Planetary Defense – Portugal News

On the other hand, there are about 18,000 asteroids this size or larger in orbit around the Sun. If Demorphos (the asteroid in NASA’s experiment) hit Earth, the impact would have the energy of a hundred-megaton hydrogen bomb, enough to destroy a city the size of New York or Lagos.

More so, in fact, because Demorphos orbits a much larger asteroid called Didymos with a diameter of 780 meters, and they will arrive together. We are now talking about almost no one alive in a city the size of Tokyo, and the devastation of a hundred kilometers around.

These things don’t happen often, of course, but they do happen. The Lunar and Planetary Laboratory at the University of Arizona estimates that there are more than three million archaeological craters more than one kilometer in diameter on Earth, although the vast majority are buried under later deposits.

The largest asteroid to hit the planet, Chicxulub in the Mexican Yucatan Peninsula 66 million years ago, was ten kilometers in diameter. It caused the last great extinction: firestorms around the world and a five or ten-year “asteroid winter” (due to the ash obscuring the sun) killed all dinosaurs other than birds and left mammals to dominate.

According to the Planetary Society, the odds of an asteroid the size of Demorphos hitting Earth are one in one hundred every century. Furthermore, we don’t even know where 40% of those asteroids are.

Go down to asteroids 30-140 meters high, still big enough to kill a city, and there are about a million of them there. We have good data on less than 2% of them, but we know that at least one will hit the planet every century. So both NASA and the European Space Agency (ESA) have “planetary defense” offices – and now they’re running the first big experiment.

NASA’s Double Asteroid Redirection Test, or DART, is a spacecraft that weighs nearly 500 kilograms full of fuel, but will be much less than that when it dives into the kamikaze at Demorphos on Monday. On the other hand, it will be moving at a speed of six kilometers per second, so the energy that it will transfer to the asteroid will not be insignificant.

The main goal of the exercise is to find out how much it can change the orbit of the smaller asteroid around the main Didymus. It won’t be much, because Demorphos has an estimated mass of 4.8 billion kilograms, but it should be enough to be detected within weeks by large telescopes.

Then, four years from now, when the European Space Agency’s Hera mission reaches Demorphos, we should know the size and shape of the crater. This would confirm or refute the growing suspicion that most of the smaller asteroids, at least, are not really solid rock, but merely clumps of rubble weakly held together by microgravity.

If so, moving them would be a lot easier, because the impact wouldn’t push the asteroid in the desired direction then. It would also shoot a lot of debris in the opposite direction, amplifying the overall momentum transferred to the asteroid by fivefold.

One step at a time. It will likely be two decades before we can divert even a Dimorphos-sized asteroid from hitting Earth and be confident that it will go where we want it instead.

It will take much longer to deal with larger but rarer rocks, which are likely to be hard rocks. However, before the end of this century, we may be able to protect the planet from all but the largest asteroids.

A ‘kinetic effect’ approach to a problem such as DART is currently the preferred technique, but alternative techniques are also being considered. The first is to land a small ion engine on a threatened asteroid with enough fuel to withstand a very small thrust for a very long time.

Another suggestion, particularly useful if we have a little warning of the asteroid’s approach, is to use interceptors to blast it into large numbers of tiny fragments just hours before impact. Many small pieces will burn in the atmosphere, and the damage caused by the rest will be much less than the damage caused by a single huge rock.

It will probably take a century to build a good planetary defense system, but at least we are moving from theoretical to practical.

The opinions expressed on this page are those of the author and not those of Portugal.