Mercury

 

Mercury, the smallest terrestrial planet in the Solar System, is also the closest planet to the Sun. Its closeness to the Sun makes it more difficult to view from the naked eye. Although, it can be observed on the western horizon before sunrise and the eastern horizon after sunset. 

The planet was formed 4.5 billion years ago due to the gravitational attraction between swirling gases and dust particles near the Sun. The planet has a single continental plate over a cooling iron core as its surface. As the core cools down and solidifies, it reduces the planet's volume causing shrink. Mercury, even today, is witnessing shrinkage due to the solidification of iron in its core.

The planet has a diameter of 4880 km, smaller than Ganymede and Titan, the largest moons of Jupiter and Saturn. The planet has a mass of 3.30*10²³kg and a density of 5.43 g/cm³, which makes it the second densest planet in the Solar System, after our home planet Earth. It has an orbital distance of 58 million km, and the mean distance from Sun being 69.433 million km. It completes one rotation in 58 days, 15 hours and 30 minutes. Although, when the planet is rotating at its top speed, every rotation is not accompanied by a sunrise and a sunset. Hence, one solar day on Mercury is equalled to 176 Earth days, making one day over the planet longer than one year, i.e, it completes one revolution around the Sun in 88 days. Mercury receives the most intense solar radiation of all the other cosmic bodies in the Solar System. The Sun's brightness over the surface of Mercury is seven times the brightness over the surface of Earth. However, it is not the hottest planet in the Solar System, the simple reason being it has no atmosphere. Yes, the proximity of the planet to the star is the main reason for the absence of atmosphere over its surface. Talking about the temperature on its surface, it ranges from -170°C to 450°C, which is the highest deviation in temperature out of any planet. This deviation is also a consequence of the absence of atmosphere. 

The planet has been accounted for having an odd spin. If an observer observes Mercury, relative to the fixed stars in the sky, the planet rotates on its axis 3 times for every 2 revolutions around the Sun. The reason for this odd spin is somewhere found in history, around 4 billion years back. An asteroid called Caloris Basin struck the planet with so huge impact that it created a 1550 km wide crater over its surface. 

Theoretically, planets generate magnetic fields if either they spin quickly or possess a molten core. Considering Mercury, it takes around 59 days to spin on its axis and is roughly one-third of the size of Earth, implying the molten iron core should have cooled off long ago. But the planet possesses a magnetic field with a strength of 1% of Earth's magnetic field. Scientists are trying to comprehend the reason behind this. Maybe, the solar wind of the Sun is playing a major role in creating the magnetic field of Mercury, or its core might have not cooled off yet. Also, one strange fact about its magnetic field is that it's 3 times stronger in the northern hemisphere than the planet's southern hemisphere. 

In 1973, a space probe named Mariner 10 was launched by the American space agency, NASA to understand the environment, atmosphere, surface and other characteristics of Mercury and Venus. This mission helped the scientist to get an insight into the planet by having three flybys around Mercury. 

Another space probe named MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging probe) was launched in 2004, to understand the inner planets. It got settled in Mercury's orbit in 2011 and took a 100% image mapping of the planet in 2013. It helped scientists to detect Mercury's magnetic field and found out the icy water caps in its north pole. The probe got disconnected by crashing into the surface of Mercury in 2015. 

Mercury, no doubt is the smallest planet in our Solar System, but it has many chapters to unfold. Scientists are trying to understand its behaviour and then predict its fate. 

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