NASA defines near-Earth objects (NEO) as asteroids or comets with orbits that bring them inside 120 million miles (195 million kilometers) of the sun, meaning they’re near Earth’s orbit. The overwhelming majority of those NEOs are asteroids, or near-Earth asteroids (NEAs).
There are over 600,000 known asteroids within the solar system, and over 20,000 of those are NEAs, in line with the European Space Agency (ESA). Many of the rest are situated within the foremost asteroid belt between Mars and Jupiter. NEAs are thought to make their way out of the asteroid belt and toward Earth’s orbit as they’re nudged by the gravity of other solar system bodies. The vast majority of NEOs range from about 10 feet to 25 miles (3 meters to 40 km) wide, in line with NASA.
Kinds of near-Earth asteroids
NEAs are divided into 4 significant families based on their orbital parameters: Atiras, Atens, Apollos and Amors.
Atiras are NEAs with orbits which might be contained entirely inside Earth’s orbit. They’re named after the asteroid 163693 Atira.
Atens are NEAs that cross Earth’s path and whose orbits have semimajor axes smaller than that of Earth’s orbit across the sun. They take their name from the asteroid 2062 Aten.
Apollos are NEAs that cross Earth’s orbit with a semimajor axis larger than that of our planet. They get their name from the asteroid 1862 Apollo.
Amors are Earth-approaching NEAs with orbits that bring them throughout the orbit of Mars but don’t bring them throughout the orbit of Earth. Their name comes from the asteroid 1221 Amor.
One concerning category of NEAs are so-called potentially hazardous asteroids (PHAs), which the NASA Jet Propulsion Laboratory’s Center for Near-Earth Object Studies (CNEOS) defines based on an asteroid’s potential to make a threatening close approach to Earth. Specifically, this concerns the thing’s “minimum orbit intersection distance (MOID)” — the space an asteroid is from Earth when its orbit crosses or touches the orbit of our planet — and the brightness of the thing if it were situated at the identical distance from Earth as Earth is from the sun (1 astronomical unit, or AU), often called absolute magnitude.
PHAs should have a MOID of around 4.65 million miles (7.48 million km), or 0.05 AU, and an absolute magnitude of twenty-two or brighter. Because MOID is used to calculate the diameters of asteroids, bodies smaller than 460 feet (140 m) wide aren’t classified as PHAs, irrespective of how close they arrive to Earth, per CNEOS.
Only a small fraction of NEAs are considered potentially hazardous, but their potential threat to our planet implies that space agencies across the globe are working hard to discover and track these dangerous space rocks.
Near-Earth asteroids FAQs
What’s a near-Earth asteroid?
NASA defines a near-Earth asteroid as an asteroid with an orbit that brings it to inside 120 million miles (195 million km) of the sun. This enables these space rocks to go through Earth’s neighborhood within the solar system.
Is an asteroid going to hit Earth in 2029?
For nearly 20 years, the asteroid Apophis sat atop NASA’s Sentry risk table because the asteroid most definitely to affect Earth in the following 100 years. But now that the orbit of the asteroid, which was discovered in 2004, has been higher constrained, astronomers realize it won’t hit Earth for at the least 100 years.
That implies that when Apophis skims Earth on April 13, 2029, it is going to not hit our planet. Passing by at around 19,000 miles (31,000 km), the 1,100-foot-wide (340 m) asteroid will come closer than some satellites and needs to be so vivid that over 2 billion people within the Eastern Hemisphere will have the ability to witness it with the naked eye.
Will Bennu hit Earth?
With Apophis falling within the Sentry risk table rankings, the next-riskiest asteroid is Bennu. Yet NASA estimates that there is no such thing as a likelihood that Bennu will hit Earth for at the least a century.
When Bennu makes an in depth approach to our planet on Sept. 24, 2182, there’s a 0.037% — or 1 in 2,700 — likelihood that the 1,600-foot-wide (488 m) asteroid will strike our planet.
How will we track near-Earth asteroids?
A fantastic deal of asteroid tracking data is collected by NASA-funded observatories, comparable to the University of Hawaii’s Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), the Catalina Sky Survey, and the University of Hawaii’s Asteroid Terrestrial-impact Last Alert System (ATLAS).
Data regarding the positions of NEAs around Earth are gathered by the International Astronomical Union’s Minor Planet Center (MPC). The MPC handles the identification, designation and orbit computation for these objects after which pronounces discoveries to space agencies comparable to NASA.
Once a possible NEA is discovered, the thing is followed up on by projects comparable to NASA’s space-based Near-Earth-Object Wide-Field Infrared Survey Explorer (NEOWISE) telescope, together with planetary radar projects, like JPL’s Goldstone Solar System Radar Group.
The science of NEAs falls to several bodies inside NASA. As an example, CNEOS characterizes the orbits of all currently known NEOs after which predicts their close approaches to Earth. With this information, CNEOS could make comprehensive impact hazard assessments, that are supplied to NASA’s Planetary Defense Coordination Office in Washington, D.C.
Performing long-term assessments and predicting PHAs’ orbits with the Sentry impact monitoring system, CNEOS also maintains the Scout system, which monitors potential NEAs to evaluate possible impacts. After an NEA is detected but before it’s confirmed, it’s placed on the Minor Planet Center’s NEO Confirmation Page (NEOCP). The Scout system then monitors these candidate NEAs over the approaching days and weeks to evaluate their trajectory and possible impacts.
