2-7 Flashcards
What is the Fermi Paradox?
Contradictions between the probability and existence of extraterrestrial life and the evidence for such civilisations
How will we prove the Fermi Paradox?
either exploration of the galaxy and beyond or communication with an alien race
When do we have records for life on the plannet?
No records for the first 0.5-1 billion years but the following 3 billion years
How old is the earth and our solar system?
4.6 billion years old
When was the oldest fossil form of life and what was it?
3.6 billion yrs ago - simple cells: prokaryotes
How are the rocks and fossils dated?
Radiometric dating
When were the first fossils of animals found?
600 million years ago
when did modern humans appear?
300,000 years ago
What are the two ways of identifying the ways in which the universe began?
Hypothisis driven and discovery science
What is hypothisis driven science?
GUess how it happened and then re-create scenario in lab
What is discovery science
Seeks examples in nature that might provide vital clues
What is copernicus’ model?
The theory that the sun is at the centre and there are other planets, in 1543
What is the scientific method?
Ask Questions > Background research > construct hypothosis > Test with experiment > analyse results > true or false»_space; report and if false , reconstruct hypothsis
What happens if a hypothsis is true, after a large number o different testing methods?
It achives the status of a law
Why are laws important for science?
They provide the underlying basis of scientific speculation, allowing us to pridict things that have not yet been observed
What is cosmic loneliness
The growing responsibillity of our responsibillity to planet earth
What is the golden age of astrobiology?
new ideas and tech help scienticst from many diciplines answer fundemental questions about life in the universe
What is SETI?
Search for extrarerrestrial intelligence
What is a star?
- Ball of plasma held together by its own gravity
- where nuclear fusion takes place at the core
- the temprature and luminosity are determined by the stars mass
- most stars are hydrostatic - at equilibrium between gravitational collapse and outward radiation pressure
What is a temprature luminosity diagram?
- The Hertzsprung-russell diagram shows the temp (X) and luminosity (Y) of stars
- most stars fall on the main sequence and go from hot and bright (top left) to cool and dim (bottom right)
What is stefan-boltzmann’s law
- hotter stars are the brighter ones
- luminosity goes up very fast with temprature
What is luminosity
Brightness
- Bigger stars have more surface and are brightter
Where do white dwarfs, red giants and red supergiants fall on the HR diagram
- white dwarfs fall bellow the main sequance
- giants fall above it
What are stars in the main sequence doing?
Stars in the main sequence spend most of their time fusing hydrogen into helium
How are the spectral element of stars calculated?
Letters O-M, our sun is G
Tell me about our sun
- 150 million km from earth
- 330,000 times larger in mass
- G type on the main sequence
- Surface temp is ~5800K
- 4.6 billion years old
What is a sunspot?
Cooler regions in the solar photosphere due to intense magnetic strength which inhibits convection
What is known as the proton-proton cycle
Nuclear fusion - conversion of mass into energy (E=mc^2)
What is the proton-proton cycle
- Two protons fuse to produce deutrium + a positron + a neutrino
- Another proton fuses with the deuterium to produce a nucleaus of helium and a photon
- two helium nuclie to produce a single helium with 2 more protons
what is the rate of mass to energy on the sun?
~4.2 billion kg of mass is converted to energy a second on the sun
What is the mass of the sun
~2x10^30 - so the sun will last 10^10 years (10 billion)
Why is temprature important for fusion?
- for proton-proton cycle, the protons need to come close together
- normally this would be hard because they have identical charges but with enough speed, they overcome the mutual electrostatic repulsion
- they need to get less than 10^-15m of each other for fusion - can only be achieved when above 10 million K
- the heat generated by a star also balances out the inflow of gravitational energy
What is the natural self balancing method?
if the star procuces more energy, it expands slightly. the expansion causes it to cool slightly and reduces the energy output and vice versa
How does the mass of a star affect its lifetime
Larger stars with more mass have higher temps and faster fusion, so burn up their mass quicker. Smaller ones have lower, so burn for longer
USe the equation ;;;
Lifetime = 1 m (mass)^2.5
Why are only certain stars able to facilitate nursaries of life?
