Astronomy Final
Reasonable estimates suggest there are about 1 billion habitable worlds in our galaxy (maybe as few as 300 million, or as many as 5 billion - let's go with 1 billion). only 1% of habitable worlds develop life, 10% of worlds with life develop intelligent life, and only 10% of worlds with intelligent life develop a high tech civilization Then approximately how many high technology civilizations would we expect in our galaxy?
100,000
Imagine that the Kepler mission lasted 10 years. In that case, what would be the longest orbital period planet that could be detected?
3-5
If you know the density of a planet, what other property of the planet can you estimate?
Composition
If you know the mass and radius of a planet, what other property of a planet can you calculate?
Density
With the transit technique, we can detect planets whose orbit...
Face on
Why are high mass stars not suitable for life?
High mass stars have short lifespans
Which of the following general rules lets you estimate the lifespan of a star?
Multiply by its mass and divide by its luminosity mass/luminosity
Earth has had a technological civilization that can interact with the universe beyond our solar system for...
about 100 years
Which type of star requires greater pressure to halt its collapse:
high mass star because it will have a greater inward gravity
A star with a higher luminosity is using up its fuel at a ____ rate.
higher
Which of the following is true about a high mass star?
it uses fuel much faster than a low mass star and has more fuel than a low mass star
What is the general relationship between a star's mass and its luminosity?
more mass, more luminous
what is the orbit of a Kuiper belt object?
regular circle, outside of plutos orbit
The basic building blocks of life (amino acids and sugars):
-Were present in the disk of gas and dust that formed our solar system -Are quite common in the giant clouds of gas and dust that form new solar systems -Naturally form in types of environments that were present on the early Earth
What kind of signals are astronomers looking for from aliens?
-radio signal leakage -intentional messages sent via radio -short pulses of laser light
Imagine that there were about 1,000 stars within a 100 light-year diameter sphere. Our galaxy is shaped approximately like a disk, with a diameter of about 100,000 light-years and a thickness of about 1,000 light-years. What would then be the best estimate for the number of stars in our galaxy?
1,000/100 = 10 10 x 100,000 x 1,000= 10,000,000,000 stars
About 1% of planetary systems can be detected using the transit technique. Imagine that you studied a group of 10,000 stars for many years, and you have discovered 10 planetary systems - stars with planets orbiting them. Among the original group of 10,000 stars, how many actually have planets?
10,000/10 = .1% 1,000 actually have stars
About 1% of planetary systems can be detected using the transit technique. Imagine that you studied a group of 10,000 stars for many years, and you have discovered 100 planetary systems Among the original group of 10,000 stars, how many actually have planets?
10,000/100 = 1% 100% actually have planets, so 10,000 stars
There are about 10,000 stars within a 100 light-year diameter sphere centered on our sun. Our galaxy is shaped approximately like a disk. Imagine that it had a diameter of about 10,000 light-years and a thickness of about 1,000 light-years. What would then be the best estimate for the number of stars in our galaxy?
10,000/100 = 100 10,000 x 1,000 x 100 = 1,000,000,000 stars
Reasonable estimates suggest there are about 1 billion habitable worlds in our galaxy (maybe as few as 300 million, or as many as 5 billion - let's go with 1 billion). nearly 100% of habitable worlds develop life, 10% of worlds with life develop intelligent life, and nearly 100% of worlds with intelligent life develop a high tech civilization Then approximately how many high technology civilizations would we expect in our galaxy?
100 million
About 1% of planets can be detected via transits. If you study a group of 1000 stars, and detect a planet around 10 of them, how many stars have one or more planets? What percentage of stars have planets?
1000/10 = 1% about 1000/1000 stars have planets 100% of stars have planets
Reasonable estimates suggest there are about 1 billion habitable worlds in our galaxy (maybe as few as 300 million, or as many as 5 billion - let's go with 1 billion). nearly 100% of habitable worlds develop life, 50% of worlds with life develop intelligent life, and nearly 100% of worlds with intelligent life develop a high tech civilization, and nearly 100% of high tech civilizations are around now, then approximately how many high technology civilizations would we expect in our galaxy now?
