The speed of crater formation on the planet depends on the distance to the Sun, and in this way it is very difficult to study Mercury because of the proximity to the star. Now the NASA MESSENGER spacecraft, which revolved around the planet from 2011 to 2015, has provided the best images to date with a spatial resolution of only 5 metres per pixel in some regions.
Compared to the Earth, the surface of most other solar system objects seems to be largely static, and scientists have long believed that space stone strikes are the main source of changes on these surfaces and that the speed of such impacts decreases over time; estimates of the age of almost every surface outside the Earth and the Moon are based on this "speed of crater formation".
In order to improve the estimation of crater rates on Mercury, the authors of the new study examined 58,552 pairs of MESSENGER images. By comparing the images "before" and "after", they identified surface changes and calculated the estimated annual rate of change per square kilometre. The study was published in Geophysical Research Letters.
The authors found 20 new structures in the data set, 19 of which were quasi-circular structures ranging from 400 metres to 1.9 kilometres in diameter, one of which was surrounded by radial rays typical of impact craters in Mercury.
Nineteen new impact craters over the four years of the MESSENGER mission mean that their rate of formation for small impactors is 1,000 times greater than scientists thought.
They have revised the rate of crater formation and instead put forward an alternative hypothesis, and scientists have stated that many of these surface features are endogenous geological changes, which means that the surface of Mercury is more volatile than previously thought.