After decades of sending missions to Mars, NASA is now zeroing in on regions of the red planet that they think have the best chance of determining whether the world has hosted — or hosts — life.

The big picture: Scientists are now able to point to parts of Mars that were once likely wet and warm, with geological signatures similar to the rivers, deltas and lakes on Earth — upping the odds that those parts of Mars could have once been friendly to life.

"Habitable and inhabited are two very different questions. You can build a house and you can furnish it nicely and put food in the fridge, but that doesn't mean someone lives there."

— NASA's Melissa Trainer to Axios

Driving the news: A new study finds NASA's Mars 2020 rover will land in an area that could be the perfect place to hunt for the fossilized evidence of past life.

The landing site — known as the Jezero Crater — once was home to a long-lived lake and river delta billions of years ago.

The rim of the crater could be rich with carbonates, which can help preserve signs of ancient life in fossilized form.

The Mars 2020 rover is expected to investigate the possible rock deposits and explore the delta that once fed the lake in the crater.

Meanwhile: Last week, NASA announced that Curiosity — which found Mars was habitable for microbial life in the past — detected a small amount of oxygen on Mars, but no one is quite sure where it's coming from.

The discovery adds to the mystery around the rover's possible detection of methane also reported earlier this year.

Yes, but: It's possible methane and oxygen could have been created through natural geological processes that have nothing to do with life.

Finding the origins of these molecules is exceedingly difficult, scientists say, without other pieces of evidence that point to living things on Mars.

Parsing out whether a methane molecule came from a living thing or geology could involve digging into its isotopic composition, but even then, it's not a sure-fire way to confirm the origins of the detection, scientists say.

The 2020 rover is planning to cache rock samples for eventual return to Earth on a future mission in order to confirm any possible discovery that points to life.

"There's always this uncertainty when we look at Mars."

— NASA scientist Lindsay Hays to Axios

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