xkcd.WTF!?

Explanation ➲

This comic may be inspired by the recent discovery of asteroid 2024 YR₄, which, on the date of the comic (February, 10, 2025), was estimated to have about 1-in-48 chance of striking Earth on December 22, 2032. Its size is estimated to be 40-90 meters. Currently, it is rated a 3 (out of a maximum of 10) on the Torino scale, a metric designed to evaluate the danger of a potential strike from a near-Earth object. On this comic's scale (see details below) it would be placed on the fourth label, the first label with bad news, as it could wipe out a city with a direct hit.

The Torino scale specifically addresses the future chance of impact, however, as well as the resulting energy (rather than pure mass or size) brought by the prospective impactor, and the retroactive Torino 8 classification of the similarly-sized Tunguska meteor, given as an 'example' in the table, is not really in the intended scope of the rating system, with events that have already happened already having reached 100% possibility with nothing left to plan for. For all foreseeable events, it is expected that the odds of impact (and therefore the Torino number) will continue to change as further observations refine the expected path into the vicinity of Earth, one or more times; it is generally hoped that all objects of interest will eventually reduce to zero, but for anything to reach levels 8 to 10 indicates the near-certainty of three distinct ranges of significant impact, which would need to be prepared for in one or more ways.

This comic provides a log scale correlating the size of any incoming asteroid to whether its arrival is good or bad news. While asteroids on the smaller end of the scale are good news for sky watchers, as the upcoming objects get bigger, the potential for catastrophe grows. Many astronomy enthusiasts would be happy to see bigger meteors, as bigger generally means more exciting pictures. Of course, once the meteors grow past a certain size even the most enthusiast astronomer might grow concerned about their imminent extinction.^{[citation needed]}

The title text adds an additional point about asteroids on the larger end of the scale, which have enough mass to change Earth's orbit. If it changed enough it might intersect the orbit of other planets (probably Venus or Mars, since those are the closest, (maybe)). This might lead to Earth colliding with that planet. Also, even without a collision, the changed orbit might perturb their orbits due to the Earth's gravitational force and cause negative consequences by either invoking or revoking orbital resonances between the various inner planets.

Sizes and consequences

Size	Randall's news	Explanation
1 cm	Good news! Meteors are pretty!	Burn up in the atmosphere, becoming nothing more than a streak in the sky.
30 cm	Great news! You might see a fireball!	Might descend far enough for the flames of its entry to be visible with the naked eye (bolide).
3 m	Okay news, unless you have expensive windows or are very unlucky.	Can descend far enough for the shockwave of its passing to shatter windows. The comic mockingly claims this is only a problem if your windows are expensive or happen to get directly hit by it. Of course, the shattering windows are also concerns for safety, as the Chelyabinsk meteorite, which sits near the upper bound of this category at approximately 18 m in diameter, damaged more than 7,000 buildings and injured around 1,500 people with its shockwave.
60 m	Bad news, especially if you live near the city it's aimed at.	The Tunguska meteor, which flattened and burnt over 2,000 km2 of Siberian forest in 1908, was 50-60 m across. It would have been rated an 8 on the Torino scale as a certain collision with localized destruction, the very lowest level of active concern for any (near-)certain event.
600 m	Bad news, especially if you live on the continent it's aimed at.	Can easily cause localized extinction, and can be expected to have effects on the rest of the world as well.
9 km	Bad news for your species.	The Chicxulub asteroid that wiped out non-avian dinosaurs was about 10 km in diameter.
50 km	Bad news for your phylum.	Our phylum is primarily all the vertebrate animals. The implication is that an asteroid over five times as wide (thus 125 times as massive) as the asteroid that wiped out the dinosaurs would cause the extinction of every animal with a spinal cord, which includes all of the higher life forms on earth (fish, and mammals). Presumably other, less complex, forms of life would survive.
300 km	Bad news for your biosphere.	A global extinction event is pretty much guaranteed.
2,000 km	Good news for any life that might someday evolve on Earth's new moon.	Earth's moon is believed to have been formed when Earth, in its infancy, was hit by an object of roughly this size. The comic assumes that another moon would form from another such impact, hypothesizes that life might evolve on that moon, and pretends that it's good news. Is is almost guaranteed that this would be so disruptive it would eliminate all life on earth either directly (via the heat and shock of the impact) or indirectly (via the loss of the oceans, much of the atmosphere, dust blocking the sun, or the entire surface of the earth being covered in magma) - however, there are extremophiles which could possibly survive the resulting conditions.
25,000 km	Bad news for whatever planet is about to get hit by Earth.	At this size, the "asteroid" is over twice as large as Earth itself (whose diameter is about 12,700 km) and would only not be a planet due to a lack of a "clear neighborhood". Therefore, the comic points out, it would be more accurate to describe the Earth as crashing into the "asteroid"/other planet, not the other way around. Since the Earth would be totally destroyed in such an event, it would be the planet it hits that feels the aftermath of the impact, and would thus be classed as very bad news for anyone living on that planet, insofar as there could be anybody to experience any aftermath. This was actually a plot point in the film Melancholia where it turns out that it is Earth that is colliding with the much bigger planet Melancholia, not the other way around. To be positioned well beyond the bottom end of this diagram, the film When Worlds Collide entails a collision between the Earth and a vastly larger star passing through the solar system, or vice-versa, with no noted ill-effects to that star, nor to a planet (in orbit around that star) to which the few survivors from Earth escape.