Mankind has sent a total of 35 missions to Mars and 40 to Venus, but only two spacecraft have ever visited the planet Mercury.
Why?
Because you’re heading Sunward into a star’s enormous gravity well and must use rockets if you want to slow down and check out this little planet.
Visiting Mercury actually takes more fuel than you would need to exit the Solar System!
It’s so difficult that of course we tried to do it…and succeeded.
Mariner 10 and Messenger
In the 1970s, Mariner 10 used the gravity of Venus to slow down (and incidentally became the first spacecraft ever to visit multiple planets during flight). Mariner imaged parts of Mercury as it flew by. Then it was shut down and probably orbits the Sun now.
In the 21st century, a more complex craft called Messenger used a flyby of Earth and two flybys of Venus to get into a Mercury orbit – the first one ever achieved. The mission is ongoing. Messenger is mapping parts of Mercury that Mariner couldn’t reach, as well as analyzing the planet’s surface, space environment and geochemistry.
These two missions have shown that Mercury is one of the Solar System’s most interesting objects.
Cool Facts About Mercury
The Hubble Telescope can’t be turned toward the Sun, but today we know quite a bit about Mercury, thanks to Mariner 10 and Messenger.
What you’d see if you went to Mercury
- The surface is generally gray and has been shaped by impacts, nonexplosive volcanism, and planetary “wrinkling.”
- One of the largest impact craters in the Solar Systems is Caloris Basin
- Just like our Moon, Mercury has maria-like smooth plains, but they’re the same gray as the rest of Mercury’s surface rock. The Moon, by comparison, has white anorthosite highlands contracting with the dark basalt in its maria.
- If you were standing on Mercury, the Sun would be more than three times larger, per NASA. I don’t know why it wouldn’t fill the sky
- Mercury turns on its axis approximately once every 59 Earth days and orbits the Sun once every 88 or so Earth days. However, thanks to Mercury’s eccentric orbit and the perturbations on that orbit caused by the Sun and other planets, the planet is locked into something called spin-orbit resonance: it turns on its axis three times for every two orbits. This means that while the planet itself rotates once every 59 days, a day there (just going by the apparent movement of the Sun across the sky) takes roughly 176 Earth days!
Could you live on Mercury?
Not very easily.
- The daily temperature swings between -290 degrees F (-180 C) and 800 degrees F (430 C) in some equatorial regions
- The planet has occasional “magnetic tornadoes” that funnel the solar wind down onto the surface
- Mercury is too small and hot to have a regular atmosphere. There’s just an ever-changing collection of, mostly, vaporized oxygen, sodium, hydrogen, helium, and potassium floating around. It’s probably from degassing. meteor impacts, and sublimation of water ice
- Yes, water ice. Ice has been detected in deep craters at both Mercurian poles and scientists believe it’s most probably frozen H2O
- You would weigh 62% less on this planet than you do on Earth, or about the same as you would on Mars (even though Mercury is smaller than Mars, it is very dense and so has more overall gravitational pull)
Mercury’s place in the Solar System
- Mercury’s passage in front of the Sun was the first planetary transit ever observed on Earth (in 1631, by Pierre Gassendi). Mercury’s transit on June 3, 2014, was seen by the Curiosity rover on Mars – the first planetary transit ever observed from another planet
Mercury Rising: I saw the planet cross the sun—a 1st from any planet but Earth http://t.co/IvdbcYgd86 pic.twitter.com/eg1LVgnpFb
— Curiosity Rover (@MarsCuriosity) June 10, 2014
- Besides being the smallest planet, Mercury is also smaller than two of Jupiter’s moons. It is slightly larger than our Moon
- Mercury has no moons or rings
- There are no tall volcanoes on Mercury, unlike Mars and Earth. However, its smooth plains are of likely volcanic origin
- Mercury has a very high density (second only to Earth). This is probably because its core makes up an estimated 80% of its volume and is probably mostly iron
Interesting science-related things
- Vulcan was the name of a hypothetical planet proposed in the mid-18th century to explain slight perturbations in Mercury’s orbit. It has never been found. Perhaps Nero got there before we did
- Changes in Mercury’s orbit verified Einstein’s theory of relativity
- Mercury’s surface appears folded in places. These ridges criss-cross the plains and probably formed tectonically as Mercury cooled some 3.7 billion years ago. The surface also flexes frequently – the Sun exerts a tidal force there that’s 17 times as high as ours.
- The first planet from the Sun also has a section of hilly “weird terrain” on the opposite of the planet from Caloris Basin. No one knows how it formed, but some scientists suggest that either shock waves or ejecta from the Caloris impact might have circled around tiny Mercury and converged at this point.
“The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!’ but ‘That’s weird…'” Issac Asimov, allegedly. Image source
Planned future missions
The BepiColombo missino will start for Mercury in August 2015. A composite spacecraft will carry two orbiters. JAXA, Japan’s space agency, is sending an orbiter to study the planet’s magnetosphere. The European Space Agency is providing a mapping orbiter to study the surface and internal structure.
Mercury is one of the least-studied of the Sun’s planets. Mariner 10 and Messenger have revealed some surprises there. Future missions to Mercury will probably uncover even more, as well as teach us more about the internal structures of planets and how magnetospheres, like the one that shields our planet, form and interact with the solar wind.
A manned mission to Mercury isn’t in the cards for the foreseeable future. Perhaps this is as it should be. Let us respect the memory of Icarus.
Update, October 15, 2020: Here is a close-up of Venus taken by the latest Mercury mission, BepiColombo, as it passed by!
A spacecraft on its way to Mercury took these amazing black & white images of Venus *yesterday* from a distance of around 10,000 km. The 64 images were taken every 52 seconds by @BepiColombo, which arrives at Mercury in 2025 (https://t.co/CtyYRUnZ9I) pic.twitter.com/QGiqeQG4zW
— Dr James O'Donoghue (@physicsJ) October 15, 2020
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Sources:
- The Solar System: Mercury. NASA
- Mercury. Wikipedia
Flight To Wonder 