Not that long ago, although people believed there probably were planets orbiting other stars, it was deemed unlikely we’d ever be able to know for sure.  Similarly, there could be life on some of those planets, but it was unlikely we’d find out. However, thanks to a lot of scientific and technical ingenuity and hard work, we are actually making progress in answering these questions.

These days the main way to look for planets orbiting other stars is to search for the minute dimming of a star when one of the planets orbiting that star moves across in front of it. So far we have discovered almost 400 planets orbiting other stars, with amateur astronomers discovering some of them. Now, almost incredibly, the measurements can be used to dig out additional information. Variations in the duration of the transit tell us that planet has at least one moon.  This raises an interesting possibility. The planets we are finding tend to be big ones, gas giants, like Jupiter in our solar system, because big planets are easier to detect. However, even though the planet is not suitable for life as we know it, its moon might be.

If a planet or moon has an atmosphere, the spectral signature of the star changes when that moon or planet moves across in front of it. That is enabling us in at least some cases to see what gases are present in that body’s atmosphere. If we find oxygen, that will be a give-away for life, because oxygen is so very reactive it does not appear in a planet’s atmosphere naturally, and if present it gets removed quickly. Therefore the presence of oxygen says “life as we know it, alive and well at the time that starlight started on its way here.”

Recent research has come up with another piece of evidence that carbon-based life could be quite widespread in the universe. We know that the hydrogen formed at the birth of the universe is processed by stars into all the other elements.  When the stars die those elements are released into space, where they accumulate in dark cold clouds.

In those clouds they slowly react to form water, carbon monoxide, ammonia, hydrogen cyanide, methanol, formaldehyde and lots of other chemicals that form part of the chemistry of carbon-based life. Moreover, when we pass an electric discharge through this mixture, we get amino acids, the building blocks of proteins.

Now researchers have got even further, they have found that under the right conditions, which includes a dose of ultraviolet light, this primordial chemical mixture can be persuaded to form ribonucleic acid, or RNA. This chemical is a fundamental ingredient of life as we know it, and so complex that for a long time it was not clear how it could form without living things to form it. If Mother Nature has the universe tuned this well to turning out the key ingredients for life; it is very unlikely we are alone in it. We must just keep searching. However, the fact life is carbon-based does not mean it has to look anything like us. For example, have you ever seen a sea cucumber?

* The sun reaches its northernmost point at 10:46 p.m. on June 20,marking the summer solstice.  Mars and Venus are close together in the eastern sky before dawn. Jupiter rises around midnight; Saturn lies in the southwest these evenings. The moon will be new on the June 22.

Ken Tapping is an astronomer with the National Research Council's Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory in Penticton.