Scientists have discovered that Mercury, the smallest planet in the solar system, is shrinking in size. According to them, the loss in girth is due to cooling of its iron core.

In a span of 3.8 billion years, the planet, also the closest one to the Sun, has lost around 14 km in diameter. Maps taken over time that show its landscape also provide evidence to support the fact that it has lost much more of its size than previously thought, almost twice as much as previous estimates.

The size measurements were made through the NASA MESSENGER, a sun-shielded spacecraft that has been orbiting the planet since 2011. The images captured have given scientists a picture of the planet’s geology, which is now said to be contracting and thus leading to the formation of wrinkled ridges and edged cliffs on the landscape.

All the planets in the solar system are cooling and losing diameter as well, due to the fact that the Sun is much cooler than it was during the formation of the system. However, in spite of being closer to the Sun, it has lost more girth than its counterparts.

To calculate the exact extent of Mercury’s contraction, scientists studied its surface features changes in its observable geology. Unlike the Earth which has many layers in its crust, Mercury has just one.

They noted that besides its crater-marked surface, cliffs that could be almost 3 km high had formed from mountains, as well as long ridges along the planet’s surface. One formation called the Enterprise Ruples, goes up to a height of nearly 1,700 km!

The faulting on the planet’s surface also illustrates the progressing seismic activity.It is found that enormous rock slabs on the planet are sliding against each other, with the movement being similar to that of tectonic plates on the earth.

Paul Byrne, planetary geologist at the Carnegie Institution for Science in Washington, D.C., said that the girth lost by Mercury was actually very less when compared to its size, however, he also said that the loss was substantial enough to have an effect on its geology.

With this study, scientists have finally concluded on the planet’s radial contraction, which makes the resultant radius about 2,440 km. The cooling of the core, which leads to heat loss in the planet, is said to drive its processes and subsequently its evolution.

The discovery can aid research that focuses on analysing the compositions of planets beyond the solar system, since Mercury is a prime example of how a planet would behave on being cooled over time.

However, it will remain impossible to analyse Mercury’s newly formed geography on foot in a manned mission, since surface temperatures can still reach 430 degrees Celsius. This was enough to melt any heat-resistant material we currently have. Instead, scientists observe the surface of Mercury from images sent to NASA from the MESSENGER spacecraft.

Scientists working on Mercury have formulated new questions as a result of this discovery. These include why the planet was shrinking when the deformation of the surface began, the extent of the seismic activity, and how fast its diameter contracted.