Earth’s Second Trojan Asteroid

There’s been a lot of talk lately about asteroid mining and resources, particularly among the space-exploration investment folks. The topic is something you hear a lot about from players in the New Space arena. But, how likely is it that we’ll find nearby asteroids to explore and exploit? If you’re an astronomer, how much chance will you get to study asteroids without having to send probes beyond Earth’s orbit?

Those questions and many others are behind the search for nearby ones in stable orbits. They’re called Earth Trojan asteroids. They should lie at the same distance from the Sun as Earth, at orbital positions called LaGrange points. Most of the other planets have their own Trojan asteroids, too, so it shouldn’t be a surprise to find them near our planet.

As it turns out, today we know of two of Earth trojan asteroids. Astronomers confirmed the first one in 2010. It’s called 2010 TK7. and measures about a third of a kilometer across. The second one was just confirmed and announced in the journal Nature Communications on February 1, 2022. It’s called 2020 XL5. It’s bigger, about a kilometer in diameter. There are probably more of these near-Earth and “safe” asteroids nearby, but we haven’t found them yet. Still, they do offer a good place to study for planetary scientists. For the corporate types who see space as a place to make their fortunes, these could be places to mine for resources.

Trojan Asteroids Offer Riches

Earth Trojans have the potential to give us a lot of information about conditions in the solar system at the time Earth formed. That’s because their compositions might be pretty similar to the planetesimals that formed our planet. They could have been orbiting in the same part of the inner solar system as Earth and the Moon. That means their orbital histories may give us insight into the dynamical motions of the time.

Since they’re relatively close to us and in the same orbit as Earth, they could also make good targets for future space missions. The energy requirements are much lower than heading out to Mars and beyond. Finally, in an age where people are talking about mining asteroids, these might be good places to look for scarce minerals.

Finding Earth Trojan Asteroids

These little asteroids are tough to spot. Since they orbit at Earth’s L4 or L5 points, they generally are be seen close to the Sun from Earth. That gives observers a pretty small window of opportunity to observe them. In addition, observing conditions aren’t great at the time when they can be seen, generally just before sunrise. People run the risk of saturating their telescope detectors with sunlight. In addition, they are looking through a thicker part of the atmosphere at the horizon. It’s a risky business to aim a large, expensive telescope during an asteroid search, but there are rewards for those who do.

The Spanish team that found this second Earth Trojan asteroid used the 4.3-meter Lowell discovery telescope in Arizona and the 4.1-meter SOAR telescope in Chile. This discovery was the result, and it’s encouraging news. Certainly, there are others out there; it’s just going to take time and patience to find them out at Earth’s LaGrange points.

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