Understanding the Momentum of Voyager: Why Voyager 1 and 2 Are Not Left Behind in Interstellar Space

The question often arises: If our heliosphere is moving in a vortex through space at 70,000 km/hr, shouldn't Voyager 1 and 2, after leaving the heliosphere and entering interstellar space, be left behind? To address this, we must delve into the principles governing the movement of objects in space and the characteristics of the Voyager probes themselves.

Key Concepts: Momentum and Newton's Laws of Motion

The Voyager probes, including Voyager 1 and 2, Pioneer 10 and 11, and New Horizons, are in motion based on the cumulative velocity they achieved during their launch and journey. According to Newton's first law of motion, an object remains at rest or in uniform motion in a straight line unless acted upon by an external force. Given the conditions in interstellar space, no such force exists that would alter their momentum.

Momentum and Orbital Velocity

The Voyager probes retain the velocity they gained by combining the Earth's rotational velocity, their launch velocity, and the acceleration achieved by their rockets. This means that once launched, they are traveling in the same direction and velocity as the Earth, even after the Earth no longer exerts a gravitational pull on them. This notion is akin to standing on a speeding train and jumping off - you retain the same velocity as the train unless an external force (like a fall or collision) slows you down.

Interstellar Space and its Environment

Interstellar space, while seemingly vast and devoid of air resistance, is not completely devoid of matter. It contains cosmic dust and gas, which exist in turbulent cells caused by supernovas and other galactic events. However, these tiny particles do not impart a significant force against the Voyager probes. The probes are essentially sailing through a vast expanse of material that does not influence their momentum to any noticeable degree.

Orbital Dynamics and the Solar System

Furthermore, the Voyager probes remain within the gravitational influence of the solar system, much like a satellite in orbit. Their trajectory is a vector that is an extension of the Earth's orbit around the Sun. As they venture out, they continue to follow this vector, albeit extremely slowly because the gravitational pull of the Sun diminishes with distance.

Potential Future Changes

It is worth noting that the Voyager probes are on a trajectory that takes them away from the heliosphere, which is the region of space influenced by the Sun's solar wind. As they move out of this region, they are venturing into new interstellar regions where the local density of matter, and turbulence, might change over a period of a few thousand years. However, the effects of these changes are expected to be minimal and would not significantly alter the probes' trajectories.

Reference: “New Scientist”. 18 February 2023.

Conclusion

In summary, the Voyager probes retain their velocity due to their initial launch, the Earth's rotational velocity, and the Sun's gravitational pull. The interstellar medium, although present, exerts negligible forces on the probes. Hence, they are not left behind by the heliosphere's movement. Any changes in their trajectory would require an external force, which is currently not expected in interstellar space.