Asteroid

I'll try to keep this brief.

In one of my WIPs I decided that a massive asteroid (at least half the size of Earth, if not larger) would work better than nuclear weapons.

My question is: would it be possible for such a massive asteroid to move slowly so that it could be seen in a clear sky? Like a massive, moving moon? So, instead of rocketing through space and colliding with Earth in a matter of seconds or minutes, that it would be something that would take hours until finally colliding with Earth?

I still have to figure out how such a thing could go undetected until only days before its collision... Even if it weren't visible from simply looking up at the sky, surely the world governments and their space programs would detect such a thing. That might be a better question for Plot though.

 

Your goal is to completely pulverize Earth?

 

Yeah. Obviously such an event would annihilate all of Earth. It's the ticking time bomb of the story; in some sense, part of the ending is known more or less from the start. The story is about the ways that the characters deal with it.

EDIT: @Friedrich Kugelschreiber That wasn't meant to sound snarky. Tone lost over text, and all that.

 

An asteroid that size would completely strip the Earth of its crust and atmosphere, if not demolish Earth almost entirely. That's how the Moon formed - the early Earth collided with a Mars sized protoplanet (Mars is only a third the size of the Earth), which caused the crust to split off. Over millions of years, the debris re-coalesced into the Moon and the Earth.

The asteroid that wiped out the dinosaurs was "only" 6km in size.

There's no way an object that size would go unnoticed. But that hardly matters - there's nothing we could do about an object that size with current technology.

 

Right!

I just want to know if it's possible for an asteroid to move and hit the Earth that "slowly", to the point that from the time it's seen in the sky and the point that it hits, half-a-day-or-so could transpire.

To use your example, if another Mars-sized space body were to collide with Earth. I want to know if it's reasonable or realistic if it could be moving that slowly.

I guess the problem is that if it were, the space programs would have known about it for a LONG time, and probably could've done some basic (for them) math to figure out its collision course years ahead of time.

 

I think the gravity field would begin to do damage long before collision is immanent. Well, maybe not 'long before', but definitely before. It would probably first be noticed by weird tidal effects, and then I have no idea, people who know more would be able to fill that in. Probably something similar to really powerful tidal pull, but affecting more than just water, beginning to effect other materials, lifting them upwards strongly. Then earthquakes. Plus I'm seeing a scenario now where it 'hooks' the earth and they begin to go into a dual orbit. Of course by that time probably all life is extinguished, so not as much fun as I would like.

 

In terms of moving slowly - I think it's unlikely. A body that size would have to have been ejected from another star system due to a capture of another star into the system, which would have imparted significant momentum to it. For reference, the escape velocity of the Solar System is 42km/s, but a body ejected from another star system would be moving significantly faster than that with respect to the Earth - and it would accelerate as it falls in towards the Sun.

At that speed, it would take 4 hours to hit the Earth from a distance twice that of the Moon.

HOWEVER...

If the object was travelling along a similar trajectory to the Earth's orbit (i.e. moving towards the Earth from "behind" its orbit path), it's velocity relative to the Earth would be much slower. It is hypothesised that Theia (the protoplanet that collided with the Earth) could have struck at a speed of around 4km/s, at an angle of 45 degrees. At that speed, it would have taken 3 days if measuring from 4 times the distance of the Moon, at which distance a back-of-a-fag-packet calculation tells me it would be about a third the size of a full Moom.

Of course, I could be talking total rubbish here. I'm basing this on a highly amateur understanding of astrophysics and astronomy. Take it with a pinch of salt.

 

What a chaotic question! Got me searching all over and daring to try estimating things I never thought about estimating. I thought I could (of course I did at 5 o clock in the morning, duh!) but... it's too complicated. Apart from figuring out its visibility from earth (at which distance it'll become visible to the naked eye) you also have to calculate its' growing acceleration (the greater the mass the greater the acceleration) which is... tough shit. The numbers are so huge they make me sneeze.

https://www.space.com/asteroid-1998-or2-earth-flyby-no-danger.html

Can't do the math, but I think this article helps to speculate along the lines. It also has NASA scientists explain how they keep track of asteroids and "just-in-case" scenarios.

Why don't you try posting your question on NASA's forum? Not meaning to demean our awesome, intellectual bunch but they're more relevant I think. Some helpful folk around there.

 

Is there an asteroid that big that has been found?
Mars is about as close to the size you are talking about.
With current tech, we would see something that big
coming well in advance. Though we have no way of
really stopping it, so still screwed with a timer of
when it hits, not if.

Ceres is considered a planetoid, but much smaller than what you are
talking in terms of size and mass.

So yeah, you would be better off using a moon thrown out of orbit
from another planet, or simply Mars, since they will be big enough
and have the mass required to totally obliterate Earth, while being
impossible to stop with current tech.

