Will the Earth be hit by a large space rock? Of course - the question is when

Update 21st February:

NASA has changed the chance of the impact on Earth of 2024 YR4 to 0.28% after further observations. This will likely change as further investigations and observations are carried out. 

There's also now a 1% chance it could also hit the Moon!

Check out more at the NASA Blog here - 

https://blogs.nasa.gov/planetarydefense/

Cheers,

Earl White - BINTEL

There's been lot of media coverage over the last few weeks about an asteroid called 2024 YR4.

This is a hunk of space rock currently orbiting the Sun and the path it’s on means there’s a non-zero chance of it hitting the Earth on the 22nd of December 2032. 

It’s estimated it’s between 40m and 100m in size. (You’ll see a lot of articles and posts with varying sizes. We still don’t have enough observations to make a more accurate estimate.) This is the not in the same class of object that wiped out the non-avian dinosaurs, but it would cause major damage across a large area if it were to hit a populated area. 

Will it hit Earth?

First of all - 

Hand's up anyone who hasn't played Lotto? I won't remind you about the enormity of just how difficult it is to win a first or even second division. Nice to happen, but pretty much impossible.

On the other hand, it's not uncommon for to win a consolation prize in the lowest division and the chance of this happening are around the same as 2024 YR4 impacting Earth in a few year's time.

NOT an image of 2024 YR4  - this is the asteroid Bennu but 2024 YR no doubt looks similar. Image via NASA

How was 2024 YR4 found?

It was reported to the minor planet centre on the 27th of December 2024 and found by the Asteroid Terrestrial-impact Last Alert System or ATLAS based in Chile. We talked a little while ago about ATLAS in this BINTEL article here. While this system is mainly designed to do exactly this - find objects that might pose a threat to the Earth - it’s also very good at finding comets and that’s why so many comets in discovered in recent years have ATLAS in their name.

ATLAS scans the skies and looks for any unknown objects that move against their background stars from night to night. Anything that is not in the database of known objects is reported for further investigation. There's a lot of bodies that have been discovered in the Solar System. If you're playing pub trivia and one of the questions is "roughly how many near Earth space objects have been identified?" The answer is close to 38,000!

How dangerous is it?

2024 YR4 has been classified as an Apollo class asteroid. This is because its orbit crosses Earth's own orbit.  We measure just how dangerous near Earth objects are by the Torino Scale. This goes from 0-10, with 0 being nothing at all to worry about and 10 being certain disaster for humanity.  There's a BINTEL article from a couple of years ago when there was an object at one on the scale. You can always check out the Minor Planet Center here.

Currently, 2024 YR4 is three on the Torino scale. (There was an object that briefly reached four some years ago. More detailed refinements observations of its orbit showed it to be harmless.)

Torino ratings of two to four are classed as "Meriting attention by astronomers".

An illustration showing the progress of 2024Y4 through the inner Solar System. Image via NASA

We know where it is, how big it is and what direction it’s moving in. Why can’t we get a good prediction now? 

The issue is that we don’t know these things with enough accuracy to make a more detailed prediction.

For example, scientists estimate the size of an object like this by the amount of light they reflect. As they learn about the composition of 2024 YR4 they’ll be able to calculate its size and path with more accuracy. Currently its moving away from Earth making observations more difficult.

The James Webb Space Telescope (JWST) will make detailed observations of 2024 YR4 in March and May and from these we'll learn more about its composition and size. 

We will be closer to the asteroid during an encounter in 2028 (with zero chance of collision during then.) This will also an ideal time to learn more about 2024 YR4.

What’s the chance of it impacting Earth and why did this appear to increase over the last day or so?

As of today, the chance is 1 in 43 or about 2.3%. This increased from the estimated 1.8% last week due to refinements in the predication around its orbit. 

What’s happens if in a couple of years the chance of impact become very likely?

This could happen. The Earth has been struck by several major impacts in recent decades. Probably the most famous is the Tunguska event in June 1908 where a rocky asteroid exploded over a part of Russia releasing energy similar to an atomic explosion of up to 50 megatons. The area is so remote and difficult to access, it was some years before it was investigated by scientists.

It was also a near miss in space terms. Arriving a few hours later the asteroid might have wiped out London, Paris or other European centres and possibly change the history of the 20th century. 

Aftermath of the Tunguska event. Image by Leonid Kulik

This is the largest asteroid impact in recorded human history, although impact craters which were caused by larger bodies are scattered right across the surface of the Earth.

Many of our readers would remember the Chelyabinsk event in February 2013 where an asteroid exploded over Chelyabinsk in Russia, injuring some 1,500 people and damaging over 3,000 building. There was some amazing footage of this, much of it caught on the dash cams of Russian commuters!

Russian dashcam captures the Chelyabinsk event

Rocky bodies often explode as they reach Earth. Heating during the brief journey through our atmosphere causes enormous internal strains that can cause them shatter.

It's worth noting what exploded over Chelyabinsk was not picked up by any detection system in place at the time prior to it arriving at Earth.

If - and it’s still a big IF at this stage - it was determined that 2024 YR4 posed a threat to Earth then various Planetary Defense measures would swing into action depending on the actual threat.

The most obvious would be to simply send a fleet of rockets up to meet 2024 YR4 and blow it up using Hydrogen bombs. This might be problematic and split, with asteroid into large chunks still heading towards Earth. (Hey, we’ve all seen the movies!) A more realistic approach might be to either attach some kind of thrusters to one side of the asteroid, slam spacecraft into it or even detonate devices to nudge it off the collision course with Earth. 

While this does all sound like a sci-fi movie, NASA has carried out tests during its DART Mission where it slammed a spacecraft into an asteroid to change its course.  Read more here. 

While the chance of 2024 YR4 impacting Earth remain low, it's still considered dangerous enough to activate the first step in NASA's planetary defence system.

Will the chance of impact go up or down?

Asteroids on orbits that cross Earth's own orbit are common. There have been numerous objects that were a worry, but they have always been shown to be harmless as more data about them is collected.  While 2024 YR4 might cause damage to Earth, it's a pretty sure bet that as we learn more about it the chances of an event happening will be more like winning the big on Lotto and quite likely beyond that. 

It's unlikely to cause any damage on Earth but it's a reminder that the Solar System is a busy and crowded neighbourhood. While the chances of any particular asteroid hitting us is low, when one does is not a matter of if, but when.

Cheers,

Earl White

BINTEL

7th February 2024