In 1519, Ferdinand Magellan set sail on a greuling and dangerous quest: the first-ever voyage around the world. But since that first daring adventure, advances in sailing technology and navigation have made the trip much more common. Today, even families—children and all—have accomplished the lengthy venture.
But there is at least one ocean path that's likely never been traveled: the longest straight-line sailable path on Earth. This 19,940-mile trip runs from the Pakistan coast through the passage between Madagascar and Africa and around to northeastern Russia—and is the longest straight-line someone could (theoretically) sail without touching land.
As David Schultz reports for Science, this straight-line path has just been scientifically verified for the first time thanks to work by Rohan Chabukswar, a physicist at United Technologies Research Center Ireland, and Kushal Mukherjee, an engineer at IBM Research India in New Delhi.
The path was first mapped five years ago by Reddit user Patrick Anderson, who goes by the screenname kepleronlyknows. To create the map, Anderson used a set of coordinates that appeared in a Wikipedia entry titled “Extreme points of Earth.” This was supposedly the longest straight line on Earth that can be sailed without hitting land.
Interested in testing the route, Chabukswar and Mukherjee used data from the National Oceanic and Atmospheric Administration’s ETOPO1 Global Relief model of Earth, which can map features down to about a mile in size. As Schultz reports, this gave the scientists relative certainty that the points of the map were all within the ocean.
To calculate the possibilities, they first found the number of great circles on Earth. Great circles are the paths around a sphere whose distance is equal to the circumference of that sphere. Following one of these paths across the Earth is the shortest distance between two locations, but because our planet is circular, the path does not appear as a straight line on a 2-D map. They are used for many types of navigation, such as helping pilots find the shortest distance between two cities.
But there’s hundreds of millions of different possible great circles, each with tens of thousands of points to verify. In total, that would require examining more than 5 trillion possible points, Schultz writes. So instead, they turned to the “branch-and-bound” algorithm, a computer program that tests only a few possibilities of the longest path before tweaking the search again for the best possible line.
In just 10 minutes of using this program, the researchers had support that the Wikipedia entry and Anderson’s map were correct. They detail their work in a study that they uploaded to the preprint server arXiv.
As the scientists write in the paper, the original map sparked lots of debate about whether Anderson was right. It also led to some attempts at finding the longest distance on land without hitting a major body of water.
Chabukswar and Mukherjee also tested to find the longest drivable straight-line path. This time, it took the computer 45 minutes, but it found a 6,985-mile path that started in eastern China and ended in western Portugal.
Unfortunately, Gabart probably won’t be sailing the newly verified path anytime soon. In fact, the researchers don’t recommend that anyone sail or drive these paths since the algorithm analysis does not ensure safe conditions along these tracks.
As they write in their paper: “The problem was approached as a purely mathematical exercise.”