Why BepiColombo is going to explore our smallest, wrinkliest planet

Right now, it feels like every man and his moon-dog starts is talking about sending expeditions to Mars. But for the European Space Agency (ESA) and the Japanese Aerospace Exploration Agency (JAXA), the focus has been on the first rock from the sun, Mercury.

The BepiColombo mission is set to spend the next seven years making its way to Mercury in a bid to learn more about how the planet was formed, what its made of and what it tells us about the birth of our Solar System.

The mission, named for Italian mathematician Giuseppe “Bepi” Colombo, (the first person to explain Mercury’s curious rotation pattern) is only the third mission to set its sights on Mercury, after NASA’s Mariner 10 and Messenger missions. But even though Mercury hasn’t had that much attention over the years, it still has a lot to show us.

In this week’s edition of Watch This Space, we take a look at Mercury and the BepiColombo mission and work out the big questions it has to answer. 

What is Mercury made of?

We know about the sub-surface lake on Mars, and we know what Jupiter sounds like, but we know very little about Mercury’s composition. BepiColombo is going to investigate what Mercury is comprised of, whether it has a solid or liquid core, and whether the planet is packed with iron like we suspect. 

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 was formed. And what we have seen 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.

What does it take to 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 some 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. 

But it also has no real atmosphere to speak of, so there’s very little to stop impacts with the planet’s surface (see: craters) and temperatures are extreme. According to NASA, it’s sun-facing side gets temperatures of 801 degrees Fahrenheit (427 degrees Celsius), but the side facing away from the sun drops to -279 degrees Fahrenheit (-173 Celsius). How does this affect life (or lack thereof) on Mercury?

Is there any ice on Mercury

According to the ESA, we know there’s already existing 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. 2018, BepiColombo has an almost decade-long mission ahead of it. Pop these key dates in your diary: 

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

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