module 3

From your textbook’s chapter 21.3, explain why it is easier to search for planetary systems when the protoplanetary disk contains a lot of dust and gas before it gathers into planets instead of when planets have formed from all of the dust and gas in the disk.

We can detect radiation from spread-out individual dust particles. Each dust particle is heated by the young protostar and radiates in the infrared region of the spectrum.

From your textbook's chapter 21.4, describe two reasons why the majority of exoplanets found via the Doppler wobble technique are "hot Jupiters".

1- the planets cause the biggest wiggles in motion of their stars and the biggest doppler shifts in the spectrum

2- giant planets that orbit close to their stars

From your textbook's chapter 21.4, explain how we deduce the approximate size (or radius) of transiting exoplanets. Also, how do we deduce the density of these exoplanets in order to determine whether they are rocky or gaseous?

Size: bigger the planet, bigger eclipse

density = mass/volume of the planet. More stars moving, the bigger the planet (mass) so we can predict mass.

From your textbook's chapter 21.4, explain why it is easier to use the infrared part of the spectrum (instead of the visible part) in order to directly image planets orbiting around other stars.

Infrared is the optimal wavelength range in which to observe because planets get brighter in the infrared while stars get fainter, which makes it easier to detect a planet against the glare of its star.

From your textbook chapter 21.5, figure 21.23 is a bar chart showing the percentage of each category of planet size detected by the Kepler mission.  Figure 21.24 is a bar chart showing the ACTUAL percentage of each category of planet size in the galaxy.  Explain why these two bar charts are different (in other words, why are there more small-sized planets out there compared to what Kepler found).

The first graph shows the number of planets of each size range found among the first 2213 Kepler planet discoveries. The second graph shows the average number of planets per star in each planet size range so the distribution shows that earth-sized planets may actually be the most common type of exoplanets.

We can estimate the size of the planets and how many planets are there but when we correct our bias on how many planets there are (including the ones we can’t see or detect), it seems that there are a lot more small sized planets like earth.

From your textbook chapter 21.5, in figure 21.25, there is a curve that implies that as the mass (horizontal axis) of a mostly Hydrogen planet increases, the size (vertical axis) also increases. But that relationship changes once the planet’s mass is about 1000 times Earth’s mass. At that point, the more mass you add to the planet, the *smaller* it gets. Explain why this happens.

This occurs because increasing the mass also increases the gravity of the planet, so that compressible materials will become more tightly packed, shrinking the size of the more massive planet.

From your textbook chapter 21.5, we find that gas giant planet sizes for hot Jupiters (planets that are mostly Hydrogen) are much larger than predicted for our most basic assumptions about mass and planet size. We expect as we begin to find more "cold Jupiters" in more distant orbits, their sizes will be more "normal." Describe the two effects that cause "hot Jupiters" to be much larger than expected.

1- planets orbit really close to their star (more heat) where they intercept a significant amount of radiate energy that is trapped in its atmosphere and causes planet to expand

2- star will raise tides in these planets that circularize the orbits and cause tidal dissipation of energy that inflates the atmosphere.

From your textbook chapter 21.6, explain how astronomers think hot Jupiters form differently from the way we think our planet formed.

Planet forms with substantial amount of gas that remains in the disk, so planet’s orbital angular momentum can be transferred to the disk. As it loses momentum, the planet will spiral inward. This will transport giant planets closer to the central star, producing hot Jupiters.

From your textbook chapter 21.6, why was it surprising to find a number of rocky worlds in orbit around the star Kepler-444?

Periodic elements come from stars; if a star formed recently, it shouldn’t have many elements. This star was very young but still had a lot of elements which was surprising.

From your textbook chapter 30.1, explain what is the Copernican Principle, and provide at least two historical examples that have motivated scientists to believe this is a valid idea.

The Copernican principle is the idea that there is nothing special about our place in the universe.

1- we used to think that the earth was the center of the universe which is wrong

2- life around older stars may have started a billion years ago

From your textbook's Chapter 30.2, describe what was discovered in the Miller-Urey experiments.

Biochemists stimulated conditions on early earth and have been able to produce some of the fundamental building blocks of life including the forms of proteins and other molecules like nucleic aids. The most interesting chemistry found was reducing gas like ammonia and methane.

