Saturday, September 29, 2012

Left Side of the Aisle #75 - Part 5

And Another Thing: Voyager 1 and 2 nearing true interstellar space

A few weeks ago marked a couple of significant anniversaries in space exploration: the 35th anniversaries of the launches of the Voyager spacecrafts way back in 1977.

August 20 was the anniversary of the launch of Voyager 2. September 5 was the anniversary of the launch of Voyager 1.

That's not a mistake; Voyager 2 was launched first. The reason for the numbering was that because of the different paths the two spacecraft were to take, Voyager 1 was going to pass Voyager 2 and reach the initial goal, which was to do flybys of Jupiter and Saturn, first. They carried out that mission using computers with just 8000 words of memory and 8-track tapes.

They sent back data on Jupiter's big red spot and Saturn's rings. They discovered erupting volcanoes on Jupiter's moon Io; saw hints of an ocean below the icy surface of Europa, and found signs of methane rain on the Saturn moon Titan. Voyager 2 went on to fly by Uranus and Neptune. It is still the only spacecraft to have done so.

And then they just kept on going - and kept on sending back data. Voyager 1 is now about 11 billion miles from the Sun. That is about four times further from the Sun than Neptune, far beyond the solar system, twice as far as the Kuiper Belt. Voyager 2 is not all that far behind: about 9 billion miles from the Sun.

And now they are about to make space history yet again: They are about to become the first human-made objects ever to enter actual interstellar space.

The heliosphere is a giant bubble of charged particles the Sun blows around itself and which actually serves to help shield the solar system from the most intense cosmic rays. The heliosheath, where the Voyagers are now, is the outermost layer of the heliosphere. It marks the boundary between the region of space affected by the Sun and true interstellar space. The heliosphere is thought to extend to somewhere between 11 and 14 billion miles from the Sun - which means Voyager 1 is pushing against the edge. It could cross over literally any day.

Still, bear in mind that the limit to the heliosphere still could be something like 3 billion miles further out. Even though Voyager 1 travels a million miles a day, three billion miles is still 3,000 days, or a little over eight years. But when you've been waiting for something for 35 years, that doesn't seem all that long.

The Voyagers have enough electrical power to last until 2020, with conservation efforts after that keeping at least some instruments going another five years. When the last instruments are shut down around 2025, Voyager 1 and Voyager 2 will have been sending back data for 48 years.

After that, they will take up positions of honor, orbiting the center of our galaxy essentially forever.


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