Two shields made from remnants of the Twin Towers protect cables on two NASA rovers on Mars and serve as an interplanetary memorial to the events of 9/11.
According to the International Business Times, the rovers were outfitted with these aluminum shields -- each with an American flag -- to protect cables on the rovers, and were sent to the Red Planet in 2003, landing in 2004:
The tributes were made possible by Stephen Gorevan, the founder and chairman of Honeybee Robotics, which was based less than a mile away from the World Trade Center at the time of the Sept. 11 attacks.
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Through Gorevan's contacts, the team was able to acquire pieces of aluminum from the World Trade Center site on Dec. 1, 2011. The fragments came with a note from former Mayor Rudy Giuliani's office reading, "Here is debris from Tower 1 and Tower 2."
The rovers, which scientists say should be able to last on the dry planet for millions of years, aren't the only NASA tribute to 9/11, there were astronauts up there at the time who caught a rare view of the day's events.
Space.com has more:
The United States had one citizen off-planet on Sept. 11, 2001 — NASA astronaut Frank Culbertson, who was commanding the International Space Station at the time.
Culbertson had a bird's-eye view as the terror attacks on New York City's World Trade Center went down.
"I didn't know exactly what was happening, but I knew it was really bad, because there was a big cloud of debris covering Manhattan," Culbertson recalled in a NASA video marking the 9/11 anniversary. "It was like seeing a wound in the side of your country, of your family, your friends."
After 9/11, NASA scientists and its satellites helped find aerial contaminants near Ground Zero. Endeavor, which was launched later in 2011 as the first shuttle after 9/11, carried nearly 6,000 tiny American flags into space.