Asteroid Day is a global awareness movement where people from around the world come together to learn about asteroids and what we can do to protect our planet. Observed 107 years to the day of the Siberian Tunguska event, a 200 to 600 ft asteroid that exploded around 6 miles high in the atmosphere with the strength of 1000 Hiroshima atomic bombs of Hiroshima on top of an uninhabited forest.
Although asteroids would seem like mere rocks floating in space, they are actually objects of great importance for astronomers, geologists, planetary scientists, among others. On the evolutionary field, they are pristine objects from the dawn of the Solar System, building blocks of planets, moons and comets that never came to be. They maintain their original chemical composition that speaks to us about how our solar neighborhood was like 4.5 billion years ago. The preferred term is "minor planet," as asteroid was never well defined with the International Astronomical Union, the main worldwide body that supervises naming, definitions and astronomical discoveries. Asteroids are irregular objects either from shattered remnants of bodies within the Solar System or individual objects that never grew large enough to become planets and that do not present the characteristics of comets.
Also on the evolutionary field, but that which concerns living organisms on Earth, they have tilted the balance. At least three big mass extinctions during Earth's past has been associated with meteor (asteroids reaching Earth's surface) collisions . The most famous one happened 66 million years ago, impacting in present-day Yucatan peninsula in Mexico, wiping out the dinosaurs. But mass extinctions in the Carboniferous (305 million years ago), Triassic-Jurassic (200 million years ago) and Palaeogene (40 million years ago) eras have been related with impacts. How do we estimate this? Asteroids abundantly hold an element that is rarely found on Earth, called iridium. When they impact our planet, they disintegrate and their components are usually spread around Earth and then covered up through millions of years of erosion and debris. Very defined layers of iridium have been found worldwide at the same depths, pointing at specific cataclysmic events.
On the scientific field they present a challenge. We know of approximately 1,500 potentially hazardous objects (PHOs), which are floating rocks in space at least 330 ft in diameter which will fly by Earth in the next century at a distance closer to 4.6 million miles. They are assigned an impact hazard value from 0 to 10, called the Torino Scale. Zero to three represents no danger, ten means imminent impact with global repercussions. Today, not a single PHO has a value over 0, so none currently represents danger due to its current orbit. Asteroids change orbits easily due to the gravitational pull of larger bodies in the Solar System (mainly Jupiter and Saturn) and through collisions between them. Planets in the Solar System have dispersed the asteroids during billions of years, mostly cleaning up the planet's orbit around the Sun. Dwarf planets (spherical, smaller planets such as Ceres or Pluto) don't have the gravitational force to be so effective in cleaning up asteroids in their path around the Sun; that is what makes them enter the category of dwarf planets. It's not really their size, but their ineffectiveness at cleaning their neighborhood of asteroids, that categorizes them as "dwarfs." Most asteroids today lie in two reservoirs: they asteroid belt between Mars and Jupiter, where Ceres, the closest dwarf planet to the Sun resides, and on the Kuiper Belt, a rocky ring of debris found farther away than Neptune, where Pluto, Makemake, Haumea and Eris (the other so-called dwarf planets) exist.
Yet, we think that we have not discovered 30 percent of these objects and astronomers need to turn their telescopes to find them and track them. Tracking is of great importance, these objects can change orbits with ease due to their relative low masses and the gravitational pull of planets, so constant monitoring is of essential importance and the sheer number to be tracked represents a challenge. Also, we are missing the smaller asteroids, which exists in much higher quantities but are below the limit of detection of existing instruments (due to their size or brightness), we need more and better instruments to find them and track them also.
If we do find a hazardous asteroid on a collision course, what should we do? Several space agencies and research institutions have been studying the possibilities. Should we blow it up and risk creating a single problem into multiple, unpredictable, smaller-sized impact bodies? Do we have the propulsion technology to stick an engine on their side and push them? If we could change their route, have we spotted them with enough time to spare to actually push them to the side? Can we put a very massive spacecraft next to it, so that the gravitational pull of the machinery slowly attracts the asteroid, allowing it to change course and miss us? Must we paint some sections of asteroids white, so that photons (light particles) from the Sun slowly push it into another orbit? Some options seem far fetched, but they have all been under discussion by bright minds.
We are bound to have another impact, it is just a question of time. In 2013 an asteroid disintegrated in the atmosphere over Chelyabisnk, Russia, the resulting expansion wave hurt over 1,000 people. These types of events happen, according to statistics, every 60 years. Fortunately for us, the atmosphere disintegrates most of these asteroids, which are fairly small, due to friction; but larger rocks that would create local destruction would survive the atmospheric entry and they strike, on average, every 2000 to 3000 years. Asteroids like the one that killed of the dinosaurs collide with Earth once every dozens of million years; the last one happening 65 million years ago. Resources and research must go into detection and deflection.
Finally, on a commercial note. Asteroids are rich in metals and water. Ventures are being born to exploit their resources, worth trillions of dollars per each asteroid over 1500 ft in diameter, there are literally millions of them floating in space.
Asteroids can help us understand our cosmic neighborhood, are great mineral deposits, but also present potential risks for humanity. We require more investment in telescopes, research and technologies to keep us safe.