WASHINGTON: This week, NASA celebrates the 25th year of its two epic space journeys. Launched with little fanfare in 1977, the missions of Voyagers 1 and 2 were scheduled to last just four years.

Since then, they have sent back reams of data and pictures that have revolutionized how Earthlings look at their solar system. Voyager 1 has now travelled 12.9 billion kms — 86 times the mean distance between the Earth and the Sun — and Voyager 2 has travelled 10.2 bn kms.

And they are still going, hurling through space at 60,000 kms per hour, toward the far reaches of our solar system. Their next hurdle will be leaving the gravitational pull of the sun and passing into the interstellar space beyond.

Some experts believe Voyager 2 will enter a region with reduced “solar winds” of electric particles within a year or two. In seven to 21 years, it is expected to pass beyond the sun’s magnetic field into interstellar space.

“Voyager was the crowning achievement of our time,” the project’s former imaging scientist Carolyn Porco told the Washington Post.

“I would say that humankind, in the latter half of the 20th century, the beginning of the 21st, is going to be remembered for our efforts to explore the solar system, and Voyager was the crowning achievement of that.

“It was the mission that opened up the solar system.”

Voyager 2 was launched August 20, 1977, and the identical Voyager 1 blasted off on September 5 from Cape Canaveral, Florida. Voyager 1 caught up and is now the most distant man-made object in space.

On their odysseys, the one-ton probes visited Jupiter in 1979 and they reached Saturn in 1980 and 1981, respectively.

Parting ways with its twin, Voyager 1 was then hurled upward out of the plane in which the nine planets orbit.

Voyager 2 travelled on to Uranus and Neptune, which had never before been visited by human probes, before it dropped down and out of the planetary plane.

It now takes a radio signal from Voyager 2 more than nine hours to reach NASA’s Jet Propulsion Laboratory in Pasadena, California. Experts there are hopeful the twin Voyagers will keep beaming back information for another 20 years.

After that, their on-board power reactors will run out, leaving the Voyagers silent as they continue their epic journeys through the universe that could last millions of years.—dpa