Spacecraft often make super surprising discoveries. We build them to accomplish one set of science objectives, and we give them what we hope is enough flexibility to handle any random discoveries that are made along the way. For one mission, the random discoveries started before the mission was even launched. 

Lucy is an upcoming probe that will do flybys of Trojan asteroids – those chunks of rocks that share an orbit with Jupiter that are gravitationally clumped up ahead and behind the planet in its orbit around the Sun. This mission is being put on a very elliptical orbit that will allow it to visit first the leading Trojans, and then on its next orbit to visit the lagging Trojans. The orbit was specifically designed to allow the mission to do close flybys of seven known objects, and it’s expected newly discovered objects may be added over the course of the mission. 

In January 2020, it was realized one object would actually be added beforehand: one of the seven Trojan asteroids was discovered to be a binary object. Continued observations using the ground-based Asteroid Terrestrial-impact Last Alert System (ATLAS) based in Hawaii have found that the leading and trailing clouds of asteroids have different average shapes, with the leading asteroids tending to be more elongated and smaller. According to research on ArXiv led by Andrew McNeill, the leading cloud also has more objects in it, and this combination of facts seems to indicate that with more objects to collide, more collisions have indeed taken place, each one reshaping the asteroids involved. 

Launching in October of this year, Lucy is expected to reach this leading cloud in 2027 and then visit the trailing cloud in 2033. Expect more discoveries in the years before the encounters, as observers here work to make sure Lucy doesn’t encounter any surprises out there!

More Information

SWRI press release