The New Horizons probe has just joined the very closed club of vessels at least 50 Astronomical Units (AU) from the Sun. Still active, the ship searches for its new target.
The American probe New Horizons has just passed the 50 astronomical unit mark separating it from our star. As a reminder, an astronomical unit is equivalent to the Earth-Sun distance. This therefore represents a journey of approximately 7.5 billion kilometers since its launch. At such a distance it takes more than 6.5 hours so that the signals sent by the probe, currently in the Kuiper belt, reach Earth at the speed of light.
A very closed club
Only four ships have traveled so many “cosmic terminals”. Launched in 1972, Pioneer 10, which was the first probe to cross the asteroid belt and fly over Jupiter, crossed the 50 AU mark on September 22, 1990. It sails today about 129 AU from Earth.
Launched in 1973, its twin, Pioneer 11, reached 50 AU a year later in 1991. This spacecraft was the first to make direct observations of Saturn. It is now evolving about 105 AU from Earth.
Of course, we must not forget the Voyager probes. Voyager 1 was launched on September 5, 1977, sixteen days after its Voyager 2 twin. The first observed Jupiter and Saturn, while the second also observed Uranus and Neptune. Voyager 1 is now 152 AU from Earth and Voyager 2 is 127 AU. And, unlike Pioneer 10 and Pioneer 11, which went out of business years ago, the two Voyager probes are still active today, now cruising through interstellar space.
New Horizons play extra time
More than just a milestone, reaching 50 AU also means New Horizons has just exceeded its expected lifespan.
“One of the first things you do when designing a spaceship is to define requirements. And one of the things we had to define was the maximum distance we could operate without too much of a problem.“Says Alan Stern, mission manager at the Southwest Research Institute in Boulder, Colorado. For New Horizons, this “goal line” was set at 50 AU. In other words, always active, the probe plays overtime.
New Horizons, which flew over Pluto in 2015 before performing the most distant flyby in history (to date) on January 1, 2019, capturing the first close-up sightings of a small Kuiper Belt object (“Arrokoth ”) At a distance of 43.4 AU from the sun, therefore continues on its way and looks for new targets. The goal for the researchers will be to find it before the probe runs out of fuel.
Although it draws its electricity from a nuclear battery (a radioisotope thermoelectric generator, or RTG), the plutonium supply to the ship generates 33 watts less every decade. In the late 2030s, when New Horizons is at or near 100 AU from the sun, it may not be powerful enough to operate.