There’s nothing more frustrating than having to pick up someone else’s discarded trash, so you can imagine the Natural History Museum in London’s fury at having to house a meteorite callously ditched on Earth by Mars for the past 20 years. To teach the Red Planet a lesson, and in an unprecedented intergalactic game of pass the parcel, the cosmic rock will be returned to Mars as part of the 2020 rover mission. The meteorite will be used to calibrate an instrument on the rover’s arm after which it will remain on its home turf.

This is the first time in history a museum has returned a meteorite sample to its point of origin for the sake of science, and, appropriately titled the Mars Sample Return, the mission is the most ambitious campaign since Apollo in terms of planetary exploration. The Mars 2020 rover, named Perseverance, will launch on July 30, and as well as returning the meteorite the campaign intends to select and retain samples of Martian rock to bring back to Earth on a future mission. The rock swapping just never ends.

The meteorite, referred to as Sayh al Uhamiyr 008 or SaU 008, was retrieved in Oman in 1999 and is needed to calibrate the Mars rover’s SHERLOC  (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) instrument so that it can effectively identify and collect rock and regolith samples for a possible return to Earth. Once Perseverance has landed at Mars’ Jezero Crater in February 2021, the meteorite will be used as a testing material by SHERLOC to decipher the composition of rock samples and assess if they are worthy of a place on the return journey.

“Every year, we provide hundreds of meteorite specimens to scientists all over the world to study,” said Professor Caroline Smith, head of Earth Sciences Collections at the Museum, principal curator of Meteorites, and member of the Mars 2020 Science Team, in a statement. “But this is a first for us: sending one of our samples approximately 100 million km away back home, to further our knowledge of Mars.”

To be effective as a calibration material, the meteorite needed to best reflect the properties of samples the rover might come across and so SaU 008 was chosen as it’s made up of basalt, a material found all over Mars. According to Professor Smith, SaU 008 was probably blasted off of the Red Planet between 600,000 and 700,000 years ago, so it will be a long-awaited reunion.

“The piece that we are sending was specifically chosen because it is the right material in terms of chemistry, but also it is a very tough rock,” Professor Smith continued. “Some of the Martian meteorites we have are very fragile. This meteorite is as tough as old boots. In addition, studying this sample over the course of the mission will help us to understand the chemical interactions between the Martian surface, and its atmosphere.”

As well as hunting for samples to bring back to Earth, Perseverance will be searching for signs of past life. The Jezero Crater has been chosen as the landing site as it’s believed to have been the most potentially habitable environment in the past. Perseverance will also be carting around some tech to see if oxygen can be generated from carbon dioxide in the Martian atmosphere, painting a picture of its suitability for human life in the future.