AST 248 HW for Chapter 7
Ryan Richards
Review Questions
Why do we expect the elements of life to be widely available on other worlds? How does the
requirement of organic building blocks further constrain the prospects of habitability?
We expect the elements of life to be widely available on other worlds since they are abundant in
the universe. Planets were built when particles condensed from gas, which eventually formed
into planets. As mentioned in the book, we would expect to see heavier elements than hydrogen
and helium due to the condensation process. These elements, of course include carbon.
The requirement of organic building blocks further constrain prospects since these molecules
need aqueous solution, in particular water.
How does the strength of sunlight vary with distance from the Sun? Discuss the
implications for photosynthetic life.
The strength of sunlight varies as the inverse square of the distance from the Sun i.e. d-2 as we
know from the first exam. As a result, photosynthetic life would have to be much larger than life
on Earth, much more efficient in collecting sunlight, and/or slower metabolic and reproduction
rate. (Plant biology is the reason why I STOPPED studying biology)
Why do the Moon and Mercury seem unlikely to be habitable? Does evidence for ice in
lunar craters affect the answer? Explain.
Both the Moon and Mercury seem unlikely to be habitable due to the lack of water. There is little
water on both the Moon and Mercury. In particular, the book mentions that during the day
Mercury is far too hot for liquid water and at night it is far too cold for liquid water. As for the
Moon, there is water ice hidden at the bottom of polar craters which has been confirmed.
However these craters would not help since the ice never melts.
Why does Mars seem such a good candidate for life?
Mars seems like a good candidate for life because of the possibility of underground liquid water.
Even though the surface water is frozen (due to the climate change), it has enough internal heat
to have liquid water underground.
Would You Believe It
I was part of the first group of people to land on Venus, where we found huge, ancient
cities that had been hidden from view by cloud cover.
This is highly not believable. Even though one may argue that the Sun was dimmer in the past,
we have to remember that the high level of carbon dioxide in the atmosphere of Venus causes it
to be very hot. This would not allow for the presence of oceans and it is too hot for ancient cities
to be there.
We deposited bacteria that get energy from chemical reactions with sulfur compounds into
the upper clouds of Venus, and they are surviving.
This is believable. The book mentions that the on the upper clouds of Venus the greenhouse
effect is far weaker compared to the surface. Due to the sulfur content, chemical reactions may
provide enough energy for extremophiles to live in the upper clouds.
The drilled sample showed no signs of life on asteroid B612, but we found many complex
organic molecules.
I would believe this. As we have continuously learned, there is organic matter on meteors and
asteroids even in the absence of life. Therefore we should not be surprised.
Quick Quiz
Oxygen and carbon are (c) the third- and fourth-most-abundant elements in the universe
On an asteroid that is twice as far as the Earth from the Sun, the strength of sunlight would
be (c) ¼ as great as on Earth
Compared to liquid water, liquid methane is (a) colder
Frozen lakes often have liquid water beneath their icy surfaces primarily because (b) ice
floats and provides insulation to the water below
Temperatures on Mercury are (b) very hot in the day and very cold at night
On Venus, liquid water (c) exists only high in the atmosphere
The reason that Venus is so much hotter than the Earth is (c) its thick, carbon dioxide
atmosphere creates a far stronger greenhouse effect