How Many Hydrated NEOs Are There?

Abstract

Hydrated minerals are tracers of early solar system history and have been proposed as a possible focus for economic activity in space. Near‐Earth objects (NEOs) are important to both of these, especially the most accessible members of that community. Because there are very few identified hydrated NEOs, we use the Ch spectral class of asteroids as a proxy for hydrated asteroids and use published work about NEO delivery, main‐belt taxonomic distributions, NEO taxonomic distributions, and observed orbital distributions to estimate the number of hydrated asteroids with different threshold sizes and at different levels of accessibility. We expect 53 ± 27 Ch asteroids to be present in the known population of NEOs >1‐km diameter, and using two different approaches to estimate accessibility we expect 17 ± 9 of them to be more accessible on a round trip than the surface of the Moon. If there is no need to define a minimum size, we expect 700 ± 350 hydrated objects that meet that accessibility criterion. While there are few unknown NEOs larger than 1 km, the population of smaller NEOs yet to be discovered could also be expected to contain proportionally many hydrated objects. Finally, we estimate that hydrated NEOs are unlikely to bring enough water to account for the ice found at the lunar poles, though it is possible that asteroid‐delivered hydrated minerals could be found near their impact sites across the lunar surface.

(704) Interamnia: a transitional object between a dwarf planet and a typical irregular-shaped minor body

“…For instance, the bulk density is compatible within 1 σ error with those of the two largest C-type asteroids, Ceres (2.161±0.003 g · cm −3 , Park et al 2019) and Hygiea (1.94±0.25 g · cm −3 , Vernazza et al 2019), but also of silicate bodies such as (25143) Itokawa (1.90±0.13 g · cm −3 , Fujiwara et al 2006) or (433) Eros (2.67±0.10 g · cm −3 , Veverka et al 2000). Current estimates of the densities of asteroids with masses greater than ∼5 × 10 18 kg imply a small amount of macroporosity within these bodies (Carry 2012;Viikinkoski et al 2015b;Marsset et al 2017;Carry et al 2019;Hanuš et al 2019), and spectroscopic observations of Interamnia in the 3micron region have revealed the presence of hydrated material at its surface (Usui et al 2019) and spectral similarity to Ceres (Rivkin et al 2019). Therefore, we can assume that Interamnia's bulk density is close to that of Ceres.…”

Near-infrared observations of active asteroid (3200) Phaethon reveal no evidence for hydration

“…Ali-Lagoa et al 25 also showed that the albedo of the B-types in Pallas collisional family (p v0 .14) is higher than the average albedo of non-Pallas family Btypes (p v~0 .07). However, Pallas exhibits a sharp and deep 3-µm band (~20%), attributed to the presence of phyllosilicates on its surface 13 , unlike asteroid Phaethon (Fig. 3).…”

“…(2) Pallas has a prominent 3-µm band (~20%) suggesting its surface is phyllosilicate-rich unlike asteroid Phaethon. The prism spectrum of (2) Pallas is from the MIT-UH-IRTF Joint Campaign for NEO Reconnaissance database and the LXD spectrum of (2) Pallas is from Rivkin and DeMeo 13 . The prism spectrum of (3200) Phaethon is from Kareta et al 9 Error bars were calculated using Spextool software and based on the Robust Weighted Mean algorithm with a clipping threshold of 8 (sigma).…”

“…Bus and Binzel 11 classified this asteroid as a B-type according to the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) taxonomy, though it is an F-type in the older taxonomy of Tholen 12 . Other B-type asteroids (e.g., (2) Pallas, (101955) Bennu) are composed of hydrated minerals, as evidenced by a strong absorption near 3 μm 13,14 . However, Phaethon's surface can reach temperatures sufficient to destabilize hydrated materials because of its small perihelion distance.…”

Sharing Planetary Science in Plain Language

“…Authors sometimes ask me for examples of plain language summaries to use as models in preparing their own. Among many strong plain language summaries, here are a few more examples of papers that clearly articulate the main points in plain language (Chabot et al, ; Pan et al, ; Poston et al, ; Rivkin & DeMeo, ; Sizemore et al, ). What is notable about the summaries in these articles is that they provide the relevance of the work clearly to our scientific colleagues at all levels and often in ways that also resonate beyond our scientific community.…”