Asteroids are rocky bodies that are smaller than a planet and have not entered a planet’s atmosphere, a necessary prerequisite to become a meteoroid. Usually, the term is used to refer to bodies specifically within the solar system, although there are certainly millions of asteroids outside of the solar system. As with tons of objects within our solar system, asteroids can have unique orbits around the sun, and pass within the orbits of other bodies, including that of the Earth, which are dubbed near-Earth asteroids. In fact, dozens of asteroids pass between the Earth and the Moon each year, with asteroid 2020 LD being no exception. The special case here lies within the asteroid’s size: 89-200m, the largest one of the year as of June 9th, 2020. The asteroid had actually passed by on the 5th of June, but had gone undetected until two days after the event on the 7th. Fortunately, at a distance of 0.8LD (80% of the distance to the Moon from Earth), the asteroid was not a significant threat, but a peculiar situation nonetheless.
With such a colossal object in proximity to Earth, the question of how astronomers and physicists can sometimes miss the presence of asteroids by days or even weeks, and other times predict them years in advance still remains. To answer it, one must first look into the process of how near-Earth objects (NEOs) are discovered. To put it simply, wide-field telescopes from various facilities work in conjunction to search for moving objects. They take images over several days, leaving computer programs to point out the moving objects. From there, positions of the NEOs are sent to the Minor Planet Center (MPC), which is responsible for the identification, designation and orbit computation of minor planets, comets and outer irregular natural satellites (including NEOs)”. Other organizations (such as the Center for Near-Earth Object Studies, or CNEOS) can then use the MPC’s huge database to calculate orbits and predict future trajectories of NEOs. The CNEOS has tagged over 18,000 objects from asteroids, comets, and space debris in proximity to Earth. However, an otherwise effective process of tracking and predicting paths of NEOs can be hindered by various factors. For one, as with everything in the universe, the orbits of NEOs can be morphed by other objects (planets, for example), making a long term prediction of a NEO more likely to be inaccurate than a short term one. In addition, some of the smaller (yet dangerous) NEOs pose problems due to shining less brightly in the sky, requiring them to grow nearer to Earth (and more of a threat) in order to be spotted. The sun’s intense luminosity also provides an enormous ‘blind spot’ for NEOs to be discovered. This is because the telescopes used to identify NEOs are on Earth, rather than in outer space. A prime example of the difficulties with tracking NEOs is the asteroid 2019 OK. It had a similar premise to 2020 LD, being somewhat large (although smaller) and was discovered just before it passed. Scientists had attributed the cause to a number of possibilities: the path of 2019 OK’s orbit, for example. According to Alan Duffy, a scientist at the Royal Institution of Australia, 2019 OK’s “very elliptical orbit” would allow it to skyrocket past planets in only a short few weeks, and limited the amount of time that they would be able to spot it in the sky. Perhaps the case of 2020 LD is similar to that of 2019 OK and other asteroids that are undiscovered until just before their closest approach, or afterwards. However, this is all speculative. As of now, a project to construct an infrared space telescope is underway, accurately dubbed the “NEOCam”. If and or when completed, it would provide a crucial angle from which to discover NEOs, and potentially address some of the difficulties with only using grounded telescopes.
Ultimately, it should be said that as vast as our solar system is, we are not entirely isolated as a planet, and due to that, objects like near-Earth asteroids pass a lot more often than most people might imagine them to. The solar system, similarly to our planet, is subject to changes within itself and unexpected events. Because of this, it’s important to remember that although vast, the solar system is not empty by any means, just like how the world is vast yet full of excitement. That, and we have a long way to go in order to ensure that potentially life threatening NEOs are spotted well in advance of their impacts.
Sources
Asteroids. 9 Dec. 2019, solarsystem.nasa.gov/asteroids-comets-and-meteors/asteroids/in-depth/.
“Biggest Asteroid to Pass Close (and Undetected) This Year.” EarthSky, 2020, www.earthsky.org/space/asteroid-2020-ld-closer-than-moon-june-5-2020.
Blašković, Teo. “Asteroid 2020 LD Flew Past Us at 0.8 LD - the Largest within 1 Lunar Distance since 2011.” The Watchers - Daily News Service | Watchers.NEWS, 2020, www.watchers.news/2020/06/09/asteroid-2002-ld/.
Chiu, Allyson. 'It Snuck up on Us': Scientists Stunned by 'City-Killer' Asteroid That Just Missed Earth. 26 July 2019, www.washingtonpost.com/nation/2019/07/26/it-snuck-up-us-city-killer-asteroid-just-missed-earth-scientists-almost-didnt-detect-it-time/.
“Finding Asteroids Before They Find Us.” NEOCam, California Institute of Technology, 2019, neocam.ipac.caltech.edu/.
Near-Earth Object Observations Program. Edited by Tricia Talbert, 28 Mar. 2019, www.nasa.gov/planetarydefense/neoo.
Near-Earth Object. 14 Aug. 2020, en.wikipedia.org/wiki/Near-Earth_object.
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