On December 12, 2025, NASA announced an ambitious plan to map our galaxy in detail using the Nancy Grace Roman Space Telescope. This is the first major galactic survey that this new infrared observatory will conduct as soon as it begins its five-year primary mission. In just one month of effective observation, spread over the first two years of operation, Roman is expected to record the positions and properties of tens of billions of stars and reveal structures of the Milky Way that we have not been able to see until now due to thick dust and the limitations of existing telescopes.

The heart of this endeavor is called the Galactic Plane Survey – a survey of the galactic plane that will focus on the brightest, densest band of our galaxy, where the majority of stars, gas, and dust are located. Scientists expect that the combination of a wide field of view, fine spatial resolution, and sensitivity in the infrared range will turn this survey into a kind of "mining expedition" through the Milky Way, with an unprecedented amount of new data on stellar nurseries, dying stars, compact remnants, and exotic binary systems.

Roman's Galactic Survey as a New Reference Map of the Milky Way

The Galactic Plane Survey will be the first general astrophysics survey selected for the Nancy Grace Roman mission. It will build upon three fundamental, so-called core surveys that have already been defined for the mission, as well as the technological demonstration of the coronagraph, an instrument that will test advanced methods of blocking starlight to directly image exoplanets and the dust disks around them. Within the primary mission, it is foreseen that at least a quarter of the total observation time will be open to the scientific community through competition, so a whole series of additional specialized programs is expected, but it is precisely the Galactic Plane Survey that will provide the most comprehensive "skeleton map" of our galaxy.

The plan is for Roman to cover about 691 square degrees of the sky in the main survey component, which corresponds to a visible area of approximately 3,500 full Moons lined up next to each other. That part of the survey will be directed along the visible band of the Milky Way in the sky, that is, along the plane of the galactic disk. An additional component will focus on a smaller, but repeatedly observed region with an area of about 19 square degrees – roughly 95 full Moons – where changes in the brightness and position of stars will be monitored dozens of times to record short-term phenomena and dynamic processes.

The third, deepest component will cover a series of small fields with a total area of about 4 square degrees. In these areas, Roman will use a full set of filters and spectroscopic tools to obtain detailed information on the chemical composition, temperature, velocity, and distance of objects. Together, these three levels of survey will provide a multi-layered insight into the structure of the Milky Way: from the global geometry of the galactic disk to the local physics of individual stellar nurseries and compact objects.

Estimates by the scientific team suggest that Roman could map up to 20 billion stars, whereby high spatial resolution and repeated observations will enable precise measurement of tiny shifts of stars in the sky. Such astrometry is key to understanding how stars orbit the center of the galaxy, where spiral arms are located, how dark matter and visible mass are distributed, and in what way the Milky Way has developed throughout cosmic history.

New Telescope as Successor to Hubble and Complement to Gaia

The Roman Space Telescope continues the tradition of space observatories like Hubble and James Webb, but with a focus on wide-angle infrared observations. The telescope will be placed in a halo orbit around the L2 point of the Sun–Earth system, where a stable thermal environment and a constant view towards space allow for long-term, precise measurements. According to NASA's plan, the mission should be launched no later than May 2027, with the team currently on a trajectory that would allow for an even earlier start, as early as the autumn of 2026, on a Falcon Heavy rocket from launch pad LC-39A at the Kennedy Space Center in Florida.

The telescope itself recently passed an important milestone: the integration of the two main segments of the observatory was completed, officially finishing the construction. In the largest clean room at NASA's Goddard Center, the module with optics and instruments was connected to the service module with power, propulsion, and communication systems. The next phase includes a series of rigorous tests in vacuum chambers, on vibration tables, and in thermal environments to verify how Roman withstands launch conditions and operation in space.

Roman carries two main scientific instruments. The Wide Field Instrument is actually a camera with a resolution of about 300 megapixels, sensitive in the visible and near-infrared range. Its field of view width will be about one hundred times greater than what Hubble achieves in standard imaging mode, while the sharpness of individual pixels will remain comparable. This means that a single Roman image will contain details that we would otherwise have to collect from a hundred separate Hubble frames.

