John Glenn, who was the first American to orbit Earth, has passed away at the age of 95 in Columbus, Ohio.

Glenn was also a decorated war hero, former astronaut and senator, educator, husband, father of two, and defender of humanity who worked against the proliferation of nuclear weapons.

In the wake of the news, scientists and space luminaries have taken to Twitter with an outpouring of condolences, memories, and love.

We'll update the list here as more space-related celebrities chime in, but below are some of the more notable tweets we've seen:

Paul Allen, Microsoft co-founder, philanthropist, and creator of private aerospace company Stratolaunch Systems

Peggy Whitson, a US astronaut and the first female commander of the International Space Station

Mae Jemison, the first woman of colour in space and leader of the 100 Year Starship project

Neil deGrasse Tyson, an astrophysicist and populariser of science

Jeff Bezos, the founder of Amazon and spaceflight company Blue Origin

Scott Kelly, a US astronaut who spent more than 520 days in space

Chris Hadfield, a Canadian astronaut and former International Space Station commander

Carolyn Porco, a lead scientist on NASA's Cassini mission at Saturn

Elon Musk, PayPal co-founder and founder of SpaceX

Bill Nye, "the science guy" and CEO of the Planetary Society

This article was originally published by Business Insider.