One year passes in the blink of an eye in terms of the age of our universe, but 2017 has made significant contributions towards unravelling the deep mysteries hidden in its vast expanse, giving the search for alien life a big boost. From the first observations of a merger between two faraway neutron stars to stunning discoveries of a number of exoplanets in the habitable zone of a nearby star and the continued march of China as a serious space player, this year has had plenty of memorable developments to excite scientists and the public at large. Marked as the “breakthrough of the year” by the journal Science, the merger of the two neutron stars 130 million light years away generated tiny ripples in the fabric of space-time called gravitational waves.

The first detection of gravitational waves two years ago has already brought scientists the 2017 Nobel Prize in Physics, but sensing the space-time ripples after the merger of the neutron stars marked the first-ever detection of gravitational waves as well as light produced and emitted during the same cosmic event, a phenomenon that scientists like to describe as hearing and seeing the violent universe. While the observation of this collision provides scientists clues on how heavy elements like gold and platinum are produced in our cosmos, and advances understanding of the universe in myriad other ways, the discovery of several Earth-sized planets orbiting stars outside our solar system has whetted the thirst for finding signs of life in worlds other than our home planet.

In February, NASA’s Spitzer Space Telescope revealed the first known system of seven Earth-sized planets around a single star — the TRAPPIST-1 star — an ultra-cool dwarf located at about 40 light-years from Earth. The researchers determined that three of these planets are firmly located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water. The discovery set a new record for maximum number of habitable-zone planets found around a single star outside our solar system. In yet another first for the year, scientists spotted an “interstellar object” entering our solar system.

The discovery was made on October 19 by the University of Hawaii’s Pan-STARRS 1 telescope during the course of its nightly search for near-Earth objects for NASA.The discovery, termed “historic” by the US space agency, revealed the interstellar interloper to be a rocky, cigar-shaped object with a ratio of length to width unlike any asteroid or comet observed in our solar system. The team from the Pan-STARRS observatory has chosen the name “Oumuamua” for their discovery. Of Hawaiian origin, the name means a messenger from afar arriving first. In 2017, NASA made progress in the preparations to send astronauts to Mars and it became clear that the agency would have to make plans for returning astronauts to the Moon in preparation for human missions to the Red Planet and other destinations of our solar system.

The year also marks the end of Cassini’s 13-year tour of Saturn as the spacecraft made a fateful plunge into the atmosphere of the ringed planet on September 15. The mission is often credited for transforming our understanding of ocean worlds, where life may potentially exist beyond Earth. In April, NASA said that its Cassini spacecraft discovered hydrogen in the plume of gas and icy particles spraying from Saturn’s moon Enceladus. The discovery means the small, icy moon — which has a global ocean under its surface — has a source of chemical energy that life can feed on. And even as the spacecraft is gone, scientists hope that its enormous collection of data about Saturn — the giant planet, its magnetosphere, rings and moons — will continue to yield new discoveries for decades to come.

The year also marks some giant strides taken by China to emerge as a formidable space power. One of its satellites, which was sent to the skies to look for evidence of the annihilation or decay of dark matter particles in space, detected for the first time unexpected and mysterious signals in its measurement of high-energy cosmic rays, bringing scientists closer to proving the existence of the invisible matter.

Here are few highlights of 2017:

First observations of a merger between two faraway neutron stars

The Moon became a key focus point for the US space agency in 2017, whether it was blocking out the Sun during the August 21 total solar eclipse, or reinvigorating the agency’s human space exploration plans

End of the Cassini spacecraft’s 13-year tour of Saturn

Discovery of the first known system of seven Earth-size planets around a single star outside our solar system

First known interstellar object to travel through our solar system spotted

A Chinese satellite detected mysterious signals in its measurement of high-energy cosmic rays, bringing scientists closer to proving the existence of dark matter.