The liquid is hidden deep beneath the planet's surface. California planetologists have discovered large reserves of water in the crust of Mars at a depth of 10-20 km. The conclusion is based on an array of data collected by a seismometer, which was delivered to the planet's surface by the InSight spacecraft in 2018. Over 4 years, the device recorded more than 1,300 earthquakes. By analyzing the propagation speed of seismic waves, scientists were able to guess with a high probability through which material they travel. This technology is routinely used on Earth to search for water, oil and gas. The presence of water on Mars is not in doubt: the planet's polar caps are wrapped in permafrost and there are traces of vapor in the atmosphere, but this is the first time large reserves of water in liquid form have been discovered. The desolate red planet as we know it today was once full of rivers and lakes. Scientists believe there may be life in the open ocean, and the composition of preserved water reserves will answer many questions about the history of Mars.