Chasing nomadic worlds: A new class of deep space missions (original) (raw)

Acta Astronautica

Abstract

Nomadic worlds are objects not bound to any star(s), and are of great interest to planetary science and astrobiology. They have garnered attention recently on account of their detection in microlensing surveys and also from the recent discovery of interstellar planetesimals. In this paper, we evaluate the prevalence of nomadic worlds with radii of 100 km ≲ R ≲ 10 4 km, which might permit habitable conditions. The cumulative number density n > (> R) appears to follow a heuristic power law given by n > ∝ R −3. Therefore, smaller objects should be much more numerous than the largest rocky nomadic planets, and thus statistically more likely to have members relatively close to the inner Solar system. Our results suggest that tens to hundreds of planet-sized nomadic worlds may populate the spherical volume centered on Earth and circumscribed by Proxima Centauri, and thus may comprise closer interstellar targets than any stellar planetary system. For the first time, we systematically analyze the feasibility of exploring these unbounded celestial bodies via deep space missions. We investigate what near-future propulsion systems could theoretically enable us to reach nomadic worlds (of radius > R) on a 50-year timescale. Objects with R ∼ 100 km are within the purview of multiple propulsion methods such as electric sails, laser electric propulsion, and solar sails. In contrast, nomadic worlds with R ≳ 1000 km are accessible by laser sails (and perhaps nuclear fusion), thereby underscoring their vast potential for deep space exploration.

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