# What will happen to space machines if Earth is destroyed?

What will happen to rovers, satellites, and probes if Earth is destroyed? What will their behaviour be like? How long will they keep functioning? Do they have any programmed actions to take in case of complete silence from Earth?

Most of them are held on a "short leash", i.e. they are too costly to give them too much autonomy. They get regularly commands from the NASA teams dealing with them.

If no signal is coming from the Earth, most of them will think, that there is a communication error with the Earth. So, they will try to contact us, until they can. They will possibly use their backup channels, too.

Anyways, they will execute their last commands.

They will do it until some battery depletion or malfunction doesn't end their career.

By "destroyed" I assume you mean that human civilization collapses. @peterh already answered that.

But what if you meant "destroyed" Death Star style by overcoming the Earth's significant gravitational binding energy to blow it apart? It would be very bad for anything near the Earth. And by "near" I mean within about 1 billion km.

We can estimate how much debris passes through a given orbital shell as the mass of the Earth distributed over the surface of an sphere. The sphere has the radius of the Earth + radius of the orbit's height.

$$\text{Area} = 4 \pi (\text{Earth radius} + \text{Orbital radius})^2$$ $$\text{Earth radius} = 6.371 x 10^6 m$$ $$\text{Mass of the Earth} = 6 x 10^{24} kg$$

I'm using meters because a square meter is something we can visualize easily. It's roughly the size of a coffee table.

Our highest satellites are in Geosynchronous orbit at 35,786 km or 41,637 km radius for a $$2.2 x 10^{16} m^2$$ area. Assuming the mass of the Earth is flung out equally in all directions, each square meter of orbital area at that distance has 300,000,000 kg of Earth pass through it. That's something like a fully loaded cargo ship passing through an area the size of a coffee table. Lower orbits undergo an even more intense bombardment. All artificial Earth satellites are destroyed.

The Moon orbits at about 380,000 km. That's about 10 times higher than Geosynchronous orbit. Area is the square of the radius, so 100 times the area meaning the face of the Moon gets 3,000,000 kg / m^2, plus whatever falls into its gravity well. Imagine the space shuttle slamming into a coffee table. Now imagine it happening to the entire face of the Moon.

These shuttles will slam into the Moon with at least its escape velocity, $$2.4km/s$$. Kinetic energy is $$\text{mass} \times \text{velocity}^2$$. Each shuttle delivers $$8 x 10^{12} \text{Joules}$$ of energy to every square meter of the face of the Moon. This is roughly the same as 2 kilotons of TNT per coffee table. The face of the Moon has $$4 x 10^{13}$$ coffee tables. That's $$3 x 10^{26}$$ Joules or roughly the equivalent of 700 dinosaur killer meters all at once. This will be bad for the Moon.

All of our artifacts on the Moon; rovers, flags, golf balls, lunar descent modules... with a few exceptions these have all landed on the near side of the moon. They will all be destroyed by falling shuttles. All except Ranger 4 and several Lunar Orbiters which crashed on the far side. And the little Yutu-2 rover which landed on the far side currently exploring the far side of the Moon. They will survive the initial impact, though they'll likely be destroyed by falling debris from the enormous impact.

If Yutu-2 somehow survives it will sit awaiting commands that will never come. It can charge using its solar panels, but eventually its radioisotope heater will become too weak to keep it warm through the 14 day lunar night and it will shut down for good. Its sister Yutu-1 survived for almost 3 years, but without Earth commands Yutu-2's life will likely be far shorter.

We currently have three lunar satellites operating, Lunar Reconnaissance Orbiter and 2 ARTEMIS satellites.

LRO is in a nearly circular very low polar orbit "skimming the Moon" at between 35 and 65km. It has a roughly 50/50 chance of being on the far side when the dense wave of space shuttles hits. However it completes an orbit every two hours so it might come around and slam into the debris field anyway.

The two ARTEMIS satellites are in highly eccentric orbits and will bare the full brunt of the shuttle attack.

Queqiao, part of the Chang'e 4 mission to the far side of the Moon, is in a halo orbit around the Earth-Moon L2 point beyond the far side of the Moon. It's purpose is to maintain contact between Earth and the far side, so it's halo orbit is larger than the radius of the Moon. This means it will not be shielded from the shuttle wave emanating from the destroyed Earth. Even if it were at L2 with the Moon directly between it and the Earth it's possible the Moon's gravity would bend significant amounts of debris passing close to the Moon towards L2. Even Queqiao is destroyed.

But wait, there's more! We have several satellites at the Sun-Earth Lagrangian points. DSCOVR and SOHO are at Sun-Earth L1. Gaia is at L2 and JWST will join it if it ever gets off the ground. These are about 1.5 million km out. At this point the gravitational influence of the Sun means the debris field will no longer be a simple expanding sphere, but instead stretched out. And it would be interesting to play with Universe Sandbox to watch how the field expands. But if it remained spherical these L1 and L2 satellites would receive about $$200,000 kg / m^2$$ or roughly a blue whale per coffee table. These 30 quintillion whales will each contemplate the meaning of their very short lives. They'll be destroyed.

If they managed to avoid destruction, with no more Earth there will be no more Sun-Earth Lagrangian points. They would likely continue on in solar orbits forever. Similarly any Near-Earth asteroids caught in the Sun-Earth L4 or L5 points will be released.

The Earth trailing Spitzer Space Telescope is about 150 million km away, as far away as the Sun. So are the pair of STEREO satellites. Assuming our debris sphere remained spherical (it wouldn't, but let's assume) they will receive about $$20 kg / m^2$$ at that distance. That's a medium sized dog per coffee table. They are destroyed.

At roughly 1 billion km, somewhere between Jupiter and Saturn, the debris sphere has dropped to 1 kg / m^2 or about a liter of soda per coffee table. This is still plenty to effectively destroy any artificial satellite, and it would be very bad for the Earth. Dawn, orbiting Ceres in the asteroid belt, would probably be rendered non-functional by the debris. Juno, currently in orbit around Jupiter, might be protected by Jupiter's immense size and gravitational field. Again, because of the Sun's gravity it won't remain a sphere, that's just to simplify the calculations.

The only man-made things which would survive would be our deep space probes speeding out of the solar system: Pioneer 10 & 11, Voyager 1 & 2, New Horizons.

It's an interesting way to appreciate just how massive the Earth is.

• Thanks for the detailed answer! Really interesting! – Tofig Hasanov Feb 15 '19 at 23:47