Major Peake was at W5 as part of his post-space mission tour of the UK.
Earlier in the day, he officially opened the Thales’ space propulsion facility in the east of the city.
The children also heard about the many important scientific experiments conducted on the International Space Station (ISS) during the mission.
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The former army helicopter test pilot spent six months living and working on board the ISS after launching from the Baikonur cosmodrome in Kazakhstan in December 2015.
More than 15,000 people watched live coverage of the launch at events held across the country.
Many more following his daily life on the ISS through his regular social media posts, including video footage of the Earth from outside its own atmosphere.
In response to a question from Luke McKay of Larne Grammar, Major Peake said there was so much water across the vast universe, as well as organic matter, “that the chances of there being life elsewhere in the Universe are exceptionally high. In fact, I think we are quite close to finding evidence of past life on Mars.”
Although he would not rule out the possibility of finding intelligent beings, Major Peake said any discovery was likely to be single cell micro organisms “not complex life forms like human beings.”
He said particles floating in space were being examined and the results were extremely interesting.
“Scientists are analysing this rock – they have broken it open – and they have already found organic compounds...the building blocks of life if you like.
“These are not terrestrial, they have not come from planet Earth, so we know that the solar system and the Universe are seething with organic compounds.”
Ten-year-old Eoin Kelly from St Mary’s Primary in Kircubbin was in the audience and had his question at the ready in case he got to speak to his space hero.
He said the best thing about following the space mission was the fact that one of the astronauts was from the UK.
“Just knowing that someone from our part of the world went to space was great. I would really enjoy going to space,” he said.
“I’m going to ask him ‘does it feel weird drinking your own pee?’ They use this thing that purifies it,” he added.
The visit to Belfast was one of a number of events taking place across the UK as part of the post-flight tour which began in Cardiff last week.
London is hosting the final leg of the tour on Wednesday. The other cities involved were Leicester, Manchester, Glasgow and Edinburgh.