When it comes to the wonders of the universe, how does one begin to rank the awe-inspiring events that have unfolded in the cosmos over the past two decades? The truth is, every one of these achievements carries its own magnificence and unique story. What follows is a subjective countdown, by the editors of Ars Technica, highlighting the most exciting developments in space exploration from the dawn of the 2000s through 2023. Here, we celebrate the moments that have expanded our horizons and captivated our imaginations.

25. The Artemis I Mission

NASA's Artemis I mission, which launched an uncrewed Orion spacecraft around the Moon in late 2022, marks a pivotal step in humanity’s return to deep space. Despite its significance, it surprisingly slipped under the radar of many space enthusiasts. This ambitious program is set to lead the way for future crewed missions to the lunar surface, continuing the legacy of human exploration after a hiatus of half a century.

24. The Parker Solar Probe

NASA's Parker Solar Probe, launched in 2018, is the fastest spacecraft ever created. Designed to study the Sun up close, it reached a speed of approximately 690,000 km/h (430,000 mph). As it dives into the Sun's outer atmosphere, it collects vital data about solar phenomena and solar wind, charting the dynamics that shape space weather—a subject incredibly relevant for our own technology-dependent world.

23. The Curious Case of ʿOumuamua

When ʿOumuamua was spotted in our solar system in 2017, it piqued curiosity globally. As the first confirmed interstellar object, this elongated, cigar-shaped entity attracted astronomical speculation regarding its origins. While many theories abound about its nature, it remains a mystery, a testimony to our limited understanding of the universe.

22. Falcon 9 and the Starlink Revolution

Since its debut in 2010, SpaceX’s Falcon 9 rocket has executed hundreds of launches and brought about a revolution in the aerospace industry with its reusable first stage design. The rapid deployment of the Starlink satellite constellation—over 7,000 satellites—has prioritized global internet access but raised concerns about space debris and its impact on astronomical observations.

21. The Mysteries of Dark Matter and Dark Energy

The cosmic landscape continues to confound us. While prior discoveries hinted at the presence of dark matter and dark energy, ongoing research throughout the 21st century seeks to unveil their secrets. Together, these two components make up about 95% of the universe's total mass-energy content, and understanding them could unlock the mysteries of the cosmos.

20. The Return of Sample Missions

NASA's Stardust and Genesis missions marked a resurgence in sample-return missions. Stardust collected comet dust, while Genesis aimed to retrieve solar wind samples. Though Genesis struggled in its return, both missions laid groundwork for more advanced future endeavors.

19. Cassini’s Revelations on Enceladus

NASA’s Cassini spacecraft delivered awe-inspiring findings about Enceladus, one of Saturn’s moons. Its detection of geysers spewing water vapor and organic compounds highlighted the possibility of life beneath the moon’s icy crust—an exciting frontier for future explorations.

18. The Resurgence of Lunar Exploration

In the wake of countless lunar missions during the Cold War, interest in the Moon surging back to life has been noteworthy. China’s successful Chang’e missions and NASA’s renewed ambitions, including Artemis, signal a new era of exploration and potential lunar habitation.

17. Demo-2: A Milestone for SpaceX and NASA

SpaceX’s Demo-2 mission in 2020 not only marked the return of crewed missions to American soil but also the emergence of private companies capable of astronaut transportation to the ISS. This shift is paving the way toward a more vibrant, commercially driven space industry.

16. Gravitational Waves Detected

The detection of gravitational waves in 2016 confirmed a key tenet of Einstein’s theory of general relativity, providing new tools for astrophysicists to study cosmic events such as merging black holes, thereby deepening our understanding of the universe.

15. The Dawn of Space Tourism

With Dennis Tito's historic flight in 2001 and subsequent developments from Virgin Galactic and Blue Origin, the era of space tourism began to emerge onto the public stage. Today, the blueprint for accessible private space travel is being drafted, fostering ambitions for a future with ordinary citizens reaching the stars.

14. Continuous Martian Presence

NASA's rovers Spirit and Opportunity opened a continuous line of exploration on Mars, monitored until Opportunity’s mission officially ended in 2018, followed by the Curiosity and Perseverance rovers. Their data has continually shaped our knowledge and perceptions of the Martian environment.

13. Asteroids Under Surveillance

Asteroid exploration has surged, as missions like Hayabusa and OSIRIS-REx targeted these celestial bodies to understand their compositions and ensure planetary defense against potential impacts. NASA's DART mission demonstrated a tangible approach to redirecting asteroids.

12. China’s Ambitious Lunar Program

China’s space program has achieved remarkable milestones with its Chang’e lunar missions. The historic landing on the far side of the Moon and ongoing sample-return efforts elevate China as a key player in the new space race.

11. Starship’s New Era of Spaceflight

SpaceX's revolutionary Starship program has drawn attention with its extraordinary capabilities. The successful recovery of a Super Heavy rocket showcased a futuristic approach to launch operations, inspiring beyond Earth’s atmosphere.

10. The Voyager Legacy Continues

NASA’s Voyager spacecraft have traversed the cosmos for nearly half a century, collecting vital data about interstellar space and continuing to send messages back to Earth—an enduring legacy of exploration.

9. Kepler’s Exoplanet Discovery

NASA's Kepler mission transformed our understanding of exoplanets, discovering thousands of new worlds and revealing that planets may outnumber stars in our galaxy, thereby fueling the ongoing search for extraterrestrial life.

8. The Launch of the James Webb Space Telescope

The James Webb Space Telescope, launched on Christmas Day 2021, is a marvel of engineering that promises to deepen our understanding of the universe. Its intricate design and groundbreaking capabilities are paving pathways to countless astronomical discoveries.

7. Huygens’ Journey to Titan

Huygens probe’s touchdown on Titan in 2005 offered humanity our first look at this exotic moon, revealing a world with lakes of methane and the potential for prebiotic chemistry.

6. The International Space Station: A Space Haven

For over two decades, the International Space Station has hosted humans in the microgravity environment, fostering international cooperation and scientific progress while setting the stage for the future of human space exploration.

5. The Historic Falcon 9 Landing

SpaceX’s first successful vertical landing of the Falcon 9 rocket in 2015 revolutionized rocket science, demonstrating the practicality of reusability and reshaping the future of space launches.

4. New Horizons Visits Pluto

The New Horizons mission captured the world’s imagination with its Pluto flyby in 2015, unfolding new knowledge of this distant world and the Kuiper Belt, igniting curiosity about our solar neighborhood.

3. Philae Routs a Comet

In 2014, the Philae lander made history by becoming the first spacecraft to land on a comet, unveiling secrets about the primordial solar system and adding rich data about cometary characteristics.

2. Ingenuity’s Historic Flights on Mars

The Ingenuity helicopter dazzled the world with its pioneering flights on Mars, marking the first powered flight on another planet. Its success has opened avenues for various aerial explorations in planetary science.

1. The Falcon Heavy Launch Spectacle

SpaceX’s Falcon Heavy launch in February 2018 left an indelible mark on modern space history. The launch showcased stunning visuals, and the unparalleled dual landing of the boosters symbolized a new era of space exploration and commercial access to space, further asserting private contributions to space endeavors.

Each of these milestones illustrates humanity's relentless pursuit to understand and explore the unknown. The coming years promise even more astonishing revelations from the last frontier: outer space. While we may be fools for dreaming, it is precisely this intoxicating drive that propels us towards a future where the cosmos hold no limits.