A rock 'twice as big as Earth' pushed Uranus onto its side

Researchers speculate the crash may reveal a "missing planet" beyond Pluto. Uranus's magnetic field is also lopsided.

Atomic clocks so precise they can measure the distortion of space-time

These clocks are so accurate they'd lose just half a second if they lasted the age of the universe. The clocks' exquisite precision, outlined in Nature today, means they can measure how space-time distorts under gravity forces.  Eventually, astrophysicists could enlist their help to detect mysterious dark matter.

Biggest black hole collision yet detected by gravitational waves

Some 9 billion years ago, a pair of black holes — around 51 and 34 times the mass of the Sun — merged in a colossal collision.  They formed a new black hole around 80 times the mass of the Sun, and the ensuing blast in their final seconds sent gravitational waves coursing through space-time.  Travelling at the speed of light, those infinitesimally tiny ripples washed through Earth on July 29 last year.