Categories: Astronomy Cast

# Astronomy Cast Ep. 375: The Search For Life in the Solar System

With the discovery of water ice in so many locations in the Solar System, scientists are hopeful in the search for life on other worlds. Guest Morgan Rehnberg returns to Astronomy Cast to explain the best places we should be looking for life.

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Fraser Cain

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

• caw says:

Wherever life is found in our solar system, The fun question will be "Where did it originate?" The most reasonable / logical answer will of course be "earth." The debate will last a long time, but I believe that will be the final conclusion - though it's not very sensational.

• FarAwayLongAgo says:

If any single protein is the same on Earth as in alien life, then we know for sure that we have the same origin. The possible number of proteins is so enormous that two identical protein molecules never have and never will occur independently in the visible universe.

Let's do the math!

The median length of a protein on Earth is about 375 amino acids. There are 20 amino acids which life on Earth uses. That gives 20^375 possible proteins of median length.

How many different versions of the median length protein can maximally exist in the universe? Assume that all matter in the universe (10^55 kg) consists of only proteins of length 375 (10^25 per kg, I think), and please count 10^50 years to include everything from first star to the last star remnant cooling down to less than 1 Kelvin, and assume that every protein mutates once every nanosecond (i.e. times another 10^17 per year). That adds up to only about 10^147 protein molecules, which is nothing compared to 20^375 possibilities. You see that it is physically impossible for the same protein to occur independently twice, regardless of when and where, in the history of the visible universe.

Evolution never has anything to do with the initial selection of possible proteins, because evolutionary selection only works on stuff that actually exists, not on stuff that only potentially exist. So why does life on Earth use this tiny subset of 10^7 or so different proteins? Luck is mathematically excluded when it is on the order of 10^100+, so it must mean that almost any random subset of possible proteins will be life.

• caw says:

My point was if we find life elsewhere in the solar system, how can we be certain it didn't originate on earth? It might look different, but maybe (likely) we haven't yet found it here? It will be an interesting and difficult puzzle to solve.

• FarAwayLongAgo says:

And my point is that if ANY protein of theirs is the same as we can find anywhere on Earth, then we know that it is has at least been in contact with life on Earth. The existence of two independent but identical proteins in the universe, is impossible.

• Sgt Heart says:

Water water everywhere, but can't there to drink it.

• Rick Bennette says:

We already know life can exist in the most seemingly inhospitable conditions on Earth. At the bottom of the sea near heated vents and in icy polar conditions, primitive life can be found here on Earth. So it stands to reason if we find water encased beneath ice layers in Jupiter's moon Europa or Saturn's moon Enceladus, then it stands to reason primitive life might exist there as well.

In fact, with all the trillions of planets known to exist throughout the Universe (based upon mathematical predictions from the thousands of planets confirmed around nearby stars), I'm certain life must exist on some of them. What I don't think exists is our ability to positively detect life beyond our solar system, at least not for generations to come. This is due primarily to the vast distances between stars we need to someday conquer to make such observations.

When future generations do have this ability, I'm pretty sure the life they discover will be based upon the same building blocks as life here on Earth. Why? Because whatever is the Creator of life here on Earth is likely the same Creator of life throughout the Universe.

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