Discovering asteroids in space used to be a privilege reserved for astronomers – until now, thanks to a project led by the University of Arizona Catalina Sky Survey, which made it possible for several members of the public to spot a previously unknown near-Earth asteroid on its orbit around the sun. 

Named 2023 TW, the newly discovered asteroid is the closest to ever be discovered by a citizen science initiative, according to Catalina Sky Survey researchers. Initial calculations indicate it ventures into Earth's vicinity at a "mean orbital intercept distance" of 375,000 miles, about 35,000 miles past the average distance between the Earth and the moon. 

"The mean orbital intercept distance describes how close an object approaches Earth's orbit," said Carson Fuls, director of the Catalina Sky Survey, which is based in the UArizona Lunar and Planetary Laboratory. "Earth might not be anywhere near the asteroid when it approaches a spot in its orbit."   

Despite its close proximity to Earth, 2023 TW does not pose a threat. There is no chance of 2023 TW impacting Earth, and even if this asteroid did enter our atmosphere, severe consequences would be unlikely, Fuls said.

Spanning 164 feet, 2023 TW's diameter is similar in size to the meteor that created the 0.8-mile-wide Barringer Crater, also known as Meteor Crater, a popular sightseeing stop along Interstate 40 east of Flagstaff, Arizona. This is well below the threshold of 459 feet for potentially hazardous asteroids, according to Fuls. 

"For an object to be considered a potentially hazardous asteroid, both the distance and size need to be taken into account," Fuls says. "This asteroid meets the distance requirement, but not the size requirement."

The project's public-facing portal, dubbed the Daily Minor Planet, began operating in June and allows volunteers to pore over images collected with a telescope on Mount Lemmon. Each night, the telescope surveys about 200 patches of the sky. A software algorithm flags anything that appears like it might be an object that is moving relative to the fixed stars in the background. A typical night of observing yields hundreds of such candidate detections. This is where the volunteer observers come in. Their task: decide which detections are actual asteroids and which ones are artifacts or other phenomena unrelated to asteroids.

Aside from discovering 2023 TW, the project has reached the milestone of reporting 1,200 newly discovered, individual objects to the Minor Planet Center of the International Astronomical Union – the clearinghouse that decides whether objects detected anywhere in the solar system are real. Most of the objects reported through the project have been asteroids, but it also picked up the occasional comet. Comets are different from asteroids in that they contain water and other ices and typically reside in the outer reaches of the solar system. 

Before 2023 TW was found, the project's volunteers detected many other candidates for near-Earth asteroids. However, the timing is tricky: Many asteroids, particularly those close to Earth, whip around our planet quickly before heading out into space for another trip around the sun. 

To establish and publish an asteroid as a new discovery, asteroid trackers need to understand the object's orbit, which requires repeated observations over several days. 

Image

"Close approaching asteroids appear so briefly in our sky and are moving so quickly that any delay in processing or reviewing the data increases the chance that they cannot be re-observed and confirmed," Fuls said. "Very close approaching asteroids may zip right past the Earth and quickly become too faint due to distance or go into the daytime sky where we can no longer see them."

In other words: Time is of the essence. The recent asteroid discovery was made only two days after the initial observation. Beyond the time pressure, knowing how to tell real objects and false detections apart is a central component of the data collection process.

"A real object has a very consistent appearance in that the images follow a linear pattern," Fuls said. "Often there are false detections that are image artifacts, which are caused by factors like dust on the telescope's optics. Any real object will move in a fairly straight line, whereas most artifacts will make a star pattern."

Recognizing the differences between artifacts and real objects is easier said than done, said Elisabeth Chaghafi, one of the volunteers involved in the discovery of 2023 TW.

"It took me about 10,000 images to get a proper sense of what I was looking for," she said. "Initially I kept getting it wrong, which was a little frustrating, but after a couple of weeks of getting thrown by background stars and artifacts I noticeably improved, and by now I'm able to classify most images in a couple of seconds."

Why citizen science matters

Chaghafi, who is a Renaissance scholar at the University in Tübingen, Germany, is one of the more than 3,700 volunteers tracking down asteroids for the project. The fact that the initiative is open to the general public helps lighten the load for individual observers. 

"Each observer may look at 4,000 candidates each night," Fuls said. "Our volunteers help divide up an entire night shift."

The project's tangibility feeds into its accessibility. Volunteers do not need a background in astronomy to hunt for asteroids.

"There is a sense of familiarity because almost everyone has seen movies like 'Deep Impact,' 'Armaggeddon' or 'Don't Look Up,' or might have even held a meteorite in their hands," Fuls said. "Because we work with images, it makes asteroids feel a lot more tangible."

Chaghafi said she is convinced the skill sets from other fields complement the project.

"Pattern recognition and spotting details are integral to my area of expertise," she said. "I work with old manuscripts, and to do well at that you do need a good eye for detail – which applies to identifying asteroids as well."

The accessible and collaborative nature of the project has established a strong sense of community. Through Zooniverse, the online portal the project uses, volunteers discuss broad topics in astronomy – everything from irregular galaxies volunteers observed to the annular solar eclipse this past October. 

Virgilio Gonano, another member of the team that discovered 2023 TW, said, "I have met people from all over the world with the same passion as me, and we enrich ourselves by exchanging advice and experiences. Working with professional astronomers is also a beautiful thing."

"Asteroids are the leftovers from the formation of our solar system," Fuls said. "They are essentially the test particles that can help us understand how planets and other objects in the solar system came to be. By identifying asteroids we are filling in the map of our solar system via telescopes."

To date, the Catalina Sky Survey has turned up about 10,700 near-Earth asteroids of the NASA-specified size requirement of measuring 460 feet or more. It is thought that this number represents about 45% of the total population of objects in that size range, according to Fuls. 

"Of the larger near-Earth asteroids, those spanning 1 kilometer (0.6 miles) or more, we have discovered about 1,000," he said, "which accounts for 98% of that population."

To achieve its goal of finding and cataloging all near-Earth asteroids, the Catalina Sky Survey will continue to rely on volunteers. Case in point: In the short time between researching and writing this article, the citizen science project netted yet another near-Earth object, dubbed 2023 VN3, filling in another blank spot on the vast map of our solar system.