SMALL & GETTING SMALLER
Mercury, the smallest planet in our Solar System, is closest to the Sun of the eight planets. Its surface temperature rises above 400 degrees Celsius in the day.
But Mercury is cooling down, causing it to shrink. Over the last 3.8 billion years, the planet has shrunk by up to 14 kilometres to reach its current diameter of 4,800 kilometres, scientists at the Carnegie Institution for Science in Washington said on March 16, 2014.
A NASA image released April, 16, 2013 shows the Donalaitis crater on the surface of Mercury. Image credit: AFP PHOTO / HANDOUT / NASA
How did these scientists find out that Mercury is shrinking?
By looking at its surface.
Mercury is believed to have a superhot metallic core, just like Earth. But there is a big difference in the surface of these two planets.
Earth has tectonic plates that bump and slide to handle the stress that heat loss causes on its crust. Mercury has just a single, rigid (inflexible) top layer. When Mercury loses heat, the stress is transferred directly to its surface, causing it to wrinkle into ridges and hollows.
By studying pictures of Mercury's surface, scientists managed to estimate how much Mercury has shrunk. The pictures were taken by NASA's Messenger spacecraft.
An image of Merury's crater-filled surface taken from NASA's Messenger spacecraft. Image credit: AFP PHOTO/NASA
Other cool facts about Mercury
1. Though Mercury is so hot in the daytime, it can get as cold as 180 degrees Celsius below zero at night.
2. Mercury can be seen from Earth in the early morning or late evening sky, but only for a short time. Because it shines so brightly, it is often called a morning star or evening star.
3. Mercury has no atmosphere. That's because it is too small to have enough gravity to hold onto an atmosphere. Any gas that is released by Mercury quickly escapes into space.
Can you imagine what Earth's surface would be like if it had only one single tectonic plate, like Mercury's single layer? Would Earth be as mountainous as it is now?
Featured image: This February 21, 2013 NASA image shows a colourful view of Mercury. These colours are not what Mercury would look like to the human eye. Rather, the colours show the chemical, mineralogical, and physical differences between the rocks that make up Mercury's surface. AFP PHOTO /NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
