A 3D model of Mercury, the innermost planet. Move the cursor around to see its pockmarked surface! Source: NASA Visualization Technology Applications and Development (VTAD)
The smallest planet in the solar system, Mercury is only slightly larger than Earth’s Moon and is one we have explored the least. This closest planet to the Sun has no moons and is ring-less. One day on Mercury (the time it takes for it to rotate or spin once with respect to the stars) takes 59 Earth days and one day-night cycle takes 175.97 Earth days. Mercury makes a complete orbit around the Sun (a year in Mercury time) in just 88 Earth days. So, a year there takes less time than a full day-night period. What a strange feeling that would be!
Do you know which is the closest planet to Earth? No, it’s not Venus. On average Mercury is the closest planet to Earth because of its orbital eccenriticity (how much an orbit deviates from a circle).
(Check out the blog on the Voyager spacecrafts)
Mercury formed about 4.5 billion years ago during the early days of our Solar System, when gravity pulled swirling gas and dust together. Like the other terrestrial planets (Venus, Earth and Mars), Mercury has a central core, a rocky mantle and a solid crust. Because it is so close to the Sun, the temperatures and solar radiation that make up Mercury’s environment is too extreme for organisms to adapt to, and it is not conducive to life as we know it.
The first spacecraft to visit the planet was NASA’s Mariner 10, which flew by Mercury twice in 1974 and 1975, mapping out its surface and studying its atmosphere and magnetic field. Then, a second spacecraft, NASA’s Messenger (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), launched in 2004, orbited it for the first time ever in 2011, and also mapped 100% of its surface in 2013.
But it is not over yet!
Europe’s launched its first Mercury mission, Bepi Colombo, on October 20, 2018, from Europe’s Spaceport in Kourou. After a seven year journey, Bepi Colombo will arrive at Mercury in 2025. This is a joint mission between the European Space Agency (Esa) and the Japanese Space Agency (Jaxa), comprising of the Mercury Transfer Module carrying two spacecraft: the Mercury Planetary Orbiter (MPO) and the Mercury Magnetoshpere Orbiter (Mio).
It is named after Giuseppe “Bepi” Colombo (1920–1984), the scientist who first proposed the interplanetary gravity assist manoeuvre used by the 1974 Mariner 10 mission, a technique now used frequently by planetary probes.
Which is why, to enable it to get to Mercury and enter its orbit, BepiColombo has to undertake a number of gravity assist fly-bys of Earth, Venus and Mercury itself. The mission completed its first flyby on April 10, 2020, when it came less than 12,700 km from Earth, capturing stunning images of our home planet just before closest approach, as we face one of the most challenging times in recent history.
Source: European Space Agency
The Bepi Colombo Mission is a challenging one because of Mercury’s proximity to the Sun and its harsh environment, which means that the orbiters and their instruments have to withstand and survive extreme temperatures. The reason it takes so long for a spacecraft to reach Mercury is because the planet’s orbit is difficult for spacecraft to reach and a lot of energy is required to successfully brake it into a suitable orbit around the planet. However, once Bepi Colombo does slide into orbit in 2025, we can look forward to a lot of exciting photographs and scientific data from our smallest planetary neighbour. In the meantime, we can enjoy these amazing images of Earth that it took enroute. (Watch the video podcast on Jupiter)