On October 15, 2024, the Euclid Space Telescope released the "first page" of the cosmic atlas it is constructing. This achievement is built based on 260 sets of observation data collected between March 25 and April 8, 2024, containing up to 208 gigapixels of data. The mapped area is approximately 500 times wider than the full moon as seen from Earth. It includes not only tens of millions of stars within the Milky Way but also about 14 million distant galaxies outside the Milky Way. Astonishingly, this massive piece of the puzzle accounts for only 1% of Euclid’s total survey over the next six years. Valeria Pettorino, Euclid Project Scientist at the European Space Agency (ESA), stated: “This stunning image is the first in a six-year effort that will eventually map more than a third of the sky. It’s just 1% of the final atlas, yet it’s packed with various cosmic sources that will help scientists develop new ways to describe the universe.” Euclid’s goal is to trace the shapes, distances, and motions of galaxies 10 billion light-years away. This will not only create the largest 3D map of the universe ever made but also is expected to help scientists unlock the mysteries of dark matter and dark energy. In humanity’s unremitting exploration of the universe, the Euclid Space Telescope stands as a brave pioneer, tasked with lifting the veil on two of the cosmos’ greatest mysteries—dark matter and dark energy. Since its launch, it has continuously brought surprises and shocks to the scientific community, giving us a brand-new understanding of the vast universe. ### 01 Technology Forges Extraordinary Capabilities to Support In-Depth Exploration #### Intricate and Sophisticated Structural Design The Euclid Space Telescope was launched on July 1, 2023, aboard a SpaceX Falcon 9 launch vehicle from the Cape Canaveral Space Force Station in Florida, USA. After a 30-day journey, it reached the Sun-Earth Lagrange Point L2, 1.5 million kilometers from Earth, where it operates in a special orbit. With an overall height of approximately 4.7 meters, a diameter of about 3.7 meters, and an on-orbit mass of 2 tons, it consists of an 850-kg service module, an 800-kg payload module, 210 kg of propellant, and 40 kg of balance mass. The 1.2-meter-diameter telescope, housed within the payload module, is equipped with a visible-wavelength camera (Visible Instrument) and a near-infrared spectrometer and photometer. The selection of materials and colors embodies both technological aesthetics and scientific considerations. The sunshield, cylindrical body, and service area use gold, silver, white, and black materials respectively. The gold and silver thermal insulation materials can withstand the extreme temperature differences in space; the upper lens barrel and middle image sensor of the telescope are painted white to dissipate heat at extremely low temperatures; the service area equipment, which has less strict temperature requirements, is painted black. In addition, the solar panels provide over 2 kilowatts of electricity to the spacecraft while also serving as a sunshade. Below the solar panels on the same side are two antennas: one for transmitting observation data, and the other for monitoring flight attitude and detecting information. To maintain its position in the special orbit, the telescope relies on its own thrusters. Its optical guide star sensor is wrapped in gold material and uses micro-thrusters for pointing correction. #### Advanced and Outstanding Optical and Detection Systems The ceramic structure of the Euclid Space Telescope is made by casting, polishing, and silver-plating silicon carbide powder through a complex process. Compared with metals, silicon carbide is less affected by temperature changes, more stable, and non-deformable, which effectively enhances the focusing and observation capabilities of the optical system. Although silicon carbide is extremely brittle, engineers have successfully overcome this challenge to ensure the instrument operates normally in the space environment. A dichroic filter behind the telescope’s primary mirror splits the collected light into two paths, directing it to the Visible Instrument and the near-infrared spectrometer and photometer respectively. The Visible Instrument has a sensitive observation range of 550-900 nanometers, uses 36 charge-coupled devices arranged in a 6×6 grid, has an average image resolution of approximately 0.23 arcseconds and 600 million pixels, and can image an area of about 0.56 square degrees in a single shot, capturing celestial objects as faint as magnitude 24.5. The near-infrared spectrometer and photometer are equipped with 16 mercury-cadmium-telluride near-infrared sensors, covering a field of view of about 0.55 square degrees, and include a camera and an integral field spectrometer. The camera can observe wavelengths from 900 to 2000 nanometers, has 65 million pixels, and can detect objects down to magnitude 24; the spectrometer decomposes near-infrared radiation (1100-2000 nanometers) into spectra to determine the spectral redshift of galaxies. ### 02 Focus on Two Mysterious Domains to Explore the Nature of the Universe #### Unveiling the Mystery of Dark Matter Based on observations and data analysis of cosmic microwave background radiation, approximately 4% of the total mass-energy of the universe consists of detectable, visible matter, while about 96% is composed of the mysterious dark matter and dark energy (with dark matter being a major component of this 96%). Although dark matter cannot be directly observed, numerous scientific analyses have confirmed its existence. It is a collection of unknown particles that exerts an influence on the cosmic gravitational field. Initially, people thought dark matter might be hydrogen atoms in the atmosphere, but in reality, these "new particles" do not interact with light, making them difficult to observe with ordinary telescopes. In the 1990s, the Cosmic Background Explorer satellite discovered slight temperature variations in the cosmic microwave background radiation. This indicated that fluctuations caused by differences in atomic distribution were insufficient to explain the observed galaxy clusters, suggesting the presence of invisible matter at work. As early as the 1930s, astronomer Fritz Zwicky measured the velocities of galaxies in the Coma Cluster and, by