UR: Characterising the Risk to Earth of Potentially Hazardous Asteroids

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Leah Bigwood

Durham University

Leah Bigwood is a fourth year undergraduate Physics and Astronomy student studying at Durham University in the UK. This research was carried out as part of the Level 3 Advanced laboratory module, supervised by Professor Mark Swinbank.

Near Earth asteroids (NEAs) are asteroids with orbits in close proximity to Earth, conventionally defined as having a perihelion distance less than 1.3 AU. The interval between Earth impacts by NEAs is predicted to be at least 10,000 years; significantly greater than the time interval between natural disasters that cause a similar level of regional damage. However, the international endorsement of the Alvarez hypothesis in 2010 stated that a hugely destructive NEA impact has happened before. The hypothesis states that a massive asteroid, with an estimated diameter of 10 km, caused the Cretaceous–Paleogene mass extinction which resulted in the eradication of numerous animal groups, most notably the non-avian dinosaurs. Therefore, despite impacts being less likely compared to natural disasters, NEA collisions have more significant consequences– shared only by nuclear war – in the potential breakdown of civilisation. 

For my research project, I assessed the risk of three potentially hazardous NEAs. During the autumn of 2020, we observed the targets Ryugu, 2002 UQ3 and Hermes several times a week using the AstroLab telescopes at Durham University to track their equatorial coordinates. I then determined the best-fit Keplerian orbit for each target using the software ‘Find_Orb‘. This allowed us to generate their positions with respect to Earth until 26th March 2121. 

The image shows a 3D diagram of the trajectory in space that Ryugu, 2002 UQ3, Hermes and Earth follow with respect to the Sun, over one full orbit.  Four additional diagrams are displayed below, showing the orbits at different orientations.  Earth’s orbit is circular, whereas the orbits of asteroids are more eccentric, with 2002 UQ3 having the largest eccentricity. The orbit of 2002 UQ3 is inclined at the greatest angle from the Earth’s orbit around the Sun, whereas Ryugu’s orbit has only a small inclination with respect to the plane of the Earth’s orbit.
3D diagrams of the orbits of Ryugu, 2002 UQ3, Hermes and Earth with respect to the Sun, with the subfigures showing this at different orientations. Distances are in Astronomical Units (AU), with the Sun fixed at (0,0,0) and the x-y plane the plane of the Earth’s orbit around the Sun.

Defining a close approach as a target coming within 0.05 AU of Earth, I predict that only Ryugu will fulfil this criteria. Ryugu will make a close approach between 24th November 2081 and 24th December 2081, reaching a minimum distance from Earth of 0.018 ± 0.001 AU on 9th December 2081 – approximately seven times the Earth-Moon distance. We define a safe close approach distance as distances greater than the Earth’s radius, though this neglects effects which can perturb the orbit, such as the Yarkovsky effect. From this, we conclude that alongside Hermes and 2002 UQ3, Ryugu poses no risk of impacting Earth in the next 100 years and no mitigation plans are currently required.

Astrobite edited by: Emma Foxell

Featured image credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST.

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