Watch Live: Astronaut Scott Kelly Talks About His Year in Space

American astronaut Scott Kelly returned to Earth this week after spending a year in space and will speak about the experience in a NASA news conference on Friday afternoon.

Kelly spent a year on the International Space Station, a mission that aimed to to help scientists understand the effects of prolonged zero-gravity exposure on the human body. Kelly’s twin brother, a retired astronaut, participated in parallel studies on Earth.

Kelly and Russian cosmonaut Mikhail Kornienko landed back on Earth in Kazakhstan on Tuesday after a historic 340 days in space.

Read more: Inside the Gigantic Operation to Meet Astronauts Coming Home

TIME chronicled the year-long mission for a documentary series, A Year in Space, which premiered Wednesday on PBS.

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Write to Katie Reilly at Katie.Reilly@time.com.