Visible Spectroscopy from the Mission Accessible Near-Earth Object Survey (MANOS): Taxonomic Dependence on Asteroid Size

Abstract

The Mission Accessible Near-Earth Object Survey (MANOS) aims to observe and characterize small (mean absolute magnitude H ∼ 25 mag) Near-Earth Objects (NEOs) that are accessible by spacecraft (mean ∆v ∼ 5.7 km/s) and that make close approaches with the Earth (mean Minimum Orbital Intersection Distance MOID ∼ 0.03 AU). We present here the first results of the MANOS visible spectroscopic survey. The spectra were obtained from August 2013 to March 2018 at Lowell Observatory's Discovery Channel 4.3 meter telescope, and both Gemini North and South facilities. In total, 210 NEOs have been observed and taxonomically classified. Our taxonomic distribution shows significant variations with respect to surveys of larger objects. We suspect these to be due to a dependence of Main Belt source regions on object size. Compared to previous surveys of larger objects (Binzel et al. 2019Perna et al. 2018), we report a lower fraction of S+Q-complex asteroids of 43.8 ± 4.6%. We associate this decrease with a lack of Phocaea family members at very small size. We also report higher fractions of X-complex and A-type asteroids of 23.8 ± 3.3% and 3.8 ± 1.3% respectively due to an increase of Hungaria family objects at small size. We find a strong correlation between the Q/S ratio and perihelion distance. We suggest this correlation is due to planetary close encounters with Venus playing a major role in turning asteroids from S to Q-type. This hypothesis is supported by a similar correlation between the Q/S ratio and Venus MOID.

A common origin for dynamically associated near-Earth asteroid pairs

“…The observed fraction of V-type NEOs is ∼2-4% (Perna et al, 2018;Binzel et al, 2019;Devogèle et al, 2019) and the debiased fraction is lower ∼1% (Stuart & Binzel, 2004). Thus there is only a ≤ 0.2% chance of finding two V-type NEOs if randomly selecting any two objects from the population.…”

“…The envelopes of the best fit taxonomic types for each spectrum are shown in grey in the background. Both objects are in the S-complex, with a preference towards specific types that have experienced low degrees of space weathering.ulation(Perna et al, 2018;Binzel et al, 2019;Devogèle et al, 2019), thus EE7 -FP124 do not offer strong constraints on the probability of two random asteroids in near-Earth space having the same spectral type. (Debiased estimates also find a high fraction ∼40% of NEOs are in the S-complex,Stuart & Binzel, 2004).…”

A million asteroid observations in the Sloan Digital Sky Survey

“…With the advent of charge coupled devices (CCDs) in the 1990s, multi-filter photometry moved toward low-resolution spectroscopy in the visible (Xu et al 1995;Bus & Binzel 2002a) and was later extended to the near-infrared (DeMeo et al 2009). After three decades of targeted observations, spectra (visible, near-infrared, or covering both wave ranges) have been collected for about 9,000 asteroids (albeit disseminated over a myriad of articles, e.g., Bus & Binzel 2002b;Lazzaro et al 2004;Fornasier et al 2014), including around one thousand NEAs (mainly from the NEOSHIELD2, MANOS, and MITHNEOS surveys; Perna et al 2018;Devogèle et al 2019;Binzel et al 2019). However, compared to the current census of over 20,000 NEAs and more than 860,000 MB asteroids, these 9000 are only the tip of the iceberg.…”

Predicting Asteroid Types: Importance of Individual and Combined Features

“…An additional Xn class was later added by Binzel et al (2019). That system helped explain the compositional distribution of the asteroid main-belt and the delivery efficiency of various taxonomic types to the near-Earth asteroid population Carry et al, 2016;Barucci et al, 2017;Binzel et al, 2019;Devogèle et al, 2019). Laboratory work and asteroid observations later identified space weathering processes that cause the transformation from S though Sq to Q-types in that taxonomic system (Strazzulla et al, 2005;Vernazza et al, 2009a).…”