The 9/11 Memorial on Mars

Of all the tributes to the victims of 9/11 – from the small and personal to the national and epic – few will prove as enduring as the one created by JPL and employees at Honeybee Robotics: two small pieces of the World Trade Center towers currently sitting on the surface of Mars.

The little-known story of how a part of the Twin Towers ended up on the Red Planet began a decade ago, when Honeybee was tasked with building a pair of tools for grinding weathered rinds off rocks for the twin Spirt and Opportunity rovers. Based in lower Manhattan, the company's offices were less than a mile away from the World Trade Center. On the morning of September 11 2001, Honeybee founder and chairman Stephen Gorevan was riding his bicycle to work when he heard American Airlines Flight 11 hit the North tower.

"Mostly, what comes back to me even today is the sound of the engines before the first plane struck the tower," he says. "Just before crashing into the tower, I could hear the engines being revved up as if those behind the controls wanted to ensure the maximum destruction. I stopped and stared for a few minutes and realized I felt totally helpless, and I left the scene and went to my office nearby, where my colleagues told me a second plane had struck. We watched the rest of the sad events of that day from the roof of our facility."

In the weeks following the attacks, a JPL engineer named Steve Kondos, who was working closely with the Honeybee team, came up with the suggestion for including something on the agency's rovers as an interplanetary memorial. An early hurdle was acquiring an appropriate piece of material from Ground Zero. Through Gorevan's contacts, a parcel was procured and delivered to Honeybee Robotics from the mayor's office on December 1 of that year, with a twisted plate of aluminum inside and a note: "Here is debris from Tower 1 and Tower 2."

Tom Myrick, an engineer at Honeybee, figured out a way of machining the aluminum into cable shields for the rock abrasion tools. He hand-delivered the WTC material to the machine shop in Texas that was working on other components of the tools. When the shields were back in New York, he affixed an image of the American flag on each. The Mars Exploration Rover, Spirit was launched from Cape Canaveral Air Force Station on June 10, 2003, with Opportunity's launch following in July. Nobody on the rover team or at Honeybee spoke publicly about the source of the aluminum on the cable shields until later that year.

"It was meant to be a quiet tribute," Gorevan told a New York Times reporter writing a November 2004 story about Manhattan's participation in the rover missions. "Enough time has passed. We want the families to know."

Last year, both the Spirit and Opportunity rovers stopped moving forever. At least until we or someone else finds them, their onboard memorials could remain in good condition for millions of years.