The understanding of the compositional distribution of NEOs is important to reconstruct their dynamical and physical evolution, assess the damage potential in case of an impact, and estimate the resources that can be obtained from these bodies in the not-so-far future. Also, there is still a discrepancy between the compositional distribution of meteoritic material found on Earth and the overall composition of the NEO distribution.
The most common way to investigate the compositions of asteroids is to perform spectroscopic observations: wavelength-dependent variations of the surface reflectance can be diagnostic for the composition of an object and allow for a taxonomic classification. However, spectroscopic observations are usually only possible for bright and large asteroids and require large telescopes for small asteroids.
By applying a special observing mode and strategy, we are able to constrain the taxonomic classification of even the smallest NEOs.
Most NEOs are discovered when they are close to Earth, just because that is the time of their peak brightness. After their closest approach, they fade quickly as they move away from Earth. By observing them as soon as possible after their discovery, we are able to observe even small NEOs with small to medium sized telescopes. This observing strategy is called rapid response.
Also, we do not perform spectroscopy, which yields a fully resolved reflectance spectrum over a specific wavelength range, but spectrophotometry, which provides coarse spectral information by performing photometry in standardized filter bandpasses. Photometry is easier to obtain and more efficient than spectroscopy on smaller telescopes.
By combining spectrophotometry and rapid response observations, we are technically able to constrain the taxonomic class of every newly detected NEO.
We perform our observations in the optical and near infrared regimes, which are particularly indicative for asteroid taxonomy, using two different instruments and telescopes: WFCAM on UKIRT (3.8m, located on Mauna Kea, Hawai’i) and RATIR on the 1.5m telescope at San Pedro Martir, Mexico. Target selection, observation, data reduction, and analysis are mostly automated for both telescopes, allowing for a high throughput with minimal human interaction. Target asteroids are selected based on their observability, bright NEOs are observed by RATIR, fainter ones by UKIRT.
First results from UKIRT are available and have been presented at the Division of Planetary Science meeting in Tucson, 2014 and the IAU General Assembly, 2015. The latest poster is available here. Our first paper has been published in AJ.