Asteroid serendipity with JWST MIRI: first results

Even when not targeting them, MIRI on JWST detects a large number of asteroids serendipitously. We have started a program to extract those observations in order to obtain constraints on asteroid size and albedo. The sampled asteroids are dominated by main-belt asteroids that were too small for previous mid-IR surveys (IRAS, WISE, ...) to detect them, down to the smallest objects discovered so far and beyond.

We present our method to identify imaged asteroids, pipeline modifications to account for their proper motion, and first asteroid diameters obtained from serendipitous MIRI imaging. Over the mission lifetime, we expect to assemble a sizable catalog, extending our knowledge of asteroid sizes and albedos to sub-km MBAs.

We limit our search to asteroids that were discovered otherwise. Due to MIRI’s unprecedented sensitivity, the dataset is teeming with previously unknown asteroids. Their sizes will be measured once they’re discovered using other assets.

The figure shows a MIRI commissioning observation with 4 dither points using filter F1500W (some 15 micron). Two asteroids are clearly visible: one has been identified as 2018 HP10, the other one does not appear to be known so far.