From your textbook's Chapter 30.2, explain what is the definition of an extremophile organisms, and explain why their existence on Earth makes us more optimistic that life in some form may exist elsewhere in the Universe.

An organism that tolerates or even thrives under conditions that most life would consider hostile like very high or low temperature or acidity. Life forms exist in earth where water’s frozen, boiling, and even the bottom of our ocean so what makes us think this doesn’t happen on other planets.

From your textbook's Chapter 30.3, explain how we know (thanks to observations made by NASA’s Cassini mission) that Saturn’s tiny moon Enceladus likely has a sub-surface ocean like Europa.

The mission performed a close flyby of Enceladus and discovered plumes of gas and icy material associated with salts were venting from the moon’s south polar region. This suggests their source is a liquid water ocean beneath like on Europa.

From your textbook's Chapter 30.3, suppose we find traces of Oxygen in the atmosphere of a planet orbiting a dim, red M-dwarf star. Would it be correct to conclude that life likely exists there? Explain why or why not.

It has been hypothesized that oxygen could build up to substantial levels on planets orbiting M-dwarf stars through the action of ultraviolet radiation on the atmosphere. So, maybe oxygen could mean life exists but intelligent life may be hard to come by and rare.

From your textbook's Chapter 30.4, explain why Astronomers believe that if aliens do exist, our first contact is more likely to come through some sort of distant communication as opposed to an in-person visit by a UFO.

Interstellar space travel would be very slow and expensive and consume a lot of electrical energy.

From the Scientific American article “A Planet is Born,” explain why some stars appear brighter in the infrared part of the spectrum that we expected.

Stars were surrounded by disks of dust so the grains would get heated by the star and then radiate thermal emission in the infrared range.

From the Scientific American article “A Planet is Born,” we learn that there are, broadly speaking, two different sizes of dust particles: tiny (like smoke particles) and large (like sand grains). Why do we think it is more productive to look for the larger sandlike grains in order to determine whether planets are present in orbit around another star?

They are less effected by interactions with interstellar gas so they offer the best opportunity to uncover the underlying disk structure and unseen planets through their gravitational influence.

From the Scientific American article “A Planet is Born,” what is the main weakness (or bias) in the two most popular exoplanet detection techniques (transit and radial velocity), and how do the observations of the ALMA telescopes enable us to spot solar systems more like our own?

We must be able to detect giant planets at large distances from their host stars in old systems. Planets have to be close enough for the star to wobble. Bias because we have to wait to see if planets make sun wobble and relies on their orbit around the sun which is many years and need to be watched countinously.

With ALMA, we can use the resolved structure of circumstellar disks, providing a powerful complement to other methods of exoplanet detection. Using observations of similar structures in extrasolar debris disks (looks at patterns of dust), we can use them to infer the presence of unseen Neptune analogues.

From the short Scientific American article “The Earth Next Door,” (a) What are the properties of Proxima Centauri's suspected planet, Proxima b (estimated mass and orbital period), and (b) what is Proxima Centauri and how does it relate to Alpha Centauri?

a) 1/3 heavier than earth, 11.2 day orbit

b) it is a red dwarf star that is too faint to be seen with the naked eye and it drifts at the outskirts of the Alpha Centauri.

From the short Scientific American article “The Earth Next Door,” name and briefly explain three potential problems Proxima b might have due to its close orbit that may prevent the planet from providing a stable environment in which to host life?

1- tidal heating causes it to be hot

2- harsh x-rays and ultraviolet radiation could strip its atmosphere

3- has a layer of hydrogen that gradually evaporates under harsh starlight

From the Scientific American article "The Galactic Archipelago," describe three of the proposed “solutions” to Fermi’s question that the author discusses to explain why we have seen no evidence of extraterrestrial life.

1- cost in resources of attaining the ability to rapidly traverse interstellar space is too high even to a superbly technological species

2- great filter idea that there is something that always limits a species leading to implosive extinction of all potentially technological life

3- zoo hypothesis that we are being kept deliberately isolated and in the dark by alien powers

From the Scientific American article "The Galactic Archipelago," explain why it would be difficult for us to determine whether or not an advanced civilization lived on our planet millions of years ago. What is an example of evidence we might plausibly find that would indicate the existence of a past advanced civilization on Earth?

