Your starship enters another star system. How do you find the planets?

Highly-advanced aliens (call them, oh, I don’t know, Thermians) show up tomorrow and give humanity instructions on how to build a much-FTL starship. However, for their own inscrutable reasons, they don’t want to tell us how to build equally-advanced sensors or scanners. What astronomical or scientific instrucments, available now in 2006, would we put aboard our brand spankin’ new starship?

And when we arrived at Alpha Centauri, Tau Ceti or Wolf 359, how would we use those instruments to actually find planets? Do we now, for instance, have any means of sensing the gravity well of a planet?

We would have to build several dozen better than Hubbles space telescopes to take with us on our ships and deploy in the system we visit and wait for the obsevations to come in. As we visit additional star systems our expertise at locating planets with grow much greater.


since you’d have a FTL-drive (and plenty of dilithium crystals), couldn’t you zoom from one end of the alien solar system, take a bunch of observations… zoom to the other end of the SS in an hour or so, and take a bunch of other observations, then compare them to find the nearby planets? Once you’ve located them, you can just zoom on over to the newly discovered Megalon-4 and take a look-see.

Seems to me that we could do exactly that- take shots from several angles, then via computer analysis, we could determine which things are near, and which are far.

I suspect it wouldn’t really be that tough to come up with a pretty detailed ephemeris using this method, if you observed over a sufficiently large period of time.

I say you’d make observations of the system as you approached it. Assuming we’re not talking about instantaneous travel, you’d be able to have a good look with your telescopes at the system coming at you, and pick out the planets from the stars before you got there.

Maybe you were already assuming this in the OP, but just in case you weren’t - you know the way the star spins, therefore where the star’s “equator” is.

You’d do well to look primarily in and close to the plane of that equator (using methods already mentioned).

stop at a nearby space station (the Thermians would surely have set up a few of these along the way) and ask directions :wink:

Yes. It’s done by measuring the trajectory (orbit) of objects in the star system. The “objects” can be natural (planets, moons, asteroids) or artificial satellites (probes). You can use either radio waves (radar or signal from satellite), or optical telescopes, or both, to measure its orbit.

But it’d be a lot easier to search for planets visually. All you need to do is take a complete set of photos of the “sky” from several different positions, or several times from the same location. If you just want to find big planets, an ordinary film camera would do. If you want to find fainter objects, you need a sensitive electronic detector (CCD) attached to a wide-field telescope.

Sorry, I meant “optically,” not “visually”. (Though you could do it visually too, if you’re good at making sketches.)

Is everyone aware of how hard it is to locate Jupiter in the night sky even when you know its location?
**Elendil’s Heir’s ** question is a difficult one that Science fiction usually glosses over or invents powerful sensors/detectors to resolve the problem.
I have a friend who is a Professor of Astronomy in Sacramento. Maybe I can lure him to the Dope to answer this question, as he is also a Star Trek fan.

From my understanding, to locate new planets in a strange solar system you would new millions of base observations with additional observations to look for sufficient change in arc to narrow down local (in solar system) objects. From this subset, you would need enough observations to determine orbit and distance.
Just zooming the system snapping pictures probably will not narrow the search in a timely fashion.

Jim {Not that I have ever spent any time thinking about things like this, Elendil, I wish you lived closer, I get the feeling we would end up hanging out}

Sorry, I swear your posts were not there when I hit Submit.

One of my favorite sections in Heinlein’s Orphans of the Sky is near the very end. His generation starship colonists are “escaping” in one of the landing craft, and he points out just how many hurdles they’d have to overcome to get safely down to the planet. The first hurdle was simply identifying the planets. He says something like “We’re used to seeing solar systems drawn in three-quarter view, with orbit lines showing the planets’s paths around their sun. But out in space you only see bright spots of light. Is that a nearby planet or a distant star? Choose the wrong one and your descendants may still be waiting to arrive.” It was the first time I’d encountered the concept (It was also one of my first SF books).

Back to my suggestion - if you observe the system as you approach it, your shifting point of view means you can quickly determine which objects are changing position slowly (distant stars) versus rapidly (nearby objects). Knowing to look along the star’s equator reduces observation time even further. I don’t think that in this scenario the problem would be all that hard.

You still have to have an enormous amount of computing power to sift through the data. I assume you do not want to spend 10 years in system analyzing the data. I could easily be wrong, but I think you are simplifying the problem too much.


You don’t need millions of observations by better than Hubble telescopes, our ancestors discovered 5 planets with their naked eyes.

Let’s assume we aren’t interested in iceballs like Pluto, or ice giants like Neptune and Uranus.

Here’s what you do. Travel FTL to the habitable zone of the star. Look for bright objects. If there is are planets near the habitable zone, they are likely to be as bright as Venus and Mars are from Earth. Venus is the third brightest object in Earth’s sky, after the Sun and Moon. If you see a really bright object you have a candidate planet. Zoom FTL perpendicular to that bright object an AU or so. Did it move against the fixed stars? You found a planet with your naked eyes.

And if you have a telescope–backyard hobbyist quality–you don’t need to move, you can just point your telescope at that bright object. Does it resolve into a disk? If so you’ve found a planet.

We don’t need to catalogue every planet in the system, not even every large planet, because we don’t care about planets above the boiling point of water or below the freezing point of carbon dioxide. You don’t need to check every faint spot of light for movement like astronomers did when they found the outer planets because we don’t care about the outer planets. When you’re in the inner system any inner system planet is going to be as bright as Mars or Venus and is going to show a disk through a hobbyist telescope and is going to change position against the stars every day.

And a small radio telescope could tell us if the native use radio. Any planet putting out lots of radio waves is very likely to be inhabited. Be careful of those ones.

Well the star will be rotating, that alone gives you a good idea as to the plane in which the majority of planets should reside. Then I guess you could stand a few AU back from the edge of the eco-sphere and take a few shots. You’re looking for bright shifting objects with crescents.

Once you have a few planets you should be able to use them as a baseline to search fro others.

Or what Lemur866 said. :slight_smile:

I guess I don’t follow - what’s hard about locating Jupiter when you know its location?

Okay, if we’re talking about carrying a bunch of Pentiums onto our FTL ship, then yeah, we would still have the problem. So maybe I’m assuming the FTL ship will come with a badass future-computer. :slight_smile: Even so, look at how computers are progressing - we might be able to crunch those kinds numbers in only 50 more years!

Let us break this down into detail chores then*.
How long will it take to determine the rotation of the star?
How long will it take to locate the orbital plane and the eco-sphere?
How long will it take to locate the Bright objects and resolve them into planets?

**Elendil ** asked how to locate the planets; the methods above would locate some but not all.

  • Assuming there is no convenient radio broadcast or a local Traveler’s Guild to help us.

On preview:

Have you done this in your backyard. It take quite a while. If you do not know what you are looking for or where to look it becomes much harder.

As far as advanced computers, you still need to write the programs to do the rapid analysis even if you have the computing power available. You need the interfaces between the telescopes and the computers. This would all be with our technology and I do not think from the Op we can assume a gift of new Super computers. So think in terms of a the best computers we could provide contained within the space of our Starship.