How to take out an asteroid and save Earth

“Ground truth” information from NASA’s OSIRIS-REx rendezvous could save Earth from a killer asteroid.

Bringing rock samples back from asteroid Bennu on the OSIRIS-REx mission will help computer modelers refine plans for deflecting an asteroid or comet on target for Earth.




Stopping an Earth-Bound Asteroid in Its Tracks

Even though asteroids don’t hit the Earth very often, they do hit at random, so there is a chance that an extinction-level event could happen to us. Planning for a way to protect ourselves is important.

Stopping an Earth-Bound Asteroid in Its Tracks

We really need to plan ahead.

By Cathy Plesko, Ph.D.

Cathy Plesko, Ph.D., is a research scientist at Los Alamos National Laboratory in New Mexico. She contributed this article to's Expert Voices: Op-Ed & Insights

In a couple of weeks, at the Planetary Defense Conference just outside of Washington, D. C., I'll be taking my turn at one of the highest-stakes role-playing games on the planet: an emergency response drill where astronomers, emergency management experts, planetary scientists (like me), meteoriticists, rocket scientists and other experts work together to practice our response if a large asteroid or comet were heading toward us. Like a fire drill, we practice our roles and test new technology and scientific data to see how it changes what we think the best response would be.

Even though asteroids and comets large enough to be dangerous don't hit the Earth very often, they do hit at random, so there is a chance that an extinction-level event (like what happened to the dinosaurs<) could happen to us. It would be like winning the worst lottery prize ever. So planning for a way to protect ourselves is important.

Fortunately, we're getting to the point where we can see these potentially hazardous objects coming and maybe even do something about it. Astronomers using Earth- and space-based telescopes have discovered almost 20,000 near-Earth objects so far, and the pace of discovery is speeding up. Like a new pair of glasses, future telescopes such as the upcoming NeoCam space telescope have the potential to show us hazards that we couldn't see before.

Once the telescopes reveal what an object is and where it's going, we can simulate its orbit for hundreds of years into the future. If that orbit crosses our planet's path at any point, the United Nations' International Asteroid Warning Network will notify member governments and serve as a clearinghouse for information about it.

If the object has a chance of hitting Earth — say, one in a few thousand in the next 20 years — NASA's Space Missions Planning Group would coordinate among governments that are working on a defense plan so that everyone is on the same page when any action is required. A threatening object probably won't be kept a secret, because all the information about it will be published and the object will be visible to telescopes in many countries.

Most objects are announced with estimated probabilities of impact similar to betting odds in Vegas. As more observations come in, the odds typically go to zero as we figure out that their orbit and Earth's don't actually cross. If, instead, data tells us that the object is more likely to hit than we thought, the Space Missions Planning Group would coordinate any space missions to go look at it up close or to push it off course or destroy it.

Using science to answer the question, 'What if?'

As a research scientist at Los Alamos National Laboratory, I study what happens to the atmosphere and crust of a planet when an asteroid or comet hits and possible ways to stop that from happening. I use the supercomputers at Los Alamos, some of the fastest in the world, to run high-fidelity simulations to accurately model the physics of an impact. These simulations are constantly updated with cutting-edge data from NASA missions and Earth-bound laboratory experiments.

I work on a team of scientists from national laboratories and NASA centers studying particular what-if scenarios, and report the results to the Planetary Defense Coordination Office.

Our first what-if case study focused on asteroid Bennu, the target of the NASA OSIRIS-REx mission. Bennu is about as wide as the Empire State Building is tall, and weighs as much as 800 aircraft carriers. It approaches Earth once every six years, so astronomers can study it well and even use the Arecibo and Goldstone radio telescopes to make a 3D model of its shape. Fortunately, Bennu has only a one in 2,700 chance of hitting Earth, about 100 years from now.

We used computer models to study two ways of pushing Bennu off course so it wouldn't hit us: smashing it with a cannonball-like kinetic impactor or roasting one side by detonating a nuclear explosive device from a couple football fields away. We fed the best estimates of Bennu's shape, composition, mass and strength into our computer models and predicted what would happen in each scenario. Then we designed a spacecraft that could do the job.

We learned that moving Bennu would be a big challenge if it was made of the type of rock that NASA meteoriticists hypothesize. We would need to launch that spacecraft 10 to 25 years before the predicted impact in order to push it off course. And we would need not just one, but a full fleet of kinetic cannonball impactors — more than we could currently launch in time.

We published our predictions in a scientific journal last year, before OSIRIS-REx got to Bennu. For the Planetary Defense conference exercise, the OSIRIS-REx team is providing us with everything they are now learning by orbiting the asteroid. Soon, they'll use a robotic arm on the spacecraft to grab a sample and send it back to Earth for analysis. We'll feed that data into our models and rerun them to see what difference it makes.

While we wait for OSIRIS-REx to send that space-rock sample back to Earth, we're studying another asteroid, Didymos B, or Didymoon, which is the smaller member of a binary asteroid system. NASA is designing the Double Asteroid Redirection Test, or DART mission, to test what really happens when we hit an asteroid with a kinetic cannonball impactor. They're targeting Didymoon to alter its orbit around another asteroid in the system, Didymos A, without changing either asteroid's orbit around the sun. That experiment will allow them to test the kinetic impactor deflection process without accidentally knocking Didymoon onto a collision course with Earth.

I'm glad we're doing this research now, while we can take the time to carefully study the problem and triple-check our models without the pressure of a specific, potentially hazardous object coming at us. If we prepare well, then for the first time our species could prevent a major natural disaster. We can't yet push a hurricane off course, cork a volcano or lock an earthquake-prone fault, but in a few years, we could be ready to stop a comet in its tracks.

