3049: Incoming Asteroid

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Incoming Asteroid

Title text: The bottom ones are also potentially bad news for any other planets in our solar system that have been counting on Earth having a stable orbit.

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.

List of sizes and consequences

Sizes are approximate.

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.

Transcript

[A log chart is shown with several labels. Above it there is header:]

An asteroid is headed straight for Earth! That's...

[A log scale of lengths is shown on the left with a label at the top with an arrow pointing to the first number from the top shown next to the scale.]

Asteroid size

[The log scale starts with only 7 smaller ticks before the first large tick, and then there are the regular 9 small ticks in log fashion between each of the ten larger ticks, and then only 8 small ticks beneath the last large tick. Each of the 10 larger tick is labeled with a length size. With the first at the top being the one with an arrow pointing at it:]

1 cm

10 cm

1 meter

10 meters

100 meters

1 km

10 km

100 km

1,000 km

10,000 km

[Around but not precisely at each labeled size there are ten descriptions of what should follow the header given such a size asteroid was about to hit Earth:]

[1 cm:] ...Good news! Meteors are pretty!

[30 cm:] ...Great news! You might see a fireball!

[3 m:] ...Ok news, unless you have expensive windows or are very unlucky.

[60 m:] ...Bad news, especially if you live near the city it's aimed at.

[600 m:]...Bad news, especially if you live on the continent it's aimed at.

[9 km:] ...Bad news for your species.

[50 km:] ...Bad news for your phylum.

[300 km:] ...Bad news for your biosphere.

[2,000 km:] ...Good news for any life that might someday evolve on Earth's new moon.

[25,000 km:] ...Bad news for whatever planet is about to get hit by Earth.

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Discussion

Asteroids are surprisingly destructive even at small sizes - I remember reading somewhere that the Armageddon movie asteroid was supposed to be "the size of Arlington, Texas", but that it sounded too small so they changed it to "the size of Texas" which is a drastic size increase and also proportionally far more deadly. For scale, Arlington is 250 square km and Texas is 700 000 square km. The Chixulub asteroid that wiped out the dinosaurs was between 10 and 15 km across. If it was a perfect circle, it would have an area of between 79 and 176 sq km. Arlington would be 18 km across, still within "species" range, and Texas would be 944 km across, clearly in "new moon" territory. But it _sounds_ much cooler! Zakator (talk) 22:32, 10 February 2025 (UTC)

And that's for asteroids with normal speed (for asteroid, which is still kinda fast). The level of danger asteroid means is proportional to kinetic energy, meaning proportional to mass and SQUARE of speed, so if it's faster, it gets to extinction level even when small ... -- Hkmaly (talk) 23:29, 10 February 2025 (UTC)

"for asteroids with normal speed" - which is generally orbital velocity. If much faster, it would have left the solar system by now. If much slower, it has fallen into the Sun already. All objects (even Teslas) at a given distance soon have similar velocities. --PRR (talk) 00:04, 11 February 2025 (UTC)

It could be going at a speed (similar to Earth, give or take, for the sake of being on an Earth-incident orbit) and yet have such different effects. If basically following the Earth (or leading it), it'll be relatively gentle, at least before you start considering the Earth's (and the asteroid's, in the event it's significantly large) gravity well pulling it. Well, 'gentle' in comparison to one doing the 'same speed' but in the anti-orbit, for a full head-on impact. Course, that's why we need to think of velocities, and in particular the relative ones. 172.71.241.37 01:31, 11 February 2025 (UTC)

Considering just two-body physics... Escape speed for the Sun at the distance of Earth's orbit is 42 km/s, so that's the upper limit anything is likely to be going (otherwise it's just got one shot at us). That would be something falling towards the Sun from a very large distance. If the asteroid is moving in the opposite direction as Earth, that gets added to Earth's orbital speed of 30 km/s, for a total of 72 km/s. On the other hand, Earth has an escape speed of 11 km/s at the surface, so that's the lower bound for an impact. A 6.5x factor on speed is about a 40x factor on impact energy. Which, I'm not sure exactly how that would scale devastation, but ... I'll take the low end for anything big, thanks. 172.70.111.22 14:18, 11 February 2025 (UTC)

The upper limit is actually someting in the range of 500-600 km/s - for an interstellar object... That'd be an astronomically huge bad luck! Or should we consider an intergalactic rogue planet... -- Malgond (talk) 23:28, 11 February 2025 (UTC)

ORRRR... we could go for getting crushed between two rogue planets moving at relativistic speeds in opposite directions! :-) BunsenH (talk) 01:33, 12 February 2025 (UTC)

The 1m danger makes me think of the meteor impact that was caught on a home security camera last July in Prince Edward Island. But the Sky & Telescope article https://skyandtelescope.org/astronomy-news/hear-the-first-ever-recording-of-a-meteorite-slamming-into-the-ground/ says that it would have been only a 6-7 cm across. Barmar (talk) 00:42, 11 February 2025 (UTC)

The sizes in the explanation are out of sync with the image. Has Randall updated it, or may it be location dependent? ~~Guest~~ 07:12, 11 February 2025 (UTC)

I saw the comic before any explanation was put up and it was the same as it is now, all exactly powers of 10. But the labels aren't exactly at those spots, so people are probably estimating the exact point where the labels are at, though my interpretation would be that Randall meant for the labels to be attached to ranges rather than points. Tharkon (talk) 11:45, 11 February 2025 (UTC)

