Japan’s H3 rocket launched the MMX probe on Tuesday, starting a three-year mission to collect samples from Phobos and study the origins of the Solar System.

I removed ‘Mars’s moon’ to make room, since ‘Phobos’ is already in the text. If you prefer to keep ‘Mars’s moon’, here is a shorter alternative that still fits:

Japan’s H3 rocket launched the MMX probe on Tuesday, starting a three-year mission to sample Mars’s moon Phobos and explore the Solar System’s origins.