Ask Erik: Episode Fifteen

Here at Ask Erik, we've spent a lot of time reading books and comics, watching movies, and browsing through the Internet in the hopes of finding the answers to life's biggest mysteries.  Is there such a thing as a perfect circle occurring in nature?  Why do certain colors influence our brains in certain ways?  What's the point of Delaware?

Having instead amassed a vault of useless knowledge stored in his head, Erik instead tackles your questions and tries to find the answers you care about (or a reasonable facsimile).  Or, if you don't care, he'll at least try to make you laugh and forget you just wasted time you could spend doing anything else.



To Erik: How do they look for life on other planets?

...wow.  A question that doesn't involve pop culture references.  I didn't really think I'd get one of these for a while, so this is a pretty interesting change up.  Okay, let's see how I do.

The last I checked, there are only three reliable methods to learn if there is life on other planets besides having it show up and blow us up like in every single alien movie ever made.

Well, maybe not every single movie, but in those it turns out that man is the real monster anyway, so someone still gets obliterated.

But yeah, how would we know what planets to investigate once we can reliably travel from one planet to another?  How can we determine whether we should head in one direction or another?  Up or down?

Well, the first step is to know that there's even a planet there.  To do that, we have to look for them, but unless it's in our solar system, we don't have the technology right now to see planets in other systems.  So how do we know they're there?

There are four standard methods.  I won't go into the detailed science, but I'll try to keep it simple in case anybody wants to know:

1&2)  Planets make stars wobble slightly.  Even a small planet still tugs on a giant ball of flaming gas, and it can shift slightly as a planet spins around it.  That's the joy of gravity, it works both ways.  Now, if a wobble is mostly side to side compared to our point of view, our telescopes can track its shift in relation to other stars.  It won't move much, but our measurements are getting more and more precise every day.  The other method is that if the major wobble causes the star to move forwards and backwards, it causes the frequency of the light to change from redder to bluer.  If we measure the light frequency for an extended amount of time, any regular variations could be the responsibility of one or more planets gently moving the star around.

Try to picture the two methods like...well, the first is pretty simple.  Imagine you see some people at the other side of a football field, and they're all standing on large spinning platforms.  One person also has a dog on a leash on the same platform, but the dog is trying to pull away from the person.  The person is going to lean back slightly to compensate, so while everybody else looks like they're staying in place, one person might appear to be wobbling slightly.

The second is like if someone attaches a giant ACME bungee cord to the back of a car that's driving towards you.  Hopefully, people remember the Doppler Effect from school, and know it's why the sound of a car changes as it gets closer to you, drives past, and then drives away again.  In this case, the car gets close, and then gets pulled back before it starts driving forward again.  You're going to hear a constant shift in the sound.  Now, light is just different kind of wave, like sound, so we can measure that.

Still with me?  Good.

3)  Planets bend light.  If a star suddenly appears to be in a different location in the sky than it should be for a short time, it could be that a planet has moved into its path and is bending the light around it so it appears somewhere else (for a neat example of how this works, simply take a tall glass of water and drop a spoon in it.  Watch how the light bends to show the spoon somewhere else in the glass than where it is.)


4) Planets move in the path of the star.  If a star suddenly dims for a short time on a regular basis, it's probably a good sign that something big is moving in front of it and in a regular pattern, which probably means a planet is floating right there.

This one is also pretty simple to demonstrate.  Shine a flashlight against a wall.  Now move your hand across the beam's path.  That's essentially the same thing (it's also what we call an eclipse, if you want to stick with planetary bodies).

So, those are our four methods.  Now, from my understanding, we've discovered over 800 planets in other galaxies by primarily using methods 1 and 2.

So, we know there are planets, and eventually we'll either have satellites whizzing past them, ridiculously powerful telescopes pointed at them, or we'll find a way to duplicate those magical pools of water that let you see across distances.  I think Rita Repulsa had one on Mighty Morphin Power Rangers.

 But, when we can see them from a distance, how can we even know if it's possible to have life on them?  That's where you have to get creative.

The easiest way is we point a giant microphone at the sky and pick up a radio signal.  We've been beaming radio signals into space for a long, long time now (just think, the first impression of humans that aliens get will be that our horses talk like Mr. Ed), so once we get them back, we'll be able to narrow where it's coming from and realize there's life out there beaming out messages that we can get.  Radio signals, and those aren't bothered by things like space dust or the like, and we've been beaming for quite some time now.  I think the last I heard, our "radio bubble" had expanded out to 70 or 80 light years from Earth, so aliens might know we exist, but maybe their bubble hasn't reached us yet.

Now, here's my favorite method.  Something I learned at my trip to the Kitt Peak Observatory in Arizona is that we can determine what the atmospheres of other planets look like by seeing how light, in its various forms, moves through it.  We get an entirely different spectrum of colors when light passes through, say, neon than if it passes through hydrogen.

Now, here's something to blow your mind:  Only worlds with life have oxygen in the atmosphere.  Oxygen bonds with so many different elements, that only worlds that first developed plant life will have oxygen drifting free in the atmosphere.  This will give those worlds a unique color to the spectrum of their atmosphere, and if we can see that, then we'll know for certainty whether or not life could exist there.

Another gas that only exists on planets where there's life?  Methane.

The one other method is also a bit of a cheat, and it requires a planet, any moons it has, and the sun to be in a pretty precise line-up.

Picture, if you will, that night falls over the United States.  The moon moves into just such a position that the light from the sun cannot reach it, so the moon is completely dark.  However, the side of Earth that faces any aliens currently has sunlight on it.  If aliens were looking at Earth and trying to determine if there was life, they might not look at Earth, they might look at our moon.

Any large amounts of artificial light (such as, say, major metropolitan centers) would reflect off of the moon much the same way the sun reflects off of it when we see the moon in the night sky, and that would pretty much be instant proof that there's not just life on the planet, but life advanced enough to have invented the light systems needed to produce that much visible light.

Of course, touching back on that second method, aliens looking at our atmosphere could also just look for pollution.  If the sample of light they get passes through Los Angeles or Shanghai, then they'll know that not only are we here, but we're also pretty ridiculously irresponsible.

And that's the methods I know about that can tell us there's life on other worlds!  Now, it really would be simpler to know there's life out there if it appears in the sky and starts giving us presents like "free energy" or an apology for mutilating so many of our cattle, but in the meantime, we'll have to settle for reliable old science.