Potentially hazardous object

Toutatis

Potentially Hazardous Object (PHO) refers to a near-Earth object (NEO) that has the potential to make threateningly close approaches to the Earth and is large enough to cause significant regional damage in the event of an impact. These objects are of particular interest to astronomers, planetary scientists, and space agencies around the world due to the potential risk they pose.

Definition

A PHO is defined based on parameters that measure the object's potential to make threatening approaches to the Earth. Specifically, an object is considered a PHO if its minimum orbit intersection distance (MOID) with Earth is less than 0.05 astronomical units (AU), and its absolute magnitude (H) is 22 or brighter, which corresponds to a diameter of roughly 140 meters or larger assuming a typical reflectivity. These criteria are used to identify objects that are capable of causing significant destruction in the event of an impact and that come sufficiently close to the Earth's orbit to warrant close observation.

Discovery and Tracking

PHOs are discovered through various telescope surveys and space-based observatories dedicated to scanning the skies for NEOs. Once identified, these objects are tracked over time to refine their orbits and predict their future positions. The Minor Planet Center (MPC) serves as the central node for reporting new discoveries, and the Jet Propulsion Laboratory's (JPL) Center for Near Earth Object Studies (CNEOS) provides precise calculations of their orbits and future close approaches to Earth.

Risk Assessment

The risk posed by a PHO is assessed using sophisticated computer models that simulate the object's orbit for hundreds or even thousands of years into the future to identify any potential impacts with Earth. The Torino Scale and the Palermo Technical Impact Hazard Scale are two risk assessment tools used to categorize the potential impact hazards of PHOs. These scales take into account the probability of impact and the potential energy release, providing a way to communicate the risk to the public and to policymakers.

Mitigation Strategies

Various strategies have been proposed to mitigate the threat of an impact by a PHO. These include kinetic impactors, which would involve sending a spacecraft to collide with the PHO to change its trajectory; nuclear deflection, using a nuclear explosion near the PHO to alter its course; and gravity tractor methods, where a spacecraft would fly alongside the PHO and use its gravitational pull to slowly change the object's path. The feasibility and effectiveness of these strategies depend on the size of the PHO, its composition, and the amount of warning time before a potential impact.

Notable Potentially Hazardous Objects

Some well-known PHOs include (99942) Apophis, which has been closely monitored due to its initially calculated potential to impact Earth in 2029 or 2036, and (4179) Toutatis, a large, irregularly shaped asteroid that has made several close approaches to Earth. Ongoing observations and improved orbital calculations have since ruled out any impact by Apophis for at least the next century.

Conclusion

Potentially Hazardous Objects represent a significant area of study within planetary science and space safety. The ongoing discovery, tracking, and analysis of these objects are crucial for understanding the potential threat they pose and for developing strategies to mitigate that threat. As our detection capabilities and technologies improve, we will be better equipped to protect Earth from the possibility of a catastrophic impact.