Why it matters: NASA launched the Nancy Grace Roman Space Telescope on Sunday, adding a wide-field infrared observatory to the growing fleet of space telescopes designed to tackle some of astronomy's biggest unanswered questions. Roman will map billions of stars and galaxies, search for an estimated 100,000 exoplanets, and collect data that could help researchers better understand the roles of dark matter and dark energy. Its key advantage is not simply its resolution, but the amount of sky it can cover in a single observation.
The telescope carries a 2.4-meter primary mirror, the same size as Hubble's. But its Wide Field Instrument is designed for a different kind of work. The 300-megapixel camera uses 18 detectors to capture a much broader image, giving Roman a field of view at least 100 times larger than Hubble's and allowing it to survey the sky up to 1,000 times faster.
That scale will make Roman as much a data-gathering platform as an observatory for selected targets. A single full-resolution Roman image would require more than 500,000 high-definition television screens to display. Its images will cover about 0.28 square degrees of sky at a time, more than the apparent area of the full Moon.
The instrument will observe light from visible wavelengths into the near-infrared, a range that allows it to look through dust and detect distant, redshifted galaxies. It includes eight imaging filters, along with a grism and a low-resolution prism for slitless spectroscopy. These components will allow the telescope to collect spectral data across broad sections of the sky.
The Roman Space Telescope enclosed in the Falcon Heavy payload fairing ahead of launch.
Roman's primary science program will focus in part on the universe's accelerated expansion. Dark energy is the name given to the unknown phenomenon associated with that acceleration, but its physical nature remains unresolved. Measurements of the expansion rate derived through different methods also differ by about 9%, a discrepancy that has raised questions about whether the standard cosmological model is incomplete.
The telescope will also help researchers map the distribution of matter across the universe. Although dark matter has not been directly detected, its gravitational effects can be measured through the motions of galaxies and the way its mass bends light from distant objects. Roman's large surveys are intended to give scientists a more detailed view of that structure.
Exoplanets are another major part of the mission. Roman will use gravitational microlensing, which occurs when the gravity of a foreground star – and sometimes one of its planets – temporarily magnifies light from a more distant background star. The method can identify planets that do not pass in front of their host stars from Earth's perspective, including colder and more distant worlds that can be difficult for transit-based searches to detect.
More than 6,000 exoplanets have been found so far, but Roman is expected to provide a broader census of planetary systems in the Milky Way. Its findings could help researchers understand how common planets are around different types of stars and at different orbital distances.
The observatory also includes a Coronagraph Instrument, though it is not the mission's main survey system. Roman's coronagraph is a technology demonstration that uses optical masks and deformable mirrors to block starlight. It will test whether the telescope can directly image planets and debris disks up to a billion times fainter than their stars.
"When it launches, it's going to do things that currently are impossible," Shawn Domagal-Goldman, the head of NASA's astrophysics division, said at a July news conference. "In many ways, the astronomical target that Roman is chasing, is designed to study, is the universe itself."
Roman is named for Nancy Grace Roman, NASA's first chief astronomer, who helped establish the agency's space astronomy program. Her work contributed to NASA's early investment in orbiting observatories that could avoid the distortion and wavelength limitations created by Earth's atmosphere.
That effort led to Hubble, the Compton Gamma Ray Observatory, the Chandra X-ray Observatory, and the Spitzer Space Telescope. Later missions, including Kepler and James Webb, expanded the search for exoplanets and pushed observations deeper into the early universe.
Roman will serve a different role from Webb, which is designed for highly sensitive observations of selected targets. Roman's wide surveys will give astronomers large datasets and identify targets for more detailed study by Webb and other observatories.
Julie McEnery, who leads Roman's science team, said the mission has "foundational new capabilities that are going to open new discovery space."
