About this Article

The Nancy Grace Roman Space Telescope is on schedule for launch in October 2026. The Roman Space Telescope will employ its Hubble-like sensitivity and resolution to survey the near-infrared sky at speeds over 1,000 times faster than can be achieved with Hubble. During its primary five-year mission, Roman’s observing program will be comprised of three large Core Community Surveys and competitively selected Principal Investigator-led General Astrophysics Surveys undertaken with Roman’s Wide Field Instrument (WFI), as well as three months of technology demonstration observations with the Coronagraph instrument.

Expanding the Scientific Reach of Roman’s Surveys

The Core Community Surveys will serve as the mechanism through which Roman will investigate the nature of dark energy and dark matter (through the High-Latitude Wide-Area and Time-Domain Surveys) and extend our knowledge of the demographics of exoplanets (through the Galactic Bulge Time-Domain Survey). To meet Roman’s science requirements in cosmology and exoplanet demographics, the execution of the surveys will require the majority of the observing time during Roman’s primary five-year mission. Thus, an equally important consideration in their design is to enable a broad range of science investigations.

A community process was developed to solicit and incorporate input from the global community of scientists interested in using Roman data. The goal of the community process was to optimize the survey designs in a way that maximizes their overall scientific potential. More than 1,000 scientists from over 350 institutions contributed to this community process. Nearly 200 science pitches and white papers were submitted, describing science investigations that could be enabled with one or more of the surveys using Roman’s imaging and slitless spectroscopy capabilities from 0.5 to 2.3 microns.

Definition Committees were formed for each survey, with members drawn from the science community to represent the range of science investigations that were advocated for in the science pitches and white papers. To arrive at their recommended survey implementations, the definition committees reviewed the science pitches and white papers, requested additional community input, and received scientific, technical, and logistical support from Roman project partners (the Project Science Office at NASA Goddard Space Flight Center (GSFC), the Science Operations Center at STScI, the Science Support Center at IPAC, and the competitively selected Project Infrastructure Teams).

The definition committees were charged with creating three implementation options for each survey — a nominal, an underguide, and an overguide design — that would meet Roman’s science requirements for cosmology or exoplanet demographics while maximizing the science investigations that each survey would enable. The allotted time for each survey implementation option was set by Roman’s Project Science Office. The definition committees began their work in January 2024 and delivered their reports to the Roman project and the Roman Observations Time Allocation Committee (ROTAC) in December 2024.

Selecting the Survey Designs

The ROTAC was formed to advise Roman’s Project Science Office on which of the implementation options to adopt for each Core Community Survey. In doing so, the ROTAC was charged with considering the overall balance between Roman’s Core Community Surveys and General Astrophysics Surveys. As in the case of the definition committees, the ROTAC membership was selected to represent the breadth of science investigations that can be pursued with the Core Community Surveys. In addition, ROTAC members were selected to represent the interests of those who will propose for future General Astrophysics Surveys.

The ROTAC met over the course of five months to review the proposed implementation options for each survey and discuss the scientific benefits and tradeoffs of the various survey design choices in the context of Roman’s primary five-year mission. The ROTAC familiarized themselves with Roman’s science requirements and discussed the implementation options in depth with representatives of the definition committees. The committee worked with the Roman Project Science Office and Science Centers to understand if there were any scheduling conflicts or other operational impacts to consider, either among the proposed survey implementation options or potential General Astrophysics Survey programs. The ROTAC’s recommendations were released to the Roman Project Science Office and the science community in late April 2025.

The committee recommends the High-Latitude Wide-Area Survey be implemented with three tiers, which include imaging in multiple filters and slitless spectroscopy covering approximately 2,400 deg², an additional 2,700 deg² of imaging in a single band, and deep imaging and slitless spectroscopy over 19 deg².  It will enable studies of dark energy, cosmic lensing, the relationship between galaxies and dark matter, high redshift galaxies, and stars in nearby galaxies and the Milky Way.

The recommended High-Latitude Time-Domain Survey implementation will include wide and deep tiers of imaging (~18 and 6.5 deg²) and slitless spectroscopy (~4.5 and 0.5 deg²), with filter-dependent cadences as short as approximately five days. It will capture the transient universe, enable Type Ia supernova cosmology out to a redshift of approximately 2.5, and discover new and rare high-redshift transients.

The recommended Galactic Bulge Time-Domain Survey implementation will include high-cadence imaging (approximately every 12 minutes) of five fields in the Milky Way bulge and one field on the Galactic Center. The imaging will occur over six contiguous 70.5-day seasons, with three seasons scheduled early in the mission, and three seasons scheduled toward the end of the primary five-year mission. Significantly longer cadence observations of these fields during “off” Galactic Bulge seasons are also recommended. It will enable a census of exoplanets, free-floating planets, stellar mass black holes, and studies of asteroseismology and variable sources.

The recommended Core Community Survey implementations require 74.5% of the time reserved for science operations with the WFI during the primary five-year mission. The remainder of the WFI science operations time, 25.5%, will be reserved for General Astrophysics Surveys. The ROTAC’s report, which includes the reports submitted by the definition committees, has been posted on arXiv. A recording of the April 24, 2025 Roman Community Forum at which the ROTAC presented their recommendations can be found on GSFC’s Roman Community Forum page.

A similar community process is being followed to define an Early Definition Galactic Plane General Astrophysics Survey. The definition committee received community input via 60 science pitches and white papers, as well as a virtual community workshop. The committee is finalizing their report for submission to the ROTAC, which will provide a final implementation recommendation to Roman’s Project Science Office.

Drawing on the Heritage of Community Input to Roman

The survey implementations recommended by the ROTAC drew on and were directly informed by the work of a large body of scientists over the course of more than a decade. The nature of dark energy, dark matter, and the demographics of exoplanets were identified as key scientific questions by the “New Worlds, New Horizons” Astro2010 Decadal Survey, which recommended as a top priority a large space-based mission (then termed “WFIRST”) that could address these questions.  

A series of science teams chartered by NASA (the Science Definition Teams), and later competitively selected through the NASA-ROSES 2016 call (the Science Investigation Teams), explored the survey strategies and observatory requirements that would enable the cosmology and exoplanet demographic objectives. This work informed Roman’s planned observational program and the design of the observatory (see Green et al. 2012, Spergel et al. 2013, 2015, and the 2021 Roman Science Team Community Briefing). Project Infrastructure and Wide Field Science teams, selected and funded through recent NASA-ROSES calls, along with other members of the community, continue to provide scientific guidance and input into the development of Roman’s science operations and observing program, through Roman’s open and community-supported working groups.      

The collected expertise of the more than 1,000 scientists who have contributed to the development of Roman’s observational program has resulted in Core Community Survey designs that will provide powerful datasets. These datasets will have transformational impacts across astrophysics, cosmology, and planetary science.