Government drones, errant weather balloons, experimental spy planes, rocket launches and exhaust plumes are just some of the aerial phenomena that have generated U.F.O. sightings.

Whatever the source, there is no end to the public’s fascination with mysterious objects darting across the sky.

In recent years, the government has sought to disclose more of the information — including videos, historical documents and grainy images — that it has collected on what it calls unidentified anomalous phenomena. Congress has held hearings in its own search for answers.

On Friday, the Pentagon released what it called “new, never-before-seen” files related to unidentified flying objects on a webpage with fonts and graphics reminiscent of a 1990s sci-fi thriller.

President Trump described it as a promise fulfilled.

“Whereas previous Administrations have failed to be transparent on this subject, with these new Documents and Videos, the people can decide for themselves, ‘WHAT THE HELL IS GOING ON?’” he wrote on Truth Social.

The Pentagon said more records would be released on a rolling basis.

Some of the initial files include documents from the 1960s space race between the United States and the Soviet Union, when both countries were pushing beyond Earth’s limits.

One of the documents — which has been previously cited in books — was a 1969 technical debriefing of Neil Armstrong, Buzz Aldrin and Michael Collins, the three American astronauts on the Apollo 11 moon mission.

In it, Mr. Aldrin recalls that when he was trying to sleep during the mission, “I observed what I thought were little flashes inside the cabin, spaced a couple of minutes apart.”

Mr. Aldrin also recounts seeing “what appeared to be a fairly bright light source, which we tentatively ascribed to a possible laser.”

A 1963 government memorandum reflects concerns within the Kennedy administration that the United States was not preparing for the possibility, however remote, of humans encountering aliens.

In it, Maxwell W. Hunter II, a prominent aerospace engineer, warned that, without some planning, “our policy will be determined in the traditional manner of grand panic.”

Here’s a look at some key events in the recent push for information about U.F.O.s.

May 2019

A New York Times report detailed strange aerial phenomena witnessed by Navy pilots, including flying objects that they said had no visible engines or infrared exhaust plumes, but could reach 30,000 feet and hypersonic speeds.

June 2021

The Office of the Director of National Intelligence released a report cataloging 143 unexplained aerial phenomena dating to 2004. The report did not draw conclusions or offer explanations for most of the events.

November 2021

The Pentagon announced a new group to investigate reports of unidentified aerial phenomena in sensitive areas, work that would be overseen by both military and intelligence agencies.

May 2022

Pentagon officials, testifying at the first congressional hearing on military reports of U.F.O.s in more than a half-century, showed a previously classified video of a reflective spherical object speeding past a military jet. It remains unexplained. Officials testified that the government had not collected material from any aliens.

June 2022

NASA announced a new study of unidentified aerial phenomena. An agency official described it as “high-risk, high-impact kind of research” that could uncover new scientific phenomenon — or nothing at all.

December 2022

President Biden signed an $858 billion military spending bill that included a requirement for the Pentagon to review historical documents related to U.F.O.s dating to 1945. That was the year that, according to one account, a large, avocado-shaped object struck a communication tower in a patch of New Mexico desert now known as the Trinity Site, where the world’s first atomic bomb was detonated.

September 2023

NASA appointed its first director of research on unidentified anomalous phenomena. The position was recommended by an independent study team that called for the agency to play a bigger role in examining U.F.O.s.

March 2024

A Pentagon report found no evidence that the government covered up knowledge of extraterrestrials and no evidence that any U.F.O. sightings actually were aliens visiting Earth. The 63-page report was a sweeping rebuttal to claims that the government had secretly harbored alien spacecraft or alien technology.

February 2026

Former President Barack Obama tells a YouTuber that aliens are “real, but I haven’t seen them and they’re not being kept in Area 51.” The clip ricocheted across the internet, stirring wild speculation. Mr. Obama later clarified that he believed extraterrestrials likely exist in the universe, but “I saw no evidence during my presidency that extraterrestrials have made contact with us. Really!”

February 2026

Mr. Trump directed his administration to begin releasing files related to aliens, extraterrestrial life and unidentified flying objects. He also attacked Mr. Obama for his comments about aliens in the YouTube interview, insisting he “gave classified information; he’s not supposed to be doing that.”

May 2026

Days before the Trump administration released the latest files, Mr. Obama said in an interview with Stephen Colbert that the government was not hiding aliens. “For those of you who still think we’ve got little green men underground somewhere: One of the things you learn as president is the government is terrible at keeping secrets,” Mr. Obama said.