Voyager 1 officially in interstellar space

Washington Post : After 36 years and more than 11 billion miles (17.7 billion km), Voyager 1 has officially entered interstellar space. Its crossing of the heliopause —the boundary line between the area in which the energetic solar wind dominates and the area of cooler, denser matter—occurred sometime around 25 August 2012. Earlier reports that hinted at the crossing were based on ambiguous data, so the mission scientists were unwilling to make an official statement. However, on 9 April 2013, a solar flare that had occurred on 17 March 2012 caught up with Voyager 1. It caused oscillations in the particles in the space around the craft, which were detectable by onboard instruments. Measuring the oscillations allowed the scientists to calculate the density of the surrounding matter at 80 000 particles per cubic meter, significantly higher than the density of space inside the heliosphere. Despite having reached interstellar space, Voyager 1 is still inside the solar system because it has not yet passed through the Oort cloud , a swarm of comets orbiting the Sun at a distance of nearly one light-year.