Unit 10 Topic 3.5 Out of our Neighbourhood Flashcards
1
Q
What is the Drake Equation?
A
N = R* × fp × ne × fl × fi × fc × L
2
Q
What does the Drake Equation calculate/find?
A
- Formulated as a guide for estimating the potential number of communicative civilizations in our Milky Way galaxy; understanding the factors influencing the existence of extraterrestrial intelligence.
3
Q
R*
The Drake Equation
A
- R* represents the average rate of star formation in our galaxy
4
Q
fp
The Drake Equation
A
is the fraction of those stars that have planets
5
Q
ne
The Drake Equation
A
stands for the average number of planets that could potentially support life
6
Q
fl
The Drake Equation
A
fl is the fraction of planets where life actually develops
7
Q
fi
The Drake Equation
A
is the fraction of planets with intelligent life
8
Q
fc
The Drake Equation
A
is the fraction of civilizations that develop technology capable of interstellar communication.
9
Q
L
The Drake Equation
A
is the lifespan of technologically advanced civilizations.
10
Q
Until recently, the only reasonable estimate we had was for…
A
- R*, around 7 stars per year (with about 1 or 2 of them similar to our sun). The galaxy has an estimated 100 – 400 billion stars
- Now, however, we have started to consider estimates of fp and ne.
11
Q
How was the first exoplanet discovered?
A
- While it was long suspected that other stars had planetary systems, the first exoplanet wasn’t discovered until 1992.
- This initial discovery was unusual, as the planet orbited a pulsar, the remnant of a massive star that exploded in a supernova.
12
Q
Finding Exoplanets
Difficulties + wobble (how can wobble be detected)?
A
- Direct imaging of exoplanets was difficult due to the overwhelming brightness of their host stars.
- However, planets exert a gravitational pull on their stars, causing them to “wobble“
- This wobbling can be detected by observing changes in the star’s light, known as Doppler shifts
13
Q
Doppler Effects/Shifts
A
- Shifts are caused by the star’s motion towards or away from the observer
- As an object in space moves toward you, the frequency of the light waves reaching an observer will be higher (blue light), while those moving away from you will have a lower frequency (red light)
14
Q
Redshift/blueshift for an orbiting exoplanet
A
The light shifts towards the red end of the spectrum as the star moves away from the observer and towards the blue end as it moves close
15
Q
How did the Kepler mission detect exoplanets?
TRANSITS
A
- When a planet moves in front of its star (transits), the light getting to Earth dims just a little.
- If the blink repeats, it represents a planet orbiting its star. The higher the blink frequency, the closer the planet is to its star (thus, faster orbit)
16
Q
What else can be found out from transiting exoplanets?
A
- In addition, the amount by which the star dims depends on its size and the planet’s size.
- If you know a planet’s mass by measuring the Doppler shift technique and the size of the planet (volume) from transits, you can also calculate a planet’s density: Density = Mass / Volume.
17
Q
When can a planet be confirmed?
A
A planet is considered “confirmed” once it is verified through additional observations using two other telescopes.
18
Q
Categories of Exoplanets
A
- Gas Giants
- Neptune-like planets
- Super-earths
- Terrestrial planets
19
Q
Gas Giants
& example
Categories of Exoplanets
A
- Gas giants, like Jupiter and Saturn, are primarily composed of helium and hydrogen
- 51 Pegasi-b, the first exoplanet discovered orbiting a sun-like star, is a gas giant located 50 light-years
- It’s believed that 51 Pegasi-b formed in the outer regions of its solar system (beyond the snow line) and only subsequently migrated inwards towards the star
20
Q
Neptune-like planets
Categories of Exoplanets
A
- These planets are gaseous, similar to Neptune in our solar system.
- They have a range of compositions but are mostly made of hydrogen and helium.
21
Q
Super-Earths
Categories of Exoplanets
A
- Super-Earths are rocky planets that may or may not have atmospheres.
- Larger than Earth but smaller than Neptune
- Some Super-Earths with thick atmospheres are called Mini-Neptunes.
- There are no Super-Earths in our solar system, although they appear to be common in planetary systems around other stars
22
Q
Terrestrial Planets
Categories of Exoplanets
A
- Planets close to Earth-sized or smaller
- Projecting the current discovery of exoplanets to the scale of the galaxy, it is thought that around 50% of the sun-like stars may have rocky planets in the habitable zone.
23
Q
Finding Other Earths
What are “other earths”?
A
- “Other Earths”: a planet with an oxygen-rich atmosphere and a biosphere
- However, determining which (if any) exoplanets have a biosphere is very difficult
- We can narrow the search by focusing on planets similar to the only world in the universe that we know has life, our own.
- So, if we are looking for another Earth, we need to find rocky planets within the habitable zone of their stars where surface temperatures would allow for liquid water on its surface.
24
Q
Habitable zones - where have earth-sized planets been found around?
