A 450-million-year-old meteorite fragment discovered in Oman has been returned to Mars, Nasa said.
Sayh Al Uhaymir 008 was discovered in the Wilayat of Haima, Al Wusta province, in 1999.
The meteorite crashed to Earth 450,000 years ago.
Nasa's Arabic Twitter account announced the imminent return of the rock, detailing the history of its discovery and analysis, including the co-ordinates where it was found – a possible nod to aspiring space-rock hunters.
While the origin of the rock was confirmed through testing in a laboratory in Germany, researchers wanted to take the sample to an area of the Red Planet that is thought to have once hosted life.
The rock was kept in the Natural History Museum in London before it began its journey back to Mars.
Why is the Omani rock being taken back to Mars?
Researchers want to compare the rock to samples on Mars, using a device known as Sherloc, which combines a camera, a spectrometer and a laser.
It is hoped that a high degree of certainty about the composition of rocks on the surface of the planet can be obtained by testing the meteorite fragment at the site.
Nasa used the example of a picture of a room in yellow lighting to explain the experiment. We might know the walls of the room are white in daylight, but to fully understand the characteristics of the room, we need to see it in natural light, hence the rock must be examined on Mars, with its light and dust.
"Scientists will be looking for rocks that may have formed in water, possibly preserving evidence of the chemical building blocks of life," Lori Glaze, director of the Nasa planetary science division, said last year.
What is the Perseverance rover doing on Mars?
"What we're looking for is evidence of past life, either direct chemical or organic signs in the composition and the chemistry of rocks, or textural evidence in the rock record," Jim Bell, a professor at the School of Earth and Space Exploration at Arizona State University, told The Conversation podcast last month.
"The environment of Mars is extremely harsh compared to the Earth, so we’re not really looking for evidence of current life. Unless something actually gets up and walks in front of the cameras, we’re really not going to find that."
Jezero, the area of Mars where the Perseverance rover landed, is probably the "best place" to search for signs of life, he said.
"There are lots of things we don’t know, but there was liquid water there. There were heat sources – there were active volcanoes two, three, four billion years ago on Mars – and there are impact craters from asteroids and comets dumping lots of heat into the ground as well as organic molecules," he said.
"It’s a very short list of places in the solar system that meet those constraints and Jezero is one of those places."