A kinematical age for the interstellar object 1I/’Oumuamua

Abstract

1I/'Oumuamua is the first interstellar object observed passing through the Solar System. Understanding the nature of these objects will provide crucial information about the formation and evolution of planetary systems, and the chemodynamical evolution of the Galaxy as a whole. We obtained the galactic orbital parameters of this object, considering 8 different models for the Galaxy, and compared it to those of stars of different ages from the Geneva-Copenhagen Survey (GCS). Assuming that the galactic orbital evolution of this object is similar to that of stars, we applied a Bayesian analyses and used the distribution of stellar velocities, as a function of age, to obtain a probability density function for the age of 'Oumuamua. We considered two models for the age-velocity dispersion relation (AVR): the traditional power law, fitted using data from the GCS; and a model that implements a second power law for younger ages, which we fitted using a sample of 153 Open Clusters (OCs). We find that the slope of the AVR is smaller for OCs than it is for field stars. Using these AVRs, we constrained an age range of 0.01-1.87 Gyr for 'Oumuamua and characterized a most likely age ranging between 0.20-0.45 Gyr, depending on the model used for the AVR. We also estimated the intrinsic uncertainties of the method due to not knowing the exact value of the Solar motion and the particularities of 1I/'Oumuamua's ejection.

Interstellar Objects in the Solar System: 1. Isotropic Kinematics from the Gaia Early Data Release 3

“…7.1. Type 1 Objects: ISOs from the Thin Disk Galactic velocity dispersions tend to increase with time, which can be used to estimate "kinematic ages" and was used to conclude that 1I is a relatively young object, with a kinematic age of ∼0.20 to 0.45 Gyr (Almeida-Fernandes & Rocha-Pinto 2018;Hallatt & Wiegert 2019). Siraj & Loeb (2020) discussed (using a simple gaussian kinematic model for stellar velocities) the broadening of the ISO velocity distribution by the ISO velocity at ejection from their originating stellar system (the outgoing v ∞ ), which could potentially be as large as 50 km s −1 for eject of objects by a rapidly orbiting M dwarf planet in its habitable zone.…”

Dust bombardment can explain the extremely elongated shape of 1I/’Oumuamua and the lack of interstellar objects

“…The time it takes an asteroid to change its shape to an 1I like axis ratio ranges from millions to a couple of billion years (see Fig. 3), which is reasonable taking into account that the planetary system 1I originated from is most likely not in the Solar neighborhood (Mamajek 2017;Almeida-Fernandes & Rocha-Pinto 2018). It should be noted that the required time for slightly change of the asteroid shape (to erode 1 mm of the surface) are about 10 years in the "b)" case and from 3000 to 100000 years in the "a)" case.…”

“…According to the latest research 'Oumuamua has a distant extrasolar origin and has been traveling in interstellar space for a long time (Mamajek 2017;Almeida-Fernandes & Rocha-Pinto 2018). Throughout this journey, the asteroid must have encountered gas molecules and interstellar dust grains at high relative speeds.…”

The Natural History of 'Oumuamua

“…'Oumuamua's random velocity is 9 km s −1 from the Local Standard of Rest, far smaller than the ∼50 km s −1 velocity dispersion of nearby stars 59 . This small random velocity could imply that 'Oumuamua is dynamically young 1 , with a statistically-derived dynamical age of <2 Gyr 60,61 .…”