 In 1772, French mathematician Louis Lagrange discovered five points around orbiting objects where gravitational and centripetal forces cancel themselves out. L1, L2 and L3 are on the line connecting the two bodies. They are unstable. That means it takes a small amount of work to maintain and orbit at or around these points. L4 and L5 are on the orbital path of the smaller body. They are found by using equilateral triangles. They are stable, and Lagrange claimed that small objects could orbit these Lagrange points. 134 years later, between 1906 and 1908, four such minor planets were found around Jupiter's L4 and L5 Lagrange points. Asteroids at Lagrange points are called trojans. As of May 2017, we know Jupiter has at least 6,515 trojans. Such objects have also been observed in the orbits of Mars, Neptune and several moons of Saturn. In 2010, we discovered a trojan asteroid orbiting Earth's L4 point, 60 degrees ahead of the Earth called 2010 TK-7. Here we see an animation of 2010 TK-7's orbit. The clock shows how the orbit changes over time. Over the next 10,000 years, it will not approach Earth any closer than 20 million kilometers. That's 50 times further away than the Moon. Our space program takes advantage of these points when we position satellites to observe the Sun. Here we see that L2, where the James Webb Space Telescope will orbit, is four times further away from us than the Moon. We'll cover this a bit more in our section on the heliosphere.