Once the NEA is confirmed, it’s faraway from the NEOCP. Then, all of the information are compiled within the Sentry risk table , which lists the NEAs with the best probability of impacting Earth over the following 100 years. That is probability-based, since it takes a few years of observations to constrain the orbit of an NEA, and even then, there are measurement uncertainties.
What are the risks of near-Earth asteroids?
Earth is under constant bombardment from space rocks. NASA estimates that around 48.5 tons (44 metric tons) of fabric falls to Earth day by day, most of which burns up within the atmosphere and infrequently creates “shooting stars.” In response to NASA, space rocks smaller than about 82 feet (25 m) will most definitely burn up as they enter Earth’s atmosphere and thus cause little or no damage.
Earth’s geological history is a stark reminder, nonetheless, that larger asteroids could make it through the atmosphere and that impacts by large space debris can have disastrous consequences. This is especially evident within the case of the asteroid that caused the Cretaceous-Tertiary extinction event 66 million years ago, which eliminated 80% of plant and animal species on Earth, including the nonavian dinosaurs.
Due to the destructive capability of asteroids, CNEOS has a task along with monitoring real asteroids around Earth: It conducts hypothetical asteroid impact exercises, which have given us an idea of the sort of devastation that might result from a collision inside an NEA.
Fortunately, NASA suggests that the larger an asteroid is, the less likely it’s to affect Earth. While around 100 tons (90 metric tons) of dust- and sand-size particles reach Earth day by day, a roughly car-size asteroid strikes Earth’s atmosphere around annually, burning up and leading to a fireball over Earth.
Around every 2,000 years, Earth encounters an asteroid around the dimensions of a football field — about 330 feet (100 m) wide. The numerous destruction brought on by such an impact could be localized, with the asteroid likely vaporizing just over Earth’s surface and destroying buildings inside a radius of 9 miles (14 km) and shattering windows inside a radius of around 60 miles (100 km). More widespread damage might be brought on by seismic tremors and rock hurled into the atmosphere by such an impact.
During a CNEOS asteroid impact exercise in April 2023, NASA researchers revealed the damage that might result from impacts of larger asteroids.
For instance, a 1,000-foot-wide (300 m) asteroid could represent destruction on a continental scale, releasing as much energy because the detonation of two,000 megatons of TNT — such as 133,000 times the estimated energy released by the bomb that destroyed Hiroshima at the top of World War II. Earth experiences an impact from such a body around every 70,000 years.
The devastation would grow significantly for a 2,000-foot-wide (600 m) asteroid. An impact with an asteroid this size would border on global catastrophe, releasing as much as 20,000 megatons of energy. This implies a doubling in asteroid size has resulted in a rise in devastation power by an element of 10. Fortunately, asteroids of this size are predicted to hit Earth only once every 200,000 years or so.
For a 3,330-foot-wide asteroid (about thrice as tall because the Eiffel Tower), an impact scenario as calculated by CNEOS would turn out to be dire. Indeed, asteroids of this size are considered potential “planet killers.” A planet-killer impact would release around 100,000 megatons of energy — such as 6.6 million detonations of the Hiroshima nuclear blast. These impacts are estimated to occur around once every 700,000 years.
The dinosaur-killing asteroid, often called the Chicxulub impactor, had an estimated width of 6.2 miles (10 km) and released around the identical amount of energy — 720 megatons of TNT — when it hit what’s now the Yucatán Peninsula in Mexico at around 45,000 mph (72,000 km/h). Asteroids above 3 miles (5 km) in width, just like the Chicxulub impactor, are predicted to strike Earth once every 30 million years.
In response to the University of California, Berkeley, size is not the only characteristic that affects how much damage an NEA would cause if it hit Earth. Other aspects include the asteroid’s composition (for instance, is it a loose rubble pile or a complete lump of iron?) in addition to the angle and speed of the impact and whether the asteroid hits Earth on land or within the ocean.
Additional resources
In case you’re anxious about potential NEA encounters, you may regulate NASA’s Sentry risk table. In case you’d prefer to estimate the damage that would result from an asteroid of a particular size and density, the Earth Impact Program, from Imperial College London and Purdue University, is an amazing resource. It also means that you can input hypothetical impacts on land or water and even vary the depth of water during which the space rock lands. On YouTube, math professor Nils Berglund simulates what would occur if an asteroid struck Earth within the North Pacific Ocean.
Bibliography
NEO Basics, NASA, [Accessed 06/10/23], [https://cneos.jpl.nasa.gov/about/basics.html]
Asteroid Watch: Keeping an Eye on Near-Earth Objects, NASA Jet Propulsion Laboratory, Caltech, [Accessed 06/10/23], [https://www.jpl.nasa.gov/asteroid-watch]
NEO Observations Program, [Accessed 06/10/23], [https://www.nasa.gov/planetary-defense-neoo/]
NEO Earth Close Approaches, [Accessed 06/10/23], [https://cneos.jpl.nasa.gov/ca/]
Space Safety: ESA’s Planetary Defence Office, ESA, [Accessed 06/10/23], [https://www.esa.int/Space_Safety/Space_Safety_ESA_s_Planetary_Defence_Office]