Ah, gotcha. Yeah, narrowing it down to solar system is the easy part, tracing how it wound it’s way through the solar system is the difficult part.
Of course, considering we included a frikkin’ map on the darn thing, they shouldn’t have much problem solving our cypher, if they plan on making a visit.
Tracing the path back to our star should be relatively easy for the next several hundred thousand years or longer, but let’s say it wanders into a solar system which harbors a race equal in intelligence and technology as us right now, and they spot the thing (which would be a long, dead, inert object).
They’d be able to determine with a high probability which star it came from, since in this area of the Milky Way, stars are so few and far between. But, they’d have as much trouble as we would in determining the size and number of orbiting bodies around that star; let alone try to reverse-trace its trajectory back to its origin.
There’d be a concentrated effort, I’m sure, in trying to unveil the planet of origin, but they’d probably never be able to resolve our planet directly (barring far more advanced tech), even using the Gold Record for reference, and would only probably be able to figure out the vaguest of properties of Earth from spectrography (high amounts of hydrogen and oxygen, etc.) and calculations from our gravitational influence as to our mass and vague planetary structure, then deduce what certain chemical properties might manifest and display (like liquid water) from our distance from our sun.
Of course from there, they might try listening in on a wide range of radio bands, but our sphere on that technology is very thin, less than a century, and will only get tighter and weaker from this point as we switch to digital/satellite forms of global broadcasting and communication.
Actually, we’re pretty darned close to having the technology to (barely) resolve an Earthlike planet around another star-- NASA’s proposed Terrestrial Planet Finder could do it. The only catch is that we don’t have the funding for it, but if a genuine and indisputable alien artifact were discovered, that funding would show up plenty quickly.
Too cool. I wasn’t aware of that tech. Thanks for pointing it out.
Ahhhhh… Got it. Thanks.
But while we are in the process of contributing to my education…
I don’t understand the slingshot effect.
I understand that as an object approaches a planet it will accelerate due to the effect of gravity. But on its departure from the planet, wouldn’t the same gravitational effect then slow it down again? Wouldn’t the net effect be a zero sum?
I acknowledge that my logic is inconsistent with observation, but I don’t understand why.
And the planet it came from should be about…here.
Huh. Nothing there but a Hyperspace Bypass.
IANAAstronomer, and I believe you are right about the “net” effect. But that must take into account two bodies. The small spacecraft gains energy (speed), and the large planet loses energy, but the planet’s loss is negligible. Energy is transferred from one object to the other, never lost.
Relative to the planet, the probe comes out at the same speed as it came in with. Relative to the Sun, though, the planet is moving, and so the spacecraft’s speed relative to the Sun changes.
For an analogy: A baseball player tosses a ball in the air in front of him, and then swings at it. Relative to the ballplayer, the ball starts off with close to zero speed, and ends up with a considerable speed. Relative to the bat, though, the ball leaves with about the same speed as it entered. The ballplayer in this analogy is the Sun, the bat is Jupiter, and the ball is Voyager.
Thanks for the reply, but I’m not clear in understanding your analogy.
The baseball bat, at time of impact, would transfer energy to the ball; thus causing it to accelerate. In this instance, there is only one transfer of energy.
However, in the case of Voyager approaching Jupiter, it seems to me that there would be two transfers of energy: the first occurs on the approach, the second on departure.
Assuming this accounts for all energy transfers, I think the net effect of this would be zero.
Or are you saying that that the energy balance is:
Incoming = gravitational pull + orbital motion of Jupiter
Outgoing = (-)gravitational pull
Net acceleration = incoming - outgoing
= orbital motion of Jupiter
In your analogy, are you saying that the impact with the bat is equivalent to the orbital motion of Jupiter?
The Gravitational Slingshot is not primarily about changing speed, it is about changing velocity (i.e a vector quantity with a direction and a speed).
As you approach your gravitational assist, the force from the gravity well is pretty well in line with your velocity, and you accelerate. As you get closer, the angle between your velocity and the gravitational force increases, and your velocity vector changes (as well as some speed gains). You keep your distance so your path/speed is close to the escape velocity vector. At about the closest approach (maximum speed with the velocity vector pointing close to your destination, you add velocity with your engines - this pushes you over escape velocity in the direction you want to go with a minimum of expended fuel. You may need to make some corrections later, but you have changed your velocity vector (speed and direction) with a minimum of input. It is not just about going faster.
You can do the same thing using earth orbit. Starting in a mostly circular orbit (constant speed, changing direction), you use small burns to make the orbit more eccentric (elliptical). This gives widely varying speeds. When the orbit is very eccentric you are going very fast (near escape velocity) at some point close to earth. A well timed thrust at that point pushes your probe past escape velocity, and you are away in your chosen direction.
Si
Ahhhhh…! I get it now.
Thanks for the explanation.
A baseball bat collision can also be divided into two parts, approach and departure. Have you ever seen extreme-slow-motion footage of a golf club hitting a ball? First the club compresses the ball, and then the ball uncompresses as it’s leaving the club.