lt’s the size of Texas, Mr President.

At one point in the future we’ll be faced with a threat from an asteroid coming our way. Hopefully we’ll know about it long before it’s even close to Earth. What in your opinion is the best way to redirect an asteroid using current or future technology?
Andrew Rader (SpaceX engineer, MIT PhD, author)

I have a video about that:

The larger an object is and the faster is it moving, the more momentum and kinetic energy it has. Large objects moving in space are nearly impossible to stop, but if detected early enough, they can be deflected. Just a infinitesimal course correction can have a major effect on an object's trajectory months or years down the road. The key is to nudge the path of an asteroid early enough so that it grazes peacefully past our planet. Even simple things like painting an asteroid with absorbing or reflecting paint changes modifies the effect of solar rays, and could help steer the asteroid clear of disaster. Alternatively, you could attach a solar sail or small efficient engine. The key to any solution is early detection.

Antonio Paris (Astronaut Candidate, Astronomy Professor, Planetary Scientist, Space Science Author)

Every year, astronomers discover new asteroids in the Solar System. Current and past Near Earth Objects (NEO) programs, such as the Catalina Sky Survey (CSS) and The Minor Planet Center (MPC), currently use optical telescopes at high altitude with thermo-electrically cooled cameras. These methods require dark skies with a high transparency, extended camera exposure times, and image data processing. Although the entire process is cumbersome, these surveys have been responsible for detecting and discovering hundreds of asteroids in our Solar system. Recently, Congress signed the NASA Transition Authorization Act of 2017, which directed NASA to expand the NASA Near Earth Object program to detect, track, catalog, and characterize potentially hazardous NEOs less than 140 meters. The act, moreover, leverages the capabilities of the private sector and philanthropic organizations to the maximum extent practicable in carrying out the NEO Survey Program. Asteroid impact events, specifically on Earth, have played a major role in the evolution of the Solar System. These events have shaped the history of our planet and numerous theories suggest that an impact from an asteroid formed the Moon, shaped life on Earth, and caused at least 5 mass extinction events on Earth. These private and public asteroid detection programs, however, are not responsible for redirecting an asteroid that could impact Earth nor do we have the current capability to do so.

NASA’s Planetary Defense provides several mitigation strategies to prevent an asteroid impact – but none of the proposed strategies have not materialized into anything other than blueprints. Nonetheless, there is a noteworthy piece of information that, according to NASA, is required prior to attempting an asteroid redirect mission: “changing the velocity or trajectory of the object by less than an inch per second years in advance of the predicted impact”. In the past 50 years, a variety of proposals have recommended several approaches to stopping or redirecting an asteroid from impacting Earth. Some of these include the use of nuclear weapons to destroy the asteroid, towing the asteroid away by using gravity or a cable, or landing a robot on the asteroid, which would them use propulsion to slightly move the asteroid into a different trajectory. Unfortunately, we currently do not have the technology to advance any of these proposals or motivation from Congress to spend billions or trillions of dollars to develop them.

The possibility that one day another asteroid will impact Earth is mathematically probable. The best-case scenario is that we would detect the asteroid well in advance for NASA or the private space industry to develop one of these programs to stop it. Personally, of all the proposals, my choice to stop the asteroid would be the gravity tractor, as proposed by NASA. If we could detect the asteroid years in advance, the asteroid’s path could be changed by using the gravitational pull of a spacecraft. The spacecraft, which could be launched from the Moon, would travel alongside the impactor for several years and gently pull it out of Earth’s path. The spacecraft, moreover, could be controlled remotely from Earth or the Moon and thus provide the best solution against Earth impact event.

Fraser Cain (publisher at, co-host of Astronomy Cast)

The bottom line is that we just don't know. Maybe it'll be by shooting a laser at it? Or maybe by detonating a nuke near it? Or putting a railgun on it and blasting out material. Until we have the commitment and courage to send a mission to an asteroid and practice some of these different techniques we won't truly know the best way to redirect them.

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