Video Observations of Tiny Near-Earth Objects with Tomo-e Gozen

TL;DR

This study used video observations to analyze tiny near-Earth objects, discovering fast rotators and a truncation in their rotational period distribution, suggesting a new YORP effect dependence.

Contribution

First to systematically observe tiny NEOs with high temporal resolution, revealing their rotational properties and proposing a novel explanation involving the tangential YORP effect.

Findings

Discovered 13 fast rotators with periods less than 60 seconds.

Identified a truncation in the D-P distribution around 10 seconds.

Proposed tangential YORP effect as an explanation for the observed pattern.

Abstract

We report the results of video observations of tiny (diameter less than 100 m) near-Earth objects (NEOs) with Tomo-e Gozen on the Kiso 105 cm Schmidt telescope. A rotational period of a tiny asteroid reflects its dynamical history and physical properties since smaller objects are sensitive to the YORP effect. We carried out video observations of 60 tiny NEOs at 2 fps from 2018 to 2021 and successfully derived the rotational periods and axial ratios of 32 NEOs including 13 fast rotators with rotational periods less than 60 s. The fastest rotator found during our survey is 2020 HS7 with a rotational period of 2.99 s. We statistically confirmed that there is a certain number of tiny fast rotators in the NEO population, which have been missed with any previous surveys. We have discovered that the distribution of the tiny NEOs in a diameter and rotational period (D-P) diagram is truncated around a period of 10 s. The truncation with a flat-top shape is not explained well either by a realistic tensile strength of NEOs or suppression of YORP by meteoroid impacts. We propose that the dependence of the tangential YORP effect on the rotational period potentially explains the observed pattern in the D-P diagram.