Official 30 - lecture 3
astronomy class.
there have been lot of talk recently about life on Mars, at level of micro-organism anyway, mainly because of few important discoveries and inventions.
for example, one major discovery was that at one point water was presented on Mars. How do we know?
in 2004, an exploration robot discovered Jarosite there.
黄钾铁矾 (Jarosite)
Jaroside is yellowish-brown mineral with crystalline structure that's also found on earth. it contains iron, potassium and hydroxite.
mineral 矿物质 [ mĭn′ər-əl ] A naturally occurring, solid, inorganic element or compound having a uniform composition and a regularly repeating internal structure.
mine 矿山，矿井（读法与mineral不同！）
hydroxite 氢氧化物
carbon dioxide 二氧化碳
the interesting thing, on the earth at least, it needed high acidic water to form.
so we got water, or had it at one point.
and since most planetary scientists believe that water is essential to life, the presence of Jaroside means one prerequisite for life was once present on Mars.
but there is another thing about the jaroside, one step in its formation on Earth involves microorganisms.
they actually speed up the formation of jaroside dramatically
now theoretically it is possible for Jarosite to form without the help of biological lifeforms
but we don't really know for sure if this happens, because every conner of Earth has some form of biological life
but the Jaroside on earth incorporates all kinds of microorganism into its crystalline structure
so it is possible that if the Jaroside on Mars was also formed with help of microorganisms, we might be able to detect the remnant of them with the samples we find.
and we have instruments now, that enable us to try to do this.
for example here is new instrument call micro fabricated organic analyzer or MOA.
the organic analyzer is an amazing tool, it will be able collect soil sample and any them right there on Mars, pure untouched samples
it will let us eliminate the risk that (we would take) of contaminating the sample if they were brought back to Earth.
and what they will look for specifically in the soil is amino acid.
amino acids, as you may know, are the building blocks of proteins.
in fact, there are 20 standard amino acids involved making proteins, and lots more that aren't. (更多的不涉及)
and here is the important thing, amino acids are what we call handed.
they can exist in two forms, there are mirror images of each other.
like hands, right and left hand have same number of fingers in the same order plus one thumb.
but right and left hands are the same, they are mirror images.
well like hands, amino acids can be right or left- handed, and 20 of them that make up proteins on the Earth are all left-handed.
one reason the MOA is so impressive is that it tests not just for presents of amino acids, but also for the handedness of amino acids
if amino acids are found, it would be especially interesting if they show a prevalence of one type of handedness, either left, like amino acids on Earth, or right.
see, other physical processes in space, processes that don't involve living organism can create amino acids.
but one synthesized through abiotic processes which is to say not involving microorganisms occur in equal number of right and left handed.
abiotic processes 非生物
which is to say ...
so a prevalence of left handed amino acids would indicate they were biological in origin which would be amazing
a prevalence of right handed ones that would be really amazing.
because the organisms that created them would be unlike anything we have on earth which only produce only left handed ones.