Although you might initially think there's been a cosmic mix-up, the reality is that you've stumbled upon
But there's more to this similarity than meets the eye. Both worlds boast towering mountainous ridges that stretch across thousands of kilometres — an intriguing result of their billion-year-long cooling process.
While missions to explore the moon's surface are numerous, the same cannot be said for Mercury. However, older observations continue to unveil the planet's secrets, and the latest discovery indicates that Mercury is shrinking, with its most recent contraction occurring more recently than previously believed.
Unlike Earth, Mercury features an outer crust encasing a molten metal mantle, with a crucial difference: its crust doesn't break into tectonic plates like ours. Consequently, as its molten interior cools and contracts (similar to how mercury in a thermometer shrinks with decreasing temperature), Mercury's outer shell attempts to contract as well. However, this solid and singular crust resists shrinking in the same manner.
As energy accumulates, sections of the crust begin to push against each other, forming the snake-like ridges along the surface, giving the planet a wrinkled appearance. A similar process occurs on the Moon, albeit to a lesser extent.
Although these structures, known as 'scarps,' suggest Mercury is undergoing contraction, they do not precisely reveal how long this tectonic activity has been ongoing. To determine that, scientists turn to impact craters on the planet's surface.
Given that Mercury experiences frequent planetary impacts, researchers can estimate the age of a particular scarp by assessing whether it intersects with older craters. Additionally, if newer craters appear on top of the scarps, it implies that the scarps formed before the associated impacts.
However, a team of scientists has introduced a new method for dating these scarps, shedding light on the last time Mercury contracted. This novel technique involves examining relatively smaller fractures on the scarps, known as "grabens."
As portions of Mercury's crust push against each other, some strips may become trapped and bend, leaving long, crack-like fractures on the scarps — similar to how a slice of bread bends, creating cracks along the fold. Interestingly, this phenomenon is also observed on the Moon.
As Mercury cools, seismic activity causes the planet to shake, potentially loosening boulders and debris that eventually find their way into these grabens. Impacts from extraterrestrial bodies can also dislodge and shift terrain in a similar fashion. Therefore, the presence of unfilled grabens suggests that not much time has passed since their formation.
Armed with this innovative parameter, scientists embarked on a quest to identify such surface anomalies on Mercury's crust. They identified not just one or two but a remarkable 48 large scarps marked by tiny grabens. An additional 244 scarps displayed "probable" grabens, though further examination is required to confirm their nature — perhaps the
The team determined that most of these grabens are likely less than 300 million years old, indicating that Mercury's most recent contraction occurred relatively recently — possibly within the last few million years.
The next piece of this puzzle will likely emerge once BepiColombo provides clearer images of Mercury. Until then, we hope our alien tourist enjoys the renowned Earthly beaches.