The Search for Extraterrestrial Life ~ Review of Course Module 4
What does "N" represent in the Drake Equation?
"N" represents the calculated estimate of active extraterrestrial civilizations in our galaxy that we can communicate with. DOES NOT include past, fallen civilizations.
(HW Question) How is the "Fermi Paradox" normally stated?
"Where is everybody?"
(HW Question) What is/are examples for possible biosignatures?
-The large abundance of free oxygen in Earth's atmosphere -The seasonal variation in Mars's atmospheric methane abundance -The characteristic change in surface reflectivity due to the presence of vegetation -The seasonal variation in Earth's atmospheric CO2 abundance
The term "L" depends on...
... the level of technological development of a civilization.
Assuming we receive a signal from a civilization on the other side of our galaxy, a two-way conversation with them is...
...Unlikely, because of the great distance involved.
(HW Question) Given how many times intelligent civilizations could have appeared over the universe's history, it is most likely that if other civilizations exist, they will...
...be much more advanced than us.
Since 1961, we have gone from solely understanding "R" of the Drake Equation, to understanding...
...fₚ and Nₑ as well!
(HW Question) The range of frequencies that are contained in a particular radio signal is referred to as its...
...high intensity, narrow bandwidth
(HW Question) The factor L, in the Drake equation depends on...
...how long civilizations survive once they have arisen.
(HW Question) The ratio of an animal's brain weight to body weight is thought to be roughly proportional to its...
...intelligence
(HW Question) The complete version of the Drake equation allows us to estimate the number of...
...intelligent civilizations capable of communicating in our galaxy now
The biggest obstacle to interstellar travel is...
...the vast distances to the nearest stars. Even our fastest moving spacecrafts take tens or hundreds of thousands of years to reach them.
(HW Question) Given that life on Earth appears to have arisen quite easily and rapidly suggests that the factor fₗ, in the Drake equation could be close to
1
What are the four non-intentional signals?
1.) Leakage radiation like radio, TV, and other broadcasts from us. 2.) Alien communications between home planets/colonies. 3.) Megastructures 4.) Products of technological activity, like gamma rays from fusion propulsion systems, etc.
What two methods do we consider when deciding where to point SETI telescopes?
1.) Sky survey; surveying the entire sky with the telescope's "beam". 2.) Targeted search; Pointing at the nearest (>50-1000 light yrs) stars roughly like the Sun.
What two conclusions were had at the 1961 convention where the Drake Equation was presented?
1.) There are 1000 to 100 million active, communicative civilizations in the galaxy. 2.) The most constraining parameter of the equation is the L component (avg. lifetime of civilizations). Once a civilization gets to the point of communication, they also get to the point of self-determined extinction.
(HW Question) The Luyten 726-8 binary system is approximately 9 light-years away. If we send a spacecraft to visit this system traveling at 90% of the speed of light, how long will a one-way trip take (as measured from the Earth)?
10 yrs
(HW Question) Try the following sample numbers in the Drake equation (Number of Civilizations = Ne x flife x fciv x L). Suppose there are 1000 habitable planets in our galaxy, that 1 in 10 habitable planets has life, that 1 in 4 planets with life has at some point had an intelligent civilization, and that 1 in 5 civilizations that have ever existed is in existence now. How many civilizations would exist at present?
5 civilizations
What is a lightsail, and how has the Breakthrough Starshot aided in its development?
A lightsail is a highly reflective sail, pushed by immense radioactive pressure from gigalazers to accelerate said lightsail to 20% the speed of light. Breakthrough Starshot is a project that aims to do exactly that, but with a smaller sail, and a nanochip attached to collect data.
(HW Question) Which of the following cases in the Drake equation would be the minimum necessary condition for us to be the only intelligent civilization currently in our galaxy?
Any one of the factors to be zero.
What is the difference between Artifact SETI and Communication SETI?
Artifact SETI aims to prove that some observed phenomena cannot be natural, while Communication SETI casts an impossibly wide net to search for unnatural signals originating from alien civilizations.
(HW Question) Traveling at their current speeds, how long would it take the Pioneer and Voyager probes to travel the distance to the nearest stars?
At least 100,000 yrs
In short, what does Fermi Paradox say?
At the speed our technology can travel, other, faster civilization's technology should have reached us already, given the 10 billion year old Milky Way Galaxy we live in. "Where is everybody?"
What is bandwidth?
Bandwidth is the range of a frequency.
