Photograph by NASA/JPL/JHUAPL

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This four-image mosaic of the asteroid Eros shows one of its biggest craters, which is four miles (six kilometers) wide.

Photograph by NASA/JPL/JHUAPL

Asteroids Offer Stepping-Stones to Mars, Expert Says

Rather than lassoing asteroids, NASA could use the space rocks to prepare for a visit to Mars.

Nearby asteroids are humanity's ticket to Mars, says a planetary scientist who's calling for an ambitious survey to map ones that could serve as stepping-stones to the red planet. (Video: "Would You Go to Mars If You Could Never Come Back to Earth?")

NASA sees Mars as its "ultimate human destination" and is making plans for a flyby past, or even a landing on, the red planet sometime after 2030. In preparation for that trip, the space agency plans to retrieve a truck-size asteroid, or a boulder off a bigger one, for astronauts to explore. That project, known as the Asteroid Redirect Mission and scheduled for around 2025, would provide an interim goal for the large Space Launch System (SLS) rockets that NASA hopes will someday carry humans to Mars. (See: "NASA Announces Plan for Capturing Asteroid.")

"There is a better way," writes MIT planetary scientist Richard Binzel Wednesday in the journal Nature. "Thousands of shipping-container-sized and larger asteroids pass almost as close as the Moon each year."

Hop, Skip, and Jump

Instead of retrieving an asteroid, Binzel suggests mapping the nearly ten million uncharted space rocks more than 33 feet (10 meters) wide that orbit between Earth and Mars. He estimates that ground-based telescopes have located only about 0.1 percent of them so far.

Once they were all located, the space agency could plot a series of missions that would allow astronauts to visit some of them. The trips would be for progressively longer periods, which would build experience and confidence to take on the years-long voyage to Mars itself. (Related: "Proposed Mars Missions Challenge NASA Health Standards, Panel Warns.")

To pull off the asteroid mapping, Binzel says, the space agency, which now has a $17.8-billion budget, would need to launch a roughly $800-million space telescope dedicated to detecting space rocks.

As an added bonus, he points out, the mapping effort would help us detect any asteroids that might be headed for Earth, like the 66-foot-wide (20-meter-wide) one that slammed into central Russia in 2013. (See: "Chelyabinsk Meteor: The Animated Movie.")

"We have to leave the cradle of Earth sometime," Binzel says. "Asteroid missions could be a win-win for exploration-and for safety."

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NASA's Mars Reconnaissance Orbiter took this shot of Phobos, one of Mars's two moons, in 2008.


Unveiled in 2010, NASA's goal of asteroid retrieval has faced some criticism, mostly from those who would rather see astronauts head back to the moon.

Last May, Congressman Steven Palazzo, a Republican of Mississippi and chairman of the space subcommittee of the House Committee on Science, Space, and Technology, called the asteroid-retrieval mission a "detour for a Mars mission." (See: "A Mars Mission for Budget Travelers.")

Supporters of the mission, such as Louis Friedman of the Planetary Society, have countered that learning to retrieve a small asteroid will offer lessons for possible future missions to divert an asteroid headed toward a catastrophic encounter with Earth.

An asteroid-hopping campaign essentially splits the difference, Binzel argues. "Sooner or later we are headed to Mars," he says. "We have to find positive ways to move us closer."

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