Defunct NASA satellite re-enters Earth's atmosphere after 21 years in space.
Scientists baffled by the unexpected return of the long-lost spacecraft.
Satellite's re-entry provides valuable data on space debris and re-entry dynamics.
The returned satellite could offer insights into materials' durability in space.
Recovery efforts underway to collect and analyze satellite's remains.
Experts hope to learn about potential threats posed by space debris.
Satellite's return highlights the need for improved space debris tracking systems.
Researchers aim to understand how orbits decay over time, informing future missions.
The unexpected return may aid in developing strategies for safe disposal of spacecraft.
NASA celebrates the satellite's homecoming as a rare opportunity for scientific discovery.