Prospects for Trans-Neptunian Exploration with Interstellar Probe

Abstract:

Interstellar Probe is a NASA Heliophysics Division mission concept that would leave the solar system on a 50-year prime mission with a primary objective to study the heliosphere and the local interstellar medium (~200 au). In order to reach interstellar space, the spacecraft must pass through the solar system itself (Brandt et al., 2020), and we focus here on the opportunities for exploring trans-Neptunian objects (TNOs) with Interstellar Probe.

The primary science instrument for TNO flyby geoscience would be a visible/infrared imaging spectrometer to enable studying a wide range of physical, chemical, and geological processes at temperatures <40 K. Reflectance spectroscopy of the infrared region (1-5 μm) is most useful for studying surface composition due to myriad fundamental and overtone absorption bands of volatile (N₂, CH₄, CO) and non-volatile (H₂O, CO₂, NH₃) ices and refractory organics (e.g., C₂H₆, tholins). A visible imager would reveal geological, albedo, and color information to investigate surface characteristics and evolution.

Interstellar Probe could contribute to the exploration of TNOs through: (1) a planned flyby of a dwarf planet along the solar system escape trajectory defined by the Heliophysics Division and (2) encounters with small TNOs, primarily cold classical Kuiper Belt Objects (CCKBOs). Potential dwarf planet targets in the window between 300-330° ecliptic longitude and -20-20° ecliptic latitude are: 2002 MS₄, Quaoar, Gonggong, Pluto, and Ixion (Fig. 1). These TNOs represent a wide range of colors, compositions, and geological processes, and 3 of the 5 are currently known to have satellites. The New Horizons flyby of the CCKBO contact binary Arrokoth (2014 MU₆₉) provided a valuable glimpse into the formation history of planetesimals and the pristine surfaces present in the trans-Neptunian region (Stern et al., 2019). Interstellar Probe could complement the Arrokoth and Pluto flybys, as well as its own primary TNO flyby, through a serendipitous encounter with a TNO <400 km in diameter, potentially revealing a new class of TNOs never before visited by spacecraft. Given the expected yields of new CCKBOs from upcoming all-sky surveys, there is a 0.001% chance of serendipitously making a close flyby, assuming the trajectory takes Interstellar Probe through the ecliptic.