But we DON’T need to crunch millions of images taken years apart. We’d only need to do that if we want to find Asteroid or Kuiper Belt objects in the new solar system, assuming the new solar system has an Asteroid or Kuiper Belt.
The planets we’re interested in are bright, move very fast, and are all located in a very small space. Yeah, it won’t be the case that we pop out of FTL right near a planet…but if you’re near the orbit of Mars, finding Earth and Venus is easy, if you’re near the orbit of Earth finding Venus and Mars is easy…and so would finding Earth. It might take hours or days to find inner planets…but it’s not going to take years or even months. And it could concievably take MINUTES. Pop out, search for the brightest object with bare eyes, train your scope on it, and see if it has a disk. Probably you won’t get that lucky, the planets could be on the other side of the star, but it wouldn’t be out of the question to find one that quickly…especially if you knew where you were going and what stars were likely to be very bright and what changes in the constellations to expect. If you were headed for Alpha Centauri most of the constellations would be nearly the same, only the very closest stars like Sirius and Procyon (not to mention Sol and Alpha Centauri themselves) would change position.
All this is assuming you know what you’re doing. If you’re a barbarian living on a generation ship where civilization has collapsed it might be quite a bit harder.
What do you mean? Jupiter is the 2nd brightest “star” in the sky. (And the 1st is Venus.)
You don’t need any computing power. All you have to do is place two star-field photos on the table (of the same part of the sky, taken at different times or locations), and find bright dots that don’t appear in the same location. Or if you want to get more fancy, use a blink comparator.
And if I were only interested in Earth-sized planets, I wouldn’t even use a camera. I’d just point a telescope at the brightest “stars” in the sky. A $200 amateur telescope would do. If it looks like a tiny point, it’s a star. If it looks like a disk, it’s a planet. Of course I’d want to do this from at least 2 positions because a planet may be hiding behind the glare of the “sun”. And determining the planet’s orbit requires several more observations with more precision.
The Sun rotates every 25 days or so. You could use star-spot tracking I guess to come up with a rough idea of how fast and in what orientation the star is rotating.
The eco-sphere can basically be predetermined since you already know about the star you’re heading to. It’s simply the region where liquid water could exist. For our system you could argue that it extends to Jupiter (~11 AU).
Not long to find the planets either. If you think about it, humans determined the orbital periods of the major Jovian moons with some lenses and the human eye. Imagine what a 20” reflector with CCD camera could do.
Wouldn’t just plain old radar work, too? If you’ve got enough power to travel FTL, you’ve got enough juice to run military-grade radar, which SETI tells me has enough range to be detectable from half a galaxy away. Would it be possible to jump in to a spot perpendicular to the plane of the ecliptic and scan with radar for a few hours until the returns have time to get back to you?
Think about how bright Venus is. People don’t need help to find Venus, they often are sitting around near sunset and think, “Whoah, what IS that bright light up there? Is it a UFO? An airplane?”
Venus has a higher albedo than Earth and is closer to the sun, so Earth wouldn’t be as bright from Venus as Venus is from Earth…but Earth would probably be the brightest object in the Venus sky, if only there weren’t those ACID CLOUDS with the POISON and the LEAD MELTING and the HEY LADY…
Glide to a graceful stop at about the same distance from the star as Earth.
Broadcast on all frequencies: “This is Optimax. This system has been claimed for the greater glory of the Empire. Please send representatives of your government to us so that we can properly indoctrinate you in your place in the New Order.”
Watch for ships. Go where they came from. Claim to know nothing about that Optimax fellow.
Not long at all. A spectrograph can measure the Doppler shift of spectral lines, which means you know if the source is moving towards you or away from you. Scan across the star’s limb and find the spot that’s moving fastest towards (or away from) you; that’ll be the equator. It’ll only take a few minutes with the right equipment.
The size of the eco-sphere depends on the star’s energy output alone; for that you just need the spectral type (color) of the star. You’ll know that as soon as you get there, if not before.
With my backyard telescope, I could probably check all the 1st magnitude stars in the sky in 10 minutes or so.
Not very well. Radar is used for observing nearby planets, but because of the huge distance involved, you need to focus your transmitter’s power into an extremely narrow beam. With such a narrow beam, it’ll take forever to scan across the entire sky.
What they mean is if someone else (an alien civilization) has a radar transmitter, and it happens to be aimed at us, we can detect it from great distances. But we can’t transmit a beam from earth and detect a reflection from another star system. We can’t even do that for the outer planets of our own solar system.
