Are enormous metal space whales possible?

Question

Is the following scenario reasonable?

Enormous metal whales, which fly through space eating planets and nebulae by:

1. Churning with blender (like mastication), then
2. Melting them down in a furnace (like a stomach), followed by
3. Fractional distillation (like intestines), and finally
4. Using the resources to sustain itself.

It would have senses analogous to our own:

1. Smell/taste: Detect traces of useful material
2. Touch: Feel pressure, heat etc.
3. Sight: See stars and other celestial bodies using solar panel-like rods and cones
4. Hearing: Hear when in gaseous regions of space.

(See also my answer here.)

EDIT: Reading the answers and comments, and other questions, I have realised that such a large celestial body would end up with its own atmosphere, given that it would swallow planets, would have an extremely hot core and would probably rotate.

So it would need to regulate its temperature, fight mutation of its own "cells" and maintain what it can of its structure. It will move very slowly, on the cosmological scale, but live for huge periods of time. (Maybe this should be split but) Would it be better for the whale to have developed from a planet or large asteroid, in the sense that the planet now serves as the body of the organism. Like this suggestion:

Only, the organism would have penetrated the crust of the planet. So that holes in the surface act like pores, and coolant/blood would be needed to transfer heat away from vulnerable structures.

Answer 1

There's nothing particularly unreasonable about that one. It's similar in nature to Gregory Benford's Leviathan, just implemented using metalics instead of organics.

If the reasonableness of this creature is essential to your book, I'd consider exploring how it might have come about. Most large space creatures, such as the Leviathan, live inside complex ecosystems, not a desolate environment full of planetary popcorn. The part of your idea which gives me the most pause is wondering where the rest of this ecosystem went. How did something that big and powerful develop? As a brainstorming solution, if a society went entirely virtual, and lost stability of their planet, they might have developed the whale as a platform for their virtual realities. Or perhaps there used to be an ecosystem, but it collapsed, and the whales are all that are left after adapting to siphoning their needs from planetary cores.

Answer 2

Without :waves hands: sci-fi technology your whales aren't possible. At least if - by planet - you mean Eart-like or bigger stellar objects.

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Digesting a planet would mean your whale would have to swallow it. Now, when you try to swallow an object with the rest mass of a planet, you have to deal with its gravity well, which means your structure would have to be strong enough to support a construction which is as huge as a planet (since it actually contains a planet) in normal Earth gravity. That is not possible even with a super-light and super-strong materials like panels made of carbon nanofibres. So if you don't want your whale to collapse into itself, you have to balance gravity or use some "exotic material" like forcefields or such.

To balance gravity you can:

• You can balance gravity with centrifugal force, but then your whale should rotate around its longitudinal axis, and has to do it really fast - which makes it really not "whalelike".
• You can do some handwaving™ and say it has "anti-gravity generators", but it's not even sci-fi anymore. It is just plain fiction and in that case why would you even need technobable?

To support your structure you can:

• You can use counterweights to nil out structural load, but that means, your whale has to have a weight of multiple planets, which barely makes it capable of interstellar travel.
• You can use a self-renewing structure (possibly nanotechnology) which constantly collapses but fixes itself.
• You might use (electro)magnetic forces to balance out gravity, but you need an extremely, surreally, mindblowingly lot of power to do that. (I mean like a dwarfstar's entire power output.)
• You again can do some handwawing™ and say it is supported by "forcefields"/"meson structures"/"negative singularity" , but then - again it's not even sci-fi anymore. It is just plain fiction and in that case why would you even need technobable?

So my short answer is no:

A whale-like metallyic planet-eating creature is not possible. (Either it can't be whale-like or it can't be metallic.)

Answer 3

I think that this is a reasonable creation. Perhaps it was created by aliens to harvest desolate star systems for materials, using the sun and planets to repair itself and then storing excess for future use. Then the creature malfunctioned, or the star the aliens lived near went supernova and they all died.

Answer 4

Let's talk scale

Creating a creature that eats planets for breakfast requires some interesting considerations on scale. The Earth ($\oplus$) is heavy: $M_\oplus = 5.97 \times 10^{24}\,\text{kg}$. The Earth is one of the lighter planets out there, yet it is massive enough that gravity pulled it into an almost perfectly spherical shape, creating pressures and temperatures in the inner core are comparable to the photosphere of the sun $(5\,777\,\text{K})$.

Why is this important? Put quite simply, anything that eats a planet has to be on roughly the same scale as a planet (probably no less than a tenth of the mass). I believe it could work, but it will be difficult! I see two main options:

1. Eat smaller asteroids / portions of planets

If you don't want your whale to be planet-sized, you can have it consume much smaller asteroids and comets instead of planets, or if you don't mind bending the whale analogy a bit, you can have your whale pulverize portions of a planet's crust from orbit with powerful lasers, missiles, etc., and then "swim" through the atmosphere scoop up the small dust and rock particles from the atmosphere (this is very similar to how whales actually eat, more or less by swimming along with their mouth open).

2. You simply make one gigantic whale!

The above heading carries the obvious risk of stating the obvious. However, I can help with the details:

Your whale needs something to prevent it from collapsing under its own gravity. At planetary masses, ordinary steel structures won't be sufficient. However, ironically, the bigger you build it (while keeping the mass the same), the weaker the gravity on the surface. The more hollow it is, and the rounder you can make it, the better. Gravity is strongest in the middle of the mass. If you can then create equivalent outward pressure that won't destroy the whale, it just might work!

Planetary Approach

If you do go with a planetary-scale whale, how it approaches planets might be of some interest to your story. It will be massive enough that its own gravity will pull the planet towards it (and the planet will pull the whale, as well). As they get nearer and nearer, without any added propulsion, they will accelerate to rather high speeds. If they collide after an uncontrolled approach, the energy released would be tremendous (and probably too much for your whale to survive, assuming you want plausible science).

So what do you do?

Caution: Fiction ahead!

I would give your whale some kind of strong propulsion system that can accelerate your whale to some fraction of the speed of light. Conventional propulsion would require enormous amounts of energy, and this energy would likely vaporize the target planet. Thus, this might be where you ask your readers to suspend their disbelief while you add a bit of sci-fi magic to your story, giving your whale some kind of fictional propulsion system that bends (or, rather, flattens) the surrounding space or uses some kind of anti-gravity to allow the whale to approach and eat the planet as slowly and dramatically as you like.