A NASA rover streaked toward a landing on Mars on Thursday in the riskiest step yet in an epic quest to bring back rocks that could answer whether life ever existed on the red planet.

Ground controllers at the space agency's Jet Propulsion Laboratory in Pasadena, California, settled in nervously for the descent of Perseverance to the surface of Mars, long a deathtrap for incoming spacecraft. It takes a nail-biting 11 1/2 minutes for a signal that would confirm success to reach Earth.

The landing of the six-wheeled vehicle would mark the third visit to Mars in just over a week. Two spacecraft from the United Arab Emirates and China swung into orbit around the planet on successive days last week.

Timing is extraordinarily important in many aspects of astronomy. If an astronomer or their instrument is looking the wrong way at the wrong time, they could miss something spectacular. Alternatively, there are moments when our instruments capture something unexpected in regions of space that we were searching for something else. That is exactly what happened recently when a team of scientists, led by Rohini Giles at the Southwest Research Institute, saw an image of what is likely a meteor impacting Jupiter's atmosphere.

The team collects data from the UVS, one of the instruments on Juno, NASA's mission tasked with studying the largest solar system planet up close. UVS is Juno's ultraviolet spectrograph, which collects data in the ultraviolet spectra from 68-210 nm. Its primary mission is to study Jupiter's atmosphere and watch for its breathtaking auroras.

Recently, when reviewing a batch of images that came in from the sensor, one of Dr. Giles' colleagues noticed a huge spike in brightness in an area outside of the normal auroral zone. As with much other science, this discovery started with someone finding interesting data when they didn't expect to see it.

Mars may now be considered a barren, icy desert but did Earth's nearest neighbour once harbour life?

It is a question that has preoccupied scientists for centuries and fired up sci-fi imaginings.

After seven months in space, NASA's Perseverance rover is due to land on Mars on Thursday, in search of clues.

Why Mars?

Other planets or moons, could also harbour forms of life, so why pick Mars?

NASA says Mars is not just one of the more accessible places in the solar system and a potential future destination for humans, but exploring the planet could also help to answer "origin and evolution of life questions".

"Mars is unique across the entire solar system in that it is a terrestrial planet with an atmosphere and climate, its geology is known to be very diverse and complex (like Earth), and it appears that the climate of Mars has changed over its history (like Earth)," it adds on its Mars programme website.