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The case for a deep search for Earth’s Trojan asteroids

Nature Astronomy volume 3, pages 193–194 (2019)Cite this article

The existence of Earth’s Trojan asteroids is not well constrained and represents a major gap in our inventory of small bodies in near-Earth space. Their discovery would be of high scientific and human interest.

Surveys for near-Earth objects (NEOs) do not usually directly observe near Earth’s L4 and L5 regions, owing to their unfavourable viewing geometry from Earth, which requires observing during twilight or dawn hours when the background sky is bright. Moreover, because ETs are never near opposition in the night sky, they present only a partially sunlit hemisphere to Earth observers. Two decades ago, Whiteley and Tholen bravely conducted a survey for Earth’s Trojans from the University of Hawaii’s 2.24-m telescope using an early generation of CCD detectors2. Although their search of the L4 region was frustrated by bad weather, they successfully surveyed 0.35 square degrees of sky near L5; they discovered no ETs brighter than the survey’s limiting R magnitude of 22.8.

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Fig. 1: A schematic diagram to illustrate the triangular Lagrange points (L4 and L5), Trojan asteroid orbits (green) and horseshoe-type orbits (blue).

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Acknowledgements

I thank NASA Nexus for Exoplanet System Science (NExSS; grant NNX15AD94G) and the US National Science Foundation (grant AST-1312498) for research support.

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  1. Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ, USA

    Renu Malhotra

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Malhotra, R. The case for a deep search for Earth’s Trojan asteroids. Nat Astron 3, 193–194 (2019). https://doi.org/10.1038/s41550-019-0697-z

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