For one thing, you'll have to clearly identify what level of technological advancement Earth has achieved at the time. If it's set in the far future, sensors/scanners would likely detect him as soon as he leaves the 'wormhole.'
Another potential problem is the fact that most meteoroids one sees in a shower are little bigger than a grain of sand. Even the ones that don't burn up in our atmosphere are reduced in size by the time they strike the ground. And those usually draw attention your character probably wouldn't want, even with our current primative (relatively speaking) technology.
Just be sure you back the scenario up with solid reasoning...like your alien is more the size of the Great Gazoo or some such nonsense. The key is that it won't be nonsense if you remain confident with your character's skill/technology, maintain at least a shred of reasonable physics (he's not pulling Immelman loops in the atmosphere, his craft reacts to friction realistically, etc.), and generally accept the fact that readers will adequately suspend their disbelief.
Inkwell
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"The difference between a writer and someone who says they want to write is merely the width of a postage stamp."
-Anonymous
[This message has been edited by Inkwell (edited June 24, 2006).]
Are we talking about present day Earth? If so, I don't think the alien needs to do all that to land on Earth undetected. A wormhole could explain how he got here, but I think he could land without too much notice.
Let's its set at a time when humans now monitor the solar system far beyond what they do now. If this guy has the ability to create a wormhole, why doesn't he have some sort of stealth or cloaking tech?
If wormholes would be possible (and since this is fiction, asking 'what if?' we will accept it in the fictional universe), I am guessing they would repel gravitionally. Maybe someone versed in physics can tell you more. But that sounds reasonable. If it existed temporarlly and was of a tiny magnitude, present day humans wouldn't be not sophistatited enough to detect it. Then again, radation would also pour out at high energies.
But even if humans detected the wormhole, so what? They would likely assume it is a natural anomoly and not be on the lookup for an extraterestial behind it.
Of course, the story has to be about something more than how the alien got here. I think, the arrival should be a given, needing little expostion. If it has to be explained, a wormhole would suffice. But that is not the core of the story.
[This message has been edited by ChrisOwens (edited June 24, 2006).]
But if I do: you'll need a reason he couldn't open his wormhole right here on Earth. Would Earth detect it, out around Pluto? Since we know nothing about wormholes, you could just say, no, it's not sending out big beacons of radiation or anything.
Now, about hiding in comets and meteors. You'll need a reason that he'd care. Once we get that, well, how big's the spaceship? If it's the size of a VW or bigger, I think someone will track it before it reaches Earth, but if it doesn't make course corrections, I don't think they'd be the least bit suspicious about what it was. YOu wouldn't even need a debris field to accompany you.
Have him get to the edge of the system via wormhole, and then come in and land under whatever propulsion system he uses. If this is Earth of the near future, and his ship is not huge (which it wouldn't be if there aren't too many people on board), it's unlikely that he would be seen in space unless he gets close to one of our satellites, and he probably has enough fuel to land slowly enough to avoid producing any significant atmospheric effects that would give him away. If you're talking about further in the future than that, he might need to disguise his exhaust and make his ship harder to see (the latter would not require very advanced technology), and I don't know how much trouble he would have actually landing without being observed.
Inkwell
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"The difference between a writer and someone who says they want to write is merely the width of a postage stamp."
-Anonymous
Right now, half the near earth asteroids we notice are ones that already passed us. We see them as they are leaving. You might not need a comet. Instead, imitate an asteroid. Keep in mind that it takes years for a fast moving space craft to reach the outer planets. I don't know if your alien wants to spend years entering the solar system. He might come in from the south of the sun and get close, then take up an asteroid orbit to sneak in. He comes in on the south side of the sun because most observitories are on the north.
If you use all the stealth technology we have today, and apply that to space, such as the shape of the ship, the coatings and such, the ship would be very difficult to detect. One might have it change shape as it enters the atmosphere to deal with ground based detectors, where the signals are coming from one direction.
One should have an idea of how technology has changed in those hundred years. Computers will likely have reached their theoretical power. We might have effective movie style robots. Space might be filled with space probes and they have a good idea where most of the asteroids were located. On the other hand, we could be living in caves and picking fleas off each other...
Entering the atmosphere slowly will be the best tactic to keep from being seen. We see meteorites simply because they burn up in the atmosphere. your alien should watch the solar system carefully before he comes in, watch the earth carefully before he decides to land.
One option is to come in like a normal meteorite and appear to explode in the atmosphere. Hit full reverse thrusters about mid way down, send out some "debris" in all directions to also explode, and come to a stop still in the ionized air. Hover there until the ship cools down. Drop down in stealth mode in a way that is difficult, if not impossible to trace.
As for the comet idea, why would an alien who used a wormhole to cross the vast expanses of space want to spend years hiding behind a comet (comet orbits are counted in decades, if not centuries)? And why hide behind something that every astronomer on Earth is going to take a look at? One of them might even notice some anomaly caused by the ships presence in the wake of the comet.
Your main problem is getting through the wormhole undetected. Assuming that the defenders know about wormholes and are familiar with at least the theory of how to travel through them, you can't hope to hide your entry signature in their home system unless your technology is far more advanced.
By the way, if you can travel through wormholes, then you can go FTL in normal space. You might have reasons for avoiding that (like how horribly dangerous it is), but it remains a possibility.
In a hundred years...either the asteroid/comet won't do much to hide him or he won't need to hide from anything we've got.