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Why BepiColombo is going to explore our smallest, wrinkliest planet

It's got a fantastic name and it's hurtling toward the center of our solar system. What will BepiColombo discover when it gets to Mercury?

ESA/ATG medialab; Mercury: NASA/JPL

Right now, it feels like everyone and their moon-dog are talking about expeditions to Mars. But for the European Space Agency and the Japanese Aerospace Exploration Agency, the focus is on the first rock from the sun, Mercury.

Their BepiColombo mission is set to spend the next seven years making its way to Mercury to learn more about how the planet formed, what it's made of and what it tells us about the birth of our solar system.

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The mission is named for Italian mathematician Giuseppe "Bepi" Colombo, the first person to explain Mercury's curious rotation pattern. It's only the third mission to set its sights on Mercury, after NASA's Mariner 10 mission, which launched in 1973, and NASA's Messenger mission, which launched in 2004. 

In this week's edition of Watch This Space, we take the big questions that BepiColombo seeks to answer about Mercury.

What is Mercury made of?

We know about the subsurface lake on Mars, and we know what Jupiter sounds like, but we know very little about Mercury's composition. BepiColombo is going to investigate whether it has a solid or liquid core, and whether it's packed with iron as we suspect. 

A look at the BepiColombo mission schedule.

Loren Roberts/The Planetary Society

Wrinkles and craters...

BepiColombo is set to map Mercury's surface and its many craters, including the dent left by the crash-landing of Messenger. It's also going to look for evidence of geological activity. From Messenger's photos of wrinkles on the surface of Mercury, we know the planet is shrinking, so what does this tell us about tectonic activity on the planet?

Where did it come from?

For a planet that's (relatively) close to us and within (relative) spitting distance of the sun, we don't know a great deal about how Mercury formed. And what we have observed doesn't quite add up.

According to David Rothery, professor of planetary geosciences at the UK Open University, "so much about it seems wrong for a planet that close to the sun." Rothery suggests that Mercury could have originated from "further out" in the solar system and that it could have collided with a "proto-Earth or proto-Venus," robbing it of its original rock. Once we know more about Mercury's early years, we can better understand the conditions that formed the planets across our solar system.

How does it survive that close to the sun?

As the closest planet to the sun (at a distance of 36 million miles, or about one-third as far as the Earth), Mercury faces extreme conditions. To start, it feels the force of the sun's solar wind, and BepiColombo is going to investigate how that solar wind interacts with Mercury's magnetosphere. 

The planet also has no real atmosphere, so there's very little to stop impacts with the planet's surface (see: craters). Temperatures are extreme. According to NASA, its sun-facing side gets temperatures of 801 degrees Fahrenheit (427 degrees Celsius), and the side facing away from the sun drops to -279 degrees Fahrenheit (-173 Celsius).

Is there ice on Mercury?

According to the ESA, we know there's water on Mercury. But BepiColombo is on a hunt to find out whether the "permanently shadowed craters" on Mercury's cold side are hiding ice. Is it pure water? And if there are other materials mixed in with the water, does that tell us anything about the origin of the ice?

What's next?

After launching in Oct. 20, BepiColombo has an almost decade-long mission ahead of it. Pop these key dates in your diary: 

  • April 13, 2020 -- Earth flyby
  • Oct. 16, 2020 -- First of two Venus flybys 
  • Oct. 2, 2021 -- First of six Mercury flybys
  • Dec. 5, 2025 -- Arrival at Mercury
  • March 14, 2026 -- Mercury Planetary Orbiter in final orbit
  • May 1, 2027 -- End of nominal mission

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