A Newly Discovered Asteroid Shares Earth’s Orbit and Could Be Key to Space Travel – Popular Mechanics

NOIRLab/NSF/AURA/J. da Silva/Spaceengine

Physicists have discovered a tiny asteroid, about one kilometer wide, that is locked into the same orbit as Earthonly the second such cosmic body of its type that has been identified to date. And now, experts wonder if that asteroid could help us with future space travel.

Known as "2020 XL5," the asteroid will be trapped in Earth's orbit for at least 4,000 years according to simulations detailed in a new paper published earlier this month in Nature Communications. After that, it will escape from that orbit and fly off into our solar system. (It's considered a Trojan asteroid of Earth, following the naming convention for Jupiter's Trojan asteroids.)

In the meantime, 2020 XL5 is held in place due to a far-out concept in orbital mechanics, or the application of the laws of physics to describe the motion of spacecraft. It's called a "Lagrange point," and it's a gravitationally balanced position in space. Earth's new Trojan asteroid orbits Lagrange point 4 (L4) in an elliptical orbit that flings it nearer to the sun than Venus and about as far away as Mars.

Toni Santana-Ros, a postdoctoral researcher at the University of Alicante in the coastal Valencia region of Spain, led the new research on 2020 XL5. His team first spotted the asteroid in December 2020 using the Pan-STARRS observatory, a 1.8-meter telescope located at the summit of Haleakal in Maui, Hawaii. The team wasn't entirely sure that they'd located a new Earth Trojan asteroid, so they followed up by taking images with the Southern Astrophysical Research telescope in Chile.

Why was it so difficult to confirm the existence of this Trojan? It comes down to the "unfavorable viewing geometry of an object orbiting Earth-Sun's L4 or L5 points as seen from our planet," the authors note in the paper. "In short, these objects are often observable very close to the sun (i.e., at low Solar elongations) and under large phase angles (the sun-object-observer angle), meaning that a significant fraction of the object is shadowed as seen from Earth, which in turn implies the object being faint."

NOIRLab/NSF/AURA/J. da Silva

Leonhard Euler, an 18th-century math and physics luminary, first observed these points. (Euler is perhaps best known for his popularizing the use of pi, as well as for his definition of the mathematical value "e," which is the basis for natural logarithms.) Euler discovered the first three known Lagrange points in the Earth-Sun system; these points of gravitational equilibrium between Earth and the sun are called L1 (Lagrange point 1), L2 (Lagrange point 2), and L3 (Lagrange point 3). All three fall along the same imaginary line that passes through both Earth and sun; two are on either side of Earth, and one is on the far opposite side of Earth's orbit around the sun.

Euler's studentJoseph-Louis Lagrange, the namesake of Lagrange pointsdiscovered the fourth and fifth such points, L4 and L5. These points fall a "distance" of two months away from Earth (both in front of and behind it), along its orbital path around the sun.

That brings us back to Lagrange points, which represent a special case of the "three-body problem," an unsolved issue for astronomers who want to track the collision course of three stars hurtling toward one another through space. The reason we can solve for Lagrange points is that the third bodyhere, 2020 XL5is tiny compared to Earth and the sun. It's like solving a system of equations by zeroing out one of the variables.

If massive gravity is one of the reasons that these Lagrange points are so stable, then it makes sense why Jupiter, the most massive (and nearly starlike) planet in our solar system, is absolutely loaded with objects in its Lagrange points. Between its L4 and L5 positions, there are an estimated 10,000 asteroids. Earth has just two known Trojan asteroids to date: 2020 XL5 and another called 2010 TK. But Jupiter's abundance of L4 and L5 objects may help scientists find more around Earth.

NOIRLab/NSF/AURA/J. da Silva

Lagrange points are mathematically cool and they represent the accumulated centuries' worth of astronomy work that has helped to create the scientific climate in which scientists discover new objects today. And Lagrange points have practical uses, too. That's because they form naturally stable little pockets where human-made objects, like satellites, can safely stay in place without using very much energy. The James Webb Space Telescope, for instance, is parked in orbit around Lagrange point 2 (L2), a gravitationally semi-stable location in space aligned with Earth and the sun.

But could we use Lagrange points in other ways? Santana-Ros notes that 2020 XL 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 a considerable velocity change; that would probably require too much fuel to be practical. The same applies to 2010 TK.

However, the new 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 Earth or the moon because their gravity is so slight. They could even hold a wealth of resources that we could mine.

Perhaps most interestingly, objects like the 2020 XL Trojan asteroid could help humans edge further and further into outer space. We can easily predict where these objects will be, and we can land on and take off from them with almost no interference from gravity. This could mean turning flights to Mars into ones with a brief layover, helping to close the technological gap between the enormous power needed to leave Earth's gravity and the much steadier "pulse engine" type power needed to travel to Mars.

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A Newly Discovered Asteroid Shares Earth's Orbit and Could Be Key to Space Travel - Popular Mechanics