US defence officials say there have been around 400 UFO sightings documented by military observers.
A study organised by NASA into unidentified flying objects (UFOs) has begun, bringing together experts from across different scientific fields.
UFOs, or what the US government calls "unidentified aerial phenomena" (UAP), have been the source of intrigue for decades.
Now an official panel convened by the US space agency will focus on unclassified sightings and other data collected from civilian government and commercial sectors.
It is made up of 16 members, and includes retired NASA astronaut and test pilot Scott Kelly.
The scope of the inquiry differs from another recently launched investigation into UFOs which have been reported by military pilots and analysed by US defence and intelligence officials.
A Pentagon report issued last year found insufficient data to determine the nature of more than 140 credible sightings documented by military observers since 2004.
Explaining the unexplainable
Senior defence and intelligence officials testified before the US Congress five months ago that the list of catalogued UAP sightings had since grown to 400 but many remain beyond explanation, either as advanced earthly technologies, atmospherics or something alien.
Among them are videos released by the Pentagon of enigmatic airborne objects exhibiting speed and manoeuvrability exceeding known aviation technology and lacking any visible means of propulsion or flight-control surfaces.
The parallel NASA and Pentagon efforts highlight a turning point for the US government after spending decades deflecting, debunking and discrediting observations of UFOs dating back to the 1940s.
Announcing the formation of its panel in June, NASA said: "There is no evidence UAPs are extraterrestrial in origin".
The agency said its panel would spend nine months devising its own strategy for how to organise and study sightings before recommending "a roadmap of potential UAP data analysis by the agency going forward".
Its first report is set to be made public in mid-2023.
"Understanding the data we have surrounding unidentified aerial phenomena is critical to helping us draw scientific conclusions about what's happening in our skies," said Thomas Zurbuchen, associate NASA administrator.
"Data is the language of scientists and makes the unexplainable explainable".
The panel is chaired by David Spergel, who formerly headed Prince University's astrophysics department.
Other members include Anamaria Berea, a research affiliate at the SETI (Search for Intelligence Life) Institute in Mountainview, California; University of Rhode Island biological oceanographer Paula Bontempi; and University of California at San Diego astrophysicist Shelley Wright.