Have any Earth-based astronauts ever set foot on Mercury? No, Earth's spacecraft have visited Mercury, but no person has ever gone into orbit around Mercury, let alone trod on its surface. Mercury's equatorial surface temperature climbs to 700 Kelvin during the day (427 degrees C). At night it drops to 400 Kelvin (275 degrees C). Astronauts aboard the Apollo space vehicles landed on the Moon instead, but those missions were part of an extensive program designed to explore Earth's nearest neighbor.
Did you know that there is a city on Mercury called Marius Hills? It was named after the first human monarch, who was also known as "the great" or "the noble" Marius.
Another interesting fact about Mercury is that it is the only planet that does not have any oceans. The only water on Mercury is held in the form of ice deposits at its poles.
However, there is evidence that under certain conditions, some of this polar ice may be able to flow off the planet back toward its sunlit side. If this did happen, it would cause some major problems for Earthlings because most of the ice deposits on our planet are found near the poles, where they provide sea shelves and act as barriers against climate change. The loss of these protective layers could have serious consequences for Earth's environment.
Here on Earth, we need ice shelves in order to maintain a stable climate.
Because Mercury is devoid of oxygen, they would require a spacesuit to shield themselves from the vacuum of space. The temperatures on Mercury, on the other hand, are substantially higher. They would need thermal protection as well.
The Earth's companion planet shares some similarities with our own world, but also some differences. They are both small planets, with a ratio of spin to orbital period that is slightly less than two-thirds that of Earth (which gives them 12 hours of daylight each day). But while Earth has one ocean and Mercury has a large iron core surrounded by a metallic crust, Mars has the same amount of water ice at the bottom of its polar caps, but with a thick carbon dioxide atmosphere that blocks out most of the sun's radiation and turns the planet into a cold desert.
Moons have been found orbiting both Earth and Mercury, but not all moons are born equal. Some more massive bodies may destroy their parent planets during or after formation through tidal forces or collisions. The Moon is a good example: It is probably a remnant from the early formation of the Solar System that was once part of another planet that was destroyed long ago.
For almost than 30 years, no spacecraft has visited Mercury. Then, in 2008 and 2009, NASA's MESSENGER spacecraft sailed by Mercury. It began its orbit around Mercury on March 17, 2011. After three months of flying over the planet's surface, MESSENGER snapped more than 100 photos and collected samples of rock and dust from within 10 miles of the surface.
You may be wondering why we need another mission to Mercury. As you probably know, Mercury is always visible in the night sky as the bright object that moves across the face of the moon. Because it is so close to the sun, however, Mercury has an extremely eccentric orbit, taking 87.9 days to complete one trip around the Sun. This makes it impossible for us to visit it permanently; any spacecraft sent there would have to return before being engulfed by the solar heat.
The first attempt to reach Mercury occurred with Soviet astronomer Lyudmila Ivanovna Chernykh's proposal for a Venus-Mercury Earth-Mars probe. Her plan was accepted but never developed due to limited resources. In 1961, the United States launched the first spacecraft to orbit another planet when Mariner 2 flew by Mars. The following year, Congress canceled further attempts at reaching Mars as well as plans for other missions including a lunar probe.