5 biggest ‘planet killer’ asteroids that pose a threat to our planet

 Here are five collosal "planet killer" asteroids that pose a potential threat to our planet. 

Artist's impression of a massive asteroid that orbits closer to the Sun than the Earth. (Image credit: NOIRLab)

Astronomers recently spotted three near-Earth asteroids (NEAs) hiding in the glare of the Sun. One of those asteroids is the largest “potentially hazardous” object spotted in the last three years and is a “planet killer” asteroid that could have a “devastating impact on life as we know it” and could also potentially lead to a mass extinction event.

An NEA is an asteroid whose orbit brings it within 195 million kilometres of the Sun, meaning that it can pass within 50 million kilometres of Earth’s orbit. Just like planets, these asteroids typically orbit the Sun. While most of the asteroids in the solar system are in the “main belt” between Mars and Jupiter.

The European Space Agency (ESA) says that over 30,000 NEAs have been discovered and we keep discovering them at a rapid pace. But not all of these pose a threat to our planet. Many of them have orbits that don’t bring them close to our planet and even for many that do, they are so small that they will burn up on entry into our planet’s atmosphere.

According to NASA’s Jet Propulsion Laboratory (JPL), a potentially hazardous asteroid (PHA) is one whose minimum orbit intersection distance (MOID) with our planet is just 0.05 astronomical units. One astronomical unit (AU) is the distance between the Sun and our planet. It also needs to be more than 140-metres wide to be classified as a PHA.

The MOID between two bodies is an astronomical measurement used to assess the chances of close approaches and collision between the two bodies. In this article, when we refer to the MOID of an asteroid, we are referring to the MOID between the asteroid and Earth.

We have put together this list of the largest PHAs discovered so far. But do note that the sizes of these asteroids are an approximation inferred from their luminosity and albedo. The following asteroids are believed to be the five largest PHAs, arranged in ascending order.

5. 3122 Florence

Coming in at number 5 on the list is 3122 Florence, which is significantly larger than the other asteroids that come below it on the list. The nearly 5-kilometre-wide asteroid was discovered in 1981 and was later named after Florence Nightingale. It has a MOID of about 0.0443 AU.

According to JPL, 3122 Florence made its closest approach to Earth on September 1, 2017, when it passed within 0.047237 AU of Earth, which is about eighteen times the distance between our planet and the Moon. Its next close approach is scheduled to happen on September 2, 2057, when it should come within 0.049952 AU of our planet.

4. (89830) 2002 CE

(89830) 2002 CE is a stony asteroid that earned its place at fourth onthe list with a diameter of approximately 5.067 kilometres. The asteroid is one of the most recently discovered among the largest PHAs. It has a MOID of 0.0277 AU, which corresponds to around 11 times the distance between the Earth and the Sun.

According to JPL, the asteroid made its closest approach to Earth on September 20, 1932, when it came within 0.48545 AU of Earth, or about 188 times the distance between the Earth and the Moon. JPL’s database does not have data about the asteroid’s most recent and next close approach.

3. 4179 Toutatis

4179 Toutatis, the third-largest known PHA, is an elongated stony asteroid with a diameter of approximately 5.4 kilometres. Toutatis makes many close approaches to Earth with a MOID of just 0.006 AU, which is just 2.3 times the distance between the Earth and the Moon.

According to JPL, it made its last close approach to Earth on December 26, 2016, when it came to within 0.25120 AU of our planet. Its closest approach to our planet happened on September 29, 2004, when it came within 0.01036 AU of the Earth, or a little more than four times the distance between the Earth and the Moon. Its next close approach is estimated to happen in 2065, when it will come within 0.36443 AU of our planet.

2. 3200 Phaethon

3200 Phaethon, the second-largest PHA, is an asteroid which has an orbit that brings it closer to the Sun than any other asteroid with a name. According to NASA, that is why the 5.8-kilometre-wide asteroid was named after the Greek mythological character Phaethon, who is the son of Helios, the sun god.

According to JPL, it made its last close approach to Earth on December 16, 2017, when it came within 0.06893 AU of the planet. Its closest approach to Earth will happen in 2093 when it is estimated that the asteroid will come within 0.01982 AU of Earth, or about eight times the distance between the Earth and the Moon. It is estimated that the next close approach of 3200 Phaethon with Earth will happen in 2026 when it will come within 0.36524 AU of our planet.

1. (53319) 1999 JM8

Topping the list is (53319) 1999 JM8, a slow-rotating asteroid that has a colossal diameter of around 7 kilometres, making it the largest PHA that we know. The asteroid has a MOID of about 0.0258 AU or about ten times the difference between our planet and the Moon.

According to JPL, the asteroid has come within 0.2 AU of Earth five times in the last decade with its closest approach on August 8, 1990, when it came within 0.03348 AU of our planet, or about 13 times the distance between the Earth and the Moon. Its next close approach to our planet will only happen in 2159 when it will come within 0.38295 AU of us.