If industrial civilization on the scale of our own had existed a few million years ago, we might not know about it, which indicates only a possibility and not a certainty. Fossil remains and other paleontological markers are so rare and contingent that they might not tell us anything. It is actually very easy for time to erase all signs of technological life on earth so the only real evidence would boil down to radioactive fallout.

From the Scientific American article "Alone in the Milky Way," the author says that even if life is common in the galaxy, the planet Earth is perhaps one of the first planets to be inhabited by life. Explain why (as part of your answer, explain the concept of metallicity).

Metallicity: Metals are created inside stars and spread through space when stars throw off material as they die. Metal material enriches interstellar clouds and continue to spread to other stars. More specifically, the sun’s composition mirror the cloud that made our solar system so the planets also have these elements. Stars older than the sun have even fewer metals making it less likely of having planets similar to earth so this means that even if we are not the only technological civilization in the galaxy, we must be one of the first.

From the Scientific American article "Alone in the Milky Way," the author argues that we live in a galactic version of the habitable zone. That is, we are not too close to the center of the Milky Way galaxy and not too far away. Explain why life is less likely to thrive on planets orbiting stars that are closer to the center of the galaxy (two reasons).

If a planet orbiting close to the galactic center = stars are more crowded and dangerous events such as supernovae and gamma-ray bursts are common.

From the Scientific American article "Alone in the Milky Way," explain two reasons why life is less likely to thrive on planets orbiting stars that are further from the center of the galaxy.

Farther from the center, catastrophic events have less impact, but stars are sparser, and metallicity is low, so there are fewer rocky planets. The galactic habitable zone is only about 7% of the galactic radius, containing fewer than 5% of stars because of the way they are concentrated toward the core so it rules out life for a majority of them.

Metallicity = metals / all atoms

From the Scientific American article "Alone in the Milky Way," explain how the origin of Earth’s Moon likely led Earth to have a very thin crust (compared to Venus) that is capable of life-sustaining plate tectonics.

Venus: thick crust, no plate tectonics, no magnetic field

The moon formed early in our solar system history. Metallic material from the earth and moon settled into earth’s center, and earth’s original lighter rocky material splashed out to become the moon, leaving earth with a thinner crust than before.

From the Scientific American article "Alone in the Milky Way," although the appearance of life on Earth only a billion years into the planet’s history would make us optimistic about discovering life elsewhere, the development of more complex life (like us) seems to be extremely unlikely because of the history of life’s development since that first single-celled organism appeared. Explain why.

Single-celled organisms merged into two types: bacteria and archaea. It seemed that the both emerged at the same time life appeared on earth. Even with multicellular organisms, they are flat creatures that lead to the variety of life on earth in an outburst Cambiran explosion. It is such a spectacular event that no one knows why it happened or if it is likely to happen elsewhere.

Given the chain of circumstances that lead to our existence, it means we are unique in our planet and in the milky way so it is certain to not happen again.

Single celled organisms = only thing existed on earth for 2 billion years so it may not be common for intelligent life to form easily

from the "Crash Course: Exoplanets": (a) Around what kind of star were the first two planets discovered? (b) Why was this discovery not very “satisfying” to Astronomers who were hoping to gain more insight into our own solar system?

a) two planets were found orbiting a pulsar, dead remnant of a star that had exploded

b) it seemed like the two planets around the pulsar were from material left over from the catastrophe which is nothing like our solar system. So, this still left us with the question: are there exoplanets orbiting sun-like stars?

From the "Crash Course: Exoplanets" video: The first planet discovered around an “ordinary” star was 51 Peg b. The fact that it is very massive (more massive than Jupiter) and also orbits very close to its parent star (8 million km compared to the 55 million km radius of Mercury’s orbit, with an orbital period just over 4 days) was surprising, because our model of planetary formation predicted that no giant planets could form that close to their parent star. So (a) how do we think 51 Peg b got there, exactly, and (b) why didn't a similar process happen with our own Jupiter (according to the idea presented in the video)?

a) the planet probably formed rather out just like Jupiter and then it moved and migrated inward towards the start as it interacted with the disk of planet-forming material around the star. Its inward spiral continued until it ran out of disk material to interact with, so it ended up really close to the star.

b) Jupitar didn’t get far in its inward motion because its interactions with Saturn put the brakes on that.

From the "Crash Course: Exoplanets" video: What was so significant about the discovery of the exoplanet HD 209458b, discovered in 1999? Explain.

