First look
The idea, in plain words
No person has ever been further from home than the Moon. Everything else that has been seen from close up, every planet, every moon, every comet and asteroid, was seen by a machine sent in our place. A machine needs no air, food or way home, and it can spend years on the journey. This line shows how far they have gone. The furthest, Voyager 1, is about 64,000 times further away than any person has been. On this line the whole of human travel is far too short to see.
The two Voyager spacecraft left the Earth in 1977. Between them they flew past all four giant planets, using the pull of each one to fling them on to the next. Voyager 2 is still the only spacecraft to have visited Uranus and Neptune. It took this photograph of Neptune in August 1989, after a journey of twelve years. Both Voyagers have now left the Sun’s bubble of wind behind and are still sending messages home.
Flying past is the easy part. Landing is much harder. This real photograph was taken on 18 February 2021 from a rocket-powered frame hovering over Mars. Hanging beneath it on ropes is a rover the size of a car, called Perseverance, about to touch the ground. A radio signal took eleven minutes to reach the Earth from Mars that day, so nobody could steer. The machine did the whole landing by itself.
Once it is down, a rover works as a geologist. It drives to a rock, studies it, drills it and reports back. This is Curiosity, which landed on Mars on 6 August 2012 and has been climbing a mountain ever since. It took this picture of itself with the camera on the end of its arm. Early on it found that the crater it landed in once held water that living things could have used.
Other machines go into orbit round a world and stay. Cassini circled Saturn for 13 years, from 2004 to 2017. On 19 July 2013 it slipped into Saturn’s shadow and looked back towards the Sun to take this picture. The rings glow with sunlight coming through them. Cassini found tall jets of water spraying from the small moon Enceladus, and it dropped a lander onto the giant moon Titan.
The newest trick is to bring a piece back. In October 2020 a spacecraft called OSIRIS-REx touched an asteroid called Bennu for a few seconds, blew a puff of gas at the ground and caught the dust that flew up. Three years later it dropped a capsule over the desert in Utah with 121.6 grams of asteroid inside. This photograph shows the container just after it was opened. In that dark dust were many of the building blocks of life.
Go deeper
That was the idea. The same subject is written again below for readers who want more, each on a page of its own.
Words used here
- Gravity assist
- Passing close to a moving planet to gain or lose speed without using fuel.
- Light time
- How long light takes to cross a gap, used as a way of saying how big the gap is.
- Heliopause
- The edge of the heliosphere, where the solar wind is stopped by the gas between the stars.
- Asteroid
- A small body of rock or metal in orbit round the Sun.
- Orbit
- The path one body follows around another, held there by gravity.
- Transfer orbit
- The path a spacecraft coasts along to get from one orbit to another, most cheaply half of an oval that touches both.
Where this comes from
- NASA, Voyager mission overview
- NASA, Where are Voyager 1 and Voyager 2 now?
- NASA Photojournal, Neptune full disk (PIA01492)
- Wikipedia, Perseverance (rover)
- NASA, Curiosity (Mars Science Laboratory)
- NASA, Cassini-Huygens
- NASA image library, The Day the Earth Smiled (PIA17172)
- Wikipedia, OSIRIS-REx
- Wikipedia, New Horizons
- Wikipedia, Parker Solar Probe
- Wikipedia, Artemis II (furthest distance of people from the Earth)
The words are written for this site. The pictures are drawn by the page from the figures in the lesson, and each one says underneath what it is based on.