As ESA’s Hera mission for planetary defence departed its homeworld it looked back to Earth to show the Moon orbiting around it. In this sequence of images the terrestrial disc gradually shrinks as the spacecraft recedes away from it, and the Moon moving around Earth changes from a half to full Moon.

The images were acquired during the initial checkout of Hera’s Thermal Infrared Imager (TIRI) instrument, provided to the mission by the Japan Aerospace Exploration Agency, JAXA.

These thermal images of Earth and Moon thermal images were acquired by TIRI as it looked down obliquely from the north relative to lunar orbit. The distance between Earth to Hera spacecraft was about 1.4 million km for the first image acquired on 10 October to about 3.8 million km for the last image acquired on 15 October.

Launched on 7 October, Hera is ESA’s first planetary defence mission, on its way to visit the first asteroid to have had its orbit altered by human action. By gathering close-up data about the Dimorphos asteroid, which was impacted by NASA’s DART spacecraft in 2022, Hera will help turn asteroid deflection into a well understood and potentially repeatable technique.

One of a suite of instruments hosted on Hera's Asteroid Deck, TIRI will image Dimorphos in the mid-infrared spectral region to chart the temperature on the asteroid’s surface. By charting the 'thermal inertia' of surface regions – or how rapidly their temperature changes – physical properties such as roughness, particle size distribution and porosity can be deduced.

TIRI was manufactured for JAXA by Meisei Electric Co. Ltd. Its design is derived from a previous instrument onboard the agency’s Hayabusa2 asteroid mission.