Why do most astronomers think that the search for biosignatures - and not SETI - will more likely lead to the first detection of probably extraterrestrial life?
Because even life on Earth was "just" microbial for most of its history, meaning it is more likely we detect microbial life than advanced life.
(HW Question) Why do most astronomers think that the search for biosignatures and not SETI will more likely lead to the first detection of probably extraterrestrial life?
Because even life on Earth was microbial for most of its time.
What is binary code and why is it important to sending signals into interstellar space?
Binary code is the use of ones and zeros to code messages, and due to its simplicity, we assume all intelligent civilizations would understand it and thus have used it in our interstellar messaging.
What is Breakthrough Listen?
Breakthrough Listen is the largest ever scientific research program aimed at finding evidence of civilizations beyond Earth. The scale of this search effort is unprecedented.
Aside from infrared/thermal radiation, how else can we detect alien megastructures?
By using the transit method, we could detect a difference in shape of what would otherwise believed to be a planet in transit.
(HW Question) Which is the most common type of spacecraft propulsion used today?
Chemical rockets
What are some of the big explanations to the Fermi Paradox?
Explanations to the Fermi Paradox are that we have been visited before (unexplained UFOs), that we are a "zoo" to alien civilizations, that technology for aliens has progresses so far that aliens choose to conceal themselves with said tech, and lastly, the Great Filter says that all life hits a filter that determines if the civilization will collapse or not.
Who is credited with the creation of SETI?
Giuseppe Cocconi and Philip Morrison are credited with the creation of SETI.
Why do we value the radio signal of hydrogen?
Hydrogen is extremely prevalent in our universe, so we believe that aliens would recognize the frequency of hydrogen.
(HW Question) Approximately how soon might we expect an immediate response from a civilization that received the signal we sent to the globular cluster M13 (21,000 light-years away) in 1974?
In 42,000 yrs
What are the two kind of signals SETI has found?
Intentional and non-intentional signals.
(HW Question) Which of the following factors in the simplified Drake equation is least well known?
L fraction of civilization-bearing planets that have intelligent civilizations on them now.
What is a Dyson Sphere?
Named after Dyson, a Dyson Sphere described a megastructure constructed by an energy-hungry civilization around a system's star, harnessing the full power of said star. This would not make detecting the star impossible, though, as the infrared radiation would still exist.
What is "noise"?
Noise, in this context, describes anything that is not an alien signal.
(HW Question) On the basis of the scientific method, which of the following would be considered conclusive evidence that we are being visited by aliens?
None of these: an eyewitness account claims of alien abduction made under hypnosis a photograph a well-done TV documentary
What two forms of nuclear, hyper-fast interstellar travel are proposed?
Nuclear fission pulse propulsion is the explosion of a nuke behind a vessel that propels the reaction forwards at 5% the speed of light. Nuclear fusion fuses hydrogen and nitrogen to create an energy reaction that accelerates the vessel at 12% the speed of light!
(HW Question) Which of the following factors in the simplified Drake equation is best known?
Nₑ; the number of habitable planets in our galaxy.
What is the importance of Optical SETI (OSETI)?
OSETI is the response to the new belief that extraterrestrial civilizations may prefer/operate off of optical signals using laser pulses.
(HW Question) Our best hope for determining that life on an extrasolar world lies in...
Obtaining spectra that allow us to determine atmospheric composition.
(HW Question) Suppose there are a million habitable planets in our galaxy, that one in ten are habitable, that one in a thousand planets with life had at some point had an intelligent civilization, and that one in a hundred civilizations that has ever existed is in existence now. Given this, how many civilizations are in existence now?
One
What is the significance of Oumuamua?
Oumuamua was the first interstellar object we've ever detected! We still aren't certain what it was, as its immense velocity, strange shape, and non-gravitational acceleration make it unlike a comet.
(HW Question) In the Drake equation, a value of fₗ that is close to one and a value of f꜀ that is close to zero would imply:
Primitive life is common but intelligent life is rare.
What is the significance of Project Ozma?
Project Ozma (1960) was led in secret by Frank D. Drake, and was humanity's first attempt to detect interstellar radio transmissions. He searched on the level of hydrogen's frequency, and received a false positive.
Why do we believe that radio telescopes are the best telescope to use to listen and/or send interstellar messages?
Radio telescopes concern radio signals, of which various frequencies allow us to have a range of perceptible signals from our universe.
Why does radio SETI focus on the 1 to 10 GHz frequency range?
SETI focuses on the 1 to 10 GHz frequency range because the background noise is the lowest at these frequencies.
