Fifty years ago today, the first image of Mars was beamed back by NASA's Mariner 4. The image, which was followed by 22 others, was first closeup of another planet.

The image arrived a day after Mariner 4 executed a flyby of Mars. Fifty years later, and NASA's New Horizons spacecraft is on the same schedule, only this time the target is Pluto, a dwarf planet.

"You couldn't have written a script that was better," New Horizons principal investigator Alan Stern, a researcher at Southwest Research Institute in Boulder, Colo., told Space.com.

Like Mariner 4 did, New Horizons is forcing science lovers to wait before the first images from its flyby are returned to Earth and shared with the world. But technology moves a bit faster now.

On Wednesday afternoon, a barrage of data and imagery is expected to be transmitted back to NASA's headquarters. That transmission will be rather quick. In 1965, each image captured by the television camera attached to Mariner 4 took 10 hours to be transmitted.

Those who anxiously awaited their arrival said it was worth the wait.

"If someone had asked 'What do you expect to see?' we would have said 'craters'...[yet] the fact that craters were there, and a predominant land form, was somehow surprising," said Robert Leighton, a Caltech geology professor, who helped outfit Mariner with its array of instruments and -- most importantly -- its camera.

Leighton, along with a number of other Caltech physicists, geologists and engineers, was instrumental in getting a newly formed NASA and its Jet Propulsion Laboratory off the ground -- literally and figuratively -- with a series of early planetary missions.

"These early flyby missions showed the enormous potential of Mars to provide insight into the evolution of a close cousin to Earth and stimulated the creation of a program dedicated to iterative exploration involving orbiters, landers and rovers," said John Grotzinger, chairman of Caltech's Division of Geological and Planetary Sciences.

Since that first flyby, 19 additional probes have skirted past, orbited or landed on Mars -- 25 others have failed.

Those early missions yielded photos. And those early black-and-white photos, however pixelated, not only confirmed scientists' suspicions about Mars' surface, they set a precedent of making the capturing of imagery a central part of NASA's scientific missions.

Images, NASA quickly realized, not only aided in the cause of scientific inquiry, but they also captured the imagination of the general public.

In the wake of the Mariner 4 mission and its history-making imagery, Leighton recalls receiving a letter from a dairy farmer. It read: "I'm not very close to your world, but I really appreciate what you are doing. Keep it going."

"A letter from a milkman -- I thought that was kind of nice," Leighton said.

July 20, marks the 39th anniversary of the first image taken from Mars surface -- captured by NASA's Viking 1 lander.