ONE of the great science fiction epics of Jules Verne could soon become reality: a leading scientist is planning to send a grapefruit-sized probe on a journey to the centre of the Earth.

The sensor, which would be made from diamonds to withstand temperatures of more than 4,000C, would be blasted into the bowels of the planet by a “reverse volcano” of liquid iron under plans advanced today by David Stevenson, Professor of Planetary Sciences at the California Institute of Technology.

Hundreds of thousands of tonnes of the molten metal would crack open the Earth’s crust, kick-started by a nuclear explosion or artifical earthquake, and allow the capsule of instruments to be carried down 3,000km (1,860 miles) to the edge of the Earth’s superheated core. The journey would take about a week.

The probe would send back the first direct data on the planet’s heart, revealing details of the core’s temperature, chemical composition and electromagnetic activity. The findings would be transmitted to the surface using seismic waves, the vibrations that cause earthquakes, because radio waves cannot penetrate such depths.

Scientists believe that the data would give valuable insights into the Earth’s electromagnetic field, generated from its core, which protects the planet against solar radiation and makes modern satellite communications possible. There may also be implications for nuclear fusion research.

The project, set out by Professor Stevenson today in the journal Nature, would cost at least $10 billion (£6.2 billion) and would require years of international co-operation. A better knowledge of our own planet, however, is more important than the exploration of space, on which resources many times greater have been lavished, he says.

“Planetary missions have enhanced our understanding of the solar system and how planets work, but no comparable exploratory effort has been directed towards the Earth’s interior. Space probes have reached a distance of about 40 astronomical units (6,000 million km, or 3,700 million miles), but subterranean probes have descended only some 10km (6.2 miles).”

The biggest challenge for a mission to the Earth’s core would be cutting a path through the crust and mantle. The Earth’s centre is 6,400km (4,000 miles) below the surface. The probe would have to travel about half this distance to reach the edge of the core.

Professor Stevenson’s solution is to create a crack the height and length of the Empire State Building — 300 metres (984ft) — but only a metre or so across. Into the crack would be poured at least 100,000 tonnes of molten iron alloy, and possibly up to 100 times more. This would create such stress on the rock below that it would force itself down under gravity, gouging a huge fissure that sealed itself at the top as it went. “You’re talking about something that’s a direct analogue of a volcano, just in reverse,” Professor Stevenson said. “It’s like plunging a huge knife of molten metal into the Earth’s surface.”

A nuclear explosion of several megatonnes, or another high-energy event such as an earthquake, may be needed to kick-start the metal’s plunge. It might be possible to take advantage of natural fissures in the crust such as the volcanic vents of Iceland, from which Jules Verne’s fictional expedition made its descent.

Iron would be used because it is cheap and abundant — 100,000 tonnes is produced in an hour by the world’s foundries — and because it would not react much with the iron-rich rocks. It would be molten to reduce friction, rather than because of the heat.

The probe would travel inside the liquid iron, and would have to be made of a substance that could withstand high temperatures. “Obviously you couldn’t use conventional micro-electronics, but diamonds would work well because they’re semiconductors at high temperatures,” Professor Stevenson said.

It would carry instruments to measure temperature, the presence of different elements, and electromagnetic activity. “We just don’t know what’s down there apart from iron,” he said. “There could be silicon, sulphur, oxygen, hydrogen, but we just don’t know.

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