Extremely young asteroid pair (458271) 2010 UM26 and 2010 RN221

Abstract

Aims. The extremely similar heliocentric orbital elements of the main-belt objects (458271) 2010 UM26 and 2010 RN221 make them the tightest known pair and hold the promise that it is very young. We analyzed the conditions of its origin and determined its age. Methods. We conducted dedicated observations of (458271) 2010 UM26 and 2010 RN221 in summer 2022 that resulted in a high-accuracy astrometric set of data. Joining them with the previously available observations, we improved the precision of the orbit determination of both asteroids. We used numerical simulations backward in time to constrain the origin of this new pair by observing orbital convergence in Cartesian space. Results. Using a large number of possible clone variants of (458271) 2010 UM26 and 2010 RN221, we find that they all converge in a narrow time interval around March 2003. They have extremely tight minimum distances (≤1000 km) and minimum relative velocities (≤3 cm s−1). These conditions require that the mutual gravitational attraction of the asteroids constituting the pair is included when its age is determined. Extending our model by this effect even improves the convergence results. We find a probability of more than 55% that the pair formed after 2000. However, quasi-satellite captures mean that the possible age uncertainty of this pair might extend to the 1960s. This is by far the youngest known asteroid pair, however. It is a prime target for future astronomical observations.