
Scientists reported this year that NASA's Voyager 1 spacecraft reached interstellar space in August 2012 after almost 35 years of traveling.
They relied on a powerful solar eruption to determine the density of the molecules in space around the craft.
Voyager 1 became the first craft to leave the solar system behind, with the transition into interstellar space, making it a significant milestone in the annals of space exploration.
It is currently about 11.66 billion miles (18.76 billion km) from the sun.