WASHINGTON — Former NASA astronaut Mark Kelly announced Feb. 12 his intent to run for a United States Senate seat in Arizona.

Kelly, a Democrat, announced his plans to run for the seat on social media, linking to a four-and-a-half-minute video largely biographical in nature. That included a mention of his career as a NASA astronaut.

“You know, seeing that sunrise from space for the very first time, it is incredible,” he says in the opening of the video. “It becomes pretty obvious pretty early when you get into space that we’re all kind of in this together.”

Kelly is running for the seat held by Sen. John McCain (R-Ariz.) until his death in August. Former Sen. Jon Kyl was appointed by the state’s Republican governor, Doug Ducey, to fill the seat, but Kyl held the seat only through the end of 2018 before stepping down.

Ducey then named former Rep. Martha McSally (R-Ariz.) to hold the seat through a special election in 2020. McSally ran for Senate in 2018, seeking to replace the retiring Sen. Jeff Flake (R-Ariz.), but lost to Democratic challenger Krysten Sinema.

Kelly is considered a leading candidate for the Democratic nomination, and was recruited by party leaders to run for the seat. McSally is expected to seek the Republican nomination for the 2020 special election. The winner of the 2020 election will have to run again for a full six-year term in 2022.

Kelly, a former naval aviator, was selected as an astronaut by NASA in 1996, in the same class as his twin brother Scott. He flew on four shuttle missions, including STS-108 in 2001 and STS-121 in 2006 as pilot. He commanded STS-124 in 2008 and STS-134, the penultimate shuttle mission, in 2011. He retired from NASA shortly after that final mission.

Kelly is married to Gabrielle Giffords, a former member of Congress from Arizona. Giffords was shot and critically wounded in January 2011 while meeting with constituents in a grocery store parking lot in Tucson. She resigned from her House seat a year later to focus on her recovery.

Giffords and Kelly have been active on gun control issues in recent years. Kelly’s video announcing his candidacy doesn’t touch on space as a policy issue, focusing on the economy, healthcare and climate change.

Kelly has kept some ties to the space field since leaving NASA, including serving as a co-founder of and advisor to World View Enterprises, the Tucson-based company developing stratospheric balloons for scientific research and other applications. The company has flown payloads for NASA through the agency’s Flight Opportunities program. He’s also emphasized his NASA background in public appearances and corporate engagements. He and his twin Scott, also retired from NASA, appeared in an Amazon.com ad aired during the Super Bowl Feb. 3 where they played astronauts on a space station.

If elected, Kelly would join an exclusive group of senators who have also flown in space. John Glenn, the first American in space in 1962, was elected to the Senate from Ohio in 1974. The Democrat served four terms there, and in his final months in office in 1998 flew again in space on the STS-95 shuttle mission.

Harrison Schmitt, who walked on the moon on the Apollo 17 mission in 1972, was elected to the Senate as a Republican from New Mexico in 1976, but lost reelection in 1982. Jake Garn was already a Republican senator from Utah when he flew on a shuttle mission in 1985, the first and to date only sitting senator to fly in space. Bill Nelson, who flew on the final shuttle mission before the Challenger accident in 1986 as a member of the House, was elected to the Senate as a Democrat from Florida in 2000 and served three terms. He lost his bid for a fourth term last November.