Testing for water on distant planets

[rov1100]

Knowing the composition of water why is it not possible to scan for water on distant planets from here on Earth? Here on Earth we have an abundance of the stuff and takes up 2/3rds of our planet. Why should it be any different on a distant colonised planet?

[boxtops]

They do - they know there is water (or water vapour) on some, it was on Brian Cox a few weeks back, but they are a long way off.

[Old_Geezer]

It may cover about 2/3rds of the surface, but nowhere near constitutes 2/3rds of the planet.

Why would it be the same on a distant colonised planet ?

[ll_billym]

It is difficult because those planets are so far away and do not actually emit their own light (i.e. they are not burning) so it's not just a case of analysing the spectrum of light to work out what the composition of elements are. The existence of a lot of planets is based not by actually seeing them but just they are inferred by the gravitational effects it has on the light from it's sun.

To produce life as we know it (carbon based) requires carbon, hydrogen and oxygen amongst other chemicals and a climate that is not too hot or too cold for life. As we cannot easily test the composition of the planet we currently look purely for planets that are the right distance from their sun to produce a temperate climate as candidates for intelligent life.

Interestingly the search for signals from extraterrestrial life has matured somewhat in that we now tend to train our radio telescopes to planets that we think would have the best chance of detecting OUR existence by the same methods that we use to detect them.

[rov1100]

Thanks ll_billym getting one sensible answer in 5 makes you beieve there is still intelligent life out there.

[jomifl]

I expect that starship enterprise has a scanner that would do the job.

[beso]

Check out the Kepler Space Telescope.
http://kepler.nasa.gov/

Its primary objective is to locate planets in other solar systems and try to determine how common habitable planets might be. So far it has a few dozen candidates for planets of similar size to the Earth in the "Goldilocks" zone around their stars.

[heathfield]

I didn't know we'd colonised a distant planet. When did this happen??!!

[modeller]

Planets do not emit light but they do reflect light and that reflected light is modified by any atmosphere it may have. By looking at that modification it is possible to deduce what that atmosphere may consist of. I say may as liquid water only exists between 0 and 100*C which limits the amount of water vapour that could be present in the atmosphere.
You use the term colonised . I assume you mean by living organisms. If that is the case you have partly answered your own question . We haven't yet detected any living organisms on any planet . If we had we could assume that water in some form was there.
The nearest we have to discovering water is that some planets have what appears to be ice sheets but that may not be water based.
You use the term 'distant planets ' I assume you are referring to our own solar system, beyond that we can't even be sure that any planets exist let alone what they consist of .

[beso]

If you read the link about the Kepler telescope you would see that there are many planets around other stars. From the relatively tiny sample so far it appears that planets are quite common.

[Old_Geezer]

You had at least 2 sensible answers before ll_billym gave a detailed one. Still it's nice to know we are all appreciated, I'll make a mental note of that then.

[modeller]

Keplar does not scan the planets it scans the light from the star and because that light is interrupted on a regular basis it is assumed that a planet may be responsible.
That is why I said // we can't even be sure that any planets exist let alone what they consist of . // There are probably millions of planets as there are stars but that is not proof. We know that planets in our own solar system exist because we can see them , beyond that we can only assume that if light bends then something has caused it to bend , such as a planet. However we now believe that black holes cause light to bend , but that also was first thought to be evidence of planets.

[jomifl]

Planets do emit light. The planet earth emits light from lightning, sprites, aurorae, and phosphorescent organisms. The form of (apparently) ball lightning associated with geological fault lines and often mistaken for alien space ships is possibly another example.

[beso]

moddler underestimates the range of potential in what is meant by "seeing". There are many astronomical phenomena which we consider as "seen" that will never be "visible" in the familiar sense of the word.

Planets are detected by the redshift as their gravitation moves the star toward and away and by changes in luminosity and spectrum as it passes across the face of the star.

This is just as valid as our what we think of reality as we assume is provided by our eyes. In fact our image of the world around us is really an illusion created by an interaction between our brain and the light falling our retinas. Solid mathematical data is easily as reliable as vision when it comes to the meaning of "seen".

[rov1100]

Its amazing that bringing up this subject the following day French scientists say they have discovered Earth like features with climates similar to our own 20 light years away.

http://www.treehugger...re-may-allow-life.php

[beso]

Claiming that they have similar climate to the Earth overstates it somwhat rov..

Although they are looking at planets with similar size to the Earth that are in the range of plausible distances from a star to allow for liquid water they do not know anything about the a very important factor. The atmosphere is a huge determinant of planetary surface temperature.