A Dark Mission

The study of one of the universe's biggest mysteries takes a key step forward this weekend as the European Space Agency looks to launch its Euclid Space Telescope tomorrow. The mission will probe the nature of dark energy and dark matter, which constitute 95% of the universe but remain poorly understood.

The existence of both has been confirmed by, among other things, measuring how galaxies move and the energy coming from distant supernovas. The term “dark” refers to the properties known about each—dark matter exerts a gravitational pull on objects but doesn’t interact with light, while dark energy remains hypothetical and needed to account for the expansion of the universe.

The Euclid mission will survey more than 1 billion galaxies, each with roughly 100 billion stars, to measure a single parameter describing the effect of dark energy on universal expansion. Read more about why the results, regardless of the outcome, will yield more questions than answers.