Ranking the 25 coolest things in space so far in the 21st century

16. Gravitational wave detection

Although he theorized about their existence a century ago, eminent physicist Albert Einstein was unsure that humans would ever be able to detect the faint echoes of gravitational waves traveling through the vastness of space. Nevertheless, experimental physicists have been striving for this for decades. Then in February 2016, two LIGO observatories announced that they had detected gravitational waves coming from two merging black holes.

This marked a triumphant moment for experimental physics and confirmed a key principle of Einstein's general theory of relativity. Now these observatories have given physicists a powerful new tool to observe violent astrophysics from afar. Since the initial discovery nearly a decade ago, physicists have detected eight additional gravitational waves originating from a variety of astrophysical phenomena.

15. Rise of space tourism

In April 2001, an engineer and businessman named Dennis Tito was launched into orbit aboard a Russian Soyuz spacecraft. He was the first private space tourist. Just over three years later, the experimental spaceplane SpaceShipOne, designed by Burt Rutan and flown by Mike Melvill, reached an altitude of 100.1 km. This was the first privately funded human spaceflight.

Subsequently, private space tourism floundered for almost twenty years. There were a handful of commercial flights on Soyuz. But it wasn't until the summer of 2021 that things really took off, first with Virgin Galactic's VSS Unit spacecraft and then Blue Origin's New Shepard vehicle that flies private citizens into suborbital space. Shortly thereafter, in September 2021, entrepreneur Jared Isaacman commanded the first private orbital mission, Inspiration4, on Crew Dragon. In December of that year, the daughter of the first American in space, Laura Shepard-Churchley, followed in her father's footsteps by completing a similar trajectory aboard a spacecraft bearing his name. Private space travel is not yet ubiquitous, but the era is finally dawning.

14. Continuous presence on Mars

At the beginning of 2004, the Spirit And Possibility rovers landed on opposite sides of Mars. Originally designed for 90 days of use, Spirit functioned until it crashed in 2009, and it stopped communications in 2010. Possibility proved more tenacious and functioned 57 times longer than its intended lifespan. By the time of last contact with NASA in June 2018, Possibility had traveled 45 km (28 miles).