KUWAIT CITY, Oct 5:  Planetary scientists published a remarkable discovery about the planet Mercury, which shows its size shrinking over billions of years.

A study published by the "Science Alert" website, Tuesday, explained that although the planet Mercury is the closest to the sun, its interior is cooling due to the leakage of internal heat, and this means that the planet's core must have shrunk in size; but it is not known to what extent the planet is still contracting today, and if so, how long this contraction is likely to continue?

Because the inner part of Mercury is shrinking, this means that the area covered by its surface gradually decreases, and this in turn leads to the formation of wrinkles on the outer crust of the planet, like the wrinkles that form on the surface of an old apple, except that the apple shrinks because of its dryness, while Mercury shrinks because of its low interior temperature, according to the study.

The first evidence of Mercury's contraction came in 1974, when the Mariner mission sent back 10 images of cliffs several kilometers high, winding for hundreds of kilometers across the terrain.

The MESSENGER program, which orbited Mercury from 2011-2015, showed many “Cracked Cliffs” But when did this happen? The accepted method for calculating the age of Mercury's surface is to calculate the density of craters resulting from wrinkles.

The older the surface, the more craters there are, but this method is difficult because the rate of wrinkles that produce craters was much greater in the distant past. The consensus opinion is that Mercury's slopes are mostly about 3 billion years old.

The study also says that “cooling the interior of the planet Mercury, which consists of massive iron, led to the planet losing 14 kilometers of its diameter, more than twice what previous estimates indicated.”

Scientists studied more than 5,900 features of the planet’s surface, including steep slopes resembling cliffs and hills, to calculate the extent of Mercury’s contraction. While the Earth's crust consists of several layers, Mercury's crust consists of a single solid, rocky layer that bears evidence of gaps and slopes.