The size of a stadium — or the Great Pyramid of Giza, as one scientist put it Monday — asteroid Dimorphos is currently about 7 million miles from Earth. It orbits a larger asteroid called Didymos. Neither pose a threat to our planet now or in the foreseeable future.
This was just a test, NASA’s first demonstration of a possible planetary defense technique called a kinetic impactor. The idea is to hit a hypothetically dangerous asteroid just enough to change its orbit.
Launched from California last November, the spacecraft was small, about the size of a vending machine or golf cart. Dimorphos is quite large – about 500 feet across, although its exact shape and composition were unknown prior to final approach. Scientists expected a plume of debris from the asteroid upon impact but no significant structural change. This is more like a bug splashing onto a windshield.
“This isn’t just bowling ball physics,” Nancy Chabot, planetary scientist at the Applied Physics Laboratory, told reporters. “The spaceship will lose.”
But even small impacts on an asteroid’s movement could prove to be planet saviors. An early collision with an asteroid, if done early enough – say 5 to 10 years before its projected encounter with Earth – could be just enough to slow it down and miss.
When engineers conceived an asteroid deflection mission, they resorted to an ingenious idea that would significantly reduce costs: hit an asteroid “moon” orbiting a larger asteroid.
To see the effects of a collision with a single asteroid orbiting the Sun would have required two spacecraft, Engineer Andrew Cheng told reporters, because such an asteroid moves at tremendous speed and the impact of a small spacecraft is minimal, hard would lead -to recognize change. A second spaceship would need to be present to study the effect.
But a moon like Dimorphos orbits its larger twin at a stately pace. The effect of the impact should be easier to capture – also by telescopes on earth and in space. No second spacecraft is required.
It will take at least a few days to determine if the DART mission was able to slow down the targeted asteroid, and to what extent. Telescopes on Earth and in space observed the collision, as did a small instrument called the CubeSat, deployed 15 days before the impact.
This is an unusual mission because it’s not about a spacecraft trying to survive a dangerous landing on an alien world or prove itself operational in the harsh environment of space, noted Robert Braun, director of space exploration at Applied Physics Laboratories .
“This is where we’re looking for signal loss,” he told reporters before the collision. “What we’re hailing is a loss of the spacecraft.”
By Monday afternoon, engineers at Laurel had sent their final course corrections to the DART spacecraft, and from that point on it was self-sufficient, making final navigational adjustments autonomously. The craft was aimed squarely at the larger, brighter asteroid, but programmed to fire thrusters that slew it toward the smaller asteroid as it came into view.
Some bizarre scenarios could not be ruled out because the shape of the asteroid would not be determined until the last hour before impact. In fact, 90 minutes before impact, only the larger asteroid — not Dimorphos — was visible in the spacecraft’s live camera image.
“If we were on the right course and it was shaped like a donut, we would fly right through it,” Braun said.
There are thousands of potentially dangerous asteroids approaching or crossing Earth’s orbit around the Sun. None are currently known to be on a trajectory to impact the planet.
