NASA listens as Voyager One nears edge of interstellar space

By Michael O’Connell
Web Editor
Federal News Radio

When NASA first envisioned the Voyager space probes in 1972, Ed Stone was there to help design them, and he was there when Voyager One launched in 1977. Thirty-four years later, Voyager One has reached the outermost edge of the solar system, still sending back signals. As the Voyager Program’s chief scientist, Stone is still listening.

“Voyager One is now about 11 billion miles from Earth,” Stone told The Federal Drive with Tom Temin on Friday morning. “It’s very close to the edge of interstellar space. It’s still inside the huge bubble the sun creates around itself called the heliosphere.”

Outside of that bubble, the space probe will pass by material from stars that exploded 5-10 million years ago.

“Voyager One is the most distant human object,” Stone said. “It will be the first to reach interstellar space. We just hope that happens while we still have enough electrical power for it to send the data back to Earth.”

For the last 34 years, the probe has transmitted data back to NASA 24 hours a day, though scientists only listen about 10 hours a day. It takes about 16.5 hours for a message to reach the Earth.

The information that NASA is now receiving concerns the million-mile-per-hour wind that blows out from the sun.

“We measure the speed of that wind,” Stone said. “We are now at the point where the wind is essentially no longer moving out radially at all but in fact seems to be turning around a bit. That tells us that we’re getting very close to the boundary, because the wind can’t go beyond that boundary. Outside is the wind from other stars. So, we’re getting close, we just can’t say how close yet.”

According to Stone, Voyager One will continue to circle the center of our galaxy forever, as it travels on a course to the constellation Ophiuchus. “It’ll be about 40,000 years before it passes another star,” he said. “At that time, it will still be much further from that star than it is from the sun today.”

Phoning home, but no E.T.

As Voyager One disappears into the vastness of space, Stone says that it’s unlikely to be the instrument that will contact intelligent beings from another world — space is just too big and empty for that to happen.

“Perhaps someday we’ll get a radio signal,” he said. “But I think it’s going to be very challenging for anything like this [spacecraft] to be found.”

If Stone had to pick one scientific discovery as the most significant of the many uncovered by the Voyager spacecraft, it would be the eight volcanoes on the moon Io identified during the first flyby of Jupiter.

“Before that, the only known active volcanoes in the solar system were here on Earth,” Stone said. “Suddenly, we had a small moon of another planet have 10 times the volcanic activity of the Earth.”

Even though Voyager One’s voyage will go on forever, scientists know that its ability to transmit messages will not. The probe uses that natural radioactive decay of Plutonium 238, which has a half-life of 88 years.

“That means we’re losing about four watts a year,” Stone said. “So, we know that around 2025 we will no longer have enough power for the spacecraft to keep transmitting.”

Though Stone will probably be retired from NASA by then, he hopes to still be in contact with his colleagues there when Voyager One makes its final transmission. “It’s really been a tremendously exciting journey from a scientific point of view and it continues to be,” he said.


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