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Robert WalkerRSS Feed of this column.

I'm Robert Walker, inventor & programmer. I have had a long term special interest in astronomy, and space science since the 1970s, and most of these blog posts currently are about Mars and space... Read More »

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One day, perhaps, brave astronauts will set forth to colonize the planet Mars. However human colonies can't be sterilized in the way a rover can be, so they may conflict with the desires of astrobiologists to keep Mars biologically pristine. Would be colonists can find this hard to understand. What is so special about an apparently lifeless or almost lifeless planet?

To understand why many scientists value a pristine Mars so much, we need to look into its geological history.

Martian micro-organisms would be of extraordinary interest for the life sciences, especially if interestingly different from Earth life. In the past Mars was much more habitable than it is now, so most of the focus was on past life, and deep habitats beyond the reach of our rovers. Recent research suggests the intriguing possibility of life in tiny micro-habitats within the top few cms of soil and in some cases, right on the surface.

This is an article I wrote for wikipedia to cover the diversity of published views on Mars Sample Return.

Sadly it was deleted from wikipedia. So I present it here as background material for: Need For Caution For An Early Mars Sample Return - Opinion Piece



The idea of a Mars sample return mission (MSR) is to return samples of rock, soil, dust, etc from Mars for study on Earth. Just about everyone involved in the debate agrees that  a MSR is well worth doing at some point.
It seems like a great idea, doesn't it, to send an automated rover to Mars to gather
 samples of rocks and dust, and return it to Earth, to study in laboratories with all the specialist instruments we have here. You can understand why so many scientists and mission planners are keen on the idea.

This describes the maths behind the sloth canon number sequences described in my Self Similar Sloth Canon Number Sequences article

It simplifies the proofs here to use a 0 based notation. So we define an integer sequence f(n) as a map from the non negative integers to the integers. The first term in the sequence is f(0).

Sloth Canon Sequences

Definition of a sloth canon sequence

The Danish composer Per Nørgård uses an endless self similar (fractal like) strict sloth canon structure in some of his compositions such as his Symphony number 2. He first discovered his sequence in 1959.