We’re in a season of anniversaries and memories, many of them exceedingly melancholy: the Lehman Brothers bankruptcy that ignited the global financial crisis, September 15, 2008 (5 years ago); the World Trade Center and Pentagon attacks, September 11, 2001 (12 years ago); the outbreak of the Yom Kippur War, 10 Tishri 1973 (40 years ago by the Hebrew lunar calendar). And, wandering only a little further afield, the outbreak of World War II, September 1, 1939 (74 years ago). And, on a more ambivalent note, the signing of the Oslo Accords on the White House lawn, which was either a great hope that’s been dashed (as I believe) or a tragic error (as some of my friends and relations believe), September 13, 1993 (20 years ago).
But something unambiguously great happened today, September 12, 2013: NASA confirmed that Voyager 1, the spacecraft launched to Jupiter and Saturn on September 5, 1977 (36 years ago), has left our solar system and entered the cold zone of deep space, the first man-made object ever to enter the vast, unknown realm between the stars, interstellar space.
The crossing actually occurred a year ago, on August 25, 2012, according to NASA’s calculations. But, as Space.com reports, the instrument that would have detected the crossing and transmitted it back to earth broke down in 1980, so scientists had to rely on complicated calculations from other instruments. It took a bit of luck, too: “A massive solar eruption in March 2012 arrived at the location of Voyager 1 about 13 months later, making the plasma around the probe vibrate, NASA officials said.”
Voyager is currently about 12 billion miles from the sun—or about 11.9 billion miles from us—and radio signals traveling at the speed of light (186,000 miles per second) take about 17-1/2 hours to reach us.
As the Los Angeles Times reported today:
The evidence was outlined in a paper published online Thursday in the journal Science.
Lead author Don Gurnett, a University of Iowa plasma physicist and a Voyager project scientist, said the data showed conclusively that Voyager 1 had exited the heliopause — the bubble of hot, energetic particles that surrounds our sun and planets — and entered into a region of cold, dark space called the interstellar medium.
CBS News explains:
Voyager 1 reached the boundary of the heliosphere in 2004, a milestone marked by readings showing the speed of the solar wind had dropped below that of sound. But it took another nine years to complete the crossing and move out into interstellar space.
The transition actually occurred in August 2012, but an instrument that would have confirmed that failed in 1980, forcing scientists to rely on less direct methods of observation.
“When we got that data, I and my colleagues just looked at each other and said, ‘We’re in the interstellar medium.’ It was just that clear to us,” Gurnett said.
Gotta give a hat tip to a post on Facebook from Brian McRae, my (actual) friend and fellow former Kibbutz Gezer-nik, for alerting me. As we discovered in chatting, Voyager is still about 24,000 light years from the edge of our galaxy, the Milky Way, but could exit the galaxy into the true unknown—in about 408 million years. When that happens, I predict CNN will have Larry King covering it live.