Here in our solar system, the sun rules space and time almost everywhere within it. The environment near a planet is locally dominated by the planet’s gravity and the curvature it imposes on the surrounding spacetime, whereas the Sun’s gravity governs the larger solar system environment. To escape Earth’s gravity, a spacecraft would need to achieve a speed of 11 kilometers per second, but to completely escape the solar system, it would need to achieve speeds nearly four times as far between Earth and the Sun.

The most notable fact about Pioneer 10’s orbit is that its gravitational collision with Jupiter gave it a velocity close to the maximum possible. After becoming the first spacecraft to reach Jupiter in late 1973, it became the first spacecraft to achieve escape velocity in the solar system. It remained the most distant spacecraft until it was overtaken by Voyager 1 in 1998, but it was also overtaken by Voyager 2 in 2023, dropping it to third place.

The Pioneer 10 mission launched with a number of instruments, and one of its science goals was to be the first spacecraft to visit Jupiter and obtain data. A portion of the first image of Jupiter taken in the field is shown to the right, showing the shadow of a total solar eclipse on Jupiter’s right side.

Pioneer 11 followed in Pioneer 10’s footsteps by actually passing through Jupiter’s moon system and then using Jupiter’s gravity as a support maneuver to take it to Saturn. While exploring the Saturn system for the first time in planetary science, he discovered Saturn’s moon Epimetheus, which almost collided with Saturn’s moon, but was ejected when it was estimated to be about 4,000 kilometers away. We were able to calculate these operations using Newtonian gravity alone.

This image shows the Pioneer spacecraft looking back at the sun as it exits the solar system. You can also see the galaxy. Both Pioneer spacecraft are now extinct, but will continue along their orbits, influenced only by gravity. We had no contact with either of them for decades.

This diagram shows the location of NASA’s Voyager 1 and Voyager 2 spacecraft in the heliosphere, outside the protective bubble created by the Sun that extends far beyond Pluto’s orbit. Voyager 1 crossed the boundaries of the heliosphere in 2012. Voyager 2 did the same in 2018. The asymmetry and extent of the bubble, especially in the opposite direction of the Voyager spacecraft, have not been well quantified.

This 1997 artwork shows the relative trajectories of the solar system’s planets and the first four spacecraft on their course. Before New Horizons launches and before the ultimate fate of the Ulysses mission is known. Voyager 1 overtook Pioneer 10 in 1998, and in 2012 it crossed the heliopause and entered interstellar space. Voyager 2 entered interstellar space in 2018 and recently surpassed the distance of Pioneer 10 in 2023. Therefore, we strongly suspect that Pioneer 10 is also in interstellar space, but it is no longer functional and cannot be confirmed.

In 1977, NASA’s Voyager 1 and 2 spacecraft began a pioneering journey across the solar system to visit giant exoplanets. Voyager is now hurtling through unexplored territory beyond our solar system. Along the way, they are measuring the interstellar medium, a mysterious environment between stars filled with debris from long-dead stars. Voyager 1 became the furthest spacecraft from Earth in 1998, but no other spacecraft launched to date has a chance of catching it.

Voyager 2 famously made a “grand tour” of the solar system, flying close to each of the four gas giant planets and imaging the planets, moons, and ring systems. To accomplish that, Voyager 2 was initially launched into a slower orbit than Voyager 1. Despite being the first to launch, it has less range and speed than its twin.

In late 2018, the cosmic ray subsystem aboard NASA’s Voyager 2 spacecraft provided evidence that Voyager 2 had left the heliosphere. The proportion of heliosphere particles hitting the instrument’s radiation detectors dropped sharply, and the proportion of cosmic rays increased significantly.

Pioneer 10 was the first spacecraft to launch on a trajectory out of the solar system in 1972, but was surpassed by Voyager 1 in 1998 and then by Voyager 2 in 2023. It will also be overtaken by New Horizons in the late 2100s. No mission launched to date is scheduled to surpass Voyager 1, which is currently the furthest and fastest-moving spacecraft ever built by humans.

Launched in 1990, the Ulysses spacecraft was designed to orbit the Sun and study it at all latitudes and from a variety of distances, both near and far. Its highly inclined orbit is expected to result in several close encounters with Mars and Jupiter in the coming decades, culminating in a gravitational collision with Jupiter in 2098, providing a gravitational kick sufficient to propel Ulysses out of the solar system.

The New Horizons spacecraft, which launched in 2006 with the fastest launch speed of any spacecraft, was slightly accelerated by Jupiter, but the biggest effect of its gravitational interaction was to change its orbit into an orbit that would lead to a close encounter with Pluto. The lack of large-scale additional gravity-assisted operations means it will never be able to catch up with Voyager 1 or 2 at that speed, and future spacecraft will be needed to reach that milestone.

Just 15 minutes after passing Pluto on July 14, 2015, the New Horizons spacecraft snapped this image looking back at Pluto’s faint crescent moon illuminated by the sun. The ice features, including multiple layers of atmospheric haze, are breathtaking. As Pluto rotates on its axis and moves toward or away from the Sun, certain volatiles can evaporate and condense, leading to various forms of precipitation, such as nitrogen and methane.

A logarithmic distance graph showing the planets, the Voyager spacecraft, the Oort cloud, and the closest star, Proxima Centauri. Launched a full 49 years ago, Voyager 1 is the farthest and overall fastest receding spacecraft ever launched from Earth. It is scheduled to reach one light day from Earth in November 2026, and any spacecraft that wants to overtake it will have to catch up to its leader, which was launched all the way back in 1977.

The idea of ​​using vast numbers of lasers to accelerate spacecraft is novel, but thanks to recent advances in laser technology and cost reductions, it could become a reality within the next few decades. But for a truly interstellar mission to be successful, obstacles such as advances in reflectivity and previously undiscovered methods of keeping payloads intact at such speeds will need to be developed.