Thermal images from the Hera mission recorded the asteroid Dimorphos cooling as it entered the shadow of its larger companion, Didymos. JAXA’s November 6 release presented observations acquired during October 28 and 29, 2026, along with subsequent images taken on October 31.
The observations came from Hera’s Thermal Infrared Imager, known as TIRI. The instrument measures thermal radiation emitted by asteroid surfaces, allowing it to observe areas illuminated by the Sun and areas in darkness.
Measuring Heat From Asteroid Surfaces
TIRI operates at wavelengths of approximately eight to 14 micrometers. This part of the infrared spectrum carries information about emitted heat. Its measurements differ from ordinary visible-light images, which primarily show sunlight reflected from a surface.
When Dimorphos enters Didymos’s shadow, direct solar heating stops on the affected areas. The resulting change in emitted thermal radiation allows researchers to examine how the surface responds as it cools.
Surface materials do not all warm and cool at the same rate. Their response depends on properties including how they store and conduct heat. Observations across a shadow passage provide information used to characterize those properties.
The October 31 images were acquired from a distance of approximately 57 kilometers. They added close-range thermal observations to the earlier cooling sequence.
Studying the DART Impact Target
Hera is the European Space Agency mission studying the Didymos system after NASA’s Double Asteroid Redirection Test, or DART, struck Dimorphos in 2022. The mission’s measurements examine the impact’s physical results and the properties of the two asteroids.
The spacecraft combines TIRI with other instruments described in ESA’s instrument overview. These instruments collect complementary information about shape, surface characteristics, and the surrounding environment. New Space Economy’s Hera mission overview explains the mission’s connection to DART.
The shadow observations add a time-dependent measurement to that investigation. They record how Dimorphos’s thermal emission changes during a specific event, providing evidence about its surface’s response to the removal of sunlight.
