If you've been paying attention to the space engineers readying NASA's Mars 2020 rover, you may have noticed a recent surprise visitor in the Spacecraft Assembly Facility clean room at NASA's Jet Propulsion Laboratory (JPL) in California.

A live feed of the clean room, which streams online here , shows technicians in the clean room's white coveralls (often referred to as "bunny suits") caring for the vehicle and preparing the Mars machinery to be shipped to its next destination, NASA's Kennedy Space Center in Florida.

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Well-dressed in bunny suit, High Bay Bob mannequin. (Image credit: NASA Jet Propulsion Laboratory with analysis from Space.com)

But if you were paying close attention, you may have noticed that one of these bunny-suited technicians looks to be frozen in time, standing completely still and wearing a pair of sunglasses. This "worker" stays in that same spot, hour after hour, day or night. Could it be a well-paid (and strangely still) security guard? A worker inexplicably shunned by their Mars 2020 rover teammates?

Andrew Good from NASA JPL's media relations team cleared up this clean room mystery.

It turns out that the silent "stand-in" is local JPL celebrity "High Bay Bob," a bunny suit-clad mannequin, Good confirmed. The extra addition to the clean room was present for a few days keeping the hardworking crew company.

High Bay Bob is gone now, his departure just as mysterious as his arrival, but you can still watch the Mars 2020 rover come together. To see live views of Mars 2020 as engineers build the rover, visit JPL's "Watch Mars 2020 Come Together" page here!

The Mars 2020 rover, which will soon be renamed, is scheduled to launch toward Mars on July 17.

In this image taken Dec. 24, 2019, NASA's Mars 2020 rover is near ready for shipping to Kennedy Space Center. The rover's launch window is from July 17 to Aug. 5, 2020. (Image credit: YouTube/NASA Jet Propulsion Laboratory)

Leonard David is author of the recently released book, "Moon Rush: The New Space Race" published by National Geographic in May 2019. A longtime writer for Space.com, David has been reporting on the space industry for more than five decades. Follow us on Twitter @Spacedotcom or Facebook.