Thread by @SquigglyVolcano

THE VALENTINE’S DAY ASTEROID SCARE

Here’s everything you need to know about asteroid 2023 DW, in one thread.

#2023DW

I’m literally writing the book on planetary defense, so I know things about errant space rocks. And asteroid 2023 DW – with its small-but-not-zero chance of hitting Earth on Feb 14, 2046 is making headlines.

So: let's sort a few things out, shall we?

Asteroids get discovered all the time, somewhat “near” to Earth.

2023 DW was first spotted on February 26th of this year by an optical observatory in Chile’s Atacama Desert. They saw it as glint of light far from home. neo.ssa.esa.int/search-for-ast…

Although imperfect, as steroids can be varyingly reflective, using an asteroid’s ability to reflect sunlight gives astronomers a rough size estimate.

This one is about 40-50 meters long.

Mass, above all else, influences the impact energy of an asteroid—and that’s related to the cube of the radius. In other words, small increases in radius = big increases in mass = big jumps in impact energy.

2023 DW would have an impact energy equivalent to 4 million tons of TNT. So, a decent-size nuke blast then. If this hit Earth, it would likely blow up somewhere in the atmosphere.

An airburst over or close to a city would devastate it.

This sort of asteroid, and anything bigger, is of concern to all of us. The odds of one striking Earth are always low, but an asteroid 40-60m across hit a remote region of Siberia in 1908 and wiped out 2,000 square km of forest.

If this hit Earth at a slightly different time that day, it would have hit Moscow and changed world history.

After 62 observations spanning about a week, the odds of this asteroid hitting Earth are, per NASA’s calculations, one-in-560. That’s a 0.18% chance of impact on Valentine’s Day in 2046.

Sounds scary, right? cneos.jpl.nasa.gov/sentry/details…

Well, put it another way: there is a 99.82% chance that the asteroid will miss Earth.

To be fair, this is the only asteroid on NASA’s Sentry Risk List – which lists all asteroids with a non-zero probability of impacting Earth within the next 100 years – that ranks as a 1 on the Torino Scale.

I know what you’re thinking: what the hell is the Torino Scale?

It was developed partly a way of communicating to the public how anxious we should be about any near-Earth asteroids, or NEOs. Everything on the risk list is currently at zero, which means the likelihood of a collision is essentially zero, so we can chill. cneos.jpl.nasa.gov/sentry/torino_…

A 1 represents a routine discovery, in which impact odds are so low and, with further telescopic observations, are likely to drop in the coming days, weeks, or months.

(The scale is out of 10, with 10 being "most of us are fucked".)

2023 DW is the only asteroid with a value of 1 on this scale at present, but plenty of newly discovered asteroids just like it have risen on the scale before dropping to zero.

This is nothing new.

The European Space Agency has its own risk list, and 2023 DW currently sits at the top.

This sort of publicly accessible data demonstrates two things: 1) nobody is trying to hide anything from you, and 2) space agencies take the threat of asteroid impacts seriously.

The odds that an event like the Tunguska impact of 1908 could happen in the next few decades are very low. But such an impact will happen again, one day, with 100% certainty. When it does, it could hit a population center if we are especially unlucky.

Fortunately, along with the telescopes we currently have, two next-gen observatories are due to come online later this decade. Together, they will find 90% of asteroids 140m+--the sort that could devastate a city or entire country.

It is possible we could get ambushed; an asteroid capable of major devastation and mass casualties could hit Earth before we are able to deflect it, or even detect it. There are 15,000+ 140m-or-bigger asteroids out there near Earth yet to be found.

We could get snuck up on.

But we can almost entirely stop this problem if we can find them in time.

Yes, it’s possible that with more observations the odds of 2023 DW impacting Earth in 2046 stays the same (very low, but notable). The impact odds could even increase with more observations.

But the most likely outcome is that more observations will reduce orbital uncertainties, and 2023 DW will become less likely to hit Earth. We just have to wait and see.

But this asteroid eep-to-phew cycle happens all the time. It is relatively routine.

TL;DR: no need to panic. Asteroid 2023 DW is already very unlikely to hit Earth, and the odds are that more observations in the coming weeks will drop those odds to insignificant levels.

If this doesn’t happen, expect me to write an article about it. ;)

The moral of the story for now? It’s fab that asteroids like this are spotted ahead of time, but we don’t want to be lackadaisical about it and assume we’re safe from any major impacts. Get NEO Surveyor up there ASAFP.  solarsystem.nasa.gov/missions/neo-s…

End. (For now.)

HOW TO KILL AN ASTEROID: the true, madcap story of the scientists planning to save the world—coming soon.

cc: @esaoperations @AsteroidWatch @wwnorton

and cc @coreyspowell too, as we were just bantering about it :)