The Mission Accessible Near-Earth Objects Survey (MANOS): First Results from the Visible Spectroscopic Survey

The Mission Accessible Near-Earth Objects Survey (MANOS) started in August 2013 and is a multi-year survey supported by the National Optical Astronomy Observatory (NOAO) and Lowell Observatory, and funded by the NASA NEOO (Near-Earth Object Observations) program. It aims at characterizing sub-km, low delta-v (typically <7 km/s), Near-Earth Objects (NEOs) by collecting astrometry, lightcurve photometry, and reflectance spectra. The physical properties of NEOs are known to be size dependent. However, some open questions remain such as whether these objects are rubble piles or monolithic bodies, or whether they are covered by regolith. A compositional discrepancy between large NEOs (>1km) and meteorite collection is also observed (Stuart et al., 2004; Vernazza et al., 2008). Laboratory measurements have also shown that grain size can cause variation in spectral slope or absorption band depth (Cooper et al., 1999;Cloutis et al., 2013). The smallest NEOs can have rotation periods under 1 minute (Thirouin et al., 2016), while asteroids larger than 150m do not rotate faster than 2.2 hours. This supports the hypothesis of small asteroids being monolithic and structurally different than larger ones. We report here the first results from MANOS on the visible spectroscopic properties. We have analysed roughly 300 asteroids with a mean size around 80 meters (H 25), and with some targets as small as few meters (H=30). This represents one of the largest comprehensive spectroscopic datasets for NEOs < 100 meters. We will discuss the compositional properties of this sample relative to other NEOs (km and sub-km) (Perna et al., 2018; Thomas et al., 2011, and DeMeo et al., 2008), and to Main Belt asteroids (Bus et al., 2002 and DeMeo et al., 2009) and compare them with the meteorite population. All spectroscopic data have been reduced using a new python based pipeline for asteroid spectroscopic reduction developed to be easily portable to any visible spectrograph. The use of the same pipeline for all data obtained by this survey allows us to obtain a consistent data set of spectral properties of small NEOs. This work is supported by the NASA NEOO program, grant number NNX17AH06G.