It had a transit, meaning that once per orbit it passes directly in front of its star so it blocks a little bit of the star’s light and we can detect a dip in the star’s brightness. This was the first confirmation of an exoplanet.

It had a transit, meaning that once per orbit it passes directly in front of its star so it blocks a little bit of the star’s light and we can detect a dip in the star’s brightness. This was the first confirmation of an exoplanet.

1- water; mercury

2- energy; star’s emit

3- organic molecules that contain carbon; comets

From the video "Life Beyond Earth, Part 1," on the five km highway of life, the first life forms are found about 3.75 km away from where we are today (3.75 billion years ago). What were the first life forms that were common on Earth for 3 billion years after this time, and what were they like? Briefly describe them.

Most complex life form on earth were blobs of single-celled bacteria and algae called stromatolites.

From the video "Life Beyond Earth, Part 1," critics of Darwinian evolution say it is impossible to produce complex life forms just from random mutations (just like it is impossible to randomly organize letters of the alphabet to produce "King Lear"). How do biologists respond to this argument?

Creation of life would not survive under changing environments unless there were natural selection taking place.

From the video "Life Beyond Earth, Part 1," (a) explain what is the habitable zone in our solar system. Also, (b) explain two reasons why, about the time we were starting to venture into space, astronomers felt that life may exist on Mars or Venus.

a) earth’s two neighboring planets that orbit close to the sun for solar energy to drive the chemistry of life but not so close to where it would boil off water or break down organic molecules

b) 1- hot molten cores that power volcanoes like the ones that sustain life on earth

2- canals found in mars that were though to be from civilization

From the video "Life Beyond Earth, Part 1," describe what the Magellan spacecraft discovered about the past history of the planet Venus, starting about 500 million years ago?

Venus turned itself inside out with dramatic volcanic floods that covered the surface features and flooded the air with greenhouse gases causing rapid change to the climate and surface.

From the video "Life Beyond Earth, Part 1," what evidence discovered by the Viking orbiters on Mars indicated the Mars must have once had a thicker, warmer atmosphere than it does today?

Discovered that mars surface had Martian soil and tested it but no clear evidence of life. However, images shows dry river beds indicating that mars once had liquid water on its surface and a denser atmosphere. It also has volcanoes.

From the video "Life Beyond Earth, Part 1," Freeman Dyson explains that there are two possibilities regarding the origin of life. Either it came into being gradually through chemistry and steps we could hope to retrace (and could presumably be reproduced elsewhere) or life is some kind of extraordinary fluke. (a) If the answer to the question of the origin of life is the first possibility, what does that imply about life beyond Earth? (b) What if the answer is the latter possibility?

a) gradual one: then life presumably happens all over the cosmos, and we should find examples of life

b) if not, then we will not find any other examples of life anywhere near us in our galaxy

From the video "Life Beyond Earth, Part 1," explain (a) what discoveries on Earth have led us to make plans to search non-traditional places like Europa for life, and (b) what is meant by the term “gravitational habitable zone”?

a) the discovery that life can grow in extreme environments here on earth. Makes us want to send a submarine to Europa to search its ocean for life since it has extreme temperatures.

b) life can exists on the other icy planets further away from earth making the habitable zone bigger than we predict. Gravitational means that the energy from the gravitational pull will cause heat within the planets that will effect their surface. Means there may be a lot more opportunities where you could have liquid water and therefore life.

From the TESS Planet Hunter discover video, NASA scientists have created two possible models to represent TOI 700 d, the Earth-sized planet orbiting in the habitable zone of its parent star. They predict that the mostly-rocky planet will have an extra feature in its spectrum that wouldn’t appear in a mostly-water planet model. What is the extra spectral signature?

When starlight passes through a planet’s atmosphere, it interacts with molecules like CO and N to produce distincts signals called spectral lines.

From the TED talk about ALMA, describe four reasons why we do Astronomy (one complete sentence that describes each reason, not just a list of words).

