The Orbit Determination and Impact Monitoring system of the ESA NEO Coordination Centre, also known as Aegis, underwent a big update about one year ago. Since then, the Risk Assessment team at the NEOCC has been working to develop new automated services to make available to users.

One of the most important upgrades introduced in the system is an automated algorithm to identify NEOs whose dynamics are affected by the Yarkovsky effect. This effect is a non-gravitational force typically noticeable on small asteroids. This tiny force is caused by sunlight, which is absorbed by the asteroid surface and then re-emitted away as heat, causing a small but continuous thrust that subtly perturbs the orbit of small celestial bodies. This effect, which is inversely proportional to the object size (see figure), causes the semi-major axis of an NEA to drift, leading to significant positional uncertainties over time.

Understanding the Yarkovsky effect is important for several reasons: for accurate orbital predictions and reliable impact hazard assessment of NEAs, to get insights about the physical composition of asteroids, and to better understand the formation of asteroid families.

With the new algorithm we introduced, data about the Yarkovsky effect on NEAs will be updated after every monthly release of the Minor Planet Center, ensuring a continuous availability of the most recent data to users through our portal. A complete description of the procedure can be found in the corresponding paper published in Astronomy & Astrophysics. Up to now, our portal shows more than 340 positive detections of the Yarkovsky effect. This number is expected to grow in the next years with the beginning of the operational phase of new high-technology observational surveys, such as the Vera Rubin Observatory and the ESA Flyeye Telescope.

Caption: Diameter vs. Yarkovsky semi-major axis drift for all the detections with signal-to-noise ratio larger than 3. Black and green dots are NEAs for which the detection is accepted. Black dots are those objects for which the diameter is known, while green dots are those for which the diameter is only estimated by the physical model. Red dots are detections that are considered spurious by the algorithm, thus discarded. The blue dashed line is a linear fit of the data, which is completely compatible with the predicted 1/D trend with the diameter. Credits: ESA / PDO.