 

There is a problem with early detection of asteroids in Near Earth Objects (NEOs). Telescopes only work at night so they can only detect asteroids that are further away from the sun than the Earth is. If the asteroid has a closer orbit, it would only appear in the sky during the day. These orbits can be chaotic.

The relative speed is measured in Km/s and the distances are astronomical (literally). If it was as far away as the moon (384,400 km) and travelling at 10 km/s it would take 10 hours to reach Earth.

https://theskylive.com/near-earth-objects

 

That's not an asteroid. That's a rogue planet. You are talking about an astronomical body of a size comparable to Mars.

So, yeah, that's a bit of an understatement. Even if you mean to wipe out absolutely everything on Earth, that's definitely overkill.

I'm not an astrophysicist or anything, space stuff isn't really my area of expertise, but I think the gravity of a body that large entering the solar system might actually disturb the orbits of the other planets and trans-Neptunian objects, which would alert astronomers before it is even directly observed. Generally I would assume that the larger/more massive your killer space rock is, the less likely it is to sneak up on us.

 

The question is, why does the impactor have to be so big? You'd only an asteroid about 10-20km in size to wipe out all life on Earth. 100km if you want to be absolutely sure.

 

Then a 100km asteroid shall suffice!

Thank you for all the comments, everyone. The "problem" still remains that if the major space programs of the world are long aware of this impending disaster (say, several years, or something like that), then it brings into question how humanity would react.

Who would try to cover it up, for the sake of making their citizens feel safe? Would their be disagreements on the calculations and whether or not it would collide with Earth? How would the masses react? The religious?

I assume there would be some desperate attempt to devise a means of redirecting the asteroid. I think there's an old cheesy movie where this is the plot; they land on the moving asteroid and detonate a nuke on it or something.

 

^ Armageddon.

 

Until a couple of years ago I always thought she said "Nuke the entire site for morbid." I was very confused, but decided it must be some phrase I wasn't aware of, meaning to leave everything dead. Finally while watching it with a friend I asked him if he had ever heard that term and, after laughing at me for a long time he told me what she really said. Forehead slap.

 

"Simple math."

lol

 

You could have the object on a 'near miss' trajectory to Earth so although the scientific community knows about it they don't think its a problem. Then the US President, eager for some positive press in an election year, decides it's a danger to humanity and it's his duty to save the world. A rocket with a nuclear warhead is then sent to destroy the offending object (against the advice of scientists). Unfortunately, the blast only damages the asteroid and slightly alters its trajectory, sending it on an actual collision-course with Earth. The president is then faced with the most pressing issue of his career: 'How am I going to win the election now?'

 

Project Icarus calculated that, to deflect asteroid 1566 Icarus from an Earth impact trajectory would required 6 Saturn V rockets (the largest rocket ever built), each carrying a 100 megaton nuclear warhead (equal to the Tsar Bomba, the largest nuclear bomb ever built).

And Icarus is only 1.4km in diameter.

 

So it's probably possible, but would require an immense effort, and likely a collective one among all sufficiently developed nations.

Lots for me to think about from this thread.

I'm curious to know if a solar winds would be sufficient to take such an asteroid from a very near-miss course and put it on a collision course. Not sure if anybody might have the answer for that. It might be a means of overcoming some of these practical issues. An unexpected series of solar flares or something that leaves only a couple weeks to prepare, as all space programs and their respective governments had been on their laurels thinking that the asteroid would narrowly miss Earth.

I will probably go onto the NASA forums or whatever somebody suggested and ask these questions there as well. Just figured I might as well ask here to get feedback from a more storytelling-centric perspective.

There's still a bit we don't know about space and what not, but I don't want to rely on modern magic. I'd like to try and find a more readily believable means of doing this, such as somewhat unpredictable but very real solar flares and winds.

@Aled James Taylor The idea of humanity trying to ensure its survival with a pre-emptive measure, backfiring and dooming themselves is really clever. I'll keep that option in mind.

 

Well, here's one possibility.

An asteroid of this size is on course to Jupiter. It poses no threat whatsoever to the Earth.

Unfortunately, it is captured by Jupiter. The transfer of momentum causes one of Jupiter's moons, let's say Thebe, which is of comparable size, to be ejected from the Jupiter system and sent on a collision course with the Earth.

I haven't calculated how long it would take for a body to reach Earth from Jupiter. In a straight line, it's 390 million km out. If you want to be less ambitious, you could postulate the same thing with Mars. The largest moon of Mars is Phobos, which is about 20km in diameter. At closest approach, Mars is 35 million km away. A body ejected from Mars at about 30km/s would take about 2 weeks to reach the Earth. A 20km asteroid would be comparable to the Cretaceous impactor, and enough to wipe out a substantial proportion of life on Earth.

 

Is that possible?

 

Yes, that's how bodies are ejected from systems. When one body is captured, it transfers momentum to another body, which in turn, either moves it into a higher orbit, or ejects it from the system completely.