the turbulent fragmentation theory may not be the only driving mechanism for star formation.
In addition to the mass function, other properties such as the disc and binary fraction can help to compare observations and simulations. Measuring these properties in brown dwarfs and FFPs is essential to test whether they have similar properties as low-mass stars, indicating a similar formation mechanism, or whether they are very different, suggesting that discs and companions may be perturbed as a result of an ejection process.
The FFPs are an exciting and relatively new field of study in astronomy. They carry important information about the early stages of star and planet formation and shed light on the mechanisms that drive star and planet formation. While recent research has made significant strides in the detection and identification of FFPs, there is still much to discover.
Source: Miret-Roig, N. (2023). The origin of free-floating planets. https://doi.org/10.48550/arXiv.2303.05522