NEOs are cosmic objects whose trajectories bring them within 1.3 astronomical units (AU) of the Sun. This includes objects that cross Earth's orbit. Scientists monitor these objects carefully because even though impact probability is low, the consequences could be catastrophic.

There are over 30,000 known NEOs, with more being discovered regularly. NASA's Planetary Defense Coordination Office tracks these objects and assesses potential threats decades in advance, giving us time to develop mitigation strategies if needed.

NEO detection relies on a global network of observatories scanning the night sky. When a new object is discovered, astronomers calculate its orbit to determine if it poses any future threat to Earth. The accuracy of these predictions improves with each observation.

Projects like NASA's NEOWISE mission and the upcoming NEO Surveyor will dramatically improve our ability to find potentially hazardous asteroids, especially those that approach from the direction of the Sun.

The most famous impact event occurred 66 million years ago when a 10-kilometer asteroid struck what is now Mexico's Yucatan Peninsula, leading to the extinction of the dinosaurs. More recently, the 1908 Tunguska event in Siberia saw an asteroid explode in the atmosphere, flattening 2,000 square kilometers of forest.

In 2013, a 20-meter meteor exploded over Chelyabinsk, Russia, injuring over 1,000 people from broken glass. These events remind us that asteroid impacts are not just ancient history—they remain an active threat that requires ongoing monitoring and planetary defense capabilities.

Asteroids are rocky remnants left over from the early formation of our solar system about 4.6 billion years ago. Most asteroids are found in the asteroid belt between Mars and Jupiter. They range in size from small rocks to objects hundreds of kilometers wide. Near-Earth Asteroids (NEAs) have orbits that bring them close to Earth's orbit. Scientists track thousands of these objects to ensure they don't pose a threat to our planet.

Comets are cosmic snowballs made of frozen gases, rock, and dust. When a comet's orbit brings it close to the Sun, it heats up and releases gases, creating a glowing head (coma) and often two tails - one made of dust and one of ionized gas. Some comets take less than 200 years to orbit the Sun (short-period comets), while others take thousands of years. Famous examples include Halley's Comet, which returns every 76 years.

A meteor is the bright streak of light we see in the night sky, often called a "shooting star." This happens when a small piece of space debris (called a meteoroid) enters Earth's atmosphere at high speed and burns up due to friction with air molecules. Most meteors are caused by particles no bigger than a grain of sand. During meteor showers, Earth passes through debris trails left by comets, creating dozens of meteors per hour.

A meteorite is a piece of space rock that successfully makes it through Earth's atmosphere and lands on the surface. Most meteorites come from asteroids, though some come from the Moon or Mars. They provide valuable scientific information about the early solar system. Meteorites are classified into three main types: stony (made of silicate minerals), iron (made of metallic iron and nickel), and stony-iron (a mixture of both).

OD arises from launch artifacts, decommissioned satellites, and spacecraft breakups. More debris is created by the Kessler syndrome, which is the collisions between orbiting satellites and existing debris. This situation is exacerbated by the absence of global consensus and regulation, and overexploitation of space. The World Economic Forum estimates that orbital debris currently exceeds 6.3 million kilograms, with projections indicating up to 60,000 satellites at risk of contributing to this problem by 2030.

Human made OD is made up of weather observation & imaging satellites, communication satellite constellations and networks (such as Starlink and Iridium), and space exploration missions such as the International Space Station.

The launch traffic to LEO, which poses 96% the debris reentry problem, is estimated to have more than tripled in the last decade, with approximately 80% of the active payloads inhabiting LEO. The scale of the debris reentry problem implies increased threats to inhabited areas, installations, and infrastructure.

A further hazard is the potential for catastrophic mid-air collisions between a reentering object and an airborne aircraft. This is a real possibility given the amount of air traffic at any given time around the Earth. Uncertainty in predicting the location of space debris reentry is often high due to the complex and variable conditions during descent.

Atmospheric Pollution

Ozone Depletion: Satellites release aluminum oxides and other metallic particles as they disintegrate, which can reach the stratosphere and contribute to the depletion of the ozone layer.

Atmospheric Heat Balance: These particles can also alter the balance of heat in the atmosphere, potentially having complex effects on Earth's temperature.

Ground Impact

Hazardous Materials: Some satellites carry hazardous fuels or radioactive materials, posing a significant risk of poisoning or harming people if these chemicals are released in inhabited areas.

Physical Damage: While rare, large sections of satellites can survive re-entry and strike the Earth's surface with significant force, potentially causing damage to property or infrastructure.

Uncontrolled Re-entry: Many re-entries are uncontrolled, leading to debris being scattered over large areas. While most debris lands in oceans, there's a small but growing chance that larger pieces could impact populated areas.

Growing Risks and Mitigation

Increasing Frequency: The number of satellites in orbit is rapidly increasing, leading to a greater probability of re-entry incidents and escalating these environmental and safety concerns.

Controlled Re-entries: To mitigate risks, space agencies are promoting controlled re-entries where satellites are guided to burn up in a designated area, often over the ocean.

Atmospheric Research: Further research is needed to understand the specific physics of satellite re-entry and its atmospheric impact, informing better satellite design and disposal strategies.

Overall Risk

The overall risk to an individual from falling space debris is extremely small. However, the long-term environmental consequences, especially concerning atmospheric pollution from the increasing number of satellite re-entries, require careful management and sustainable practices for the future of space.

NASA and international space agencies actively track near-Earth objects to identify potential threats decades in advance. Detection methods include ground-based telescopes and space missions like NEOWISE. If a threat is identified, several mitigation strategies exist: kinetic impactor (like NASA's DART mission that successfully redirected an asteroid in 2022), gravity tractor (using a spacecraft's gravity to slowly pull an asteroid off course), and nuclear deflection as a last resort. Early detection is crucial - the earlier we spot a threat, the easier and cheaper it is to deflect.

For more comprehensive information on space safety and planetary defense, visit the ESA Space Safety Programme.

Named after NASA scientist Donald Kessler who proposed it in 1978, the Kessler Syndrome describes a scenario where the density of objects in low Earth orbit becomes high enough that collisions between objects generate a cascade of more collisions. Each collision creates thousands of smaller debris pieces, increasing the likelihood of further impacts.

This scenario is particularly concerning because it could render certain orbital zones unusable for generations, effectively trapping humanity on Earth by making satellite operations and space launches too dangerous. The syndrome has moved from theoretical concern to practical reality as orbital density increases exponentially.

The challenge asks: Do we have the tools to enable the public and decision makers to understand and mitigate asteroid risks? We're developing an interactive visualization and simulation tool that uses real NASA data to help users model asteroid impact scenarios, predict consequences, and evaluate potential mitigation strategies. NASA's Planetary Science Division provides critical datasets about known asteroids, while the USGS offers geological information for impact modeling.