Astronomers discovered a new asteroid sharing Earth’s orbit – here’s why it matters
Trojans might make good staging posts for future space exploration
XL5, but no fireball
2020 XL₅ is being called a Trojan companion to the Earth by analogy with Jupiter’s Trojan asteroids. Jupiter shares its orbit with nearly ten thousand known asteroids, half of them ahead of Jupiter, and half behind. The first of those, discovered in 1906, was named Achilles after a central character at thesiege of Troyin Homer’s Iliad.
A convention developed to name each one after a hero from the same story. Only those trailing Jupiter (clustered at the Sun-Jupiter L5 position) are given Trojan names, such as Hektor, whereas those ahead of Jupiter (at L4) are given Greek names, such as Achilles. Collectively, whether at L4 or L5 they are all referred to as Trojans.
Small numbers of Trojan asteroids have now been discovered associated with Neptune (23), Uranus (1), andMars(9). But 2020 XL₅ is only the second Trojan companion of Earth to have been found. The first, 2010 TK₇, wasdiscovered in 2010. That’s only about 300 meters across, so 2020 XL₅ considerably outmasses it at about 1.2km across.
There are probably many more Earth Trojans, but they are hard to discover from Earth because they can only ever be seen fairly low in the pre-dawn sky if at L4 like both 2010 TK₇ and 2020 XL₅, or just after sunset if at L5 (where none have yet been found). Their orbits are not stable over millions of years, so they can’t be remnants that have been there ever since Earth’s formation but must have drifted into place later.
However, the SOAR observations were able to show that 2020 XL₅ appears to be a carbon-rich asteroid (called C-type). So it is a sample of what the Solar System was built from, and it would be instructive to study Earth’s Trojan companions in more detail as examples of unaltered material.
But could we mine them or use them in other ways? Santana-Ros notes that 2020 XL₅ has an orbit that bobs above and below Earth’s orbital plane. This means that to maneuver a spacecraft into a rendezvous (to orbit or land on it) would require considerable velocity change. That would probably need too much fuel to be practical. The same applies to 2010 TK₇.
However, the study points out that if other Earth Trojans are found in orbits that are less tilted, these might make handy bases as staging posts for exploration of the Solar System. They’d be much easier to take off from than from the Earth or Moon because their gravity is so slight. They could even be a source of resources that we could mine.
This article byDavid Rothery, Professor of Planetary Geosciences,The OpenUniversity is republished fromThe Conversationunder a Creative Commons license. Read theoriginal article.
Story byThe Conversation
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