500 million
What was the longest orbital period planet that Kepler could detect during its main mission, which lasted 4 years?
About 1 year
For how long have humans had the ability to make themselves known to the rest of the universe?
About 100 years
There is evidence that life on earth formed...
Almost as soon as the Earth stopped suffering sterilizing impacts by large asteroids and comets
If a star is moving towards us, then we will see every wavelength of light from it...
At a slightly shorter wavelength
The fastest spacecraft ever built, New Horizons, has taken about 10 years to travel to Pluto (about 30 AU). The closest star to our own, Alpha Centauri, is about 800,000 AU away. About how long would a journey to Alpha Centauri take?
B) 200,000 years
If a star is 5 times as massive and 100 times as luminous as the sun, how would you expect its lifespan to compare to the sun's?
B. Expect it to last 5/100th (1/20th) as long
Why did the Herschels conclude (incorrect, but it fit the data they had) that our solar system is near the center of our galaxy?
Because they saw about the same concentration of stars in every direction around a band of stars around the sky
Which wavelength is completely blocked at ground level, but can somewhat get through to high altitude, dry locations?
C) Infrared light
The 100 light-year region centered on our solar system has about 10,000 stars. The galaxy itself is disk-shaped, about 100,000 light-years across and 1,000 light-years thick. The galaxy thickness is _____ times larger than our local sample.
C. 10
The 100 light-year region centered on our solar system has about 10,000 stars. The galaxy's diameter is about 100,000 light-years across and 1,000 light-years thick. There are about ____ stars in our galaxy.
C. 10,000 x 1,000 x 1,000 x 10= 100,000,000,000
If a star is 100 times as luminous as the sun yet somehow has the same mass, how would you expect its lifespan to compare to the sun's?
C. Expect it to last 1/100th as long
It's been about 4 billion years since the first high tech civilizations could have developed (assuming Earth's history is typical). If the average technological civilization lasts 4,000 years, what would be the fraction of high tech civilizations that exist now?
C. about 0.0001% 4,000,000 / 4,000,000,000
A(n) ___________ spectrum that is _______ relative to an unmoving star.
D) absorption; redshifted
The 100 light-year region centered on our solar system has about 10,000 stars. The galaxy itself is disk-shaped, about 100,000 light-years across and 1,000 light-years thick. The galaxy is _____ times wider than our local sample.
E. 1,000
If a star is 5 times as massive as the sun yet somehow has the same luminosity, how would you expect its lifespan to compare to the sun's?
Expect it to last 5 times as long
What two things determine how much energy a planet holds on to from a star?
How much light does the planet reflect, and how many greenhouse gases are in the atmosphere of the planet?
What two things determine how much energy gets to a planet from a star?
How much light does the star emit, and how far away is the planet?
What feature of a transit light curve do we use to figure out the size of a planet?
How much light is blocked by the planet
Suppose you found a star with the same mass as the Sun moving back and forth with a period of 16 months. What could you conclude?
It has a planet orbiting at greater than 1 AU.
Life developed on Earth within about 1 billion years of the planet's formation. Earth itself will last about 10 billion years from formation to destruction when the sun becomes a red giant. Assuming that Earth's experience is close to the average, what does that suggest about fraction of habitable worlds that will develop life?
It will be a large fraction, 90 to 100%
After life formed on Earth, it took about 3.5 billion years for an intelligent species to evolve. What does this suggest about the fraction of worlds that develop life that then go on to have an intelligent species evolve?
It will be a middling fraction, 33 to 66%
Imagine that we discover a new type of star that has a mass 10 times greater than the sun, and a luminosity 100 times greater than the sun. How does its lifespan compare to the sun's?
It will last 1 / 10th as long as the sun
Imagine that aliens observed our solar system, and they happened to lie along the plane of our solar system. Which planet would be easier to detect - Earth or Jupiter -and why?
