This year, the Voyager 1 spacecraft, launched back in 1977, finally left the solar system and went into interstellar space.
It is currently 11 billion kilometres and 36 years away from Earth. However, if space is empty, how can we move from one space to another?
Actually, it is not empty, and we can identify some very specific space neighbourhoods. For example our Earth’s magnetic field forms a bubble, protecting us from the solar wind and most of the high-energy particles from the sun and elsewhere in the universe. The force of the solar wind blows the Earth’s magnetic field into a teardrop shape.
Inside the bubble we are in near-Earth space, our cosmic backyard. Most of our space activities, including the International Space Station lie in near-Earth space. Exploiting, living and working even in our cosmic backyard is still a challenging and potentially dangerous business.
The sun has a magnetic field too, which extends along with the solar wind out beyond the planets, where it finally piles up against the magnetic field of our galaxy, the Milky Way. Inside the sun’s magnetic bubble, although we are no longer protected from the sun’s activities, we are still largely protected from cosmic rays — high-energy particles coming in from our galaxy. We could call the region inside the sun’s magnetic bubble solar space, but decades of science fiction have led to us referring to it as interplanetary space. When Voyager 1 went out through the boundary between the sun’s magnetic field and that of the Milky Way, our emissary entered interstellar space.
Compared with even the best vacuums we can make in the laboratory, space is a very empty place. If we were looking through the portholes of our spacecraft as we went from near-Earth space into Interplanetary space, and then from Interplanetary space to Interstellar space, we would not see anything change. We would just see stars and an increasingly distant sun. However, by measuring magnetic fields and the speeds and nature of the particles in those magnetic fields, the transitions are really easy to detect.
When we look at the images obtained with modern optical and radio telescopes, it is easy to conclude that we know a lot about what lies out there in interstellar space. It is certainly true that we are learning a lot about the great gas and dust clouds lying between the stars. However, those clouds are very large, and we see them because there is a colossal amount of material in them. If we could send an instrumented spacecraft through one of them, detecting the cloud would be more difficult. So we don’t know much about the small scale stuff in interstellar space at all.
That is why Voyager’s venture into interstellar space is so exciting. Its instruments will tell us about the small-scale stuff, magnetic fields, local particle densities and so on and the quantities we would experience if we were out there.
It is a great credit to the engineers and scientists involved that they could come up with a spacecraft that continues to function in a hostile environment after 36 years, and is still going. There are proposals to send robot spacecraft to nearby stars, which will involve journey times of centuries. It’s encouraging that we can contemplate doing this, but few scientists like projects where they dedicate big chunks of their careers to get the spacecraft built and launched, but their descendants are the ones who finally get the data.
Ken Tapping is an astronomer with the National Research Council’s Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9. Tel (250) 497-2300, E-mail: email@example.com.