Everybody knows and adores the Moon. It has been a stalwart of the heavens and Earth's steady friend for billions of years. But it's not the only one we have.
Occasionally, a smaller object is caught briefly in the orbit of our planet, hanging out there for a few months or years, and then being sent back into space.
We refer to these asteroids as minimoons, and even while we have detected a handful of these momentarily caught asteroids, only two have ever been confirmed: 2006 RH120, which visited Earth in 2006 and 2007, and 2020 CD3, which orbited the planet from 2018 to 2020.
The new object, 2020 SO, has been discovered by astronomers and is now travelling toward Earth on a course that would likely result in a brief capture by the planet's gravity. According to projections, an object will touch down next month, in October 2020, and remain there until May 2021, at which point it will leave for surroundings somewhere.
The object's trajectory predicts that it will pass through two of Earth's Lagrange points, which are gravitationally stable regions produced by Earth's gravitational interaction with the Sun. You can see these spots in the simulation below.
If there were no twist, this would be very notable. Experts believe that 2020 SO is not an asteroid because of its Earth-like orbit and low velocity; rather, these features are more compatible with a man-made object.
In the JPL Small-Body Database, 2020 SO has been identified as an Apollo asteroid, a category of asteroids whose trajectories overlap the orbit of the Earth. Near Earth collisions with this kind of asteroid are frequent. However, there are some indications that 2020 SO is unique from the others.
The object is travelling along the same orbital route as Earth and has an orbital period of only a little bit over a year. It also has an extremely low inclination with regard to Earth's orbit. Its eccentricity, or how far from a complete circle its orbit deviates from the circular form, is somewhat greater than Earth's. And compared to an Apollo asteroid, its velocity is far lower.
Space anthropologist Alice Gorman of Flinders University in Australia told ScienceAlert that "the velocity looks to be a key one." "It's just travelling too slowly, which mirrors its beginning velocity, from what I can discern. That basically gives everything away."
Asteroids and Moon rocks have slower velocities than each other, but 2020 SO is considerably slower, according to Gorman.
All of this suggests that the object could be space trash, namely, according to Paul Chodas of JPL, the Centaur stage of a rocket that was abandoned after launching Surveyor 2, an experimental payload, to the Moon in September 1966.
Because recovery is extremely technically challenging, reusable rockets have only recently been developed. Launching multiple-stage rockets that were intended to disintegrate was a common option for decades. The remainder of the rocket, which is responsible for carrying the payload, is eventually abandoned in orbit while the booster stage falls back to Earth to be reused.
These abandoned stages contribute significantly to space debris. Gorman also claims that they are shockingly simple to lose.
It may often be rather unexpected in the space environment since there are so many variables, such as gravitational effects and other elements that impact mobility.
"These things need to be monitored because it's quite easy to lose sight of them. You won't know where it went if they do anything a little bit unusual and you glance the wrong direction. The sheer quantity of lost items is pretty astounding."
2020 SO's projected size is consistent with the characteristics of a Centaur stage from the 1960s. The object is between 6.4 and 14 metres (21 and 46 feet) length, according to NASA's CNEOS database; a Centaur stage is 12.68 metres long (41.6 feet).
A moving bright object, like a dot in the night sky, is how asteroids are seen. We can estimate the size from it and deduce the velocity and orbit, but we are unable to tell the form or composition without more thorough observations.
The 2020 SO will pass Earth twice in tight formation. It will pass by on December 1, 2020, at a distance of around 50,000 kilometres (31,000 miles). It will pass past at a speed of 220,000 kilometres on or around February 2, 2021.
Both are too far away to penetrate Earth's atmosphere, making the object completely safe. But such distances, especially at modest speeds, could be sufficient to investigate it further and figure out what 2020 SO is.
We may be able to discern a general form. If the item is painted, spectroscopy may be able to assist identify it. Additionally, the amount of light it reflects could even be useful for long-term space mission planning. If the 2020 SO spacecraft is that 1966 Centaur stage, it has been in orbit for 54 years, braving the vacuum of space.
In order to determine how rough the surfaces are and how much they have been pitted and degraded by being pummelling by dust and tiny meteorites, Gorman suggested doing some reflectance spectroscopy.
"It is human stuff that has travelled to another region of space. It would be intriguing to contrast those findings with those from material in low Earth orbit, which is much, much denser."
Of course, the characteristics of 2020 SO may aid in the future detection of such near-Earth objects, whether or not it is a rocket stage. If it's man-made, then we have a little bit more evidence to suggest an anthropogenic origin the next time we come across an item with comparable characteristics.
If it's an asteroid, we have a really peculiar rock on our hands that shows how unpredictably asteroids may move, much like rocket stages.
We will thus be able to learn a lot from our forthcoming mystery visitor, whatever the 2020 SO may be.
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