Jupiter would be easier to detect because it is 10 times larger than Earth
Imagine that aliens observed our solar system, and they could measure the back-and-forth wobble of the sun using the Doppler effect. Which planet would be easier to detect - Earth or Jupiter - and why?
Jupiter would be easier to detect because it is 300 times more massive than Earth
Which one can we only learn about Mars from a lander or rover?
Layered sedimentary rocks indicate that Mars used to have liquid water on its surface
Which type of star is most common:
Low mass, dim red stars
How can we measure how quickly a star is moving towards or away from us?
Measuring small changes in the wavelength of absorption or emission lines
Blueshift
Object is getting closer: you measure shorter wavelengths.
Redshift
Object is getting further away: you measure longer wavelengths.
Which of the following types of light can be efficiently studied using a telescope on the Earth's surface?
Radio
Which of the following would definitely be a low density planet?
Small size and small mass
Which of the following is a technique or type of observation that we have used to learn what comets are made of?
Spectroscopy of gas and dust in the tail of a comet, fly a spacecraft through the tail of a comet
Which of the following potential outcomes for technological civilizations would make the fraction that exist now, fnow, very low?
Technological civilizations tend to develop nuclear weapons while they still have many internal conflicts, develop many groups that compete for water, farmland, and other resources, dramatically impact the ability of their world to sustain them
What feature of a transit light curve is the main tool for figuring out how far a planet is from its star?
The amount of time between dips in brightness
Which property of the dips is completely NOT affected by the time it takes the planet to complete an orbit around its star?
The depth of the dips
After an intelligent species evolved on Earth (us, Homo sapiens!), it took 200,000 years for a high tech civilization that can communicate with the universe to develop. What does this suggest are the odds of a high tech civilization developing after an intelligent species evolves?
The odds are good (90 to 100%)
Life developed on Earth within about 1 billion years of the planet's formation. Earth itself will last about 10 billion years from formation to destruction when the sun becomes a red giant. Assuming that Earth's experience is close to the average, what does that suggest about the odds of life forming on a habitable world?
The odds are good (90 to 100%)
After life formed on Earth, it took about 3.5 billion years for an intelligent species to evolve. What does this suggest about the odds of an intelligent species evolving on worlds that develop life?
The odds are middling (33% to 66%)
The transit technique is a way we discover planets around other stars. In this technique, we watch for...
The slight dimming of the star when the planet passes between the star and us
Two identical stars are moving away from us. If we measure the wavelength of absorption lines from these stars, how will they compare?
The star that is moving faster will have absorption lines at slightly longer wavelengths
Reasonable estimates suggest there could be millions of high tech civilizations within our galaxy. Which of the following are realistic explanations why we haven't heard from them yet?
They don't invest the resources into communication They self-exterminate quickly, before contact can be made with others Space is big - they're too far away They're hiding, aware that other species could be an existential threat
Which of these is the most important reason that scientists want to directly study the plumes of gas and salts that shoot from the surface of Saturn's moon Enceladus?
They seem to be coming directly from a sub-surface ocean
Imagine that in the future, humanity has thoroughly explored 1000 habitable worlds. 10 of those worlds show signs of life, and 1 has developed intelligent life and a technological civilization. What would this suggest for the fraction of habitable worlds that develop life?
Very few worlds - about 1% - develop life
The first intelligent species that we are sure of first evolved...
Within the past few hundred thousand years, about halfway through the suns lifespan
Imagine that you are carrying out the first astronomical survey that can detect asteroids smaller than 1 km in size, and larger than 100 m. After a year, each night you find that nearly 100% of the asteroids you detect are NEW discoveries. What does this suggest about the fraction of asteroids of this size range that you've found?
You have found a small fraction of the asteroids of this size.
Imagine that you are carrying out the first astronomical survey that can detect asteroids smaller than 1 km in size, and larger than 100 m. After a year, each night you find that nearly 100% of the asteroids you detect are REPEAT asteroids that you already found. What does this suggest about the fraction of asteroids of this size range that you've found?
