Astronomy 5 Lecture 7: Mars

What is the average temperature of Mars?

- -50 degrees celsius -but there's a lot of variation

When did Mars probably have water? How do we know?

-2-3 billion years ago -hydrated minerals we find date that far back

Valles Marineris

-4,000 km long, 7 km deep, 120 km wide (as wide as the U.S.) -sedimentary walls are similar to the Grand Canyon; such strata might offer rich history of Martian life and global conditions -not formed by water or plate tectonics, likely by crustal forces -can fit the whole Grand Canyon in one tiny section of it -in the middle

How many spacecraft have launched for Mars? Did they all make it?

-40 -no

What is Mars' atmospheric pressure compared to Earth? Why is this important?

-<1% of Earth's pressure -water can't be liquid with this small amount of pressure, even when Mars is warm enough

What are the three lines of evidence for life on Mars?

-presence of methane in the atmosphere -results from the tests of the Viking landers -study of Martian meterorites

How does Mars compared to Earth in size?

-radius: 0.53 x Earth's radius (1/2) -mass: 0.11 x Earth's mass (1/10)

Why is Mars red?

because iron mineral in the soil oxidized (rusted) causing the soil and the dusty atmosphere to look red

What is Mars' axis tilt?

25 degrees

What were the viking biology experiments, and what results did they have?

-Carbon assimilation experiment: mixed martian soil with carbon dioxide and carbon monoxide looking for metabolic results. Both the control and sample gave the same results, indicating no life -Gas exchange experiment: mixed martian soil with nutrient "broth." Again, control and sample agreed; no evidence of life -Gas chromatography experiment: measured no organic material in the martian soil -Labeled release experiment: mixed martian soil with a radioactive nutrient "broth." The control showed the expected signs of life when heating reduced radioactivity! -Given the three negative results, most scientists concluded that the labeled release experiment gave a false positive due to inorganic chemical reactions of the soil

Tharsis Bulge

-a large volcanic region on Mars rising about 10 km above surrounding regions -northern hemisphere

Why does methane in the atmosphere point to life?

-any original methane should have been oxidized into other gases by now, the fact that some still exists means that it's being produced -AND methane is commonly produced biologically (microbes) -two other possible explanations for it are comet impacts and volcanism but impacts are unlikely and volcanism would imply liquid water so again, life

What's the deal with Mars' seasons?

-are more extreme because of the greater tilt and the more elliptical orbit one hemisphere gets short and mild of one season while the other has a long and extreme version of the opposite season -gets so cold that some of the atmosphere turns into ice at the poles -this is because Mars doesn't have a stabilizing moon like Earth

Can Mars' surface support life? Why or why not?

-at this moment in time, no -temperature is usually below freezing, and when it's not, the atmospheric pressure is too low to allow for liquid water

Why doesn't Mars have water/an atmosphere anymore?

-core began to cool which stopped internal heat and volcanic activity, not warm enough for liquid water -when core was too cold, no more magnetic field, solar wind is free to strip the atmosphere of carbon dioxide and water vapor -core cooled fast probably because Mars is small

How long is Mars' day and year? What is the Martian day called?

-day: 24 hours 37 minutes -called sol -year: 1.881 years

Briefly describe the important Mars landings.

-first successful landing: Mariner 4 in 1965 -Mariner 4 showed that Mars had craters but no canals -Mariner 9 was the first orbiter of any planet -July 20, 1976: Viking 1 landed on Mars at Chryse Planitia, two months later identical Viking 2 landed on the other side of planet -had a robotic arm to analyze soil samples and do biology experiments -results were inconclusive due to unexpected chemical soil relations -Phoenix orbiter is looking for water ice in the Martian arctic -Curiosity landed in 2012 and is much larger than Spirit and Opportunity -contains more analytical equipment -digs holes and looks for life -landed at Mt. Sharp

What's up with the Martian meteorite?

-found in Antarctica in 1984 -came from Mars 60 million years ago, landed on Earth 13,000 YA -it contains carbonate globule which only forms in liquid water -maybe microfossils but there's a lot of debate -overall: maybe signs of water and life and mars 60 MYA, but like, not for sure

What's hard/good about sending humans to Mars?

