Everything You Need to Know About Space Probes

Start at the Beginning:

A space probe is any unmanned device sent outside the Earth’s atmosphere to gather scientific data. The first was the Soviet Union’s beachball-sized Sputnik I which orbited our planet for three months after its October 4, 1957, launch. Seventeen weeks later the US sent up its own probe, Explorer 1. The “Space Race” had begun.

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As technology improved, probes went further into space, sending data back via radio signal. In 1962 NASA’s Mariner 2 had the first successful interplanetary encounter, flying within 35,000km of Venus – near enough to read its temperature and analyse its atmosphere. Just 18 months later Mariner 4 sent back the first “close-up” photos of a planet: Mars. In 1976, rovers Viking 1 and Viking 2 made the first successful landing on Mars. In November 2014, Philae, a lander launched from the European Space Agency’s Rosetta probe, made history by landing on a comet nucleus. Since July 14, Pluto has been closely probed by New Horizons.

By the Numbers


The current speed of Voyager 1.

40,140 billion km

Distance to Proxima Centauri, the nearest star to Earth. Neither Voyager is aimed in its direction.


The number of confirmed exoplanets (planets outside the solar system) known as of September 18, 2015.

How Far Into Space Have We Gone?

Although probes have become ever more sophisticated, none have surpassed the achievements of Voyager 1 and Voyager 2, launched in 1977. Both are still travelling and sending back data. More remarkable is the distance they’ve covered. Earth is around 149.6 million km from the Sun. Voyager 2 is now more than 100 times further away from the Sun. Voyager 1 has become the first human-made object to reach interstellar space by crossing the heliopause – the area where the solar wind gives way to interstellar wind. It’s currently a mind-blowing 19.9 billion km from our Sun, gathering data on the outer reaches of the solar system. The signals it sends back travel at the speed of light but with only about the power of a fridge lightbulb, yet NASA’s Deep Space Network can pick them up. They both have enough fuel to operate until at least 2025.

“If we survive as a human species, it’s inevitable – we are going to have to leave the planet … At some point we have to make the leap, and we have to find other resources in the universe – and that starts now.”
British astronaut Tim Peake

What Powers Them?

If they are “only” going to Mars, probes can gather energy from special solar panels; further from the Sun they need more power than the panels can generate, so they use small radioisotope thermoelectric generators which create electricity from the natural decay of radioactive material.

Why Are We Probing Space Anyway?

The original reason was simply to build knowledge but, according to Stephen Hawking and other commentators, this data-gathering has become essential to provide alternative possibilities when Earth can no longer sustain human life.

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