What is SETI?
SETI is the "Search for Extraterrestrial Intelligence", searching for signals from extraterrestrial civilizations and NOT biosignatures.
What is SETI@Home?
SETI@Home was a program that sent small data packages over the internet to people at home, who, when their computer went idle, would be used to process said data, before sending it back to SETI.
What is special about "Tabby's Star"?
Tabby's Star has unusual light fluctuations, sometimes dimming 22% in brightness! It's been concluded that the dimming were wavelength-dependent, becoming more dimmed in ultraviolent detections than in infrared ones.
What is the "Wow!" signal?
The "Wow!" signal was a strong radio signal from somewhere in space of unknown origin, that did not repeat.
What is the Allen Telescope Array?
The Allen Telescope Array was an array of many smaller radio telescopes to create the effect of one massive radio telescope dish. The ATA allows for 24/7 observation!
What is the purpose of the Drake Equation?
The Drake Equation calculates the number of active, communicative civilizations in our galaxy with which communication is possible.
What was the original purpose of the Pioneer Satellites?
The Pioneer satellites were first intended to observe our outer Solar System, but became the accidental first interstellar travelers.
What is the Rare Earth Hypothesis?
The Rare Earth Hypothesis is the theory that complex life (like on Earth) are extremely rare, due to a series of extremely low-probability events.
What is the SETI Institute?
The SETI Institute is the privately owned SETI institution once the US Government stopped funding public SETI research. Led by Jill Tarter, the SETI Institute created the Allen Telescope Array.
What are the Voyager Golden Records/Disks?
The Voyager Golden Records/Disks contain images and audio from Earth.
What does the "L" stand for in the Drake Equation?
The average lifetime of an intelligent civilization. In order for the "N" to be a large #, L must be a large #. (L) Once a civilization reaches the point of communication, it also reaches the point of self-determined extinction.
What does "Nₑ" stand for in the Drake Equation?
The average number of habitable planets. (Nₑ)
What does "R" stand for in the Drake Equation?
The average rate of star formation in our galaxy. (R) i.e. how many stars in the Milky Way?
What does "fₚ" stand for in the Drake Equation?
The fraction/amount of stars with planets. (fₚ)
What does "fᵢ" stand for in the Drake Equation?
The level of intelligence of the civilization. Mostly philosophical, as our definition of intelligence could be inaccurate. (fᵢ)
What does "f꜀" stand for in the Drake Equation?
The level of technology, and thus, the level of ability to communicate with other civilizations such as our own. (f꜀)
What does "fₗ" stand for in the Drake Equation?
The number of habitable planets on which life actually emerged. (fₗ)
(HW Question) Scientists acknowledge that even in careful studies, they have been unable to explain about 10% of UFO sightings. Given that fact, why don't scientists generally accept that UFOs are alien spacecraft?
There are many possible explanations for the unexplained sightings besides alien spacecraft.
(T/F) 90% of UFO sightings are caused by natural or human-made phenomena, and 10% have gone unexplained.
True. 90% of UFO sightings are explained, 10% are not.
(T/F) Excluding 1974, SETI only searches for reception of signals, and not the transmission of signals.
True. SETI searches for civilizations signals sent, not civilizations listening to us/our signals.
What are Kardashev's three classifications of extraterrestrial civilizations (based on their total power supply).
Type I: Can harness a planet's entire energy supply (K1) Type II: Can harness a star's entire output (K2) Type III: Can harness an entire galaxy's output (K3)
What do we know is almost certain when it comes to determining how alien civilizations will try to communicate across lightyears of space?
We are almost certain aliens will use photons, the fastest and cheapest way to transmit information that exists (as far as we know), to try and communicate across light years.
What kind of bandwidth do we look for when searching for alien signals?
We look for narrow bandwidths when looking for alien signals, as more power can be packed and directed into a narrow bandwidth.
Why should we use the radio frequency to listen and/or send interstellar messages?
We should use the radio frequency to send/listen to interstellar messages, as radio has no problem penetrating interstellar dust, radio photons are cheaper to send than optical photons, and above all, noise is minimal in radio signals.
(HW Question) Suppose that a civilization is never able to build spacecraft that can travel faster than a few percent of the speed of light. Could they still colonize the galaxy? Why or why not?
Yes, in principle, within as little as about ten million years.
(HW Question) Suppose that we discover life on Mars with an origin independent of life on Earth. Which term in the Drake equation would be most affected?
fₗ
