Astronomy – Is our moon Earth’s only companion?

We know that the moon orbits the earth, but did you know that we have two other confirmed companions?

If you have been following the James Webb telescope launch, you may remember that the telescope will be parked at a point far from Earth called a Lagrange point. This is where the gravitational effect of the Earth on an object is balanced by the force of the sun and moon. These points can be used by spacecraft to reduce fuel consumption needed to remain in position.

In 2010, scientists discovered a small asteroid at Lagrange Point 4 (L4), called 2010 TK7. This asteroid has been confirmed to orbit along the same path as Earth. Asteroid 2010 TK7 is nearly 300m across and currently leading the Earth by about 80 million kilometres. 

These kinds of asteroids trapped at the Lagrange points are called Trojan Asteroids and can be found around Jupiter, Neptune and Mars as well. 

In a new study, researchers confirmed that an asteroid spotted in 2020, called 2020 XL5, is a second Earth Trojan asteroid. It is found at the same L4 point as 2010 TK7 but measures about 1.2 kilometres across, almost three times longer than 2010 TK7. 

They also predict that 2020 XL5 won’t be an Earth Trojan asteroid forever. While it will stay in its current position for about 4000 years, it will eventually escape its gravity-bound location and move off into the solar system.

Could we find more of these objects at the other Lagrange points? Quite possibly. Because of their locations, it makes it quite hard to observe L4 and L5 from Earth as any asteroid orbiting around these points will only be visible during a short time window close to twilight, at very low elevations above the horizon.

We do, however, have the Pan-STARRS 1 survey telescope in Hawaii, which discovered both these Trojans. We can also use the SOAR (Southern Astrophysical Research) Telescope in Chile along with the Lowell Discovery Telescope in Arizona and the European Space Agency’s Optical Ground Station in Tenerife in the Canary Islands. This collection of telescopes may find a few more of these elusive objects.

One future option may be to mine them, as they could be filled with minerals which are very rare on Earth. Such a task would be extremely difficult and costly, but the profits could ultimately make it worth the cost.

What other hidden objects may be lurking relatively close to Earth? Only time will tell.