20 Unforgettable Moments in Space Exploration

This spring marked the 55th anniversary of the dawn of the space race, when Russian cosmonaut Yuri Gagarin became the first human to orbit the Earth in April 1961. While the Soviet Union’s accomplishment spurred the United States to put a man on the moon before the 1960s came to a close, space exploration has since become a more internationally collaborative affair.

Related: International Space Station Crew Returns Home Today. See Photos of Their Year in Space

New achievements in space travel are happening all over the world, like India's successful test launch of the country's first reusable space shuttle. Another recent major milestone occurred this spring when NASA astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko made history, returning safely home following their stint as the International Space Station’s first "One Year Crew."

What the scientific community learns from Kornienko and Kelly's experience will be invaluable to the astronauts who will be sent on a mission to Mars in the 2030s. Read on to glance back on some historic anniversaries and look ahead to what's on the horizon for space exploration.

70 years ago, on March 22, 1946, a rocket called the JPL-Ordnance Wac was the first American rocket to leave earth's atmosphere.

1946 was a big year for out-of-this-world achievements. On Oct. 24, a V2 rocket launched from the White Sands Missile Range in New Mexico equipped with a 35-millimeter camera and captured the first ever images of earth from space.

Fifty five years ago, on April 12, 1961, the space race was kicked off in earnest when Soviet cosmonaut Yuri Gagarin became the first human ever in Earth's orbit.

On May 5, 1961, astronaut Alan B. Shepard completed the Freedom 7 mission -- the United States' first suborbital flight. In July, Virgil I. "Gus" Grissom, completed the second suborbital mission for NASA.

On May 25, 1961, President John F. Kennedy addressed Congress about the necessity to invest in space exploration, famously saying, "I believe that this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the moon and returning him safely to the earth. No single space project in this period will be more impressive to mankind, or more important for the long-range exploration of space; and none will be so difficult or expensive to accomplish."

From Jan. 31 to Feb. 3, 1966, an unmanned Soviet spacecraft called Luna 9 made the first successful soft landing on the moon and then sent the first radio television transmission back to earth.

On March 1, 1966, another Soviet ship, the Venera 3, became the first spacecraft to impact the surface of another planet on its mission to Venus.

A few months later, on June 2, 1966, Surveyor 1 becomes the first U.S. spacecraft to land on the moon.

Forty five years ago, both the Americans and the Russians first set their sights on Mars. On May 19, Russian spacecraft Mars 2 became the first to make an impact on Mars, with the first soft landing on the planet following on May 28.

But on Nov. 13, 1971, Mariner 9, an unmanned NASA probe, completed an orbit around Mars and is the first spacecraft to orbit around another planet.

A month later, on Dec. 2, Russia's Mars 3 completes the first unmanned landing on Mars.

On July 20, 1976, NASA's Viking 1 was the first successful U.S. mission to land on the surface of Mars. Viking 1 ultimately spent four years and conducted 1,489 orbits of the planet, while Viking 2, which arrived on Sept. 3, 1976, worked until July of 1978. Both transmitted images and studied the terrain of the planet, searching for possible life and sending back valuable information to NASA, laying the groundwork for the Curiosity Mars Rover's memorable arrival in 2012.

2016 marks the 30-year anniversary of the Challenger Space Shuttle explosion that saw the terrible loss of the seven crew members on board on Jan. 28, 1986.

The first-ever commercial space tourist, an American millionaire and businessman from New York named Dennis Tito, hitched a ride up to the International Space Station on the Russian Soyuz-TM 32 on April 28, 2001.

Five years ago, on Feb. 24, 2011, the International Space Station got a cool new helper in the form of Robonaut 2, the first ever humanoid robot in space.

In February 2016, Richard Branson unveiled Virgin Galactic’s second SpaceShipTwo spacecraft -- the first company spacecraft to be manufactured wholly in-house. It is called the VSS Unity.

On April 8, 2016, Elon Musk’s 14-year-old SpaceX’s Falcon 9 rocket made its first ever landing at sea after successfully delivering cargo to the ISS.

And earlier this April, Amazon founder Jeff Bezos’ spaceflight startup launched and landed its reusable rocket for the third time. Bezos has said that he is looking to launch human test flights next year.

On April 13, 2017, scientists at NASA shared findings from the agency’s Cassini spacecraft mission to Saturn. It seems that a chemical reaction that is occurring underneath the icy surface of one of the planet’s moons, Enceladus, could be a sign that it could also support alien life, in another potentially groundbreaking discovery in the search for life beyond Earth.

On Feb. 22, 2017, NASA announced the discovery of a planetary system of seven Earth-sized planets orbiting around a red dwarf star. It was named TRAPPIST-1 and it is the first system that NASA has found like it. Three of the planets in the system are in what’s called the habitable zone, which means that there is a possibility that the worlds are home to liquid water and a life-supporting atmosphere.