The analogue transmissions from television, radio and radar is being phased out and this has made Earth electronically invisible from the outer space.

The conventional signals usually spread across miles into the outer space while it also reaches distant stars. On the other hand, the new digital signals are weaker and are harder to detect, according to the Dr. Frank Drake.

It is a general belief in the scientific community that like how scientists on earth continuously look for signals in the space the other life forms will be doing the same.

Search for Extra-terrestrial Intelligence (SETI) is an organization based in the United States and was established by Dr Drake 50-years ago. He says that after the phasing out of the conventional signals it will be impossible to carry out searches.

According to his estimates, the earth was surrounded by a 50 light year wide shell of radiation and the signals produced generate around one million watts. Satellites now direct most of their transmission towards earth and thus no radiation was escaping into outer space.

He added, "Now the actual amount of radiation escaping is about two watts, not much more than you get from a cell phone. If this continues into the future, very soon our world will become undetectable."

Dr Drake said that he was confident about the existence of intelligent life which is much more advanced than life here on earth. He however said in conference that he will continue his efforts to search life forms in the space.

Another astro-biologist called Simon Conway Morris has said recently that the aliens are likely to look very much like humans.