Humanity’s journey to understand and explore the vast expanse of space between stars has begun. NASA’s Voyager 1 and Voyager 2 probes have already traversed into interstellar space, marking a significant milestone. However, the question remains: Will Space Travel Ever Be Possible for humans? While sending humans to the edges of interstellar space or even to other stars currently resides in the realm of science fiction, scientists and engineers are diligently working on technologies that may one day make this a reality.
Understanding Interstellar Space
Interstellar space is not simply the empty void “between the stars.” More accurately, it is the region residing between the Sun’s heliosphere and the astrospheres of other stars. Our heliosphere is an immense bubble of plasma – a gas comprising charged particles – that emanates from the Sun. This outflow, known as the solar wind, creates a bubble that encompasses the Sun and extends beyond the planets. The Voyager spacecraft had to travel over 11 billion miles (17 billion kilometers) from the Sun to reach the heliosphere’s edge. As our heliosphere moves through space, orbiting the center of the Milky Way galaxy, it generates a bow wave, akin to the wave created by a ship’s bow.
The Immense Distances: A Matter of Time
Since warp drive remains a fantasy, traveling to interstellar space takes an incredibly long time. Voyager 1, the first spacecraft to reach this milestone, was approximately 122 Astronomical Units (AU) away from the Sun (1 AU is the distance between the Earth and the Sun), or about 11 billion miles (18 billion kilometers), when it crossed into interstellar space. The spacecraft, launched from Florida in 1977, reached interstellar space in 2012 – a 35-year journey. It is important to note that Voyager 1 didn’t travel directly to interstellar space; it initially explored Jupiter and Saturn. Voyager 2, traveling at a slower pace, also visited Uranus and Neptune, and took 41 years to reach interstellar space.
A Silent Journey: The Lack of Interstellar Photos
Unfortunately, there are no “Voyager selfies” from interstellar space. The cameras on Voyager 1 were turned off after taking images in 1990 for the “Solar System Family Portrait,” including the famous “Pale Blue Dot” photo. This decision was made to conserve power and computer memory for the interstellar mission. Furthermore, the camera software has been removed, and the ground-based computers needed to operate them no longer exist. Even if these challenges could be overcome, the cameras have been exposed to extreme cold for many years, making it uncertain if they would still function.
If it provides any solace, there isn’t much for the Voyagers to see, except for stars that would appear similar to their appearance in 1990.
Sounds from the Void: Listening to Plasma Waves
While interstellar space is a near-perfect vacuum, meaning there is virtually no medium for sound waves to travel, Voyager’s instruments are much more sensitive than human ears. These instruments were able to “listen” to other types of waves that travel through the interstellar medium. These waves, detected by the Plasma Wave Science instrument on Voyager 1, provided solid evidence that the spacecraft had entered interstellar space.
These instruments detected plasma waves generated by solar eruptions, known as coronal mass ejections. While the waves are too weak for human ears to detect, scientists amplified the sounds to make them audible.
Interstellar Visitors: Encounters with the Unknown
In late 2017, an intriguing object passed through our solar system on a steep trajectory, indicating it originated from elsewhere. Scientists determined it came from interstellar space, making it the first confirmed object from another solar system to visit our own.
The object was named ‘Oumuamua, a Hawaiian word meaning “visitor from afar arriving first.” Due to its unique nature and the limited observation time, it was difficult for researchers to draw definitive conclusions about its composition and origin. ‘Oumuamua was estimated to be about half a mile (800 meters) long, and it was last detected traveling away from the Sun at approximately 196,000 mph (87.3 kilometers per second).
The Pioneers of Interstellar Space
To date, only two spacecraft have reached interstellar space: Voyager 1 in August 2012 and Voyager 2 on November 5, 2018. The New Horizons probe, which explored Pluto and the Kuiper Belt Object Arrokoth, is also heading toward interstellar space, generally in the direction of the constellation Sagittarius.
NASA’s Pioneer 10 and Pioneer 11, while no longer functioning, are also drifting into interstellar space. Pioneer 10 is heading toward the red star Aldebaran in the constellation Taurus, while Pioneer 11 is traveling toward the center of the galaxy in the direction of Sagittarius.
Escape Velocity: Breaking Free from the Sun’s Grip
While numerous spacecraft have been launched beyond Earth, only a few are destined to leave our solar system. This is because most spacecraft are designed for specific missions, such as orbiting or landing on planets.
To reach interstellar space, a probe must be launched into a specific orbit with a rocket powerful enough to achieve escape velocity – the speed required to break free from the Sun’s gravity. The Voyager probes utilized a rare alignment of the outer planets, occurring approximately every 176 years, to gain gravity assists. This allowed them to swing from one planet to the next without requiring massive propulsion systems.
Enduring Explorers: Continuing to Explore
Voyager 1 and 2, launched 16 days apart in 1977, are the longest continuously operating spacecraft. They have explored all the gas giant planets in our solar system. Although they are currently in interstellar space, they haven’t truly left the solar system, which extends beyond the Oort Cloud – a collection of small objects still under the Sun’s gravitational influence. It could take the probes 300 years to reach the inner edge of the Oort Cloud.
The Future: What Lies Beyond for the Voyagers?
Eventually, the Voyagers will pass by other stars. Voyager 1 is currently escaping the solar system at about 3.5 AU per year, heading toward the constellation Ophiuchus. In approximately 40,272 CE, it will come within 1.7 light-years of the star Gliese 445 in the constellation Ursa Minor.
Voyager 2 is escaping at about 3.1 AU per year toward the constellations Sagittarius and Pavo. In roughly 40,000 years, it will pass within 1.7 light-years of the star Ross 248 in the constellation Andromeda.
Ultimately, the Voyagers will become silent ambassadors from Earth, orbiting within the Milky Way – possibly forever. Each spacecraft carries a Golden Record containing sounds, images, and messages from Earth.
Beyond Voyager: The Next Steps
While NASA doesn’t currently have plans to send new spacecraft to interstellar space, researchers are exploring various concepts and ideas for future missions. The Interstellar Boundary Explorer (IBEX), currently orbiting Earth, is gathering data to create a map of the boundary of interstellar space. Furthermore, NASA is preparing to launch the Interstellar Mapping and Acceleration Probe (IMAP) in 2025. This spacecraft will be positioned about 1 million miles (1.6 million kilometers) from Earth, helping researchers gain a better understanding of the heliosphere’s boundary.
Conclusion: Is Interstellar Travel Truly Possible?
While significant challenges remain, the progress made by the Voyager missions and ongoing research provide hope that interstellar travel may one day be possible. The development of new propulsion systems, advancements in spacecraft technology, and a deeper understanding of interstellar space are crucial steps toward realizing this ambitious goal. The question of will space travel ever be possible is not a matter of “if,” but rather “when.” The future of space exploration holds endless possibilities, and humanity’s quest to reach for the stars continues.
