Mars maps are filled with names that recognize places on Earth, explorers, and even cartoon characters. NASA’s Perseverance rover is currently investigating rock outcrops along the rim of Martian crater Belva. About 2,300 miles (3,700 kilometers) away, NASA’s Curiosity rover recently took a sample at a place called Ubajara. The crater has an official name; the location of the drill is determined by the nickname, hence the quotation marks.

Both names are one of the thousands that NASA missions apply to not just craters and hills, but every rock, pebble, and rock face they’ve studied.

“The main reason we chose all these names is to help the team keep track of what they’re finding each day,” said Ashwin Vasavada, project scientist for the Curiosity mission at NASA’s Jet Propulsion Laboratory in Southern California. “We can then name many hills and rocks, discuss them, and ultimately document our discoveries.” The way scientists find identifiers has changed since the early days 25 years ago when they used the names of cartoon characters. Here’s a closer look.

Official names

The difference between the official name and the unofficial name of Mars is seemingly simple: The official nicknames have been endorsed by a group of scientists known as the International Astronomical Union (IAU). The IAU sets standards for the naming of planetary objects and registers the names in the Planetary Naming Bulletin.

For example, craters larger than 37 miles (60 kilometers) are named after famous scientists or science fiction writers; smaller craters are named after cities with a population of less than 100,000. The Crater Lake that Perseverance discovered is named after a Bosniak town; Belva, an impact crater on the lake, is named after a town in West Virginia that was named after Belva Lockwood, a suffragist who ran for president in 1884 and 1888.

More than 2,000 places on Mars have official names, but even more unofficial nicknames adorn the Mars map.

The evolution of nicknames

The first missions to Mars sometimes took a peculiar route, using nicknames, or even the names of cartoon characters. “Yogi Rock”, “Casper” and “Scooby-Doo” were among the unofficial names used by the team that created NASA’s first rover, Sojourner, in the late 1990s.

Philosophy changed with the Spirit and Opportunity rovers, whose teams began using more conscious names. For example, the Opportunity team named the crater “Endurance”, named after the ship that carried explorer Ernest Shackleton’s ill-fated expedition to Antarctica. The names of the Curiosity and Perseverance landing sites honor science fiction writers Ray Bradbury and Octavia E. Butler, respectively. The InSight team named the rock “Rolling Stones Rock” after the rock pushed by the landing craft’s retrorockets during the descent. The Curiosity team named the Martian hill in honor of their colleague Rafael Navarro-Gonzalez, who died from complications from COVID-19.

Earth on Mars

Despite rare exceptions, the Curiosity and Persistence missions use nicknames based on Earth locations. Before Curiosity landed in 2012, the rover team produced a geological map of the landing site. They started by drawing a grid, creating squares or quadrilaterals equivalent to about 0.7 miles (1.2 kilometers) on each side. These quadrants will be oriented thematically to a place of geological importance on Earth.

Then, as now, team members proposed theme ideas based on sites they worked on or had personal connections to, and informally discussed which ones would be most interesting to include, with the understanding that different names would be immortalized in future scholarly work. After choosing a topic, hundreds of names matching that topic are collected. Many are needed because the number of names available can quickly dwindle, as Curiosity may remain in the quadrant for several months.

For the final quarter of Curiosity, 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 with Venezuela, Brazil, and Guyana. This was the quarter’s first South American theme. The sulfate-rich region Curiosity was now exploring reminded them of the flat-topped and steep-sided “table” mountains in the Pacaraima Mountain Range.

For Perseverance, the scientists chose a national park theme. The rover is currently exploring the Rocky Mountain quarter and has recently drilled into the rocks at what Rocky Mountain National Park calls Powell’s Peak.