Looming over Earth lies a great extinction-level threat: asteroid impacts.
Earth, as well as all planets and moons with rocky surfaces, has experienced a large number of collisions from objects of extraterrestrial origin. Any impact that’s massive and energetic enough, in principle as well as in practice, could cause a mass extinction event if we don’t do something to mitigate it. (Credit: James Thew via Adobe Stock)
The K-Pg extinction event from 65 million years ago reminds us of this grave threat.
This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth’s atmosphere to create very bright meteors, technically called “bolides” and commonly referred to as “fireballs”. Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy. The largest impactor over this time period, the Chelyabinsk meteorite, was only ~20 meters in diameter. (Credit: Planetary Science, NASA/JPL-Caltech)
A ~kilometer-sized or greater object could wipe out every human on Earth.
This infographic shows the original orbit of asteroid Dimorphos around the larger asteroid Didymos, along with the trajectory of NASA’s DART spacecraft and the presumed new orbit that will result. The new orbit changed by a much greater amount than simulations and calculations predicted, indicating that a better understanding of these redirection efforts are required before we begin relying on them to save our planet. (Credit: NASA/Johns Hopkins APL)
Our greatest hope for survival relies on early detection and successful intervention.
Flyby spacecraft Deep Impact shows the flash that occurred when comet Tempel 1 ran over the spacecraft’s impactor probe. It was taken by the flyby craft’s High Resolution Instrument, Visual CCD camera (HRIV) over a period of about 40 seconds. Black borders are the result of image stabilization. The small change in momentum resulting from this impact did not appreciably alter the motion of Tempel 1. Credit: Paul Stephen Carlin, NASA/JPL)
The NEXIS Ion Thruster, at Jet Propulsion Laboratories, is a prototype for a long-term thruster that could move large-mass objects over very long timescales. If we had sufficient lead time, a thruster (or series of thrusters) like this could save the Earth from a potentially hazardous impact. (Credit: NASA/JPL)
However, we mustn’t feel that false sense of security.
The bright star Albireo, a prominent and colorful double star system that’s a member of the Summer Triangle, was imaged on December 26, 2019. During 10 exposures lasting 150 seconds each, a train of Starlink satellites passed through that same region of sky. While this streaking effect has significant implications for professional an amateur astronomy alike, it’s the science of planetary protection that suffers the greatest losses, particularly from satellite impacts on ground-based observatories. (Credit: Rafael Schmall)
At present, nearly 30,000 potentially hazardous asteroids have been identified, with about a third of them above ~140 meters in diameter. The overwhelming majority of asteroids, including near-Earth asteroids, have yet to be found and characterized.(Credit: Alan B. Chamberlin, NASA/JPL-Caltech)
These new near-Earth asteroids were all found in an uncommon place: between the orbits of Earth and Venus.
The animation depicts a mapping of the positions of known near-Earth objects (NEOs) at points in time over the past 20 years, and finishes with a map of all known asteroids as of January 2018. It’s vital that we recognize that the most hazardous asteroids of all, i.e., the ones that cross Earth’s orbit the most frequently, have largely not been characterized at all, particularly among the populations that lie largely interior to Earth’s orbit. (Credit: NASA/JPL-Caltech)
One passes closer to the Sun than any known asteroid, enabling unprecedented General Relativity tests.
This illustration shows the precession of a planet’s orbit around the Sun. A very small amount of precession is due to General Relativity in our Solar System; Mercury precesses by 43 arc-seconds per century, the greatest value of all our planets. The newly discovered asteroid that has the smallest perihelion of any stable object will allow even better tests of General Relativity within the Solar System than have ever been performed before. (Credit: WillowW/Wikimedia Commons)
Another, at 1.5 kilometers across, is the largest Earth-hazardous asteroid discovered in eight years.
Although we’ve catalogued most of the large (greater than 1 km) asteroids in the Solar System, the population of inner near-Earth asteroids that’s greater than 0.1 km has not been well-determined at all. The number density of the smaller objects on this graph has only been estimated; a mission like NEO Surveyor will be vital toward learning what truly poses a predictable hazard to Earth. (Credit: Marco Colombo, DensityDesign Research Lab)
If a collision occurs, an extinction-level event is anticipated.
Although we’ve discovered thousands of Near-Earth Asteroids, with the majority coming from the ground-based Pan-STARRS and Catalina Sky Survey efforts, it’s the undiscovered objects, which may represent the greatest threat to Earth, that are key to discovering and characterizing. (Credit: Alan B. Chamberlain)
Hazardous object surveys primarily focus on the asteroid belt: where most such objects are located.
While the near-Earth asteroids are already posing potential hazards to Earth, most of the asteroids that are out there are heavily influenced by Jupiter. The wrong gravitational interaction, which can always occur as time goes on, could turn any of these asteroids into potential Earth-orbit-crossing hazards.(Credit: Pablo Carlos Budassi/Wikimedia.org)
The four main classes of near-Earth asteroids can be divided into groups based on their perihelia and aphelia. The Amors are completely exterior to Earth’s orbit (but interior to Mars’s orbit), the Apollos are Earth-crossing but primarily orbit farther away from Earth, the Atens are Earth-crossing but primarily orbit closer to the Sun than Earth, and the Atiras are entirely contained within the orbit of Earth. The Atens and Atiras remain primarily undiscovered. (Credit: NASA/JPL-Caltech/Center for Near Earth Object Studies)
Of these four, the Atens and Atiras are the most poorly identified.
This map, although ~9 years out of date in 2022, shows the then-known potentially hazardous asteroids that would cause regional or global devastation. The majority of these objects possess aphelia that take them quite far away from Earth’s orbit, and so they only come within a few million km/miles every few years. The undiscovered objects in tighter orbits pose a much greater existential threat to humanity. (Credit: NASA/JPL-Caltech)
On November 18, 2019, approximately 19 Starlink satellites passed over Cerro Tololo Inter-American Observatory, disrupting astronomical observations and hindering the science being undertaken in a real, measurable way. The most greatly impacted observations, which must occur during astronomical twilight, are searches for potentially hazardous asteroids, a necessity for planetary defense. (Credit: Tim Abott/CTIO)
There have been around 5000 launches since the dawn of the space age. From break-ups, collisions, failures, explosions, and all other factors, there are an estimated 670,000 objects greater than 1 cm in size, and ~170 million objects larger than 1 mm. Most are untracked. (Credit: ESA)
The NEO Surveyor mission, whose goal is to discover and categorize most of the potentially hazardous near-Earth objects, is a planetary defense mission that should find practically all of the Earth-crossing asteroids greater than 140 meters across, as well as many smaller ones. It’s a high priority mission, but one that needs to be fully funded to do its job. (Credit: NASA/JPL-Caltech)
