Mercury, like the Moon, is a planet. It has no atmosphere and is covered with round impact craters and massive spherical basins. The majority of Mercury resembles the lunar highlands; it appears to have been exposed to the same bombardment that sculpted the Moon in primordial periods. But there are also regions where you can see signs of tectonics having been at work, probably delivering water from deep within the planet's body.
Both planets have very thin atmospheres made up of gas molecules that are visible from their surfaces. On Earth, the atmosphere extends more than 6,000 miles (10,000 km), but on Mercury it is only about 60 miles (100 km).
The Sun lights up Mercury just as it does the Moon. But because Mercury is so much closer to the Sun, it gets hotter during its elliptical orbit. The surface temperature ranges from -300 degrees F to 450 degrees F, depending on the region. Water vapor may exist in the air above certain places on the planet. But because there is no air or other substance to reflect sunlight back to space, most of the planet is too hot for liquid water to remain on its surface.
Like the Moon, Mercury has had life on it at some point in the past. But unlike our moon, which is protected by its distance from the Earth's gravity, Mercury is extremely hazardous to life as we know it.
Mercury resembles Earth's moon in appearance. Mercury's surface, like our moon's, is riddled with craters created by space rock strikes. Mercury has a thin atmosphere of atoms that have been blasted off its surface by solar radiation. This atmosphere swiftly escapes into space and is renewed on a regular basis. The composition of this atmosphere is unknown but it probably contains hydrogen, helium, and traces of other elements.
Like the Moon, Mercury has been greatly affected by meteoroids from outside the Solar System crashing into it. These impacts have left characteristic marks on the planet's surface that can be seen from Earth with modern telescopes.
A number of missions to Mercury have been launched over the years. MESSENGER was the first ever spacecraft to orbit around the planet and study it from close up. It began orbiting Mercury in April 2011 and will continue to do so for three years before running out of fuel and being destroyed on impact in March 2014.
So, why are people often surprised to learn that the Moon is actually a fainter object than thought? Because it gets overshadowed by objects of greater brightness, such as stars or galaxies. The Moon isn't even the darkest object in its vicinity; deep-space dust clouds are far darker than the Moon.
The Hubble Space Telescope has revealed many interesting features about the Moon that we would never know about otherwise.
But because Mercury is so much closer to the sun, it experiences much more intense heat and pressure than our lunar companion.
The Earth's moon is always visible in the night sky, but because Mercury orbits so close to the sun, it never gets dark at Mercury's equator. Instead, it just goes from light to very bright then back again every 8 minutes 40 seconds.
Mercury has 11 days when the planet is completely illuminated by sunlight, and another 29 days when parts of it are shaded from view. The remaining 30% or so is covered by cloud cover.
During a total solar eclipse, only Mercury's east coast is fully illuminated by the Sun. Because of this, astronomers can see features on its surface they could not otherwise detect.
Total solar eclipses aren't seen everywhere, because they require a path through the atmosphere with less oxygen than usual. So if you live in an area that doesn't experience these events often enough to develop an atmosphere rich in oxygen, you're out of luck!
In general, Mercury's surface resembles that of the Moon (i.e., heavily cratered due to a lack of a heavy atmosphere to erode away primordial impacts). The only difference between the two planets is that the Earth has preserved evidence of past life, while Mercury's surface has been completely destroyed by collisions.
The most likely explanation for this similarity in appearance is that both planets were once covered in many layers of regolith (rocks broken up by ice) that were subsequently removed by meteoroids. The only way to find out if this is true is to look at other airless bodies in our solar system.
Mercury has a relatively small mass compared to the Earth and the Moon, which means that it can be significantly affected by collisions. The most recent collision with a large object probably occurred about 4.5 billion years ago, when another planet called Mars hit mercury exploding and destroying much of the planet.
After this collision, most of Mercury was turned into an extremely hot mantle surrounded by a cold crust. The remaining part of the planet consisted mainly of iron and nickel with some silicon and calcium exposed on the surface.
Mercury is a planet. Mercury is the eighth biggest planet and the closest to the sun. It orbits the sun once every 87 days.
Venus is another planet. Like Mercury, Venus also resembles Earth's moon in appearance. But because Venus is more earth-like, this makes it less lunar-like. The atmosphere of Venus is so thick, it's made up of 95% gas. This causes climate change, because the gas can block out sunlight! Venus has an extremely hot temperature, about 480 degrees Fahrenheit (250 degrees Celsius). Water may have once existed on Venus but it was probably completely vaporized by the heat of the sun!
Mars is the third planet. Mars also resembles Earth's moon in appearance. But because Mars is more rocky-like, this makes it more lunar-like. The atmosphere of Mars is made up of 50% oxygen and 50% carbon dioxide. There might be water under Martian soil if you look closely enough but it would be hard to find since all signs of life have been lost. Mars is smaller than Earth and takes 687 days to orbit the sun.
Jupiter is the fifth planet.