Three years have passed since humanity gained a new, more powerful view into space, a window into the infrared realm that had until now been largely hidden from our eyes. Since July 2022, the James Webb Space Telescope, the successor to the legendary Hubble and an unprecedented technological marvel, has been tirelessly observing the cosmos. Its extraordinary ability to detect and analyze infrared light, invisible to the human eye, allows scientists to witness scenes that were until recently only the fruit of theoretical considerations. Webb is not only fulfilling the promises with which it was launched – it is surpassing them to such an extent that astronomers can hardly find the words to describe the flood of new data. In just three years, this observatory has changed our understanding of everything, from the most distant galaxies at the edge of the visible universe to our own cosmic neighborhood, the Solar System.

Built with the mission to rewrite astronomy textbooks, Webb has already sparked a true scientific revolution. To date, it has successfully completed more than 860 scientific programs, with approximately a quarter of its operational time dedicated to capturing stunning images, and the dominant three-quarters to spectroscopy – the detailed analysis of light that reveals the chemical composition, temperature, and motion of celestial objects. The amount of data collected is monumental: nearly 550 terabytes of information have resulted in more than 1600 published scientific papers. Each of these papers brings fascinating results, but also opens up a series of new, even deeper questions. Below, we present ten cosmic surprises that Webb has revealed to us, which have fundamentally changed our view of the universe.

A Revolution in Understanding the Cosmic Dawn

One of the primary scientific goals of the Webb telescope was to peer into the "cosmic dawn," the period within the first billion years after the Big Bang, when the first stars and galaxies were forming. Expectations were modest – scientists hoped to see just a few faint, undeveloped galaxies, a kind of cosmic embryo that would only hint at future magnificent structures like our Milky Way. But what Webb saw was anything but modest. Instead of the expected, barely discernible, faint galaxies, Webb discovered surprisingly bright, massive, and well-structured galaxies that existed within the first 300 million years after the Big Bang. It found galaxies with black holes that seem far too massive for their young age, posing a huge challenge to existing models of black hole growth. A galaxy resembling the Milky Way in its infancy was even discovered, existing when the universe was only 600 million years old. Some of these discoveries, such as those from the JADES (JWST Advanced Deep Extragalactic Survey) program, showed that some galaxies had already "quenched" and stopped forming stars within the first billion years, while others, within 1.5 billion years, had developed into complex "grand design" spiral galaxies, like those we see in the universe today. Although hundreds of millions of years may seem like a long period, in the context of the 13.8 billion-year age of the universe, it is equivalent to a development that took place in the first few weeks of a cosmic year. These first galaxies rapidly created generations of stars, enriching the young universe with heavier elements that are the foundation of everything we know today.

The Enigmatic "Little Red Dots" Scattered Across the Deep Universe

Webb's sharp infrared vision has revealed a completely new class of celestial objects: a distant population of mysteriously compact, bright, and distinctly red galaxies that astronomers have dubbed "Little Red Dots." Their appearance raises numerous questions. What makes them so bright and red? Is their light the result of extremely dense clusters of unusually bright stars, or perhaps gas spiraling into a supermassive black hole at their center, or maybe a combination of both phenomena? Their history is also a puzzle. It seems that these "dots" appeared in the universe about 600 million years after the Big Bang, approximately 13.2 billion years ago, only for their numbers to decline sharply less than a billion years later. Did they evolve into something else? If so, how? Webb is currently conducting more detailed investigations of these objects to provide answers to these intriguing questions.

Confirmation of the "Hubble Tension": Pulsating Stars and a Triple Supernova

How fast is the universe expanding? This seemingly simple question is one of the biggest mysteries of modern cosmology, as different methods of measuring the expansion rate yield different results. This discrepancy is known as the "Hubble tension." A key question arises: are these differences just the result of measurement errors, or is something fundamental happening in the universe that we do not yet understand? Webb's data so far strongly suggest that the problem is not in measurement errors. The telescope, thanks to its incredible resolution, has been able to clearly distinguish pulsating stars (Cepheids) from neighboring stars in densely populated areas, ensuring that distance measurements are not "contaminated" by additional light. Furthermore, Webb has discovered a distant, gravitationally lensed supernova whose image appears in three different places and at three different times during its explosion. Calculating the expansion rate based on the supernova's brightness at these three points provides an independent check on measurements obtained by other techniques. Until the Hubble tension issue is resolved, Webb will continue with precise measurements of various objects, exploring new methods and deepening the mystery.

Surprisingly Rich and Diverse Atmospheres of Gas Giants

Although the Hubble Space Telescope was the first to detect gases in the atmosphere of an exoplanet – a planet outside our Solar System – Webb has taken this research to a whole new, unimaginable level. Its spectroscopic analysis has revealed a rich cocktail of chemicals in the atmospheres of distant worlds, including hydrogen sulfide, ammonia, carbon dioxide, methane, and sulfur dioxide. None of these compounds had ever been clearly detected in an atmosphere outside our system before. Webb has also enabled the study of the exotic climates of gas giants like never before. For example, on the hot, puffy gas giant WASP-17 b, it detected flakes of silicon dioxide (quartz) "snow" in the clouds. On the planet WASP-39 b, it measured differences in temperature and cloud cover between the permanent morning and evening sides of the planet, providing insight into the dynamics of global circulation on worlds that are tidally locked to their star.

