[Isomotopes]

I feel it would be hard to determine the physical appearance of aliens because if we do find aliens for all we know they won't be carbon based or even solid. They might not even have self awareness or imagination to envisage us.
I feel that until we meet aliens that have met other aliens we won't know what they look like. The varying atmospheres, pressures and temperatures of the universe makes it nearly impossible to speculate the form of life. However i do like this thread and feel light is a possible communication to aliens

[mynah]

Finding any alien life form, however simple, would be of immense interest if we could get to know anything about its biochemistry, and especially its genetic material. Unless they find us first, our current technology limits us to our own solar system for the time being. We are not overly likely to discover sentient beings in our backyard very soon, but cells no more complex than our bacteria would help us find the answers to questions like, Are there organisms with genetic material entirely unlike our own? Was earth first populated by cells that came from elsewhere in the universe? Did life evolve more than once? If life forms entirely unlike ourselves exist, would we recognise them as living?

It could also answer some questions we would rather have left unanswered...

[Moontanman]

Originally Posted by mynah

Thanks - here's a reference - it just seemed so unlikely. Goes to show again, you don't need to leave earth to find the stuff of science fiction!

I have grown a lot of the local variety of Caulerpa (Caulerpa prolifria) and it is an amazing plant, it has roots, stems leaves, and reproduces by suddenly releasing huge amounts of a milky fluid. It also changes it's form to adapt to different circumstances. Great for aquariums but not nice if released outside it's native habitat.