Browsing by discipline "Tähtitiede"

Near-Earth asteroids (NEAs) are celestial objects whose perihelion is distinctively in the inner Solar System. As these objects orbit the Sun mainly outside of the main belt, they are a separate category of asteroids. A fraction of these asteroids is especially interesting due to their small albeit existing impact probability with Earth. As acts of constant attention and interest toward NEAs, several probes have been sent to study the objects. Since the 1990s, astronomers have discovered moons orbiting asteroids. These asteroid moons also exist in the NEA population. A fraction of the primary components of binary asteroids rotates especially fast. A cause for the fast spin rates is the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect that affects the rotational period of irregularly shaped asteroids. Moreover, some asteroid moons may form due to the solar radiation phenomena of the YORP effect. Additionally, the Yarkovsky effect caused by thermal re-emission influences the orbits of NEAs over long time periods. A third potentially influencing solar radiation effect is the binary YORP (BYORP) effect, an explanatory theory for the relatively short life spans of asteroid moons. The thesis discusses NEAs, emphasizing binary asteroids, their formation, and observations. Ground-based equipment is used for a significant number of asteroid observations, making the fields interconnected. Optical telescopes and planetary radars offer diverse information on NEAs, whose discovery rates and orbital analysis have progressed prominently since the 1990s. As a case study of the observation methods, I discuss the ternary system (3122) Florence and its close encounter in September 2017 in the thesis.