NASA / JPL-Caltech / MSSS / Will Pomerantz

A detail from the Curiosity rover's Mastcam system shows the rover's sampling scoop filled with Martian soil — and a tiny bright object in the foreground. The commentary was added by Will Pomerantz on Twitter. Check NASA's Photojournal for larger versions of the photo.

NASA's Curiosity rover dug up its first scoopful of sandy soil on Sunday and swished it around like a connoisseur tasting wine. But the long-anticipated sampling session had to be put on hold when Curiosity's handlers spotted a bright and tiny object nearby.

What the heck is it? A loose screw? A cigarette butt? A piece of Martian macaroni? The mystery lit up a few Twitter feeds this afternoon, but for now, the best hypothesis seems to be that it's a bit of plastic that fell off the rover.

Such droppings aren't unusual. "All the cool landers drop stuff on Mars," joked Sarah Milkovich, a member of the Curiosity team as well as the science team for the High Resolution Imaging Science Experiment on NASA's Mars Reconnaissance Orbiter. Her Twitter tweet included a link to a picture of hardware dropped onto the Martian surface by Phoenix Mars Lander back in 2008.

The Curiosity rover's Twitter account got into the act: "Team spotted bright object on ground near me — possibly a piece of rover hardware? Gathering more data," she tweeted. Even Sarcastic Rover chimed in: "Did anyone lose an earring on Mars? Because I may have found it. Or else I'm falling apart. But let's hope earring."

Seriously, though ... The Planetary Society's Emily Lakdawalla turned up a picture from Curiosity's ChemCam imager that seemed to show a tiny shred of plastic wrap — perhaps a bit of the insulating tape that's used all over the rover.

NASA / JPL-Caltech / LANL / CNES / IRAP

A picture from the ChemCam imager on NASA's Curiosity rover appears to show a shred of plastic at the center. Is that what the tiny mystery object will turn out to be? Stay tuned.

Stopping the scooping
The object was spotted just as Curiosity was using its scoop to pick up Martian soil from a sandy site known as "Rocknest." The plan was to shovel and shake the light soil to clear out the sample collection system mounted on the end of Curiosity's 7-foot-long (2.1-meter-long) robotic arm, known as CHIMRA (Collection and Handling for In-situ Martian Rock Analysis). But today, NASA's Jet Propulsion Laboratory reported that Curiosity's team refrained from using the robotic arm in order to check out the weird object.

"Curiosity is acquiring additional imaging of the object to aid the team in identifying the object and assessing possible impact, if any, to sampling activities," JPL said in its mission status report.

As Milkovich noted, Mars surface probes will occasionally spot anomalous bits of stuff such as the "bunny ears" and the "Martian macaroni" seen by the Opportunity rover. These cases have generally been explained as bits of fabric or metal left behind by the rover, and it seems likely that the same will be said of Curiosity's "cigarette butt."

Such debris is harmless — but if even a bit of it happened to get into the rover's sensitive chemistry labs, that could ruin the scientific readings. Even before the rover was launched, scientists worried that the plastic tape would throw off the rover's chemistry experiments. That's why Curiosity's team is being so careful about what to do next.

NASA / JPL-Caltech

An image from Curiosity's left navigation camera shows a 1.8-inch-wide (4.5-centimeter-wide) divot in a sand dune at the "Rocknest" site on Mars, left behind when the rover removed a scoopful of soil.

Clearing Curiosity's throat
Eventually, the sand scooping will continue, either at Rocknest or another site. The first few samples won't undergo any chemical analysis. Instead, the material will be shaken around and sent through Curiosity's sorting and sampling chambers to clear out any schmutz that's left over from the rover's journey to Mars.

Daniel Limonadi, an engineer at NASA's Jet Propulsion Laboratory, told reporters last week that the palate-cleansing was required even though the hardware is "super-squeaky-clean when it's delivered and assembled" at JPL. "By virtue of its just being on Earth, you get a kind of residual oily film that is impossible to avoid," he said.

Once the soil has been shaken and stirred through the chambers, it'll be ejected from the mechanism and plopped back onto the Martian surface. "We effectively use it to rinse out our mouth three times and then kind of spit out," Limonadi said.

When the palate-cleansing is complete, in about a week or so, CHIMRA will start delivering samples to Curiosity's two onboard chemical labs, known as Sample Analysis at Mars, or SAM; and the Chemical and Mineralogy experiment, or CheMin. Today's mission status report from NASA notes that those two instruments "will play crucial roles in evaluating whether the study area has ever had a favorable environment for microbial life."

Determining whether Mars was potentially habitable in ancient times is the prime goal for Curiosity's $2.5 billion Mars Science Laboratory mission. The nuclear-powered rover landed in Mars' Gale Crater on Aug. 5 and is on its way to a geologically interesting spot called Glenelg, where it's expected to use its percussive rock drill for the first time. After spending several weeks at Glenelg, Curiosity is due to turn around and head for a 3-mile-high (5-kilometer-high) mountain that is thought to preserve billions of years' worth of geological history.

Update for 3:20 p.m. ET Oct. 9: The real experts on the Curiosity mission are leaning toward the plastic-tape hypothesis. Get the full scoop here.

More about Curiosity's mission:

• Mars rover gets set for its first scoop
• Curiosity rover 'checks in ' to Foursquare
• Curiosity is driving through dried-up riverbed

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.