In 1902, Ivan Yarkovsky suggested that the daily heating of an object rotating in space could exert a small force on the object. We know how the temperature on Earth gets warmer and warmer as the Sun rises, hitting a maximum somewhere in the early afternoon. The same thing occurs on an asteroid. When the heated surface of Bennu points its hot afternoon side in the direction of its motion around the Sun - the escaping radiation acts like a tiny rocket thrust, slowing it down and sending it closer to the inner solar system. Although tiny, a little push day after day, year after year for hundreds of years can change an asteroid’s orbit significantly – transforming an Earth impactor into a close fly-by or a clean miss.
Back to "Why Bennu?".