There’s something comforting about a map with “You are here” marked on it, but not when the arrow points to a spot where giant asteroids are whizzing by like cannon balls in a pirate movie. NASA has released a map of the inner Solar System showing the orbits of the 1,400 Potentially Hazardous Asteroids (PHA) known as of early this year. According to the agency, the plots show the orbits of asteroids over 460 ft (140 m) in diameter that pass within 4.7 million miles (7.5 million km) of Earth.
The illustration is one of the products of NASA’s Near Earth Object program, which is tasked with tracking and recording PHAs. Though no government yet has a policy on how to respond to confirmation of a collision, the NEO program aims to provide as much notice as possible on the grounds that it’s better to have decades of warning rather than hours. The website is of particular interest because it includes an interactive feature that allows visitors to pull up the orbital characteristics and charts of the candidate PHAs, as well as a risk table of potential colliders.
An interesting point about the orbits is how so many of them are tucked inside the orbit of Jupiter, with only a few shooting beyond to the outer Solar System. That makes Jupiter a bit of a two-faced friend. On the one hand, having a giant planet in the neighborhood is great because in the early days of the Solar System it swept up all the cosmic debris that could have made life on Earth very unpleasant and very short. Unfortunately, its gravitational pull also has a habit of knocking asteroids out of the asteroid belt or hooking comets into the inner Solar System like a carnival visitor shying balls at milk bottles.
One thing to bear in mind is the scale. The map seems pretty crowded, but that’s because the size of the planets and orbits has been greatly exaggerated to make them visible. On this map, a line thousands of miles wide would be much too thin to be seen. That’s like looking at a map from London to Edinburgh and seeing the M1 motorway depicted as wide enough to engulf Northampton.
The comforting thing it that the distance of Jupiter from our Sun is 483,800,000 miles (778,500,000 km), and the Earth has a diameter of 7,918 miles (12,742 km). Even if one of the PHAs is a mile across, there’s a bumper crop of nothing out there, and the odds of one of these asteroids hitting the Earth is extremely small.
The space agency emphasizes that not every PHA is a danger to Earth, but the fact that they pass close to Earth and are of sufficient size to cause damage makes them worth watching and making more precise measurements of their orbits.