Voyager's Journey: A Billion-Year Odyssey

A Billion-Year

Last month, I posed an intriguing question to my brilliant undergraduate student at Harvard, Shokhruz Kakharov: “Where will the Voyager spacecraft be in a billion years?” Using a detailed model for the mass distribution of the Milky Way galaxy, Shokhruz plotted Voyager's future orbit relative to the Sun over billions of years. The results, soon to be featured in a peer-reviewed paper, reveal an incredible journey.

Voyager's Future Path

Within a billion years, Voyager will reach the opposite side of the Milky Way disk relative to the Sun. By then, the Sun will have boiled off all oceans on Earth, making it uninhabitable. NASA, as we know it, might not exist to celebrate this milestone in Voyager’s journey.

This exploration may seem academic and distant from our current reality, but it has down-to-earth implications. Most stars formed billions of years before the Sun, suggesting that Voyager-like probes could have been launched from exoplanets more than a billion years ago. These probes might have reached our Solar System, detectable by our telescopes as they pass near Earth.

Detecting Interstellar Visitors

Pairing Earth-based telescopes with the space-based Webb telescope, located a million miles away, allows precise localization of these objects and detection of any non-gravitational acceleration. This setup is also extremely sensitive to trailing gases from cometary evaporation or exhaust gases from an engine. Even without surrounding gas, the Webb telescope can measure the surface temperature and size of these objects based on their infrared emissions, provided they are larger than Voyager.

For objects the size of Voyager, there isn't enough sunlight reflected for detection unless they come near Earth. If they were to collide with Earth, they would appear as interstellar meteors with unusual material strength and composition. Our next expedition to the site of the interstellar meteor IM1, which collided with Earth on January 8, 2014, aims to find large pieces of that object and determine its origin.

Galactic Orbits and Interstellar Objects

Shokhruz and I calculated the Galactic orbits of all five probes launched by NASA to interstellar space: Voyager 1, Voyager 2, Pioneer 10, Pioneer 11, and New Horizons. We also traced the past trajectories of the interstellar meteors IM1 and IM2, the interstellar object `Oumuamua, and the interstellar comet Borisov.

The fundamental question of whether any interstellar objects detected near Earth are artificial in origin will be better answered as more are discovered. The Rubin Observatory in Chile, with its unprecedented sensitivity, might find an interstellar object every few months. My postdoc, Richard Cloete, and I are developing the software to analyze Rubin's data. By tracing the orbits of interstellar objects and observing them with other telescopes, we hope to identify their origins and understand the environments they came from.

Learning from the Past

Just as humans may not be around on Earth when Voyager reaches the opposite side of the Milky Way, the senders of any interstellar probes may no longer exist on their exoplanets due to their stars' evolution. Even if these objects stopped functioning long ago, their existence implies that other intelligent beings once inhabited the Milky Way. Their "trash" becomes our treasure, providing insights into ancient civilizations through the artifacts they left behind.

In a recent public appearance, I was asked about the future of humanity. I explained that humans often see themselves as central actors on the cosmic stage. However, even on Earth, life has survived catastrophic events long before humans appeared, including a global warming event 252 million years ago that wiped out 96% of all marine species.

This perspective gives hope that life on Earth will survive the environmental challenges triggered by humans. Microbes, more resilient than humans, will likely continue to thrive. In a billion years, human existence might be a minor footnote in cosmic history. To gain a balanced perspective, we must search for other actors in the cosmos and learn from them. If none survived, we can study their history based on their artifacts.

A Humbling Achievement

We may not claim a major role in cosmic history, but we can take pride in the fact that our Voyager spacecraft will reach the other side of the Milky Way in a billion years. This accomplishment is breathtaking. Despite being short-lived, meter-scale creatures with significant physical limitations, we are ambitious and fearless enough to send our message in a bottle to the far reaches of the galaxy.

Conclusion

Voyager's journey to the opposite side of the Milky Way in a billion years is a testament to human ambition and ingenuity. This exploration underscores our potential to detect and learn from interstellar objects, offering insights into ancient civilizations and the resilience of life in the cosmos. As we continue to search for other actors on the cosmic stage, Voyager's odyssey remains a symbol of our quest for knowledge and discovery.