Compositional study of trans-Neptunian objects at {\lambda} > 2.2 {\mu}m

TL;DR

This study uses infrared photometry from the Spitzer Space Telescope to analyze the surface composition of 100 trans-Neptunian objects, identifying materials like water ice, organics, and silicates, and developing a new method for faint object analysis.

Contribution

Introduces a novel photometric method to determine surface compositions of faint TNOs using infrared data, enabling differentiation of surface materials without spectroscopy.

Findings

86% of TNOs show signs of water ice.

73% have surfaces with water ice, organics, and silicates.

Some objects may contain other ices like CO, CO2, CH4, or methanol.

Abstract

Using data from the Infrared Array Camera on the Spitzer Space Telescope, we present photometric observations of a sample of 100 trans-Neptunian objects (TNOs) beyond 2.2 {\mu}m. These observations, collected with two broad-band filters centered at 3.6 and 4.5 {\mu}m, were done in order to study the surface composition of TNOs, which are too faint to obtain spectroscopic measurements. With this aim, we have developed a method for the identification of different materials that are found on the surfaces of TNOs. In our sample, we detected objects with colors that are consistent with the presence of small amounts of water and were able to distinguish between surfaces that are predominately composed of complex organics and amorphous silicates. We found that 86% of our sample have characteristics that are consistent with a certain amount of water ice, and the most common composition (73% of the objects) is a mixture of water ice, amorphous silicates, and complex organics. 23% of our sample may include other ices such as carbon monoxide, carbon dioxide, methane or methanol. Additionally, only small objects seem to have surfaces dominated by silicates. This method is a unique tool for the identification of complex organics and to obtain the surface composition of extremely faint objects. Also, this method will be beneficial when using the James Webb Space Telescope for differentiating groups within the trans-Neptunian population.