NASA's Perseverance rover is currently searching for rock outcrops along the rim of Mars' Belva Crater. About 2,300 miles (3,700 kilometers) away, NASA's Curiosity rover recently drilled a sample at a location called "Ubajara." The crater has an official name; the drill site is identified by a nickname, hence the quotation marks.

Both names are among the thousands applied by NASA missions not only to craters and hills, but also to every rock, pebble and rock surface they study.

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"The No. 1 reason we chose all these names is to help the team keep track of what they find every day," said Ashwin Vasavada, project scientist for the Curiosity mission at NASA's Jet Propulsion Laboratory in Southern California. "Then, we can refer to many hills and rocks by their names when discussing them, and eventually document our discoveries."

How scientists come up with identifiers has evolved since the early days of using cartoon character names 25 years ago. Here's a closer look.

OFFICIAL NAMES

The difference between an official name and an unofficial name on Mars is seemingly simple: Official nicknames are approved by a community of scientists known as the International Astronomical Union (IAU). The IAU sets standards for naming planetary features and registers the names in the Planetary Naming Gazetteer.

For example, craters larger than 37 miles (60 kilometers) are named after famous scientists or science fiction writers; smaller craters are named after towns with populations of less than 100,000. Jezero Crater, which Perseverance explores, is named after a Bosnian town; Belva, an impact crater on Jezero, is named after a West Virginia town named after suffragist Belva Lockwood, who ran for president in 1884 and 1888.

More than 2,000 locations on Mars have official names, but even more unofficial nicknames are dotted on the map of Mars.

EVOLVING PSEUDONYMS

Early Mars missions sometimes took the bizarre route of using pseudonyms, even cartoon character names. "Yogi Rock", "Casper" and "Scooby-Doo" were among the unofficial names resorted to by the team behind NASA's first rover, Sojourner, in the late 1990s.

The philosophy changed with the Spirit and Opportunity rovers, whose teams began using more purposeful names. For example, the Opportunity team named a crater "Endurance" to honor the ship that carried explorer Ernest Shackleton's ill-fated Antarctic expedition. The names of the landing sites of Curiosity and Perseverance honor science fiction writers Ray Bradbury and Octavia E. Butler, respectively. The InSight team named a rock pushed and jostled by the lander's retrorockets during the landing "Rolling Stones Rock" after the band. And the Curiosity team named a Martian hill after its colleague Rafael Navarro-González, who died from complications of COVID-19.

EARTH ON MARS

Despite rare exceptions, Curiosity and Perseverance missions stick to pseudonyms based on terrestrial locations. Before Curiosity landed in 2012, the rover team made a geologic map of the landing site. They began by drawing a grid equivalent to about 0.7 miles (1.2 kilometers) on each side, making squares or quadrants. These quadrants would be themed around an area of geological significance on Earth.

Then, as now, team members suggested ideas for themes based on sites where they worked or had personal connections, and informally discussed which ones would be most interesting to include, keeping in mind that various names would be memorialized. Once a theme is chosen, hundreds of names that fit that theme are compiled. Given that Curiosity could be in a quadrant for several months, so many are needed as the available names could dwindle quickly.

For Curiosity's final quarter, the rover team chose a theme named after Roraima, the northernmost state in Brazil, and Mount Roraima, the highest peak in the Pacaraima Mountains near the border of Venezuela, Brazil and Guyana. This marked the first South American quarter theme. The sulfate-rich region Curiosity is currently exploring, with its flat-topped peaks and steep slopes, reminded them of the "tabletop" mountains in the Pacaraima range.

For Perseverance, scientists have chosen national park themes. The rover is currently exploring the Rocky Mountain quadrant and recently drilled rocks in a place nicknamed "Powell Peak" in Rocky Mountain National Park.