Small Perihelion Effects on Near-Sun Asteroids

Many comets and asteroids spend part of their dynamical lifetimes with small perihelion distances (or “low-q”) as a result of dynamical interactions with Jupiter. However, there are fewer such asteroids observed than are predicted by dynamical models, even while assuming a deficit due to collisions with the Sun or planets, or an escape from the inner solar system (Granvik et al. 2016, Nature 530). The lack of observed low-q asteroids is thought to be due to near-complete disintegration when they reach a perihelion distance q < ~0.076 au. We observe low-q asteroids and search for signs of near-Sun processes that might lead to disruption.

Thermal cracking, spin-up, meteoroid impacts, and subsurface volatile release are disruptive near-Sun processes that are likely to cause surface alteration, which might change the spectral slope of the surface. Such surface alteration could be observable from the ground using optical telescopes and provide us with a better understanding of the processes occurring and the effects they have on near-Sun asteroids. Broadband optical colors (e.g., g'-r', r'-i') can be obtained quickly for fainter objects, which makes such observations optimal for a population study.

There are 48 known asteroids that reach perihelion distances of q < 0.15 au (as of August 11, 2020), eight of which have been included in previous studies of low-q asteroids. Since 2017, we have undertaken a campaign to measure the optical colors of these objects, primarily using the 4.3-m Lowell Discovery Telescope (formerly the Discovery Channel Telescope) and the 4.1-m SOAR telescope, supplemented by data from the 2.5-m Isaac Newton Telescope and Lowell Observatory’s 42-in and 31-in telescopes. We have successfully observed 25 low-q asteroids; we attempted to observe nine more low-q asteroids but were unsuccessful, most likely due to the large uncertainties in their orbits. We report the optical colors of low-q asteroids and infer the near-Sun processes at work, including those that might lead to disruption.