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It has been 50 years since NASA 's Mariner 2 spacecraft traveled 36 million miles to Venus for the first-ever close-up view of another planet.

This is a big milestone. Not only did that mission mark the beginning of interstellar exploration , but it also came at a time when morale was low: The U.S. hadn't truly had a space "first" in five years. Meanwhile, as America's space program stood stagnant, the Soviet Union continued to advance its efforts in space.

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NASA recently released an online interactive map where you can relive this milestone and other big moments in space exploration , from 1962 through Curiosity 's landing this year.

We all probably remember the major space headlines, but what about the cool stuff that we didn't hear about? What were NASA employees' favorite memories? Mashable asked five Jet Propulsion Laboratory workers to share the space moments they will never forget. Here are their stories in their own words.

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1. My First Contact With Another Planet Rob Manning, Chief Engineer , Mars Science Laboratory Mission

At 10:30 a.m. on the Fourth of July in 1997 at the Jet Propulsion Laboratory in Pasadena, Calif., as head of the entry, descent and landing team and Chief Engineer, I was staring at a computer screen watching a series of dramatic events flip by that had been unfolding millions of miles away.

Mars Pathfinder , with the little Sojourner rover safely tucked inside, was landing on Mars. On my headset, I was straining to hear my colleagues on the other side of the Earth in Madrid who were watching analog displays showing signals from Mars via a massive dish antenna.

"I have all eyes watching," Sami Asmar says, only seconds after the time my display has predicted that the lander should be bouncing in its airbag cocoon. "We see a weak signal," he says. "A signal is barely visible!" I repeat it into my microphone while being watched by perhaps millions of people. I knew then that Pathfinder had run the gauntlet and had made a safe contact with the surface on another planet.

While versions of this story have repeated both before and since, nothing compares with the first time you reach out and make physical contact with another world. On that day, I was there on Mars.

2. My First Glimpse of Uranian Rings Dr. Linda Spilker, Project Scientist, Cassini Mission at Saturn

Favorite moment in space exploration was watching the return of the first Voyager picture of the Uranian rings at high-phase angle. Voyager had flown past Uranus and was looking back at the planet's narrow rings. The picture that came back was amazing!

The nine narrow rings were suddenly embedded in broad bands of dust that were scattering their light back to the Voyager cameras. No one had expected to see so much dust. Everyone, including me, jumped up and started pointing at the screen, speculating on what we saw in that image. From that moment on, I knew I was destined to be a ring scientist.

3. When I Knew What I Wanted to Be When I Grew Up Todd J. Barber, Propulsion Engineer, Cassini (Saturn) and Mars Science Laboratory Missions

My favorite moment was seeing the pictures of Jupiter and Saturn and their moons in National Geographic magazine around 1980. I was an 8th grader, visiting my grandmother in western Kansas, and she turned me on to the magazine. As soon as I saw these images, I knew what I would be doing for the rest of my life, with luck and lots of hard work.

4. Seeing the First Pictures of a Comet's Nucleus Marc Rayman, Mission Director and Chief Engineer, Dawn Mission to Giant Asteroids Vesta and Ceres

Favorite moment in space exploration was seeing NASA's first close-up pictures of the nucleus of a comet by Deep Space 1 in September 2001. I was in mission control when this aged and wounded bird sent back the extraordinary views from its spectacular encounter with Comet Borrelly. Coming only 11 days after 9/11, it was a wonderful reaffirmation of the power of the human spirit of adventure, the hunger for knowledge and the passion to know the cosmos.

5. The Discovery That Made My Work Obsolete, But I Didn't Care Claudia Alexander, Project Scientist, U.S. Rosetta Project (Comet Mission)

My favorite moment was seeing the first data from our very first encounter with Jupiter's moon Ganymede with the historic Galileo mission. I'd been involved, calculating Ganymede's thermal history, and I had it frozen solid (on the computer) in many different ways. As data filled the screen, line after tremulous line, the clear signature of a spacecraft passing through an ionosphere emerged.

I was so astonished I blurted out, "I can't believe it!" My boss pointed at the scratchy lines on our screen and said, "You see the evidence right in front of your eyes, and you don't believe that!" What was unbelievable (and still not explained) is that an ionosphere means that the large moon possessed a thin atmosphere interacting with a robust magnetic field. Ganymede was not frozen solid. Robust magnetic field lines require active currents within a molten, or slushy, interior.

So, in about 30 seconds, I saw evidence that all my previous work was obsolete (in a good way).

Featured photo of NASA Control Room courtesy of Flickr, NASA Goddard Photo and Video ; All photos of NASA employees courtesy of NASA

BONUS: The Year's Top Space Events



10. The Epic Supermoon On a clear weekend in May, the full moon got the closest to Earth that it will reach all year, resulting in what astronomers called the "supermoon." It appeared 14% bigger and 30% brighter than the average full moon.

Click here to view this gallery.

This story originally published on Mashable here .