Another giant leap for mankind

Io

It's pleasing that the most read article on the BBC News website tonight is a piece by BBC science correspondent Jonathan Amos, Voyager probe 'leaves solar system'. It's proving even more popular than a piece about Harry Potter. Proof of a public appetite for science stories perhaps? (BBC programme makers, take note.)

Voyager-1, which first brought us face to face with Jupiter and Saturn and then glanced back and saw Earth as a 'pale blue dot', has become the first man-made object to leave the Solar System, passing beyond the heliosphere (the protective bubble of charged particles which surrounds us) into interstellar space - another landmark achievement in human history. 

For more of the hard science behind this please check out Ron Cowan's succinct but informative article in Nature as well. 

If you follow my advice though, you'll spot that there are still some outstanding issues, prime among which is the question, 'Has it really left the Solar System?'

Jonathan Amos writes:

Although now embedded in the gas, dust and magnetic fields from other stars, Voyager still feels a gravitational tug from the Sun, just as some comets do that lie even further out in space. But to all intents and purposes, it has left what most people would define as the Solar System. It is now in a completely new domain.

Ron Cowan, however, writes: 

[Ed] Stone [of Caltech] is careful to say that, although Voyager 1 has exited the heliosphere, it has not left the Solar System. The Oort cloud, a distant reservoir of comets, lies far beyond the solar bubble in interstellar space, but it is part of the Solar System and gravitationally bound to the Sun.

But with Voyager 1 firmly outside the heliosphere, “it’s a whole new mission”, Stone says. 

So the BBC's headline, placing 'leaves solar system' in inverted commas, might have been a wise precaution. 

Still, Voyager-1 is in interstellar space. In some 40,000 years time in may reach another star.