The Roman Space Telescope as a Planetary Defense Asset

TL;DR

This paper argues that the Nancy Grace Roman Space Telescope, when integrated with Rubin Observatory and the NEO Surveyor, creates a powerful planetary defense network spanning optical and infrared wavelengths. Roman's high-resolution, space-based near-infrared observations enable rapid, high-precision astrometric follow-up, improved diameter and albedo determinations when combined with NEO Surveyor data, and initial spectral classification for small NEOs. The study quantifies how a single Roman measurement can dramatically reduce orbital uncertainties and discusses the necessity of developing moving-target processing pipelines. It concludes with a recommended pilot Roman NEO survey and emphasizes the strategic value of rapid, coordinated follow-up to enhance early warning and mitigation planning.

Abstract

NASA's Nancy Grace Roman Space Telescope, slated to launch in October 2026, will serve a critical role in the characterization and threat assessment of near-Earth Objects (NEOs), thus contributing to national and international planetary defense objectives. Operating from the Earth-Sun L2 point and observing in the near-infrared, Roman has the high sensitivity and high spatial resolution needed to measure the physical properties, compositions, and orbital trajectories of NEOs in order to understand their physical nature and potential hazards to Earth. Roman's planetary defense capabilities complement those of two wide-field survey missions: the now operational ground-based Vera C. Rubin Observatory's Legacy Survey of Space and Time and the upcoming space-based NEO Surveyor. Rubin, observing in visible light, will discover over 100,000 NEOs. NEO Surveyor, observing in the mid-infrared where NEO thermal emission peaks, will detect 200,000-300,000 NEOs, some as small as ~20 meters in diameter. With investment in developing the pipeline infrastructure required to extract information from moving target streaks, Roman will be able to observe NEOs down to the smallest sizes in order to improve our measurements of NEO orbits by 2-3 orders of magnitude, enable accurate diameter and albedo estimates in conjunction with NEO Surveyor, and reveal the spectral types and bulk compositions of the smallest NEOs. Together, these three US-led facilities will operate across the electromagnetic spectrum to form a comprehensive planetary defense network.

Figures (5)

• Figure 1: Roman has the capability to detect NEOs with a total signal-to-noise ratio of 5 (dashed black line) for all objects in the $\sim$20--140 m size range for a wide range of angular speeds. Detection of NEOs below the expected NEO Surveyor threshold (i.e., $<$20 meters) is also possible, but only at lower angular speeds.
• Figure 2: Monte Carlo simulated orbit fits for the NEO Aten assuming NEO Surveyor astrometry spaced 13 days apart (a) and NEO Surveyor astrometry followed by Roman astrometry 7 days later (b). The yellow dot shows the position of the Sun (not to scale). (c) Orbit clone distributions one month after the last astrometric data point for the NEO Surveyor only (blue) and NEO Surveyor and Roman (red) scenarios. The black 'x' is the mean position of both distributions. A single additional astrometric observation of an NEO by Roman decreases the orbital uncertainty by 95-99% up to a year later.
• Figure 3: Solar elongation (Sun-observer-target) angles for five representative NEOs over the course of 5 years starting on January 1, 2027. Roman's field of regard spans 54--126$^{\circ}$ and the grey shaded regions indicate unobservable elongation angles. Due to these viewing geometry constraints, some NEOs cannot be observed by Roman for multiple consecutive years, which increases the importance of rapid astrometric follow-up.
• Figure 4: Thermophysical model fits for (a) NEO Surveyor photometry only, (b) Roman photometry only, and (c) combined NEO Surveyor and Roman photometry. 1000 Monte Carlo trials (grey lines) were performed using an implementation of the Near-Earth Asteroid Thermal Model (NEATM; Harris1998). Red points are the photometric measurements (error bars are smaller than the symbols). Neither Roman nor NEO Surveyor by themselves are capable of obtaining the measurements needed to accurately determine the diameter and albedo simultaneously, only the combination of the two facilities is able to accomplish this goal.
• Figure 5: (a) Bus-DeMeo spectral archetypes for the three most common asteroid spectral types: C, S, and X DeMeo2009. (b) Filter throughput profiles for Rubin (blue) and Roman (red). (c) & (d) Colors of the three most common asteroid spectral types (same colors as panel a) in the Rubin/LSST and Roman photometric systems, respectively. Lighter points indicate asteroid sub-types within the C, S, and X complexes. The largest average color-color Euclidean distance between points is presented for each mission. The two missions have comparable capabilities for sorting NEOs by spectral type, but only Roman can perform this task for the smallest observable NEOs ($\sim$20--30 meters).