A Rocky Lava World with a Possible Atmosphere

Detecting, let alone analyzing, the thin layer of gas surrounding a small rocky planet is an extremely difficult task. However, Webb's extraordinary ability to measure subtle changes in the brightness of infrared light makes it possible. So far, the telescope has been able to rule out the existence of a significant atmosphere on several rocky planets. However, on the planet 55 Cancri e, a world covered by an ocean of lava orbiting a Sun-like star 40 light-years away, it has found intriguing hints of carbon monoxide or dioxide. The leading hypothesis is that this planet could have a secondary atmosphere, continuously replenished by gas evaporating from its scorching, lava-covered surface. With such discoveries, Webb is laying the groundwork for NASA's future Habitable Worlds Observatory, which will be the first mission specifically designed to directly image and search for signs of life on Earth-like planets around Sun-like stars.

Revealing the Skeletal Structure of Nearby Spiral Galaxies

We have long known that galaxies are cosmic cities made of stars, planets, dust, gas, dark matter, and black holes – places where stars are born, live, die, and are recycled into the next generation. But never before have we been able to see the structure of a galaxy and the interactions between stars and their environment in such captivating detail. Webb's infrared vision penetrates the dust clouds that obscure the view of other telescopes and reveals the "skeletal" structure of galaxies. We see filaments of dust tracing the spiral arms, old star clusters that form the galactic cores, newly formed stars still enveloped in dense cocoons of glowing gas and dust, and clusters of hot young stars whose radiation and winds "carve" huge cavities in the surrounding material. Images like that of the Phantom Galaxy (M74/NGC 628) clearly show how stellar winds and supernova explosions actively reshape their galactic homes.

The Thin Line Between a Brown Dwarf and a Rogue Planet

Brown dwarfs are objects that form like stars but are not massive and hot enough to initiate nuclear fusion of hydrogen in their cores, the process that defines stars. On the other hand, "rogue planets" form like other planets within a system but are later ejected from it and now roam space without a host star. Webb has observed hundreds of brown dwarf-like objects in the Milky Way and has even detected some candidates in a neighboring galaxy. The problem is that some of these objects are extremely small – only a few times more massive than Jupiter – which makes understanding their formation difficult. Are they actually free-floating gas giants? What is the minimum amount of material needed to form a brown dwarf or a star? We are not yet sure, but thanks to three years of observations with the Webb telescope, we now know that there is a continuum of objects from planets through brown dwarfs to stars, with blurred boundaries between them.

Can Planets Survive the Death of Their Star?

When a star like our Sun reaches the end of its life, it swells into a red giant phase, becoming large enough to engulf nearby planets. After that, it sheds its outer layers, leaving behind a super-hot core known as a white dwarf. Is there a "safe distance" at which planets can survive this cataclysmic process? Webb may have found the answer. It has discovered several candidates for planets orbiting white dwarfs. If confirmed to be actual planets, this would mean that it is possible for planetary systems, or at least their outer parts, to survive the death of their star, continuing to orbit the slowly cooling stellar ember. This opens up fascinating possibilities about the long-term fate of planetary systems.

Enceladus's Fountain Feeds the Saturnian System with Water

Among the icy "ocean worlds" of our Solar System, Saturn's moon Enceladus is perhaps the most intriguing. NASA's Cassini mission was the first to detect geysers of water vapor erupting from its south pole. However, it was only Webb that was able to reveal the true scale of these plumes. Observations showed a vast cloud of water vapor extending over more than 9,600 kilometers (6,000 miles), which is almost 20 times the width of Enceladus itself. This water spreads out to form a torus, a donut-shaped ring, that encircles Saturn beyond its well-known visible rings. While a small portion of the water remains in this torus, most of it is dispersed throughout the entire Saturnian system, and even "rains" down on the planet itself. Webb's unique observations of rings, auroras, clouds, winds, and other phenomena in the Solar System are helping us to better understand what our cosmic neighborhood is made of and how it has changed over time.

Assessing Asteroids That Threaten Earth

During 2024, astronomers discovered an asteroid for which preliminary calculations showed a certain chance of it hitting Earth. Such potentially hazardous asteroids immediately become the focus of intense observation. Webb, with its unique capabilities, was able to quickly measure the object, which turned out to be the size of a 15-story building. Although this particular asteroid is no longer considered a threat, the study demonstrated Webb's crucial role in assessing dangers from space. The telescope also provided crucial support for NASA's DART (Double Asteroid Redirection Test) mission, which intentionally crashed a spacecraft into the Didymos asteroid system, proving that a planned impact can divert the path of an asteroid that would be on a collision course with Earth. Both Webb and Hubble observed the impact, witnessing the cloud of ejected material. Webb's spectroscopic analysis of this material confirmed that the asteroid's composition is likely typical of those that could pose a threat to Earth, providing key data for future planetary defense missions.

In just three years of operation, Webb has sharpened our view of the distant universe, revealing unexpectedly bright and numerous early galaxies. It has unveiled new stars in their dusty cradles, the remnants of exploded stars, and the skeletons of entire galaxies. It has studied the weather on gas giants and searched for atmospheres on rocky worlds. It has provided new insights into the inhabitants of our own Solar System. But this is just the beginning. Engineers estimate that Webb has enough fuel to continue observations for at least another 20 years, giving us the opportunity to answer additional questions, explore new mysteries, and piece together more parts of the cosmic puzzle. The demand for observation time on Webb is higher than ever, surpassing any other telescope in history, whether on Earth or in space. What new discoveries await us?

The original article was published on the NASA science.nasa.gov portal.
Source: 3 Years of Science: 10 Cosmic Surprises from NASA’s Webb Telescope
Author: Dr. Macarena Garcia Marin and Margaret W. Carruthers, Space Telescope Science Institute, Baltimore, Maryland