Since the earliest times, curiosity has been one of man’s characteristics. We have always had the urge to know the things we do not know—those we have never had the chance to explore. If you live in a village on the foot of a mountain, you feel the urge to go round that mountain to see what is on the other side.
I remember once waking up to the news that a hyena had been killed at Nkhoma Mission, where I spent my boyhood years. I had never seen a hyena before and it was natural for me to find my way to the spot where the carcas was lying.
I was not surprised to find a crowd of people there, all wanting to catch a glimpse of the nocturnal beast. By the time I got there, the animal’s tail and nostrils had been removed. I was to learn later that a hyena’s tail and nostrils were great treasure to those who practised magic. Armed with these hyena parts, so it was claimed, one would walk stealthily under cover of darkness and engage in nocturnal errands without being detected by anybody.
It is normal for humans to want to discover their environment. When the inner environment has been discovered, curiosity shifts to the next outer environment, then the next one after that and so on.
Curiosity drove the voyages of discovery, with people such as Marco Polo, Christopher Columbus, Vasco da Gama and David Livingstone undertaking unprecedented trips to unknown lands, far from their homes. These people had to be both excited and brave enough to go to places that nobody they knew had been to before.
By the close of the 19th Century, virtually all places on Earth had been explored. Attention turned to places beyond Earth. For centuries man had known that there were a number of other worlds than Earth, which could be visited. Lack of appropriate technology hampered such visits.
Space travel started in earnest in 1960. Since then thousands of objects have been sent to all manner of destinations in space. Some of the notable ones were the Russian Venera Missions to Venus, the American Viking Missions to Mars and the crewed Apollo Missions to the Moon. When Neil Armstrong and Edwin (Buzz) Aldrin landed on the Moon in 1969, space exploration by humans had climaxed. In Armstrong’s own words, their landing on the Moon was “a small step for a man, but a giant leap for mankind”.
We have sent spacecraft, albeit unmanned, virtually to all known large bodies in the Solar System. In July of 2015 the New Horizons spacecraft flew by the dwarf planet, Pluto and sent back to Earth loads of scientific data it had captured from the Pluto-Charon system. The New Horizons proceeded to the outer parts of the Kuiper Belt and will eventually leave the Solar System.
It is hard enough to escape from Earth’s gravitational well and break into space. It is unimaginably harder to escape from the Sun’s gravitational well as the Sun is more that 300 000 times more massive than planet Earth.
Spacecraft need to be accelerated beyond a speed of 615 km/second (2.2 million km/hour) in order to leave the Solar System. Only five spacecraft have so far been set on trajectories to leave the Solar Systems. They are the Pioneer 10 and 11, the Voger 1 and 2, and now the New Horizons. Contact with both Pioneer spacecraft has since been lost. Two of the five spacecraft, namely Voyager 1 and Voyager 2, have already left the Solar System, headed in different directions. Voyager 1 is nearly 23 billion kilometres from Earth and Voyager 2 is 19 billion kilometres away.
Voyager 2 was launched on August 20 1977 and Voyager 1 on September 5 the same year. Since Voyager 1 is faster than its twin—it has gone further out, and was the first manmade object to reach interstellar space in 2012. Voyager 2 only got into intersetellar space in 2018.
Both spacecraft still communicate with Earth despite that it takes 18 hours for a signal to reach the spacecraft and another 18 hours to travel back to Earth.
For seven months, since March 2020, contact with Voyager 2 had been lost. This was so because the only satellite that is able to send signals to the craft, the Deep Space facility based in Australia, was undergoing repairs to update it. Contact was re-established on October 29, after a seven-month break.
The spacecraft that have left or are about to leave the Solar System will wander indefinitely in interstellar space.