This article originally appeared on

How we are going to deflect an asteroid
Crashing a spacecraft into an asteroid could shift its orbital path. The spacecraft DART will be test-crashed on an asteroid, providing insight into future deflection.

Never fear, an oceanic asteroid impact wouldn’t cause apocalyptical tidal waves

Asteroid deflection | Los Alamos National LaboratoryWhen a team of LANL scientists modeled what would happen if an asteroid struck Earth, they discovered a Hollywood-worthy tsunami wouldn’t be the problem. Long-term effects on the climate might. logo

Never fear, an oceanic asteroid impact wouldn't cause apocalyptical tidal waves

But it could have long-term effects on the climate

By Danny Lewis

Fans of apocalyptic disaster movies are probably familiar with the scene: a rogue asteroid spiraling in from outer space lands in the middle of the ocean, triggering massive tidal waves and throwing the world into chaos. But when a group of scientists decided to put this scenario to the test, they found that a real life Deep Impact would have very different results, Maddie Stone reports for Gizmodo.

A team of data scientists at the Los Alamos National Laboratory (LANL) modeled what would happen if an asteroid struck Earth’s vast oceans. They found that while one might expect a giant hunk of space rock to trigger enormous, Hollywood-worthy tsunamis, big waves aren’t the problem to fear.

The waves themselves would likely quickly dissipate out in the ocean. Imagine dropping a rock into a lake—the first ripples might be large, but as they spread out they get smaller and smaller. The same thing would happen in the case of an asteroid or comet impact, Stone reports, but it would still have a larger effect than dropping a pebble into a pond.

But while waves may not be the biggest threat from an asteroid impact, that doesn’t mean it wouldn’t affect our planet.

“The most significant effect of an impact into the ocean is the injection of water vapor into the stratosphere, with possible climate effects,” study leader Galen Gisler said while presenting his results at the American Geophysical Union meeting this week, Stone reports.

An asteroid impact in the ocean could vaporize hundreds of megatons of water, much of which would end up in the atmosphere. While a fair amount of that water vapor would likely turn into rain, some of it could linger slightly higher in what is known as the stratosphere. “And because it’s a potent greenhouse gas, this could have a major effect on our climate,” writes Stone.

Of course, this isn’t the only scenario possible. Many asteroids never make it to the ground, and the water would absorb much of the blast from even a fairly large asteroid exploding, Robinson Meyer reports for The Atlantic.

While that wouldn’t harm human civilization too much, an explosion over a coastal city would be a very different thing. Either way, it might not be a bad idea to figure out ways to stop space rocks before they get too close.

This article originally appeared on

Published Research

Three-dimensional simulations of oblique asteroid impacts into water

By Galen Gisler, Catherine Plesko, et al

Waves generated by impacts into oceans may represent the most significant danger from near-earth asteroids and comets. For impacts near populated shores, the crown splash and subsequent waves, accompanied by sediment lofting and high winds, are more damaging than storm surges from the strongest hurricanes. Asteroids less than 500 m in diameter, impacting deep water far from shores, produce waves that may be detectable over large distances, but are probably not significantly dangerous. We present new three-dimensional simulations of oblique impacts into deep water, with trajectory angles ranging from 27° to 60° (where 90° is vertical). These simulations are performed with the Los Alamos Rage hydrocode, and include atmospheric effects including ablation and airbursts. These oblique impact simulations are specifically performed in order to help determine whether there are additional dangers from the obliquity of impact not covered by previous two-dimensional studies. Water surface elevation profiles, surface pressures, and depth-averaged mass fluxes within the water are prepared for use in propagation studies.


Options and uncertainties in planetary defense: Mission planning and vehicle design response

By Galen Gisler, Catherine Plesko, et al

This paper is part of an integrated study by NASA and the NNSA to quantitatively understand the response timeframe should a threatening Earth-impacting near-Earth object (NEO) be identified. The two realistic responses considered are the use of a spacecraft functioning as either a kinetic impactor or a nuclear explosive carrier to deflect the approaching NEO. The choice depends on the NEO size and mass, the available response time prior to Earth impact, and the various uncertainties. Whenever practical, the kinetic impactor is the preferred approach, but various factors, such as large uncertainties or short available response time, reduce the kinetic impactor’s suitability and, ultimately, eliminate its sufficiency.



Visualization of Threats from Asteroid Ocean Impacts
Here's what would it would look like if an asteroid struck the ocean—and what would happen to the planet as we know it.

OSIRIS-REx, bringing back a bit of an asteroid
The OSIRIS-REx mission will help determine the timeframe within which we must launch a kinetic impactor or a nuclear explosive carrier.


Los Alamos Asteroid Killer
LANL scientists use a supercomputer to model what would happen if we used nuclear energy to deflect an Earth-threatening asteroid.



    Black download iconScientists from Los Alamos National Laboratory are using high performance computing to investigate how an asteroid’s kinetic energy is transferred to the atmosphere and ocean. (Download an animation by astrophysicist Galen Gisler.)

    Black download icon How would the detonation of a nuclear energy source affect an incoming asteroid? 3D supercomputer simulations help address ways to prevent objects in space from colliding with Earth.


    Cathy Plesko is a computational geophysicist with Los Alamos National Laboratory.

    Cathy Plesko

    Cathy Plesko is a Research Scientist in Applied Physics at Los Alamos National Laboratory. She uses the hydrodynamic codes on supercomputers to study what happens when asteroids and comets hit a planet and how to prevent them from hitting Earth.

    Mark Boslough | Los Alamos National Laboratory

    Mark Boslough

    Mark Boslough is a research physicist at Los Alamos National Laboratory and an expert on planetary impacts and global catastrophes. His work on airbursts challenged the conventional view of asteroid collision risk and is now widely accepted by the scientific community.


    Charles Poling, (505) 257-8006,

    Nick Njegomir, (505) 665-9394,