On September 10, 1990, approximately 25 witnesses, including schoolchildren and a photojournalist, observed a spherical metallic object with legs hovering near Alfena, Portugal. The photojournalist Manuel Gomes captured four photographs; forensic examination by Portugal's CNIFO and later by NASA consultant Richard Haines found no evidence of tampering.

The images were independently assessed by INETI (National Institute of Industrial Engineering and Technology) and forwarded to international bodies including NORAD and the European Space Agency; none produced a conventional explanation. The object was described as reflective, spherical, and approximately turtle-like in silhouette with protruding appendages. This is considered one of the most thoroughly investigated Portuguese cases on record.