In 2013, NASA announced that the spacecraft Voyager 1 had reached the interstellar medium, a region in space that exists between star systems. But not everyone is convinced, and some scientists think the spacecraft may still be in the heliosphere, the space surrounding the sun. To put the question to rest, astronomers have created a test that should show once and for all where the Voyager is. If in the next 2 years the probe senses a reversal in the surrounding magnetic field, that will verify it’s still near the sun. If a change isn’t detected, that means it really is the first ship to make it to interstellar space, according to the American Geophysical Union.