Looking for Life in Light

Gearoid_Murphy writes "Earth-like planets around distant stars may be too far away to be reached by spacecraft but scientists could still investigate whether they harbour life. Telescope technologies are being developed that will probe the very faint light from these objects for tell-tale signs of biology. These are the same "life markers" known to be present in light reflected off the Earth - so-called "earthshine"."

Comments

By the sound of it, they will be using optics

[El Cubano]

Telescope technologies are being developed that will probe the very faint light from these objects for tell-tale signs of biology.

I am guessing that they are talking about optical observations, since it appears to be an extra-atmospheric telescope they are designing. However, at those distances, how can they discern the difference between the shine from a planet and the light given off by the star(s) near the planet? I would think that we observe the earthshine from small enough distances that we can see it in spite of the Sun. I am curious how this would work for distant bodies.

Re:By the sound of it, they will be using optics

[lawpoop]

I am no expert in this either, but I think it must be a little more nuanced to be accurate.

First off, if the planet is partially obscuring the star, most of what we are seeing is the dark side of the planet. So, all we should see is a reduction in the total amount of light from the star, but not much change in the apparent percentage of constituent molecules of the star. Some of the light we are seeing is the star beaming through the planet's atmosphere, which might change the apparent spectrum signature of the star, but I think that would be a small percentage compared to the total volume or star light.

However, there are also times when the planet is kind of on either side of the star. In that case, we are looking at all the light of the star, plus a partial reflection of the star's light off of the planet. So in that case, we would see the most amount of light, plus probably more of the chemical signatures of the planet in the spectrum. So at this time we are getting extra light with a complex spectrum

Finally there will be times when the star totally obscures the planet. In that case, we should see a more 'starry' spectrum, and a normal amount of light.

To wrap up, there are four 'phases' we should see:

1. When the planet is behind the star, we will see a more typical spectrum, and we will get the same amount of light from the star for a period of time.
2. When the planet starts peaking around the star's edge, we will be getting more total light, plus some extra elements in the spectrum -- probably some stuff we don't normally find in stars. The planet is most luminous when it first emerges from behind the planet and then later on when it goes back behind it.
3. When the planet works its way around to the front of the star, it's shadow will decrease the total amount of light we are getting from the star. We might see some of the planet's elements from the light that the star beams through the planet's atmosphere.
4. Finally, the planet will reach the other side of the star, where it will again add to the total luminosity and the signature of its chemical elements. This will look like phase two, until it finally recedes behind the planet and we are at stage one again.

Perhaps a real astronomer can correct my mistakes. ;)

Re:By the sound of it, they will be using optics

[lawpoop]

I just realized a mistake --

When the planet is in front of the star, the total luminosity will increase, but it the star's light that gets beamed through the atmosphere of the planet will show absorption lines of the planet's elements. So, conveniently, that kind of works as a check -- when we see both the planet and the star, we will see extra bands in the spectrum corresponding to the planet's makeup, and when the planet is in front of the star, we should see absorption in those bands. Finally, when the planet is behind the star, we should see a regular star-like spectrum.

Re:Seems primitive. (Resolution v. Lightgathering)

[ookabooka]

Are you sure about the capabilities of such an array? There are two main properties to a radio telescope (or any telescope for that matter) and that is Resolution and Lightgathering. By increasing the diameter of the collecting dish you increase both the resolution and lightgathering capacity. By creating an array using interferometry you can increase resolution to create a "virtual" dish with a diameter equal to the distance from one end of the array to the other. This doesn't, however, increase lightgathering capacity the same way. Let me propose a crude analogy: think of dishes as buckets, you can put two buckets 50ft apart and infer how much rain fell between them by adding them and dividing by two, but if it was just a drizzle, your data wont be so hot. If however, you have a 50ft bucket, you're gonna collect a lot of water.

So an array of a bunch of teeny TV sattelite dishes wont have as much surface area as a dish a kilometer wide. So yes we could resolve a planet, but it would have to be bright enough to be seen.

Re:leaving scientology aside...

[khakipuce]

I agree that the chances of detecting a signal are very, very small indeed. However I see a different problem, that being the length of time that high-power broadcast signals are being used by a civilisation.

It seems likely that in the next couple of decades a lot of our brodacast signals on the lower frequencies that can escape the ionosphere will have been turned off in favour of internet based tv/radio, microwave signals from satellites directed at earth and spread-spectrum technologies that are indistinguishable from background noise.

So that means we will have had about 120 years of broadcast that has escaped into space. So, assuming we are in anyway typical (BIG ASSUMPTION), we are trying to find a transmission from a planet that went through this 120 year phase at exactly the right time thousands of years ago so that the signal arrives at earth now while we are listening.

I think the universe is big enough for there to be life out there, it's just that we won't find it, and we definitely won't hear it's radio transmissions.