-good: humans can't work a lot faster and a lot more efficiently/complicatedly than robots -hard: it would take a whole bunch of fuel and supplies to get there, and it'd take a long time (hard on the minds and bodies of the people) -takes 150-300 days to get there

Hohmann Transfer Orbit

-interplanetary trajectory using the least amount of propulsive energy -use rocket engine to accelerate in direction of Earth's revolution around the Sun to the extent that the energy added at perihelion will cause its new orbit to have an aphelion equal to Mars' orbit -the acceleration is tangential to the existing orbit -after brief acceleration away from Earth, the spacecraft has achieved its new orbit; simply coasts the rest of the way -BUT, must slow down at Mars in order to go into orbit or land

Hellas

-large impact crater -in southern hemisphere

What's the deal with Mars' polar ice caps?

-made of frozen water vapor and carbon dioxide -shrink in the summer and expand in the winter (no liquid state: from gas to solid then solid to gas)

What is Mars' geography like?

-many volcanoes (some much larger than Earth volcanoes -no evidence of plate tectonics: therefore magma plumes stay in one place and make bigger volcanoes instead of island chains -volcanoes and mountains are very tall because there is less gravity (won't fall under it's own weight)

What does the evidence for water mean for Mars' past?

-meandering rivers and other water evidence suggests that Mars had water for A LONG TIME -therefore, Mars had to have been wetter, warmer, and with a denser atmosphere in the past to support this water (stable)

What is Mars' atmosphere made of compared to Earth?

-mostly carbon dioxide -95% carbon dioxide, 2.7% Nitrogen, 1.6% Argon

What's up with contamination and exploration?

-must decontaminate Mars things so we don't bring Earth life to Mars -both so we don't "discover" it, and so we don't harm any ecosystem that might exist -international treaty (1967): requires that spacecraft sent to Mars must be sterilized to less than 1/1000 chance of contamination (Even better limits are achieved today) -Mars microbes cotaminating Earth however is unlikely because they'll be designed to attack Mars life not Earth life

What are the two regions of Mars and why are they different?

-northern lowland and southern highlands -southern highlands are more cratered, indicating less recent geological activity (older) -northern plains lack density of craters, shows evidence of more recent geological processes (younger)

What is the evidence for ancient water on Mars?

-orbiters and rovers as far back as the 1970's saw what looked like dried up riverbeds and tributaries and lakes -evidence of outflow channels like would happen after a flood (and some other flood indicators) -rovers found hydrated minerals in the ground that could only form in water (like opaline materials or sediment clay) -found water ice under the surface of the poles -giant Martian river delta discovered -erosion of crater rims -evidence for heating events to keep it liquid -existence of blueberries: Hematite spheres that form in shallow acidic or salty water.

Why does Mars have dust storms? Are they dangerous?

-strong winds are associated with the seasonal freezing and evaporation of carbon dioxide (see extreme seasons), changes in atmospheric pressure, and motion of carbon dioxide from one pole to the other -these winds make severe dust storms -not all are dangerous: rovers pick up small dust devils on their cameras often -but some are huge: a dust storm shut off Opportunity in June 2018, and is what prevented Matt Damon from leaving Mars

Is there evidence for water on Mars now? If there were, what would it have to be?

-there was a landslide/erosion in a Martian gullie -even if it's not water, a landslide could have been caused by water -dark streaks on some crater walls grow in summer months, implying flowing water -any such water would need to be extremely salty to remain liquid -Mars still contains an unknown quantity of water ice, perhaps with pockets of subsurface liquid water

Why didn't the Viking biology experiments show life?

-there were perchlorates in the Martian soil which eat up organic molecules and release oxygen in the same way that life would -perchlorates are salt derived from perchloric acid -these makes life harder on Mars

Why is methane not super promising for life?

-there's not THAT MUCH of it in Mars' atmosphere -Tunable Laser Spectrometer (TLS) was used six times to search for traces of methane in Mars atmosphere -found none each time

What does the martian sky look like and why?

-winds and dust storms leave a lot of dust permanently in the thin carbon dioxide atmosphere -dust scatters the light to give sky a yellowish brown color -no blue sky

What is Mars' gravity compared to Earth?

0.38 x Earth's gravity

How far is Mars from the sun?

1.52 AU, receives 43% of how much sunlight Earth gets