If NASA's OSIRIS-REx spacecraft could talk, today it might have said, "Finally!"

At 10:50 a.m. Tucson time, the van-sized spacecraft fired its thrusters to leave the safe-home orbit around asteroid Bennu and began descending toward the asteroid's surface, which the spacecraft spent two years photographing and mapping in tremendous detail. Its mission: Touch the asteroid for a few seconds and collect a sample to be later brought back to Earth. 

Members of the University of Arizona-led OSIRIS-REx mission, along with UArizona leadership, gathered at the university's Michael J. Drake Building, where the mission is headquartered, to watch NASA's live broadcast of the mission's much-anticipated Touch-and-Go, or TAG, event and listen to status updates from the spacecraft.

At 3:13 p.m. Tucson time, the atmosphere inside the building changed from one of subdued anticipation to elation and relief as a physically distanced, masked crowd started to clap and cheer.

At that time, the mission's spacecraft confirmed that it had touched the surface of asteroid Bennu for 4.7 seconds and triggered a flush of nitrogen gas with the goal of collecting the largest sample of extraterrestrial material since the Apollo moon landings.

"I can't believe we pulled this off," Dante Lauretta, principal investigator of the OSIRIS-REx mission and a UArizona professor of planetary sciences, said from the mission control room at Lockheed Martin in Denver, where NASA's broadcast was based. "This is history. This is amazing."

Shortly after touching Bennu, the spacecraft communicated that it had backed safely away from the asteroid to return into orbit and await the next phase of the mission, in which the team will pore over images taken by the spacecraft's onboard sampling camera and perform a series of measurements and maneuvers to assess whether the sampling process was successful and how much material was collected. According to the data available to the mission team immediately after TAG, the spacecraft had touched down with amazing precision – less than three feet from its target site, according to Lauretta.

"We couldn't have asked for a better outcome," he said. "The spacecraft did everything it was supposed to do. It's up to Bennu now to see how the event went."

Collecting a sample from Bennu involved what essentially amounted to parallel parking a 15-passenger van and dodging hazards including a boulder as tall as a two-story building – all 200 million miles away from Earth. Because of the time delay between Bennu and Earth, the spacecraft had been programmed to steer itself during the entire sequence.

"We spent many late nights and weekends writing commands to go up to our instruments, so it's exciting to see them execute flawlessly," said Sara Knutson, the mission's science operations lead engineer, who watched the broadcast from the Drake Building in Tucson.

"I was definitely holding my breath today," said OSIRIS-REx image processing lead scientist Daniella DellaGiustina, who was also at Drake. "But what stands out to me is just how much according to plan everything went, and that has been a standard on this mission. The fact that we have been so spot on with every first-time event on this mission is a testament to the incredible engineering and scientific efforts of so many people that have worked tirelessly to make this happen."

"This kind of fundamental discovery and the research opportunities it creates make the University of Arizona the premier institution that it is," said UArizona President Robert C. Robbins, who joined the mission members at the Drake Building. "This work fulfills something at the core of who we are as a species, and as an institution, and you should all be very proud of what you've accomplished."

Elizabeth "Betsy" Cantwell, UArizona senior vice president for research and innovation, who has a long career in space systems engineering, praised the team's work with complex engineering. 

"Massive kudos to the systems engineers who made this miracle happen. ... It is incredible that we have people like that here to support the science," she said.

While TAG was the most critical moment of the entire mission, the OSIRIS-REx team members will barely have time to catch their breath. The coming days will be spent analyzing images taken during the event and recreating the descent trajectory to get an idea of where exactly the spacecraft tagged the surface, which will provide clues to the quality and quantity of the sample that may have been caught in the spacecraft's sampling head. 

"OSIRIS-REx is kind of like a relay race," said Carl Hergenrother, OSIRIS-REx lead astronomer. "First, you get the proposal; then, you have the people who build the spacecraft and the instruments, then the people who planned the mission, made the observations to study the asteroid up close; and now, the mission isn't over. We're just handing off the baton to the next leg – to the people who are going to study the samples on the ground and really learn what really is the goal of the mission: the history of the solar system."