You have found nearly all of the asteroids of this size
Which is evidence that a small number of asteroids grew to large sizes (greater than about 1000 km) and were then destroyed by collisions in the early solar system?
a few asteroid pieces that we find on Earth are made of nearly pure metal
The fastest spacecraft ever launched by humans will take ____ to reach even the closest star systems
a few hundred thousand years
Radio or visible light sent from Earth will take ____ to reach the nearest star systems.
a few years
The habitable zone of a star is the range of distances where we would expect planets to have liquid water. How wide is the habitable zone of a star like the sun?
about 0.5 AU
Assume that some planets in our galaxy have been able to produce high tech civilizations for 5 billion (5,000,000,000) years. If the average lifespan of a high tech civilization is 5 million (5,000,000) years, about what fraction of high tech civilizations would exist now?
about 1 out of 1000
Planets are detectable at inclinations from about 89 to 91 degrees. What percentage of planets can be detected via transit?
about 1%
The planet's orbit doesn't have to be exactly edge on to be detectable. Planets with orbits within 1 degree of edge-on are detectable. What percentage of planets can be detected using the transit technique?
about 1%
Imagine that in the future, humanity has thoroughly explored 1000 habitable worlds. 10 of those worlds show signs of life, with only 1 having developed intelligent life and a technological civilization. What would this suggest for the fraction of worlds with life that develop intelligent life?
about 10%
Imagine that we could observe transits for planets with orbits that were as far as 9 degrees from edge-on. In this imaginary scenario, what percentage of planets would we be able to detect?
about 100%
how long did it take for earth to have a high tech civilization
about 4 billion years
After the development of life, intelligent life evolved on Earth...
about a third of the way through the time available (within 3.5 billion years of the 9 billion years remaining after life originated)
More massive stars are:
brighter, shorter lifespan
Which one is evidence for the Oort cloud?
comets have orbits in all directions and orientations
Our current working definition of habitable exoplanet includes those that:
could have liquid water on their surface are approximately Earth-size are mostly rock and metal
With current telescopes, what can we determine about a planet to estimate its composition?
density
What type of measurement is needed to determine the size of an exoplanet?
dips in brightness of the star, star size
What information do we need in order to estimate the surface temperature of an exoplanet?
distance from the star stellar luminosity
Life on Earth originated...
early in the time available, within 1 billion years of a total of 10 billion year existence
Estimating the fraction of technological civilizations that are around now
fnow = average lifetime ------------------ time it could exist
Since the Drake equation was first formulated, which of the following terms have we been able to determine?
fp, the fraction of stars with planets
Which of the following wavelengths can be observed easily by a telescope located in space?
gamma ray, ultraviolet, radio
Which will cause the star to wobble at a faster speed?
high mass planet, close planet, low mass
After an intelligent species evolved on Earth (us, Homo sapiens!), it took 200,000 years for a high tech civilization that can communicate with the universe to develop. What does this suggest about the fraction of worlds with an intelligent species that then develop a high tech civilization?
large fraction, 90-100%
Which will be easier to detect via the transit method:
larger planet, closer planet
What information is needed to estimate the mass of an exoplanet?
orbital distance of the planet speed at which the star moves mass of the star
What information do we need in order to estimate the density of an exoplanet?
planet size planet mass
Which of the following wavelengths would it not make much sense to observe from space?
radio
What type of measurement is needed to determine the mass of an exoplanet?
star speed, star mass, distance from star
Imagine that in the future, humanity has thoroughly explored 1000 habitable worlds. 950 of those worlds show signs of life, 100 of those developed intelligent life and 90 of those developed a technological civilization.
the fraction of worlds that develop life is about 95% the fraction of worlds with intelligent life that develop a high tech civilization is about 90%
After the evolution of intelligent life, a technological civilization that can interact with the universe beyond the solar system developed on Earth...
very soon in the time available (within about 200,000 years of the 5.5 billion years remaining after intelligent life evolved)
More massive stars have a habitable zone that is _____ and _____.
wider and further from the star