Roman's Key Science Components

The design reference mission of the Nancy Grace Roman Space Telescope, formerly known as the Wide Field Infrared Survey Telescope (WFIRST), includes three key science themes: measuring dark energy, investigating exoplanets, and great observatory astrophysics and planetary science. The design reference mission, used to set requirements on the design of the observatory, is described in detail in the final report of the WFIRST-AFTA Science Definition Team and summarized below. This science program will be addressed using two instruments, four observing surveys, and General Observer and archival Guest Investigator programs.


Dark Energy

Hubble Deep Field

The Roman Space Telescope will measure the equation of state of dark energy and its time evolution, helping determine whether it is a cosmological constant, through all of the major methods suggested thus far. Its wide-area, multicolor imaging survey, covering over 2,000 square degrees, will enable weak lensing shape and photometric redshift measurements of hundreds of millions of galaxies, which will yield precise measurements of distances and matter clustering through measurements of cosmic shear, galaxy-galaxy lensing, and the abundance and mass profiles of galaxy clusters.

Its wide-area spectroscopic survey, over the same area, will determine millions of redshifts for galaxies between z=1 and 3, thus measuring the evolution of the size of the universe and constraining the scale of baryon acoustic oscillations to 0.3%, as well as measuring the growth of structure via redshift-space distortions. The tiered supernova surveys, covering 5 to 27 square degrees, will discover and measure precise distances to thousands of Type Ia supernovae up to redshift z=2. The Roman supernova surveys will be unique in their level of precision and redshift range, and the wide-area imaging survey will have unique depth and resolution for studies of weak lensing. Both will have unique control of measurement and astrophysical systematics. Of existing and planned observatories, Roman will be the most powerful supernova, weak lensing, and redshift 1 to 2 spectroscopic facility per unit time, and will yield the densest large-scale map of structure at redshifts of 1 to 2.

Supporting Surveys: WFI High-Latitude Survey (HLS), WFI Supernova Survey


Artists' concept depicting exoplanets


Roman will use time-series microlensing imaging observations of Milky Way Bulge stars to determine the distribution of exoplanets down to sub-Earth masses in a wide range of orbital radii, including the habitable zone, the outer regions of planetary systems, and free-floating planets. An area of over 2 square degrees will be observed with 15 minute cadence over 72 consecutive days in each of six campaigns, resulting in the likely discovery of thousands of bound exoplanets, including over 100 Earth-mass planets.

The coronagraphic instrument on Roman will provide a crucial technology demonstration for possible future missions aimed at detecting signs of life in the atmospheres of Earth-like exoplanets. It will also be capable of directly imaging planets similar to those in our Solar System, measuring for the first time the photometric properties of the 'mini-Neptune' or 'super-Earth' planets — objects that Kepler has shown to be the most common planets in our galaxy, but with no analogy in our own solar system. The coronagraph will suppress starlight by factors of up to 1 billion to one, orders of magnitude better than current state-of-the-art ground or space-based capabilities.

Supporting Surveys: WFI Bulge Microlensing Survey, CGI Coronagraph


Tip of the wing of the Small Magellanic Cloud galaxy

Great Observatory Astrophysics and Planetary Science

Roman will be the first telescope to combine excellent, space-based image quality with survey power. Roman’s 300 Megapixel Wide Field Instrument (WFI) camera will have 100 times the field of view of Hubble at the same sensitivity (28th AB mag 1 in hour) and resolution (0.1 arcsec pixels). The data collected for the planned Roman surveys will form a treasure trove for archival Guest Investigator studies in many areas of general astrophysics. Single images from WFI will yield survey-sized datasets, covering the equivalent of 100 pointings with the Hubble and James Webb space telescopes.

Examples of science projects enabled by the data in the High-Latitude Survey include mapping the formation of cosmic structure in the first billion years after the big bang via the detection and characterization of over 10,000 galaxies at z > 8; finding over 2,000 QSOs at z > 7; quantifying the distribution of dark matter on intermediate and large scales through lensing in clusters and in the field; identifying the most extreme star-forming galaxies and shock-dominated systems at 1 < z < 2; carrying out a complete census of star-forming galaxies and the faint end of the QSO luminosity function at z ~ 2, including their contribution to the ionizing radiation; determining the kinematics of stellar streams in the Local Group through proper motions; and discovering and characterizing small bodies in our solar system such as Kuiper Belt objects, including asteroids and comets.

In addition, a significant fraction of mission time will be set aside for Guest Observer programs with the Wide Field Instrument. This will allow use of the broad range of Roman's capabilities, namely wide-field imaging and slitless spectroscopy, for many additional studies in general astrophysics. Examples include studying young clusters and embedded star-forming regions within the Milky Way galaxy; reaching the very faint end of the stellar luminosity function via very deep observations of Local Group galaxies; mapping the core of the Virgo cluster; and follow-up studies of systems found through WFI High-Latitude Survey (HLS) observations (high-redshift QSOs and galaxies, galaxy clusters). Upon successful completion of the Coronagraph Instrument (CGI) Technology Demonstration, it will have a Participating Scientist Program.

Appendix D of the final report of the WFIRST-AFTA Science Definition Team includes one-page summaries of many other possible Guest Investigator and Guest Observer Programs, covering areas of science ranging from the Solar System to cosmology.

Supporting Programs: WFI Guest Observer Program, CGI Participating Scientist Program, Guest Investigator program for archival analysis of data from any of the mission's surveys and programs

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