1- to find our place in the universe

2- cosmic laboratory that we can learn about energy and matter

3- technology development for astronomical research

4- STEM interest to get the public interested

From the TED talk about ALMA, why do Astronomers move the individual radio telescopes in the array into different configurations? What is the purpose of a "large" vs a "small" configuration

They move the radio telescopes so that they are not distorted by water vapor and oxygen. Great place to do millimeter radio astronomy

Large- close antennas cover large region with low resolution; large surface of antenna, radiation comes in from the side bounces off its surface comes up to the mirror and bounces off down throguh the hole of the center of the dish where theres a radio reciever

Small- when attenas are far apart, small region of sky with high resolution

From the TED talk about ALMA,, one of the ALMA observations discussed is an observation of Carbon Monoxide snow around the newly formed star TW Hydrae. How is this related to the possible origin of life on Earth?

CO2 frozen around the young star; we need to know where the line of CO2 is because comets can pass by and pick up that CO2 and could crash into earth, which might have been one way earth got CO2.

From the film "Life Beyond Earth, Part 2," explain two reasons why radio wavelengths are the best way (we think) to send messages back and forth across the vast distances of interstellar space (as opposed to flaming triangles in Siberia or strings of firecrackers). Paul Horowitz (sitting on the edge of a radio telescope) will talk about this, too, a bit later.

1- radio can carry words, pictures, numbers cheaply

2- travels at the velocity of light so it is super-fast

From the film "Life Beyond Earth, Part 2," explain why our radio signals from Earth are only detectable for the nearest 1000 or so stars nearest to our Sun.

A sphere of radio and tv broadcasts surrounds or planet. Its radius is nearly 100 light years and is expanding at the speed of light. Thus, the farther the stars are, the older the radio they will hear.

Where we are located, only our own bubble can see us so basically we don’t yet exist to the rest of the galaxy.

From the film "Life Beyond Earth, Part 2," explain what happens in the experiment that Timothy Ferris performs to test the validity Fermi’s question to show that “absence of evidence is not evidence of absence.” What was Ferris' logical mistake in the experiment, the same logical mistake we may be making when we try to explain why we haven't detected any aliens?

His experiment is to have lobster for dinner, so he waits for one to show up at his house. When no lobster shows up, he concludes that no lobsters exist. Obviously, this is not true as we know lobsters do exist, but it can be used as an analogy for aliens. The logical mistake was absence of evidence isn't evidence of absence.

From the film "Life Beyond Earth, Part 2," explain the argument Stephen Jay Gould (a prolific author of many interesting short essays on the nature of science, biology and human evolution) makes to infer that if other life forms do exist out there is the cosmos, intelligence is very unlikely to be a common trait among them.

Intelligence has only evolved from one species in the span of 4 billion years on earth and conscious has only arisen in one species out of all mammals. If intelligence was such an easy thing to achieve, other lineages would have also developed intelligence but they haven't and still they persevere (animals).

From the film "Life Beyond Earth, Part 2," (a) explain what an "emergent property" is and gives two examples, and (b) explain why this phenomenon may make intelligent life more probable to exist in the Universe.

Emergent property: apt to appear on any planet that has a sufficiently complex biological system

a) 1- patterns formed by birds in flight 2- weather system as a whole

b) If intelligence forms naturally in the biospheres of living planets as naturally as weather, there may be many other thinking beings in other worlds.

48 From the film "Life Beyond Earth, Part 2," describe the probability-based argument (also based on the Copernican Principle) made by J. Richard Gott to suggest that our human species is unlikely to last longer than a maximum of about 7.8 million years.

Formula for devising how long the human species will last. 95% likelihood that we are living during the middle 95% of humans tenure. 5100 years < future ? 7.8 million years of the longevity of humans which is similar to other species.

From the film "Life Beyond Earth, Part 2," explain why it will be easier to communicate (or find) other intelligent alien civilizations if the average lifetime of a civilization is extremely long (millions or tens of millions of years) instead of short (less than 100,000 years or so).

The longer they last, the better our chances of communicating with them because the period of their willingness to make radio contact with other worlds. If they stay long, their persistence is rewarding. If civilizations last only 100,000 years, there are few worlds on the air.

The odds of overlapping are very small when the average lifetime period is small. So, the longer the lifetime, the higher the probability of finding / communicating with alien civilizations.

From lecture, explain what are the three rules of Doppler shifting.

