Far from its home planet, a spacecraft is speeding through the emptiness of deep space. It has no crew, just equipment for exploration and communication. It has been traveling tens of thousands of miles per hour for nearly 50 years, sending images and information back to its creators. Where did this amazing technology come from? Earth!
Voyager 1 has been traveling away from Earth since the 1970s. It’s now so far away that a radio signal sent from Earth takes nearly a full day to reach it! It is the first human-made object to cross into interstellar space, the space between solar systems. But don’t expect it to reach another star anytime soon. It would still take about 70,000 more years to get close! 🙁
As you can probably tell, stars are ridiculously far away. ✨
In science fiction, humans travel easily between galaxies, jumping into wormholes or faster-than-light ships. None of these are options in the real world, though. For scientists to even consider sending humans to another solar system, there are two huge constraints they need to worry about: propulsion and the human life span.
The way we send rockets and spacecraft into space today is by burning rocket fuel. When the fuel burns, it expands and rushes out of the back of the rocket. Thanks to Newton's third law of motion, the burning fuel has an equal and opposite reaction of pushing the rocket forward.
Scientists have also used the gravitational pull of other bodies to move spacecraft faster. The Parker Space Probe, currently traveling almost 400,000 miles per hour, uses fly-bys of Venus to increase its speed. Is this fast enough to reach the next star in a reasonable time?
The short answer is: no! The Parker Probe would take about 2,000 years to travel one light year. Proxima Centauri, our nearest star, is more than 4 light years away!
Scientists have other ideas, but they are far from actual production for now. One idea is a laser-powered light sail design that could bring a spacecraft to Proxima Centauri and its orbiting planets in about 20 years. The problem is that the technology requires a spacecraft with nearly no mass - nothing a human could ride in. Another idea is using ion thrusters. They are extremely efficient, but they produce very low thrust, meaning travel times would still stretch into hundreds of years.
One of the more creative ideas is a "multi-generational" spacecraft. The original crew would live out their natural lives on the journey, then their descendants would arrive at the destination. The ship would have to support hundreds of people spending their entire lives aboard - and the descendants might decide to turn the ship around!
Here's a graph showing the distances between that galaxy's closest stars to our home planet.
Here are some questions I think of when I look at this graph:
💡What is the range of distances shown on this graph from the closest star to the one farthest away?
💡Astronomers will also use "parsecs" to measure distances between stars and galaxies. A "parsec" is 3.26 light years. How many parsecs away is the star Ross 154?
💡The distance across the entire Milky Way galaxy is 30 kiloparsecs (remember that a kilometer is 1000 meters). What is the distance across the Milky Way in light years? Why is this distance not shown on our graph above?