Investigation of the dynamics and origin of the NEA pair 2021 PH27 and 2025 GN1

Abstract

We analyse the association between the NEAs 2021 PH27 and 2025 GN1, which share similar heliocentric Keplerian elements and the same taxonomic classification. First, we confirm the spectral similarity by getting independent colours measurements of 2025 GN1 and confirming that they are both X-type. From numerical integration of the orbits up to 100 kyr in the past, taking into account relativistic corrections, we found that the two asteroids experienced five similar flybys with Venus, but none of them were closer than the Roche limit. The perihelion distance also reached values between 0.1 and 0.08 au about 17/21 kyr and 45/48 kyr ago, but still well outside the Roche limit with the Sun. So, the origin of the pair by tidal disruption of a progenitor rubble-pile asteroid appears unlikely. On the other hand, we found periods lasting several thousand years where the perihelion was below 0.1 au, and this can lead to thermal fracturing of the surface. We found that the rotation period of the primary and the mass ratio secondary/primary make the pair indistinguishable from the binary systems known among the NEAs, and the YORP effect can double the rotation period of 2021 PH27 in $150 \pm 50$ kyr. So it is plausible that the pair was formed by the rotational disintegration of a rubble-pile asteroid due to anisotropic gas emission or the YORP effect, which formed a binary system that later dissolved due to the internal dynamics of the pair. We are unable to give a value for the separation age; we can only say that it occurred more than 10.5 kyr ago and may have occurred between 17/21 kyr ago during the last and longer phase of lower perihelion distance. In this scenario, little meteoroids released in space due to the fragmentation event are still near the pair's orbit and can generate a meteor shower in Venus' atmosphere.