At certain places in space called Lagrange points, the gravity of two massive bodies cancels out, allowing objects – such as telescopes – to remain ‘parked’ there (Illustration: NASA)

With doubts brewing about the feasibility of returning to the moon or aiming straight for Mars, another option has emerged for our next steps into space: gravitational “sweet spots” called Lagrange points that lie at least 1 million kilometres away.

A White House-commissioned task force charged with reviewing NASA’s spaceflight plans is considering recommending this as part of a “deep space” option in a report expected soon. But why send humans to empty space?

Lagrange, or Lagrangian, points are great swathes of space where the gravitational acceleration from the Earth and the sun are exactly equal, letting objects stick there with very little effort.

Because they’re far from warm stars and planets, they make useful havens for ultra-cold telescopes that measure fluctuations in the temperature of deep space.


The Wilkinson Microwave Anisotropy Probe (WMAP), which measures radiation from the big bang, lives at a Lagrange point called L2 more than 1 million kilometres away. The successor to the Hubble Space Telescope, the massive James Webb Space Telescope, will also be sent to the spot, which lies in line with the sun and Earth (see illustration).

Telescope repair

“If you look at our list of future space telescope concepts, just about all of them are going to go to L2,” says Dan Lester of the University of Texas, Austin, who spoke to the spaceflight review committee in July. “That’s going to be a very busy place out there.”

But what would humans do there? One useful task is repairing and upgrading the new telescopes, like astronauts have done five times with Hubble.

“Hubble is probably the most productive scientific facility ever developed in the history of science, and it’s largely because every four or five years, we take out the old instruments … and go up with brand-new instruments that address different questions and embrace the latest technology,” Lester says. “If we want to have humans having anything to do with these new telescopes, we really have to think about Lagrange points.”

Solar system superhighway

Astronauts may not have to go as far as L2 to be useful. Lagrange points exist in the Earth-moon system, and every other planet in the solar system also boasts Lagrange points with the sun.

It takes surprisingly little energy to travel between these points. That’s because massive bodies like the sun and planets have gravitational fields that resemble mountains and hills, but Lagrange points are all at gravitational lowlands. Once set on the right path, spacecraft can coast along the gravitational contours of space between these lowlands, as if travelling on an interplanetary superhighway.

“Going back and forth between Earth-sun Lagrange points and Earth-moon Lagrange points is pretty much a matter of giving the thing a swift kick,” Lester told New Scientist.

Staging area

Future astronauts could repair telescopes at a staging area at the nearest Earth-moon Lagrange point and send them sailing back to L2 when they’re done. They could also assemble large telescopes or spaceships at the staging area and then send them out to farther-flung destinations.

Useful though it may be, is sending people to empty space the inspiring stuff of ticker-tape parades? Lester thinks it could be.

“When you send people to fix a telescope, the country gets a lot more out of it than a fixed telescope. You get excitement, pride, a chance to show off our capabilities in space,” he says. “We didn’t leave footprints or plant flagpoles when we serviced the Hubble Space Telescope, and the public was just entranced.”

Baby steps

Others see Lagrange points as stepping stones on the way to places like Mars.

“It’s a convenient crossroads on the way to a place you really want to visit,” says Lou Friedman, founder and executive director of the Planetary Society, a space advocacy group that supports sending astronauts to Mars.

“The place we all want to go is Mars. Stepping out into interplanetary space, Lagrange points present the nearest milestone to Earth that’s still beyond the moon,” Friedman told New Scientist.

Going to L2 would take about a month and communications from Earth would take about four seconds to arrive at L2, while a trip to Mars would take at least six months and would involve communications delays of about 20 minutes.

NASA could use a Lagrange mission to test technologies needed for a Mars trip – such as life-support systems and ways to protect astronauts from harmful radiation – while remaining in easy contact with Earth.

This is still not as dramatic as a straight shot to Mars, Friedman says, but he says baby steps have value. “The Gemini programme leading up to Apollo didn’t go anywhere [except low-Earth orbit] … but everyone understood that every step it took was on the way to the moon,” he says. “I see what we could do at Lagrange points in the same way. At each step we build up our capability to go further.”