However, Nelson also noted that NASA has not been able to identify evidence that UAPs - previously labeled as unidentified flying objects (UFOs) - are extraterrestrial in origin.
Just because there's no current evidence, that doesn't rule out the possibility that aliens exist, especially if there are habitable planets in outer space that have yet to be discovered or researched.
Nelson said that somewhere in the galaxy there is a planet similar in size and composition to Earth that is orbiting a star like our sun at a distance that allows for life to thrive.
NASA's Nicola Fox referred to such as a planet as Earth 2.0.
Nelson's belief that there are more than a trillion planets in outer space that resemble earth comes from information gathered by the James Webb Telescope.
“In a universe that is so vast - of course I believe that there is a replication of Earth somewhere out there,” Nelson said.
NASA recently revealed other evidence that life could exist away from Earth. K2-18 b, which is 8.6 times the size of earth and 120 light years away, is believed to have carbon-bearing molecules, including methane and carbon dioxide, and could be a Hycean exoplanet, which NASA describes says "has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface."
Still, K2-18 b is very unlike Earth, according to NASA scientists. They also added that there is still little known about the exoplanet.
While the public and government officials have reported UAP sightings, there still is a big void when it comes to proving any are extraterrestrial.
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Nelson was adamant, however, that if NASA were to find aliens, "you bet your boots" the public will be informed about it, according to the Daily Star.
NASA notes that the investigation into UAPs is ongoing and has encouraged private, commercial and military pilots to report sightings and not be afraid of a "stigma" that may come along with such claims.
Though there is still much to be investigated when it comes to the possibility of extraterrestrials, Nelson expects it to be taken seriously.
"We want to shift the conversation about UAPs from sensationalism to science," he said.
"We don't know what these UAP are. The mission of NASA is to find out the unknown," he said.
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