comparing them with the mass of visible matter, found that the galaxies were moving much faster than expected. When dark matter was incorporated into the computational model, this abnormal velocity could be well explained. Additionally, dark matter reveals its presence by distorting the light of galaxies through the "gravitational lensing effect." The Euclid Space Telescope will collect information on the shapes, sizes, and positions of billions of galaxies across approximately one-third of the sky, observe deep cosmic fields, map the shapes and distributions of galaxies, and identify galaxy clusters to understand the structure and history of the "cosmic web." Through the distribution of galaxy clusters, it will create a 3D view of dark matter in the universe. At the same time, it will use the "weak gravitational lensing effect" to conduct "tomographic scans" of dark matter distribution, attempting to reveal the total mass of cosmic neutrinos and provide clues for exploring the behavior of dark matter. #### Exploring the Mystery of Dark Energy The concept of dark energy originates from Einstein’s field equations of gravitation. Einstein introduced the "cosmological constant" into the equations to keep the universe static, but later it was discovered that the universe is actually expanding—and expanding at an accelerating rate. Since the gravitational force of matter in the universe resists expansion, yet the actual expansion is accelerating, cosmologists hypothesize that "dark energy" is driving this phenomenon, and dark energy has thus become a synonym for the "cosmological constant." According to ESA estimates, dark energy accounts for approximately 68% of the universe’s mass-energy density. Currently, scientists know very little about the nature of dark energy—some even question whether it is a form of energy at all. Some scientists have proposed that "empty space is not empty," referring to dark energy as "vacuum energy" and the corresponding force as "vacuum force." If confirmed, this would become the fifth fundamental force of nature. The Euclid Space Telescope will scan one-third of the sky, observe light from 10 billion light-years away, and study whether the universe’s expansion is uniform in all directions and locations, as well as how cosmic expansion has changed over time. By researching baryon acoustic oscillations—the traces left by oscillations in the early universe—it will accurately measure the history of cosmic expansion over the past 10 billion years and test candidate models of dark energy. ### 03 Abundant Achievements Emerge, Revealing the Diverse Faces of the Universe #### Stunning Early Discoveries On November 7, 2023, ESA released the first set of full-color cosmic images captured by the Euclid Space Telescope. These included the Perseus Cluster, located 240 million light-years from Earth, which contains 1,000 galaxies along with over 100,000 more distant galaxies in the background—many of whose light has traveled 10 billion years to reach Earth. Scientist Yannick Mellier stated: “Without dark matter, galaxies would be evenly distributed throughout the universe. Only with dark matter present in the universe can galaxy clusters like Perseus form.” Also captured in this set was the spiral galaxy IC 342, known as the “Hidden Galaxy,” which lies behind the Milky Way. Leveraging the dust-penetrating capability of its near-infrared spectrometer and photometer, as well as its ability to capture light from cool, low-mass stars, the Euclid Space Telescope imaged IC 342 with extremely high sharpness. ESA scientist Rene Laureijs noted that studying IC 342 will provide valuable insights into the Milky Way and help trace the history of star formation. Meanwhile, Euclid observed the dwarf galaxy NGC 6822, which is only 1.6 million light-years from Earth and belongs to the same galaxy group as the Milky Way. With low metallicity, studying NGC 6822 helps shed light on how galaxies evolved in the early universe. Additionally, it observed the globular cluster NGC 6397, composed of hundreds of thousands of stars and located approximately 7,800 light-years from Earth. ESA scientist Massimo Marassini explained that Euclid can observe globular clusters, distinguish the faint stars in their outer regions from other cosmic sources, and by exploring their “tidal tails,” accurately calculate the cluster’s orbit around the Milky Way—thereby gaining insights into the distribution of dark matter within the Milky Way. #### Continuing to Deliver Surprises On May 23, 2024, ESA released five new cosmic views captured by Euclid. Among them was the Abell 2390 galaxy cluster, located about 2.7 billion light-years from Earth. The image covers 50,000 galaxies in the cluster, displays giant arcs caused by the gravitational lensing effect, and a zoomed-in view reveals diffuse light within the cluster—all of which help pinpoint the location of dark matter. The “first page” of the cosmic atlas released on October 15, 2024, boasts a resolution of 208 billion pixels and includes approximately 100 million stars and galaxies. This series of achievements demonstrates the Euclid Space Telescope’s powerful observation capabilities, providing scientists with abundant data and a fresh perspective for studying the universe. ### Conclusion The initial observation range of the Euclid Space Telescope is 130 square degrees—more than 500 times the area of the full moon. Its scientific survey over the next year will cover 15% of the planned total area. ESA Director General Josef Aschbacher said: “The images of the dark universe captured by the Euclid Space Telescope are awe-inspiring. This is a gift from this ambitious space mission to all those involved, reflecting the remarkable success of international cooperation and reminding us why we must venture deeper into space to unlock more of the universe’s mysteries.” It is expected that some deep-field observation images will be released in the spring of 2025, and the first batch of cosmological data will be released in the summer of 2026. The Euclid Space Telescope is poised to enable cosmologists to study the two great mysteries of dark energy and dark matter simultaneously for the first time. As time progresses, it will present us with a more complete and detailed picture of the universe, leading humanity to new heights in the journey of cosmic exploration.