Same here, all powers of 10. I don't think it makes any sense at all to guess at where on the axis the labels are meant to be when the labels themselves give an explicit number. The labels should probably be the ranges, eg "1cm to 10cm", "10cm to 1m" and so on.Mazz0 (talk) 14:00, 11 February 2025 (UTC)

There are small markers between the labeled spots, so it's not unreasonable to estimate which marker the ellipsis points to. Barmar (talk) 14:41, 11 February 2025 (UTC)

"Good news everyone! We were supposed to make a delivery to the planet Tweenis 12 but it's been completely destroyed!" 162.158.94.203 11:24, 11 February 2025 (UTC)

It's not the first comic comparing our reaction to different scales of cosmic events, even though the asteroid "happiness level" does not peak like the supernova chart: https://xkcd.com/2878/ 172.69.195.172 (talk) 21:14, 11 February 2025 (please sign your comments with ~~~~)

Indeed. This one peaks twice, if taken at face value. ;) 172.71.241.145 21:32, 11 February 2025 (UTC)

I'd noted that technically, when it comes to "asteroid collides with Earth" vs. "Earth collides with asteroid", neither is correct. In a centre-of-mass reference frame, the two objects collide. This was removed as "pedantry", but it seems appropriate to me. Thoughts? BunsenH (talk) 01:29, 12 February 2025 (UTC)

I would say if a smaller asteroid hit Earth then yes it collides with Earth. If two similar planet sized object hit each other, then I would say they collided with each other, and if Earth hit Jupiter I would say Earth collided with Jupiter. This may not be physically correct, but it is how language and meaning works. So I would say it was correctly removed. --Kynde (talk) 11:44, 12 February 2025 (UTC)

Yet the logic is reversed when talking about vehicles on Earth. You would say "the car collided with the bicycle" and "the train collided with the car" (or the car got hit by the train). "{Bigger object} collided with {smaller object}" in this case. --StapleFreeBatteries (talk) 23:26, 12 February 2025 (UTC)

Annoyingly, the standard phrase tends to be "the bike was in collision with a car", with the implication of perhaps equal fault, if not switched round entirely. Yes, a cyclist can be the one who "hits the blameless car", or pedestrian steps into the side of the passing cyclist (or car, bus, lorry, etc, potentially), but it's more often the other way round, and the balance of sympathies (regardless of who most erred, to result in the incident) should probably be considered by who is most damaged (trickier in foot vs bike incident, one is initially struck by a lump of metal with spinning bits and various hard protusions, the other may then be struck by(/strikes) the ground). 172.71.241.37 00:09, 13 February 2025 (UTC)

Seemes there is little change between a 10cm and 1m astroid. The scale skips the 100cm step. It should be : 1cm, 10, 100, 1m 172.68.243.66 12:09, 13 February 2025 (UTC)

That is because 100 cm = 1 m. No step is skipped 172.70.126.169 (talk) 15:22, 13 February 2025 (please sign your comments with ~~~~)

Surely the other planet closest to Earth, on average, is Mercury? 172.69.23.9 23:13, 13 February 2025 (UTC)

Without crunching the numbers myself, it may depend upon which 'average' you mean. There's aparently fairly definite factual statements, out there, like "Venus'[s] average distance to Earth as around 25.7 million miles (41.4 million km), compared with 57 million miles (91.7 million km) for Mercury and 48.6 million miles (78.3 million km) for Mars", but also "Mercury is the nearest planet to Earth — and to every other planet in the solar system". I'm going to have to actually look at both claims, work out what's going on there (who is being wrong, or why they're right but for different reasons). 172.71.241.145 02:03, 14 February 2025 (UTC)

...well, seems obvious that the first one didn't mean "average (i.e. mean)", but probably "minimum". My own actual quick-and-dirty calculation (median Earth-Sun and median Planet-Sun distances, arrayed uniformly around a conjunction-to-conjunction circle for positional differences smeared free of any particular perihelion/aphelion bias, then arithmetically averaged, also without regard for any Keplerian sweeping-speeds - which should satisfactorarily smooth out the actual details unless there's a particular resonance aligning eliptic axes consistently) suggests Earth-Mercury is averaged at 1.05ish AU ('median'-based ranges from 0.55 to 1.45), Earth-Venus is 1.14ish (ranging 0.275 to 1.725), Earth-Mars 1.69ish (0.525 to 2.525), Jupiter: 5.25, Saturn: 9.62, Uranus: 19.21, Neptune: 30.21, in case I've made any stupid errors (not just approximations).

But it already had occured to me that Mercury would be the "average closest planet" to every other planet (given no particularly extreme ellipses, and orbital resonances to keep them perpetually aligned). My mental exercise was to take a basic concentrjc map of orbits, use dividers to measure any given starting planet's distance from the Sun, and then sweep a circle of that radius around the planet. Where that line crosses every other inferior orbit (and any superior orbit no more than twice the size of the starting planet), it cuts those orbits into a "nearer than the Sun" arc and a "further than the Sun" arc (for r*[n>2] orbits, it's 'all' further than the Sun), with the ratio of nearer:further lengths generally being less arc vs. more arc, tending towards 1:1 only for the smallest orbits (r=lim->0). So the larger the other planet's orbit, the larger this average would be, above the chosen planet's own solar-distance, and Mercury (in the absence of anything closer to the Sun) would end up with the least additional amount above the constant distance to the Sun itself.

Which I found interesting to work out, so maybe will be interesting for others, but didn't entirely trust myself until I hacked up the apparent emperical evidence, too. 172.70.160.182 03:17, 14 February 2025 (UTC)
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