And if you know about where you are, you can skip many of those magnitude 1 objects. “That’s Antares, skip it, that’s Betelguese, skip it, that’s Rigel, skip it, that’s Sol, skip it, that’s Canopus, skip it…”
Doubtful. The problem is the distance between worlds is so large that on top of all the radio noise you are going to pick up the divergence of the signal is such that even the tightest beam isn’t going to give a coherent return. And of course planets are not good objects for radar reflection to begin with; they’re more or less round, so most of the signal is scattered, and any planet with an atmosphere (and especially gas giants) are going to absorb radio signals. Heck, Jupiter radiates across the lower EM spectrum from VLF through near infrared. (In fact, a good way to find large gas giants and brown dwarfs might be looking for faint radio sources, except that gas giants are going to have a high albedo for optical detection anyway.)
I have to put in with scr4, Lemur866, and others who say that planet detection of close-in and large worlds would be a pretty trivial matter even with pre-XXth Century technology. Planets tend to be the brightest thing in the local sky, and they move against the relatively invariant stellar background. You can make the assumption that most worlds will fall within a fractional angle of the ecliptic plane, and stable orbital velocities (for near-circular orbits) are child’s play to calculate. Finding rocky outer worlds with low albedo (like Pluto, but covered in carbon black instead of ice) would be more tricky, but putting together a good, iterative model of the main system should give you clues to gravitational perturbations that will indicate likely orbits and masses for candidate planets. Even with just a decent amateur telescope with a medium format camera (or good CCD) and a G4 PowerBook[sup]*[/sup] with some astronomical plotting software you could do a planetary system survey in a couple of weeks. (If you’re going to resort to hand calcs and slide rule, then multiply by a couple orders of magnitude…but that’s almost all calculating accurate orbits, not detecting the actual planets.
Now, how does that FTL drive work again?
Stranger
*'Cause you can do anything with Mac, even hijack the OS and central computer of an alien mothership.
Well, they must have gotten around all these problems, since the Arecibo telescope did some Earth-based radar mapping of Venus back in the '70s and '80s. You can see the results here. Now granted, you can’t haul around an Arecibo-sized dish with you on your spaceship, but then you’re not trying to get sufficient resolution to map your putative new planets, just find them.
As scr4 indicates, getting an actual return off of a planet (even one as near as Venus at closest approach) requires collimating your beam to a very narrow angle, unsuited to scanning the entire sky. You’re going to get much better results with an optical scan, letting the central star doing all the illumination work for you.
So can we “cruise” at FTL speeds while making observations? How about:
Determine the plane in which the planets are likely to lie by the spin of the star.
Move your ship to the outermost distance you’d be likely to find a useful planet.
Orbit the star along the plane, LOOKING AT THE STAR.
Note any black spots against it.
When you finish your orbit, you should have a pretty complete catalog of everything in the system that passed between you and the star; no searching the night sky required, except to pinpoint distance later.
Earth would be pretty damn bright though, because you can see it full from opposition whereas you can only see Venus as a crescent near opposition. Think back to how bright Mars was a couple of years back. Earth would be nearer the sun, and bigger, and yes, it would be by far and away the brightest object in the Venusian night sky (with the disclaimers above).
Note that with Venus we HAD to do radar mapping. We didn’t do radar mapping of Mars, we did optical mapping…look through a telescope and take a picture, or sketch in the very early days. Except when you do that for Venus you get pictures of clouds. They needed some EM wavelength that was transparent to the clouds yet bounce off the rock, and radio does that. But they never would have done it if they could SEE the surface of Venus.
Advanced scanner and computer technology commensurate with a FTL starship would not be required to rapidly locate planets. Today’s technology would be quite sufficient.
Even if built from donated alien blueprints, a starship is a big investment, and the project planning and construction would take a while. Before departing you’d have already done extensive telescopic surveys of the destination system. You’d have a database of the position and characteristics of every star detectable from earth. The few light years to Alpha Centauri, etc. wouldn’t change things much – the data would still be valid.
Upon arriving in the system, wide-angle computerized optical telescopes would simply scan the sky and you’d subtract from that data the star database built on earth. The result would be a list of objects for further close examination.
As already mentioned you would further bound the search based on the star’s habitable region.
Scanning would not take long. Even 50 years ago, a wide-angle Schmidt telescope camera could image 6x6 degree sections of the sky. There are 20,626 square degrees in the sky hemisphere. Even if you scanned all of that, it would only take 573 6x6 degree images. Exposure time would be a factor of limiting magnitude, detector sensitivity and telescope optics, but it likely wouldn’t be long – I’d estimate a few seconds per image, max. Even today’s computer technology can rapidly sift through that. There would be little waiting.
You’d probably know where the planets were before you even finished checking out the ship after the FTL jump.