A
- Most Earth-sized planets have been found around red dwarf stars
- Red dwarfs are long-lived (around 100 billion years), smaller and less luminous than our sun and as a result, the habitable zone is much closer to the star.
- Unfortunately, this would expose any planets in that zone to high radiation levels
25
Habitable zones - OUR SUN
* Our Sun has a **broad habitable zone**, and radiation levels are much lower than those of M-type stars.
* G-type stars, however, are much less common and have a shorter life span (around 10 billion years) than M-types.
26
Habitable zones - where have earth-sized planets been found around? OTHER POSSIBILITIES
Another possibility is **Orange dwarfs**, which have properties intermediate between M and G-type stars.
27
What are the 4 candidates to support life?
* Proxima Centauri b
* The Trappist-1 system
* LHS 1140b
* Kepler-452b
28
Proxima Centauri b
## Footnote
What are the 4 candidates to support life?
* Orbits Proxima Centauri
* Similar in size and mass to Earth, **Proxima Centauri b resides within its star's habitable zone**, where temperatures could support liquid water.
29
Proxima Cantauri b - CONS
## Footnote
What are the 4 candidates to support life?
* However, Proxima Centauri is a **red dwarf star**
* This means its prone to frequent and intense flares, which could strip away the planet's atmosphere (if it exists) and expose its surface to harmful radiation, potentially hindering the development or survival of life.
30
The Trappist-1 system
## Footnote
What are the 4 candidates to support life?
* 40 light-years away, has seven Earth-sized planets, three or four of which reside within the habitable zone.
* These planets have masses and radii similar to Earth and are likely rocky.
31
TRAPPIST-1 - CONS
## Footnote
What are the 4 candidates to support life?
* Despite their potential, **TRAPPIST-1 is a red dwarf star** known for **frequent and intense stellar activity**.
* **The planets' close orbits around the star might lead to tidal locking**, where **one side always faces the star**, resulting in extreme temperature differences.
* However, a habitable zone could potentially exist between the two sides (a "twilight zone"), or a thick atmosphere might help distribute heat more evenly.
32
LHS 1140b
## Footnote
What are the 4 candidates to support life?
* **A super-Earth** located about 49 light-years away in the habitable zone of its star, LHS 1140
* It has a mass five times that of Earth and a radius 1.7 times larger.
* Initially thought to be a rocky planet with a thick atmosphere, **further observations suggest** that LHS 1140 b might be **an ocean world without a solid surface.**
33
LHS 1140b - habitable zone (and what this means for life)
## Footnote
What are the 4 candidates to support life?
* While on the **edge** of its star's habitable zone, LHS 1140 b could have surface temperatures around 23°C if it has a greenhouse effect just twice that of Earth.
* If confirmed, perhaps LHS 1140 b supports an entirely aquatic biosphere.
34
Kepler-452b
## Footnote
What are the 4 candidates to support life?
* often referred to as Earth's "cousin," is located 1,400 light-years away in the constellation Cygnus.
* It orbits a star similar to our Sun at a distance that places it at the inner edge of its star's habitable zone.
* Kepler-452b is a super-Earth, about 60% larger in diameter than Earth and has a mass five times greater.
35
Kepler-452b
## Footnote
What are the 4 candidates to support life?
* The planet's larger size and potentially thicker atmosphere could support a stable climate, but **its age, estimated at 6 billion years, raises concerns**.
* As its star ages and brightens, the planet could experience a **runaway greenhouse effect**, drastically altering its surface conditions and possibly making it inhospitable to life.
36
Using atmospheric biosignatures to observe life on exoplanets
## Footnote
Transmission spectroscopy
* **Transmission spectroscopy**, a technique that analyzes the light passing through a planet's atmosphere, offers a promising approach.
* Dark lines (absorption features) in a spectrum correspond to specific molecules or elements.
* By studying these absorption features in the light from a transiting exoplanet, we can potentially determine the composition of its atmosphere
37
Using atmospheric biosignatures to observe life on exoplanets - presence of oxygen would imply...
## Footnote
Transmission spectroscopy
* A very high concentration of oxygen in an atmosphere could suggest the presence of a process like **photosynthesis**.
* If Earth's biosphere were to vanish suddenly, the atmospheric oxygen level would significantly decrease within five million years due to reactions with rocks and other Earth materials.
* Therefore, **a high oxygen level might indicate ongoing biological activity replenishing the supply.**
* However, it's important to remember that some non-biological processes can also produce oxygen.
38
Using atmospheric biosignatures to observe life on exoplanets - other possibilities
* Another possibility is looking for **seasonal changes in gasses like methane or carbon dioxide**, perhaps representing the **variations in life processes between summer and winter**.
* The James Web Space Telescope (JWST) has been examining some planetary atmospheres using this technique, but the JWST was not explicitly designed for this task. We may have to wait for the next generation of telescopes to explore exoplanet atmospheres more fully.
39
Can we accurately estimate the value of N in the Drake equation?
* No
* Our knowledge of the percentage of planets that may support life fl is still highly uncertain.
