Martians?Life on Mars

ASTR 1420

Lecture 13

Chapter 8

Mars

• Northern low land and southern mountains impact origin?

Geography of Mars

• Olympus Mons = tallest mountain in the Solar System!

We saw evidence of liquid water on the Mars!

Climate History of Mars• We saw evidence of liquid water on the Mars.• Why was Mars warmer and wetter in the past?o If Mars had about 400 times more CO2, then it could have liquid water on the

surface via a stronger greenhouse effect and denser atmosphere.o If the composition of outgassed material was the same as Earth’s, then it should

have enough H2O to fill oceans hundreds meters deep.

• However, the Sun was dimmer in the past CO2 alone could not have warmed the ancient Mars’ atmosphere high enough…o Possible solutions

1. enhanced greenhouse effect by other gases such as methane2. Mars never had an extended period of warmth liquid water only after major impacts…

Mars was never Earth-like, but it was certainly warmer and wetter!

Small size of Mars

• Large enough to have volcanism and outgassing in the beginning…• H2O got also dissociated by solar UV radiation: 2H2O H2 + O2

o H2 got escaped quickly while O2 rusted the rocks and lost to space over time…

Small size lost internal heat

rapidly… outer core solidified weakened magnetic

field became vulnerable to

solar winds being stripped off

Martian climate:

• After losing its atmosphere and H2O, has the climate of Mars unchanged for the past 2-3 Gyr?

No. The climate had changed with period of hundreds of thousands years!

Cause of Seasons on Earth

Cause of Seasons on Earth

Seasons on Mars

Current obliquity of Mars = 25.19°

Monsoonal winds on Mars

• During the northern summer : wind blows from N S• During the southern summer : wind blows from S N• These global winds oftentimes cover the entire planetary surface!

Global dust storm

On-going short-term climate changes of Mars

• Ice ages of Earth due to the change of obliquity. 22° - 25° : small range due to the stabilizing effect of the large Moon

• Mars does not have a large moon and closer to Jupiter a much wider range of obliquity change, 0° - 80°

• Larger obliquity warm summer pole more CO2 sublimation stronger greenhouse effect warmer temperature.

Even with this increased seasonal enhanced greenhouse effect, average T cannot maintain surface liquid water, but high enough to have liquid water just beneath the surface!

Is Mars habitable?• Mars haso chemical elementso energy Sun light + chemical energy(?)

• Current surface of Mars is not habitable due to no liquid water

• However, during the high obliquity periods, Martian surface might have been habitable!

• Subsurface has been habitable throughout the period until now.

Time to search!

Evidence of Life on Mars?

• There are some scientific claims already about the existence of life on Mars

on-going debate!

• Three groups of claims1. Based on Viking lander data2. From Martian atmosphere studies3. From Martian meteorites

I. Viking Experiments

Examine the soil of Mars to see if there are any living microbes. Two Viking landers in 1976

Four experiments1. carbon assimilation experiment2. gas exchange experiment3. labeled release experiment4. gas chromatography

1. Gas chromatography – Mass spectrometer (GCMS)

A device that separates vapor components chemically via a gas chromatograph and then feeds the result into a mass spectrometer, which measures the molecular weight of each chemical it can separate, identify, and quantify a large number of different chemicals.

However, the GCMS measured no significant amount of organic molecules in the Martian soil. In fact, Martian soils were found to contain less carbon than lifeless lunar soils returned by the Apollo program.

2. Gas Exchange Experiment

Mix the soil with organic nutrients and check for any released gas (e.g., O2 for terrestrial photosynthesis)

O2 was released! But, similar result from an

experiment with no sunlight!?! O2 detection even after a thermal

treatment of the soil Non-biological process

3. Labeled ReleaseA sample of Martian soil was inoculated with a drop of very dilute aqueous nutrient solution. The nutrients (7 molecules that were Miller-Urey products) were tagged with radioactive 14C. The air above the soil was monitored for

the evolution of radioactive 14CO2 gas as evidence that microorganisms in the soil had metabolized one or more of the nutrients.

The experiment was done by both Viking probes, the first using a sample from the surface exposed to sunlight and the second probe taking the sample from underneath a rock; both initial injections came back positive.

2nd experiment a week later showed nothing!

Could Martian microbial life forms make a positive LR result and yet showed no traceable amount of organic molecules??

4. Carbon Assimilation Experiment

Mix Martian soil with terrestrial CO2 and CO (14C) : if these gases were used by life, then 14C would get incorporated into the soil

Yes! Some 14C were incorporated!The amount of carbon fixed is small by terrestrial standards; highest yields were observed in the light, but some dark activity was also detected; and heating the surface material to 90°C for nearly 2 hours had no effect on the reaction, but heating to 175°C for 3 hours reduced it by nearly 90%.

II. ALH84001

ALH84001: a 1.93kg meteorite found in Allan Hills, Antarctica on December 27, 1984

ALH84001 : Magnetite

Magnetobacteria magnetite is known in similar crystals on Earth only when deposited by bacteria

Top: macroscopic chain of magnetite crystals produced by bacteria on Earth.

Bottom: Similar chain found in ALH84001

These are smaller than it was thought free-living terrestrial organisms could be, an objection that has shrunk with the study of nano-bacteria.

ALH84001 : nano-fossils

nano-fossilselectron micrographs showing tiny structures that look remarkably l ike microorganisms or microfossils.

nano-fossils

Another microfossil-like structure from ALH84001

Methane on Earth = Life

• http://www.nasa.gov/centers/goddard/news/topstory/2005/methane.html

Methane on Earth

Sources of Terrestrial Methane

III. Methane on Mars

Methane detected from observations made by NASA IRTF and Keck telescopes (2003)

Methane on Mars

Replenishment of CH4Destruction of CH4

Possible Methane sources on Mars

Curiosity : No Methane in Martian Atmosphere• Sample Analysis at Mars (SAM, Tunable Laser Spectrometer) analyzed

Martian air and found little to no methane (Nov 2012)

Methane measurements and Curiosity ?!?!

In summary…

Important Concepts• Seasons of Mars• Reason for Mars climate change• Viking Experiments• Evidence of Life from ALH84001

Important Terms• ALH84001• nano-fossil

Chapter/sections covered in this lecture : 8.1-8.5Life on Jovian Moons : next class!!