New insights into asteroid properties: A STEP Grant update

One of the first recipients of The Planetary Society’s STEP (Science and Technology Empowered by the Public) Grant program was a project to better understand near-Earth asteroids. This year, that project achieved its main goals and scientific objectives.  

In 2022, The Planetary Society awarded a $44,842 grant to a team from the University of Belgrade, Serbia, led by Professor Bojan Novaković, for their proposal “Demystifying Near-Earth Asteroids.” This project aimed to develop and apply a new method for determining the physical properties of asteroids with orbits that come close to Earth’s orbit (also called near-Earth asteroids, or NEAs). Although tens of thousands of NEAs have been found, we only know the physical properties of a small percentage — from solid rock asteroids to collections of boulders to fluff balls. 

Over the course of their two-year project, Novaković’s team introduced an innovative tool named the Asteroid Thermal Inertia Analyzer (ASTERIA) to measure how well asteroids retain heat, giving insight into their composition and structure. 

Unlike traditional thermo-physical modeling-based methods that involve complex calculations, ASTERIA simplifies the process using a random sampling approach to predict the thermal inertia based on how asteroids drift over time due to the Yarkovsky effect — a subtle force acting on rotating bodies in space caused by the emission of thermal photons. ASTERIA is especially useful for smaller asteroids, where traditional models struggle because they do not have enough data. 

The project team tested ASTERIA on the well-studied asteroid Bennu and 10 other near-Earth asteroids. Their results were consistent with previous findings from other methods, validating the ASTERIA method while also proving it as a useful way of independently confirming findings from other techniques in the future. 

One particular part of the project focused on the asteroid Didymos and its moonlet Dimorphos, which was the target of NASA’s DART mission. When the DART spacecraft intentionally impacted Dimorphos in September 2022, it proved an asteroid deflection technique and in doing so, turned Dimorphos into an "active asteroid," ejecting debris that may have settled on both the moonlet and its host asteroid. 

Novaković’s team examined Didymos' thermal inertia before and after the impact, using ASTERIA to assess how Didymos' ability to retain heat might have shifted due to the reaccumulation of debris generated by the collision. The results suggested that Didymos' thermal inertia either remained the same or changed only slightly, below the threshold that their methodology could detect. These findings shed light on the question of how collisions might have altered the surfaces of these space rocks and add to the overall understanding of the thermal inertia of near-Earth asteroids. 

This project, made possible by the support of The Planetary Society and our members, represents an important step forward in the global effort to understand asteroids that could someday pose a threat to our planet.