The Euclid space telescope published its first high-resolution survey of the Milky Way's central bulge on June 24, 2026, providing the resolution needed to confirm candidate exoplanets flagged by ground-based surveys over the last two decades.
ESA’s Euclid space telescope published its first high-resolution survey of the Milky Way’s central bulge on June 24, 2026, releasing calibrated images and photometry catalogues covering 4.8 square degrees near the Galactic Center at 0.16 arcsecond resolution. According to the Euclid Consortium, the data makes it possible - for the first time - to directly observe the host stars behind hundreds of candidate exoplanet detections accumulated by ground-based observatories over the past twenty years.
The release, designated Quick Data Release 2 (Q2), draws on a single observation made by Euclid on March 23, 2025, using the spacecraft’s VIS instrument: a 600-megapixel wide-field visible-light camera that achieves spatial resolution comparable to the Hubble Space Telescope but across a field of view roughly 100 times larger.
For more than two decades, ground-based surveys including OGLE (Optical Gravitational Lensing Experiment) and MOA (Microlensing Observations in Astrophysics) have monitored stars in the Milky Way’s central bulge, searching for microlensing events. A microlensing event occurs when a foreground object - a star, sometimes orbited by a planet - passes in front of a more distant background star and temporarily magnifies its light through gravity. The brightness spike is brief and distinctive, and its shape encodes information about the lensing object’s mass. The technique is sensitive to planets at separations and masses where other detection methods, such as radial velocity or transit photometry, struggle.
The galactic bulge is the favoured hunting ground because its dense stellar population maximises the probability of chance alignments between foreground and background stars. That same density, however, limits what ground-based telescopes can resolve. In crowded bulge fields, atmospheric turbulence and limited angular resolution make it difficult to cleanly separate the lens star from the source star. Many microlensing detections have a well-measured light curve - enough to flag a candidate exoplanet - but an uncertain host star identification, which leaves the planet’s mass and orbital distance poorly constrained.
Euclid’s sharper view changes that. According to the Euclid Consortium, the survey’s 0.16 arcsecond resolution is sufficient to directly image the foreground lens stars of many archival microlensing events and to measure their angular separation from the source stars. That separation is the key quantity: combined with the parameters extracted from the original ground-based light curve, it allows researchers to determine the lens star’s distance and mass, and from those values to calculate the physical properties of the orbiting planet.
The Q2 data release serves a second purpose beyond archival exoplanet confirmation. NASA’s Nancy Grace Roman Space Telescope, scheduled to launch August 30, 2026, will conduct its own Galactic Bulge Time Domain Survey beginning in 2027 - monitoring the same region repeatedly to detect new microlensing events in real time at similar angular resolution.
According to the Euclid Science Center at Caltech, the Euclid survey provides the deep single-epoch reference image that Roman’s science team needs before Roman’s time-series observations begin. When Roman detects a new brightness event in the bulge, it will need a reference frame showing the field as it normally appears in order to isolate the transient signal and identify the lens star. Euclid’s Q2 data provides exactly that baseline.
The two missions are designed to be scientifically complementary. Euclid supplies reference imaging and host-star identifications for events already in the literature. Roman will search for new events in real time and, using the Euclid reference data, will be able to characterise each new detection more quickly and precisely. Scientists involved in both programmes expect the combination to produce a substantially larger number of confirmed microlensing exoplanets than either mission could achieve independently.
The Q2 package includes calibrated VIS images, an astrometric catalogue of all stellar sources detected in the surveyed area, and photometric measurements for each source. Infrared data from Euclid’s NISP instrument is not included in this release. The Euclid Consortium notes that additional data products - including multi-band photometry and deeper co-added images built from future return visits - will be issued in subsequent data releases as the EGBS programme continues.
The Euclid Galactic Bulge Survey is a dedicated side programme that runs alongside Euclid’s primary cosmological mission, which aims to map the large-scale distribution of dark matter and constrain the history of cosmic expansion across more than a third of the sky. The galactic bulge observations represent a targeted use of a small fraction of Euclid’s observing time and do not compromise the main survey.
The Q2 dataset is publicly available through the Euclid Science Archive System as of June 24, 2026.
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