Humanity has taken its first steps into interstellar space, the realm beyond our Sun’s influence. NASA’s Voyager 1 and Voyager 2 probes have already crossed this frontier. But the question remains: Can We Travel Outside Our Galaxy? While sending humans to other stars is currently science fiction, scientists are steadily developing the technologies that could one day make it a reality.
Defining Interstellar Space
Interstellar space isn’t just empty space. It’s the region between our Sun’s heliosphere and the astrospheres of other stars. The heliosphere is a protective bubble of plasma, or charged particles, blown outwards by the solar wind. The Voyager probes had to travel over 11 billion miles (17 billion kilometers) to escape this bubble and enter interstellar space. The heliosphere itself moves through interstellar space as the Sun orbits the Milky Way’s center, creating a bow wave similar to a ship’s wake.
The Immense Distances Involved
Interstellar travel presents immense challenges, primarily due to the vast distances. Voyager 1 took 35 years to reach interstellar space after launching in 1977. It was approximately 122 Astronomical Units (AU) from the Sun – about 11 billion miles (18 billion kilometers) – when it crossed the heliosphere’s boundary. Voyager 2, traveling a slower route, took 41 years. While warp drive remains a fantasy, reaching even the nearest stars requires incredibly long journey times with current technology.
The Silent Frontier
While interstellar space is often thought of as silent due to its near-perfect vacuum, Voyager’s instruments have “listened” to other types of waves. These waves, generated by coronal mass ejections from the Sun, influence the interstellar medium. Don Gurnett, principal investigator for Voyager 1’s Plasma Wave Science instrument, presented audio recordings of plasma wave data, providing solid evidence of the probe’s entry into interstellar space.
Interstellar Visitors
In 2017, scientists observed an intriguing object passing through our solar system on a steep trajectory, confirming its interstellar origin. Named ‘Oumuamua, meaning “visitor from afar arriving first” in Hawaiian, this object was estimated to be about half a mile (800 meters) long. Its unusual proportions and high speed made it difficult to classify, but it provided a tantalizing glimpse of objects traveling between star systems.
Pioneer Missions
Besides the Voyagers, other spacecraft are on trajectories towards interstellar space. The New Horizons probe, which explored Pluto and Arrokoth, is heading toward Sagittarius. Pioneer 10 and Pioneer 11, though no longer functioning, are also coasting into interstellar space. Pioneer 10 is headed toward the red star Aldebaran, while Pioneer 11 is traveling toward the galactic center.
Escape Velocity and Gravity Assists
Reaching interstellar space requires achieving escape velocity – the speed needed to break free from the Sun’s gravity. The Voyager probes took advantage of a rare planetary alignment that occurs every 176 years, using gravity assists to swing from one planet to the next. These flybys increased their velocity, allowing them to climb further out of the Sun’s gravitational grip.
Voyager’s Legacy
Launched in 1977, Voyager 1 and 2 are the longest continuously operating spacecraft. Though in interstellar space, they haven’t truly left the solar system, which extends beyond the Oort Cloud. It could take them 300 years to reach the inner edge of this region. Each probe carries a Golden Record, containing sounds, pictures, and messages from Earth, serving as silent ambassadors in the Milky Way.
The Distant Future
Voyager 1 will eventually pass other stars, heading towards the constellation Ophiuchus. In approximately 40,272 CE, it will come within 1.7 light-years of Gliese 445. Voyager 2 is traveling towards Sagittarius and Pavo and will come within 1.7 light-years of Ross 248 in about 40,000 years.
Future Exploration
While NASA currently has no plans to send new spacecraft to interstellar space, researchers are exploring future concepts. The Interstellar Boundary Explorer (IBEX) and the upcoming Interstellar Mapping and Acceleration Probe (IMAP), launching in 2025, are designed to study interstellar space from near Earth. These missions will help us better understand the heliosphere’s boundary and the nature of interstellar space, inching us closer to answering the question: can we travel outside our galaxy? The journey to other stars remains a distant dream, but continued research and technological advancements could one day make it a reality.
