An interactive tool called ThroughEarth allows users to determine the exact exit point if someone were to start digging a tunnel directly beneath the Earth's surface, passing through the crust, mantle, and core of the planet.
Despite the common misconception that a tunnel started in the United States would lead to China, this tool provides a more accurate answer. The website calculates the antipodal point—a location directly opposite the specified point on the Earth's surface. The distance between these two points is approximately 12,742 kilometers.
When a point is selected on the map, ThroughEarth demonstrates an animation of the hypothetical journey through the planet's interior, including the crust, mantle, and core, until it reaches the opposite side. The platform also provides information about the Earth's internal structure, such as extreme temperatures during the journey and the time required to cover this distance in free fall.
The idea for the project originated from a simple question posed by children. Martin Krpelan, the project creator, told IFLScience that it all started during a conversation with his children at a playground when they discussed where they would emerge if they could drill a tunnel straight into the ground.
How the antipodal point calculation works
ThroughEarth uses data from Natural Earth and NASA's well-known Blue Marble image of Earth. According to Krpelan, calculating the antipodal point is 'surprisingly simple': one just needs to invert the latitude and shift the longitude by 180 degrees. In this process, the latitude changes sign, while the longitude shifts by 180° and is then normalized to remain within the range of -180° to 180°.
Krpelan added that the most interesting aspect is the analysis performed around this calculation. ThroughEarth also considers the surrounding geography near both points, determining whether the opposite location is land or ocean. It is this analysis that allows the platform to show that only about 15% of the world's land has other land located directly opposite it.
In practice, such a journey is impossible. The deepest borehole drilled by humans is the Kola Superdeep Borehole in Russia, which reached a depth of 12,263 meters. Even this record accounts for only about 0.2% of the distance required to reach the Earth's core, meaning it is much less than what is needed to cross the entire planet. Therefore, humanity will likely never be able to physically reach the center of the Earth, let alone pass through it and emerge on the other side. For this hypothetical trip, there is only the interactive map of ThroughEarth to turn to.