The second key instrument is a coronagraph that will test technologies for extreme starlight suppression. The idea is to literally "shade" the glare of the host star with complex optical elements and deformable mirrors, opening a view to much fainter objects in the immediate vicinity – such as large exoplanets or dust disks where planets are forming. Although the coronagraph is a technological demonstration, the success of such an instrument would lay the foundations for future missions dedicated to directly imaging Earth-like worlds.

Roman will thereby complement the work of the European satellite Gaia, which has collected data on approximately two billion stars observed in visible light over the years. Although Gaia has revolutionized our understanding of the dynamics and structure of the Milky Way, thick dust in many areas of the galactic plane limits its reach. Thanks to infrared filters, Roman will "see through" those obscured areas, deeper into the galaxy's core and to the "hidden" far side of the disk, and will thus provide a far more complete three-dimensional map together with Gaia.

Cosmic Cradles: Where New Stars Are Born

One of the most exciting aspects of the Galactic Plane Survey will be the look into vast molecular clouds where stars are formed. In such regions, like the famous Carina or Lagoon, dense clumps of cold gas and dust collapse under their own gravity creating protostars. The environment is very dynamic: young stars eject powerful jets of material, sudden bursts of brightness erupt, magnetic fields twist gas flows, and shock waves from previous generations of massive stars cut through the clouds.

The infrared "vision" of the Roman telescope will be crucial for observing these processes, because most of the light emitted by the youngest stars never leaves the cloud in the visible range – it is absorbed and scattered by dust grains. Roman will see millions of objects through that dust in different stages of early development: from still deeply embedded stellar "embryos," through turbulent young stars that flash irregularly, all the way to more stable stars around which protoplanetary disks can already be recognized.

Scientists will thus be able to monitor how the rate of star formation changes with different conditions – for example, with gas density, local radiation intensity, or the presence of previous generations of massive stars. Since the Galactic Plane Survey will encompass very different regions of the galactic disk, from calmer peripheries to the bustling center, it will be possible to compare results almost as if studying a series of laboratory experiments under different conditions.

In the background of all these processes, a kind of "four-way tug of war" is being waged between gravity, radiation, magnetic fields, and turbulence. Gravity strives to compress gas into stellar cores, while the radiation of young and massive stars, together with stellar winds and supernova explosions, tears clouds apart and disperses material. Magnetic fields and turbulent gas motion additionally slow down or accelerate collapse in certain places. Analysis of hundreds of thousands of stellar nurseries that Roman will image will allow astronomers to finally quantitatively separate the role of each of these factors.

Star Clusters as Natural Laboratories

Data on star clusters – "families" of stars that formed from the same cloud and at the same time – will be particularly valuable. Open clusters, of which Roman is expected to study nearly two thousand, are usually young and relatively loosely gravitationally bound. They are often found along the spiral arms of the galaxy and are considered one of the key traces revealing where new stars have recently formed. If precise distances, velocities, and chemical compositions of members are measured on them, it is possible to reconstruct the history of the formation of the spiral structure.

On the other hand, globular clusters belong to the oldest "population" of the Milky Way. They are usually found in the halo around the galactic disk or near the center, and contain hundreds of thousands of densely packed, very old stars. The Galactic Plane Survey will focus on several dozen such objects, especially in the region near the galactic core where observations have been difficult until now due to dust and overcrowding with stars. By comparing the properties of these clusters, scientists will be able to determine in what ways the Milky Way "swallowed" smaller galaxies and redistributed stars throughout its past.

The advantage of star clusters in a scientific sense is that their stars share approximately the same age, initial chemical composition, and distance. This means that differences in brightness or color of individual stars in a cluster mainly reflect their developmental stage, not external conditions. When clusters are then compared with one another, it is possible to very precisely separate the effects of "nature" – initial conditions in the cloud from which they formed – from the influence of "nurture," that is, the environment in the galaxy through which they move.

Pulse of the Galaxy: Compact Remnants and Microlenses

Stars similar to the Sun end their lives as white dwarfs, while more massive stars collapse into neutron stars or black holes. Most of these remnants are almost invisible at great distances, especially if they do not have a close companion from which they "steal" material. Roman will, however, be able to discover even such lonely compact objects using the phenomenon of gravitational microlensing.

