Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.

I saw an interesting article about robot exploration last week.  We’ve sent robots to the depths of space and the depths of the ocean and now we’re going to send them to the depths of a cenote.  The Maya word d’zonot (cenote) means “hole in the ground” and cenotes (pronounced say noh tays) are giant sinkholes in limestone found all over the Yucatan Peninsula.  They cluster around the enormous crater rim that marks the final resting place of the big rock that took out the dinosaurs and are apparently a result of that gigantic impact.  When the giant meteor (it was about the size of central Guam) collided with the Earth, it created a ring fault that bounded the impact crater.  This ring line

intercepts the flow of groundwater, diverting it up and around the fault line so that the slightly acidic water dissolves the limestone and creates the caves and cenotes.

Yucatan’s cenotes are well-known diving spots since most of them are filled with water.  And they can be exceptionally clear and deep.  The cenotes have long been major sources of water in much of the Yucatan peninsula, most of which lacks other easily accessible year-round water.

Cenotes were sacred to the Maya and the sacrificial cenote at Chichen Itza is famous all over the world.  The Maya apparently believed that water-filled cenotes were gateways to other worlds and many objects were thrown into them including people who were sacrificed to the rain gods.  Most cenotes were explored in the first part of the 20th century.

But there’s a new era of exploration beginning at the cenotes of Mexico.  And this one is robotic.  A NASA-funded robot built by Stone Aerospace (stoneaerospace.com) plumbed the depths of a large Yucatan cenote called La Pilita last month and took a sonar picture of the cavern interior.

The DEPTH-X robot looks rather like a peeled orange and is designed to be a 3-D autonomous explorer.  While the robot is on the water’s surface, it can be run using wireless WiFi.  It can also carry an optical fiber to the depths with it for data uplink or remote control of an optical camera.  And it can be programmed to without a tether.  It can build and follow 3D maps, explore and map unknown territory, and return home using its own maps, without any aid from a GPS system. It can be commanded to drive to a known position, acquire 3D geometry, measure environmental variables, and take liquid and solid samples.  The DEPTH-X robot is rated to a depth of over 3,000 feet and the power system provides 8 hours of cruising range.  One is tempted to add “To boldly go where no one has gone before”!

DEPTH-X arrives at La Pilita

The La Pilita cenote was only the first step for the Depth-X robot.  It was a shakedown cruise to test the sampling arm, sonar mapping capabilities and to test the other scientific research the robot can do.  In May, the DEPTH-X robot will enter El Zacaton.  El Zacaton is one of a group of five interconnected cenotes and it’s the deepest known sinkhole in the world with a depth of more than 1080 feet.  Researchers and divers suspect that El Zacaton may be much deeper but before the DEPTH-X robot, there was no way to tell.

El Zacaton is a killer.  In April 1994, Jim Bowden and Sheck Exley two world famous cave divers entered the water at El Zacaton with the avowed goal of diving to over 1,000 feet.  They had planned the dive for months and although there’s a tradition in cave diving for these kinds of attempts to be made solo, Bowden and Exley dove simultaneously, following separate weighted lines 25 to 30 feet apart.  Although they were in the water at the same time, the water was so murky, they couldn’t see each other.  In 11 minutes, Bowden had reached 898 feet but his gas reserves were lower than expected and he turned upward to begin over nine hours of decompression.  Eighteen minutes into the dive, the air bubbles coming from Exley stopped.  Although his body was recovered, fellow divers still don’t know exactly why he died.

But the folks who operate DEPTH-X don’t have that kind of worry.  They intend to follow El Zacaton to the bottom wherever that might be.  And since the cenotes are interconnected they’ll probably repeat what they did on their last day at La Pilita.  They dove under a dome.  In a 22-minute autonomous dive, the rover dropped down to 100 feet and then began to move laterally passing beneath the campsite of the researchers.  It then dove down and returned to the opening it entered.  It then located what the operators thought might be another opening at a depth of around 150 feet.  The robot collected more data and narrowed the area where a tunnel might exist but left the question of another underwater tunnel unanswered.

So, why on Earth is this expedition NASA-funded?  Why is NASA interested in exploring sinkholes?
The answer to that lies in the most likely spots to harbor life in the solar system beyond Earth.  And despite our fascination with Mars, it’s not Mars.  Our kind of life requires liquid water and while Mars has plenty of water, as near as we can tell, virtually all of it is frozen solid.  Not a place for life to maintain a foothold.

But there are oceans in space.  Big oceans; with more liquid water than Earth’s Mother Ocean.  We’ve speculated for years that the ice moons of Jupiter and Saturn contain liquid water because they wobble as they circle their primaries.  You can tell if an egg is hard boiled or not by spinning it.  If it’s raw, the sloshing liquid causes the egg to wobble as it spins.  Jupiter’s Europa and Ganymede (the biggest moon in the solar system; bigger than Mercury) and Saturn’s Enceladus all wobble.  And we no longer have to speculate about whether Enceladus contains liquid water, the Cassini spacecraft has seen it erupting from the moon’s surface.

Water erupts from the surface of Enceladus

Is there life in those oceans?  One of the astronomers who studies Europa says “Do you really think you can have a liquid water ocean for 6 billion years and not have life in it?”  And, how do you initiate first contact?  How do you explore in a completely dark sea?  Meet DEPTH-X, our first step in exploring those hidden depths and maybe meeting our neighbors!