As a civilisation that rarely vacates the safety of the Earth’s atmosphere, we know an awful lot about the billions of kilometres of space around us. Of course, we don’t send human reconnaissance units on suicidal missions to scout the Solar System, because we have already have machines that can do that for us. We call them space probes.
Today in 1983, the space probe Pioneer 10 became the first manmade object to cross Neptune’s orbit, and declared to have left the Solar System. It is classed as an interstellar probe, one that has entered or is on track to enter interstellar space (the space beyond a region around the Sun called heliosphere). To date there are only five interstellar probes: Pioneer 10 and 11, Voyager 1 and 2, and New Horizons. Although Pioneer 10 pioneered the exit of the Solar System, only Voyager 1 has reached interstellar space – the others remain on interstellar trajectories.
For the space probes that are far away from the Sun (considered to be past the orbit of Mars), the intensity of light is too low and solar cells cannot generate enough power. Solar cells also add unnecessary mass to space probes, slowing them down. These space probes instead use radioisotope thermoelectric generators (RTGs), which function by converting energy released by radioactive decay into electrical energy. This is far more efficient and can work however far away the probe is from the Sun. However, plutonium is still a finite resource and scientists are undergoing research in nuclear fusion – the collision of two nuclei at extremely high speeds to form larger nuclei. To be able to harness the energy released by nuclear fusion would not only solve the issue of powering space probes, but also the issue of powering our entire planet in the future when fossil fuels are eventually exhausted.
Most space probes are equipped with a variety of onboard instruments that can study climate, chemical composition, gravity, solar winds, etc. This is in addition to the high-resolution cameras that are responsible for the beautiful photographs of the Solar System that you can find on the internet.
There have been countless space programmes, many of which have involved the collaboration of multiple nations. NASA launched Pioneer 10 in 1972, the first to explore the gas giant Jupiter. Shortly afterwards, Pioneer 11 was launched in 1973 to study not only Jupiter but Saturn also. Both Pioneer 10 and 11 carry golden plaques that feature a pictorial message in the case that the probes are intercepted by extraterrestrial life.
The twin space probes Voyager 1 and 2 were launched only sixteen days apart in 1977 with Voyager 2 setting off first (surprisingly); however Voyager 2 took a longer route that enabled it to fly by Uranus and Neptune, and remains the only spacecraft to have visited either of those planets. Voyager 1 visited Jupiter, Saturn, and Saturn’s moon Titan, which was found to be the only planet or moon in the Solar System that had clear evidence of surface liquid, other than the Earth.
Over twenty-eight years later in 2006 New Horizons was launched, and made a flyby of Jupiter later that year. The probe then spent eight years in hibernation mode to preserve onboard systems and to extend their life cycles, with the occasional check-up every year to calibrate its systems. New Horizons was woken up in late 2014 when it began the first ever visit to Pluto. Now New Horizons is on a journey to bypass a Kuiper belt object and to then follow Voyager 1’s steps to interstellar space.
Space exploration continues to define the frontiers of the technology of our civilisation. Although it is a dangerous gamble that has high costs, the benefits can be immense, especially if it can find us a new home to support our growing population.