According to the general theory of relativity, every object with mass curves space-time in its vicinity. When the light of a distant star passes by such a gravitational indentation, its path bends slightly, so the star in the sky briefly appears "amplified" to us. If the role of the lens is played by a white dwarf, a neutron star, or a black hole that hardly shines on its own, the change in brightness of the background star will reveal the otherwise invisible mass in the foreground.

A special campaign of the Roman telescope, the Galactic Bulge Time-Domain Survey, will focus on long-term monitoring of the denser, central part of the galaxy to record a large number of microlensing events. The Galactic Plane Survey will take a different approach: it will observe a wider area of the entire galactic plane, with shorter but strategically distributed series of observations. This combination will make it possible to finally obtain a complete picture of the distribution of compact objects – from white dwarfs and neutron stars to solitary black holes – throughout the entire Milky Way.

Compact binary systems are particularly interesting, in which two very dense objects – for example, two neutron stars or a neutron star–black hole pair – revolve around each other at small distances. Interactions in such systems lead to mass transfer, powerful explosions, and gradual loss of orbital energy through the emission of gravitational waves. When they finally merge, a vast amount of energy is released, which is recorded by detectors like LIGO and Virgo. Roman's data on the distribution and properties of these binary systems will help astronomers better understand the "paths" that lead to spectacular mergers of neutron stars and black holes.

Flickering Stars and Cosmic Measuring Rods

Besides short-lived microlensing flashes, Roman will also record numerous other types of variable stars that periodically strengthen or weaken. Some of them erupt suddenly, ejecting material into the surrounding space, while for others, brightness changes rhythmically because their stellar envelopes periodically expand and contract. In earlier missions, many of these phenomena were observed from ground-based observatories, but dense dusty regions of the galactic plane often remained out of reach or the stars were so packed that it was not possible to resolve them.

Roman's advantage will be the combination of sharp imagery and infrared spectrum. The telescope will be able to clearly separate individual stars even in the densest parts of the Milky Way, and infrared radiation will allow it to penetrate veils of dust. In this way, astronomers will be able to systematically map variable stars in regions that have been almost completely unexplored until now for the first time.

A particularly important group are pulsating stars whose period of oscillation is directly related to their true, intrinsic luminosity. When it is measured how fast they pulsate and their known absolute brightness is compared with the one we see from Earth, it is possible to precisely calculate the distance. Such stars serve as "cosmic measuring rods" and are key to calibrating the distance scale in astronomy.

Roman will find these "space lighthouses" much further away than was previously possible, especially in the deeper, dusty parts of the galactic core and on the far side of the disk. This will allow the shape and size of the Milky Way to be measured with great accuracy, as well as the thickness of its disk, the curvature of spiral arms, and the structure of the central bar – an elongated group of stars passing through the galaxy's core.

Data That Will Shape Astronomy for Decades

The planned survey of the galactic plane is just one part of the scientific program of the Nancy Grace Roman telescope, but at the same time the one that will most directly influence our daily understanding of the Milky Way. The enormous amount of data – from positions, velocities, and brightness of billions of stars, through detailed images of hundreds of thousands of stellar nurseries, to catalogs of microlensing events and exotic binary systems – will serve as a foundation for countless subsequent analyses.

These data will be combined with maps already delivered or yet to be delivered by other telescopes, from Gaia's precise astrometry to infrared and optical surveys from Earth. Together with results from the field of gravitational wave detection and future space missions, Roman's surveys will help build the most complete picture of the dynamics and evolution of the Milky Way that we have ever had.

For astronomers around the world, but also for astronomy enthusiasts, the announcement of the detailed Galactic Plane Survey plan means that a new "big view" of our galaxy is very close. As the mission approaches launch, and then the first scientific results, precisely this survey will become one of the key data sources for every serious study of the Milky Way – from the formation of stars and planets to the fates of the most powerful and exotic objects in our cosmic neighborhood.

More information about the mission can be found on the official NASA Nancy Grace Roman telescope page, which regularly brings news about the progress of preparations, technical tests, and planned scientific programs.