A Hollywood-like proposal to explore the center of the Earth calls for exploding a crack in the planet's surface and dropping a probe in behind tons of molten iron, which would sink and forge a path to the core.
The plan is not ready for primetime, its creator told SPACE.com, but neither is it pie-in-the-sky.
Exploring Earth's belly is ambitious in a scientific sense and could yield valuable data. The solid inner core rotates faster than the outer core, which is fluid and is responsible for Earth's magnetic field. But scientists don't know exactly why all this is so, nor do they know the exact composition or temperature of the core.
If further research showed the core mission could actually work, it would be comparable in dollar terms with many space projects, says David Stevenson, a Caltech planetary scientist who has worked on several missions for NASA. Stevenson explains his idea in an article titled "A Modest Proposal" for the May 15 issue of the journal Nature.
Splitting Earth
Stevenson figures that a nuclear device would likely be the best way to blast the necessary gap, as long and deep as several football fields and about 1 foot wide (30 centimeters). The event would be commensurate with an Earthquake measuring 7 on the Richter Scale.
At least 100,000 tons of hot iron would be poured instantly into the crack, along with a well-protected probe the size of a grapefruit.
"Once you set that condition up, the crack is self-perpetuating," Stevenson explains. The weight of the iron, which is much denser than Earth's outer regions, would open a gap all the way to the outer portion planet's core, about 1,860 miles (3,000 kilometers) below. The probe would fall at about 10 mph (16 kilometers per hour) as the crack closes up behind it.
The weeks-long mission would seek to measure the temperature, electrical conductivity and chemical composition of the core. Stevenson said the amount of iron needed is equal to what's produced on Earth in a week or less.
"We've spent more than $10 billion in unmanned missions to the planets," Stevenson said. "But we've only been down about 10 kilometers [6.2 miles] into our own planet."
Most of the universe is above us and empty, Stevenson notes, yet "the part below is crammed with interesting stuff and is also mostly unknown."
Like the movies
A spacecraft sends its observations back via radio. But radio signals don't propagate through the planet, so the Earth probe would relay data to the surface by deforming itself to create low-intensity waves akin to sending sound from a loudspeaker.
"Think of the probe throbbing like a heart," Stevenson said. "It will set the neighboring material in motion and that causes a sound wave to travel away from the probe all the way to Earth's surface."
The idea is a bit reminiscent of a recently released movie, "The Core," in which "terranauts" travel into the planet to jumpstart the core, which has stopped rotating and begun to cause all manner of peril at the surface. In an e-mail interview, Stevenson said he first conceived a core mission years ago, and that the scientific connection between the fiction and his fact-based proposal is negligible.
"But the movie prompted me to write my ideas down," he said.
The scientist, who researches the origin and evolution of Earth and the other planets, acknowledges that at this early stage of thinking about the concept, it should be considered to have a low probability of success.
"The same is true of space missions several years before they happened, or of the Manhattan project in 1940," he said. "Obviously you don't pursue it if after a lot of study it is seen to be low probability or impossible. But we're not at that stage!"
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