NASA's manned mission to the red planet, called the Journey to Mars, is slated to happen in 2030. Before that, various flights and landing will be performed starting next year. In line with the mission, three main landing sites were shortlisted for the 2020 rock retrieval mission on Mars.

In an unexpected turn of events, NASA announced last Feb. 10 that the three main options for the landing sites on Mars are Jezero, Northeast, and Syrtis. Scientists expected that the agency would favor Eberswalde and Mawrth Vallis, but the Spirit rover's former playground, Columbia Hills, was chosen instead.

The landing sites were chosen from 54 identified locations, according to a report. It was then trimmed down to eight before finally shortlisting the final three.

"If we don't find a biomarker at Jezero, then we'll really be showing that a surface biosphere did not exist at Mars," Munir Humayun, a planetary scientist at Florida State University in Tallahassee and one of the mission's science board, said in a statement.

Scientists were the ones responsible for nominating the Jezero crater for it to be considered as a landing site. A spacecraft is expected to land on the Martian regolith in 2020; thus, the identification of potential landing sites is vital.

Jezero was chosen not only because it is a prominent region on the surface of Mars, but also because scientists believe that the former ancient river delta could be home to preserved organic molecules.

The process to identify the three main options and the candidates took a grueling three-day meeting joined by 172 scientists. One of the main discussion points during the meeting is the argument about sampling ancient deltas as opposed to rocks that accumulated in what believed to be hot springs that could have catered to life.

The northeast Syrtis area was chosen due to its carbonate-rich location. Water-associated clays found in the site could be linked to hydrothermal springs. The site is also near volcanic rocks. The mission aims to retrieve samples that could be brought back to Earth.

Columbia Hills, on the other hand, was considered due to the opportunity it presented to explore the possibility of past Martian life. Nature says Matthew Golombek, a planetary scientist at NASA's Jet Propulsion Laboratory, supported this theory.

NASA's 2020 Mars rover will be able to analyze rock compositions on the red planet better than the Spirit rover.