Enlarge Image Woodruff Patrick Laputka

We know what the dirt looks like on Mars, but there are parts of Earth that remain shrouded in mystery and darkness. The Shell Ocean Discovery XPrize wants to shine a light on the esoteric and crushing depths of the ocean where humans fear to tread.

The XPrize Foundation on Wednesday announced nine finalist teams, whittled down from 19 semifinalists.

The teams have all demonstrated prototype systems that could create high-resolution maps of the ocean, take images in the deep and identify archaeological and geological features as well as biological life. The creative solutions range from underwater robotic swarms to aerial drones and advanced autonomous vehicles.

"The success of this prize will allow us to fully explore and map the ocean floor, and uncover our planet's greatest wonder and resource for the benefit of humanity," the XPrize Foundation says.

The teams hail from around the world and will split a $1 million milestone prize purse. Sure, the $7 million (£5 million, AU$9 million) prize sounds tempting, but these teams are in it for the thrill of innovation and to advance our scientific understanding of one of the most mysterious places still left largely unexplored on our planet.

They still have a lot of work ahead of them. "We are looking forward to testing the finalists' technologies in a rigorous real-world world situation that will demonstrate their ability to rapidly map the ocean floor at 4000m depths -- that's deeper than the Grand Canyon!" says Jyotika Virmani, prize lead and senior director of planet and environment at XPrize.

The real-world testing is scheduled to take place later this year with final judging of the teams set to conclude by the end of 2018.

Meet the nine ocean-exploring finalists and check out some of their fascinating prototypes:

Rebooting the Reef: CNET dives deep into how tech can help save Australia's Great Barrier Reef.

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