Hera mission

Context: The European Space Agency’s (ESA’s) Hera mission is set for a new record by becoming the first spacecraft to explore a binary asteroid — the Didymos pair.

The moon orbiting Didymos, called ‘Didymoon’ — almost the size of the Giza Pyramid in Egypt, measuring just 160 metres in diametre — will be the smallest asteroid ever explored.

Double Asteroid Redirection Test (DART):

• On the sidelines, the National Aeronautics and Space Administration (NASA) in USA will also launch the Double Asteroid Redirection Test (DART) between 2020 and 2021, which will target Didymoon as part of its planetary defence programme.
• The programme, designed to protect Earth from dangerous comets and asteroids, aims to crash DART into Didymoon in 2022 to alter its orbit around Didymos.
• DART will deliberately crash itself into the moonlet at a speed of approximately 6 km per second, using an onboard camera and autonomous navigation software.
• The collision will change the speed of the moonlet in its orbit around the main body. Following the collision, Hera would explore the asteroid in 2026 and check the impact and deflection created by DART.

Why Didymoon?

Didymoon was chosen because of its close proximity to Earth and its size. Didymoon is small and in a tight enough 12-hour orbit around its parent, that its orbital period can indeed be shifted in a measurable way.

Didymos is a binary asteroid; the primary body has a diameter of around 780 m and a rotation period of 2.26 hours, whereas the Didymoon secondary body has a diameter of around 160 m and rotates around the primary at a distance of around 1.2 km from the primary surface in around 12 hours.

Sources: down to earth.