Over the last year, ESA has commissioned and started operating the second so-called "Test-Bed Telescope" (TBT), a 56 cm wide-field optical telescope located on the premises of ESO's La Silla Observatory, on the Chilean Andes. This is the second unit, after the first one already installed in ESA’s tracking station in Cebreros, Spain. The TBTs have been designed to support NEO and space debris observations, and especially networked and collaborative experiments. They are intentionally composed of “commercial off-the-shelf” components, to demonstrate the capabilities of current instrumentation options and, in particular, to allow easy testing of novel observational approaches.

As a first test for these instruments as an NEO observing tool, we began operating the telescope almost nightly as a follow-up facility after it was assigned an MPC code W57 in late 2022. Observations from La Silla benefit from the extremely high percentage of clear nights and the Southern declination coverage offered by the telescope's location. The observatory quickly rose in the ranks of NEO follow-up facilities worldwide, significantly contributing to NEO confirmation efforts in the Southern hemisphere.

In recent months, however, we decided to devote a fraction of the telescope's time to NEO discovery survey. We developed a synthetic tracking pipeline, based on the Tycho Tracker software package and exposed and analysed a few fields per night. Our observing strategy alternates between low elongation fields and regular follow-up near the opposition region. Every candidate detection is carefully validated by our professional observers, to ensure that only reliable detections are submitted to the MPC and published.

Months of dedicated work finally paid off on Thursday, 14 March, when we were rewarded with our first discovery using this newly developed telescope and pipeline system. A set of images exposed in the Southern constellation of Hydra contained an unknown magnitude ~20.5 asteroid, which our observers immediately recognised as having a high likelihood of being real. The candidate was temporarily labelled PDO0002 and reported to the MPC, where it promptly appeared on the NEO Confirmation Page.

We immediately obtained follow-up observations with our network of telescopes and collaborators, including the Las Cumbres Observatory network, the Calar Alto Schmidt and the TRAPPIST North and South telescopes in Morocco and Chile. Thanks to the resulting astrometry we now know that the object is an NEO, similar in size to the Tunguska impactor, with a relatively small MOID of 0.006 au. Other stations also reported follow-up, and the Pan-STARRS team located a “prediscovery” unreported detection from two weeks earlier, which further improved the orbit determination.

The object has now been designated 2024 EL4. Aegis, our impact monitoring system, has processed all the available observations and shows that the object doesn’t pose any impact risk with Earth over the next century.

We hope that this discovery is just the first of many more to come, not just with these test-bed telescopes but also with ESA's dedicated discovery machine, the Flyeye telescope, which is ready to be installed and commissioned in Southern Italy.

Hot off the presses: just 4 days after discovering 2024 EL4, the same system found another NEO, which has now been confirmed and designated 2024 FS1.

Caption: The discovery image of 2024 EL4 was generated by stacking 31 images taken with a chilled CCD camera. Credits: ESA / PDO.