Yesterday, the BepiColombo probe, a joint venture between Europe’s ESA and Japan’s JAXA, launched on an Ariane 5 rocket from Kourou in French Guiana (YouTube). It marks the beginning of a 7.5 year journey to Mercury, this solar system’s planet closest to the Sun.

Getting from the Earth to Mercury appears to be simple. At their closest, Mercury is about as far away from the Earth as Mars is, and going to Mars (ie. away from the Sun) at its closest would take about 6 months. So, going from Earth to Mercury should be even easier, since you don’t have to fight the Sun’s gravity, right?

Sun’s gravity is actually the problem. First, Earth itself is going round the Sun at quite a speed, averaging about 110,000 km/h. So to get to Mercury, you have to slow down quite a bit. So much so, that there’s currently no rocket on Earth that can feasibly do this, which is why most probes going closer to the Sun rely on so-called gravity assists. BepiColombo, for example, will fly by Earth once, and then pass Venus twice, to lower its orbit far enough so it can reach Mercury. Then, it will fly by Mercury six times to slow down enough to be able to enter an actual orbit around Mercury.

Animation showing BepiColombo’s journey and gravity assists. By Phoenix7777 - Own work. Data source: HORIZONS System, JPL, NASA, CC BY-SA 4.0, Source

Which is why going to Mars at closest approach only requires a comparatively small push from a rocket to send a spacecraft to it. In fact, it took less energy to send the New Horizons probe to Pluto, a dwarf planet so far out it wasn’t discovered until 1930 (Neptune, the 8th planet in our solar system, was discovered in 1846). Both BepiColombo, and the Parker Solar Probe, whose entire point is to get close to the sun, need a lot of energy to do so.

This is counterintuitive for us. Imagine your job is to throw a ball in such a way so it reaches 10 km/h horizontal speed. Even if you can’t throw very well, it’s easy enough to. However, Earth isn’t standing still, so now imagine standing on a moving train, going at, say, 100 km/h. Your job is to throw the ball so it reaches 110 km/h (relative to Earth). Easy, right? You’re already moving at a speed of 100 km/h, so all you need to do is add 10 km/h to it, and you’re done. On the other hand, if your job were to throw the ball on the train in such a way that it reaches a speed of 10 km/h relative to the Earth, then it’s much harder. You’d have to throw the ball with enough force so it loses 90 km/h of speed. There’s not a lot of humans on Earth that could throw any ball that fast.

The other thing is that orbits don’t behave in a way that we’re used to. If you roll a ball down some stairs, it’ll pick up speed, but at the end, it will come to rest at the base of the stairs. If you’re in space, on the other hand, and you threw a ball so it got closer to the sun (rolling down the Sun’s gravity well, so to speak), it will pick up speed until it reaches its closest point to the Sun — and then it will go back up again, eventually coming back up to the point where you threw it initially (unless it hit something on the way).

It’s hard to imagine this, so this YouTube video, that neatly visualizes how gravity works (and why all the planets go around the Sun in the same direction), might help.

Busy Bees

Computers and automation were supposed to give us more leisure, instead we’re more stressed than ever. Why do we feel so busy?

Ancient Voting Systems

When 8-year old Saga Vanecek pulled a 1,500-year-old sword out of a lake, it was an archeological sensation. However, now people are proclaiming her to be the Queen of Sweden, because of King Arthur’s legend. Considering our current political climate, choosing our new heads of states based on this system might actually be an improvement.

Moonmoons

Can moons have moons of their own? Sometimes, yes! It turns out to be a similar problem to what BepiColombo is facing.

Playing Video Games for Change

Attempting to change climate change deniers minds, one battle royale at a time: How a Fortnite squad of scientists is hoping to defeat climate change.

New Social-Media User Guidelines

I hope these go into effect ASAP.

📖 Weekly Longread 📚

“After a hospital error, two pairs of Colombian identical twins were raised as two pairs of fraternal twins. This is the story of how they found one another — and of what happened next”: The Mixed-Up Brothers of Bogotá

🦄 Unicorn Chaser 🦄

Scuba Diving Magazine’s 2018 Underwater Photo Contest Winners