Doppler shifting: object emits light/sound and is moving

Rules:

If object is moving towards observer, light appears blue shifted (shorter wavelengths)

If object moving away from observer, light appears redshifted (longer wavelength)

Amount of shift depends on radial velocity

From lecture, (a) explain the difference between radial velocity and transverse velocity. (b) If you have two stars with the same velocity but star A is moving directly away while star B is moving transverse to your line of sight, which will show a larger Doppler shift and why?

a) Radial velocity: moving directly towards us or directly away from us

Transerve velocity: moving sort of towards / away from us

b) We can see red/blue shift and their oscillations patters; cant see planet but we can see star and observe if it is moving periodically in a pattern -> doppler wobble technique

From lecture, in the Doppler wobble method of exoplanet detection, explain what we observe and how that turns into a graph of radial velocity vs time.

Doppler shift vs time graph: of radial velocity vs time of doppler shift of star

Periodic variation in stars orbital speed = has unseen planet

Velocity change = stars speed = planets mass

Pattern repeats every 4 days, tells us planets orbital period

From lecture, (a) once we have a graph of a star's radial velocity vs time, what two things on that graph do we measure? (b) For each of these two things, explain what property of the companion planet do deduce (explain why is there is a relation between what we measure and the property of the planet).

Period: how long for one period (larger period = larger star -> planet distance)

Amplitude: planets mass (mass of companion planet)

Mass of companion and its distance

From lecture, if the planetary system is face-on with respect to our line of sight instead of edge-on, we will not be able to detect any exoplanets with the Doppler wobble technique, even if the star is wobbling. Explain why not.

Doppler tech relies on it being edge-on

If its face on -> traverse -> we wont see any doppler shift

From lecture, explain why it is very difficult to use the astrometric (positional astronomy) technique, which is to measure the side-to-side (angular) motion of a star over time in response to its companion planet unless that star is one of the closest 100 or so stars to us.

Why is it difficulty: during 16 years, it would move by 1/10th of its image size and almost undetectable

From a greater distance, it wouldn’t be possible to detect

Can use position of star to detect planets -> technique

Maybe for nearest stars but not a good technique for the observation of sky and angular distance would be too small

From lecture, if the planet system is tilted with respect to our line of sight, our estimate of the companion planet's mass will be too small. First (a) draw a diagram to show why a "tilted" system will show a small Doppler shift compared to the same system seen edge-on, and (b) explain why our companion planet mass estimate will be too small for a tilted system.

a) Case A: edge-on observer Vradial = Vtrue

Case B: titled observer Vradial < Vtrue

b) We use radio velocity (amplitude of graph) of the star to estimate companion planets mass. If measured velocity < true velocity, our estimate mass < true mass

From lecture, explain why some Astronomers feel that if intelligent life current exists or has ever existed in our galaxy, then we should be able to find evidence of its existence fairly easily, even on the Earth.

Right now, we have no evidence of intelligent life outside earth. 70 years spent scanning sky of artificial signals or radiation. There is also no evidence of ancient life either (not on earth) that is concrete. Even with our tech, if we got to another star, we could colonize galaxy (would take years) but if we can do it with our tech, surely someone / aliens would’ve also been able to do it but there is no evidence that has ever been done.

From lecture, explain what the purpose of the Drake Equation is and how it applies to SETI. I'm not asking for a definition of every part of it.

Drake equation: N = rationally predict how many civilizations exist in our galaxy which communication is possible

Purpose: predict search for aliens and how many civilizations there are

From lecture, if we were to encounter or detect evidence (by finding artificial signals through our searches of the sky) another intelligent, communicative civilization besides our own, it is highly likely that that other civilization will be much more advanced than our own. Explain why they would likely be more advanced than us (this is also covered in OpenStax Chapter 30.4).

It is likely they’re more advance because they detected us and communicated with us when we have already been looking for so long

From lecture, (a) explain the difference between "passive SETI" and "active SETI" and (b) describe an argument in favor of passive SETI (against active SETI), and (c) describe an argument in favor of active SETI.

a) Passive -> shut up, just listen, no broadcasting

Active -> illegal, no ones allowed to intentionally communicate with aliens

b) We all agree that one “gets an upper hand” in talking with aliens to favor certain sides like russia v usa. We shouldn’t be seeking contact bc it wouldn’t go well for us if theyre more advanced

c) In favor: our civilization has armies and we would be able to defend ourselves and protect/preserve alien culture to study and observe them. We are less likely to go to fight no reason and have more of a negotiation with aliens