After several failed mission concepts, JPL and Johns Hopkins University Applied Physics Laboratory engineers and scientists moved ahead with New Horizons; however, its mission had several limitations that had to be taken into consideration.
New Horizons only had nine minutes to take the best, most focused photos of Pluto – that’s like hitting a golf ball from Los Angeles to New York in four milliseconds!
1. Voyager 2
Voyager 2 spacecraft were launched simultaneously between 1977 and 1985 and visited Jupiter, Saturn, Uranus, and Neptune during their Grand Tour journeys. Each gold-plated copper disk of Voyager 2 carried images and sounds to greet any extraterrestrial life that may encounter it.
This craft’s cameras, ultraviolet and infrared spectrometers, plasma detector, particle, and radiation instruments provided comprehensive imaging of each planet in our solar system along with their rings and moons, as well as 22 new satellites – Io, the only place with active volcanism occurring, as well as Triton on Neptune with jets of nitrogen vapor spewing from its surface were among them.
Voyager 2’s plasma instrument observed no solar wind flow around it after passing Jupiter, an indication that it had left the Sun’s heliosphere and entered interstellar space. In several decades time, Voyager 2, and its twin Voyager 1, would both leave our solar system forever.
2. Mariner 9
Mariner 9 employed decades-old technology when it flew past Pluto and its moons on July 14, 2015. The spacecraft was only powered by its nuclear batteries for 190 watts, meaning it could only operate a handful of instruments simultaneously.
Mariner 9 was then the fastest spacecraft ever sent out into space; however, its images of Mars were less-than-impressive, leaving scientists uncertain of what they might expect at Pluto. Once there though, images revealed a fascinating landscape composed of nitrogen ice glaciers, mountains and cliffs on Charon as well as evidence for tectonic activity on Pluto itself.
In 1991, the U.S. Postal Service issued a series of stamps featuring images of all nine planets and their moons along with spacecraft that explored them. A stamp featuring Pluto with crossed out words “NOT YET EXPLORERED” became a symbol for New Horizons mission which investigates global geology, surface composition and atmosphere as well as Kuiper Belt objects such as Arrokoth.
3. New Horizons
As New Horizons approached Pluto, it collected an abundance of data that scientists are still processing. Notably, scientists observed large deposits of methane near its equator that dwarf any skyscraper on Earth; this suggests that Pluto’s atmosphere has grown over time despite theories suggesting its atmospheric pressure will decrease with distance from Sun.
The probe revealed numerous craters on both Pluto and Charon, some as wide as 100 kilometers wide. This suggests that small Kuiper belt objects impacted them directly, possibly contributing to their pitted surfaces.
After its flyby of Pluto, New Horizons spent approximately five months hibernating before continuing its voyage towards its next target: 2014 MU69. When approaching 2014 MU69 for its rendezvous encounter, New Horizons will initiate sending data back to Earth when within about 30 million miles.
4. Voyager 1
Stern noted last year in an engaging post for Astronomy that Voyager 1 “rewrote the textbooks on the Solar System.” The probe made flybys of Jupiter and Saturn to study their rings, weather, magnetic fields and moons – including Titan. At that time astronomers weren’t aware that Pluto was actually a dwarf planet; also, Hubble Space Telescope wasn’t advanced enough to detect small Kuiper Belt objects such as MU69.
Voyagers are now exploring interstellar space, an expanse of charged particles and magnetic fields surrounding our Sun. Each probe carries music, images and other forms of Earth-related information for extraterrestrials who may encounter it someday; each has more than 65,000 parts – which amounts to the equivalent electronic circuit complexity of about 2,000 color TV sets – making up its electronic circuit complexity; Voyager 1 took advantage of gravity assists at Jupiter, Saturn and Uranus to accelerate its speed and is currently traveling at 523 million km per year!