Because they are not around for long enough - F - GKM are around for long enough
How many stars in our galaxy are there where there could be life?
8 billion stars to study that could have life
what produces the energy of a star
PP chain and nuclear fusion
What is a brown dwarf
An object with not enough energy to turn on A pp chain
how do we know that stars evolve?
by comparing HR diagrams of different star clusters
What is the star nutrino problem
Models of the sun pridict we need 2-3x more neutrino flux than that which we measure on earth -
The neutrionos emmitted in the pp chain are electron neutrinos, one of 3 types of neutriono. They can change from one type to another, explaining the lower observed flux
What are stars created from
condensations in the interstellar medium
what is the interstellar medium
Matter in space, gas (ions, atoms, molecules), dust and cosmic rays
what conditons are likley to lead to the formataion of a star in the ISM
where ISM is dense and temperatures are low, because the low temp means less internal pressure and more chance of condensation
What are some examples of star site formation
Dark nebulae - have high concentrations of dust
Elephants trunk 0
Eagle nebula
What are the conditions inside a nebula
- High density - upto 10,000-10^6 particles per cubic cm
- low temperatures - rouughly 10k
What is room temprature in kelvin
293k
How large is a nebula
3-10 light years across and contains around ~1000 solar masses of material
What is the typical content of a nebula
74% hydrogen
25% helium
1% other elements
How does star formation take place
- a dense portion of the nebula begins to collapse under its own gravity (can be triggered by shockwaves) - the material usually has some small rotation which will increase to conserve angualr momentum
- The result is a spinning disk of material with a dense core (slows down spinning)
- once the density in the core reaches a critical limit, (10 million K) the fusion process switches on and the star is born
What is the temprature of a protostar>
2000-3000k
When and where to planetesmials form
at the same time as the formation of the proton star, in the cloud (rotating disk)
What happens to stars after they move onto the main sequance?
They become hotter and fainter
Describe stellar stabillity
- Stars are stable but change does take place
- sun has become 40% more liminous and 6% larger over last 4.6 billion years
- the sun will contiunue to increase in size and luminiosity until conditions on earth will be unbrarable for life 1 billion years from now
What is the effect of stellar stabillity on our plannet?
- Affect life and evolution
- galciar activity seems driven by the freqency of sunspots, influencing how much solar raditation reaches earth
How long does it take to evolve onto the MS
10,000 - 150 m years
Describe how elements heavier than helieim are formed
By fusion upto iron
exploding stars (supernovae) elements hevaier than iron
How much bigger is jupiter than earth
11.2x the sizeW
What is the order of things in our solar system?
Sun, Mercurary, Venus, Earth, Mars, Jupiter, Saturn, Uranus, neptune, Pluto
How did the sun form
- disk consisted of 98.5% gas (99% he and H) and 1.5% dust (carbon, iron and silica)
- formed protostar and planets in 100,000 yrs
- after 100,000 years, star reaches final mass and switches on as a star - disk turbulance decreases and dust settles into the centre of the disk
- this is called age zero
What factors are relevent for planet formation
Turbulence and temprature of and in disk
What is important bout terbulance in the formation of planets
If too turbulent, particles move too fast and bounce off each other
If less turbulant, greater chance particles collide and stick together
why is temprature important for the formation of planets in the disk
- at formation (4.6 billion yrs ago) temp cricial to decide which materials will be used to form which types of plannets
- temp declines at roughly 1/distnace^2 moving away from the new star
- critical point is the ice line, beyond which, hydrogen components (like water) condense inot solid ice grains
What is the ice line or frost line
critical point is the ice line, beyond which, hydrogen components (like water) condense inot solid ice grains
What is an astrimonical unit
the distance between the earth and the sun
Describe the habitation zones around a protostar
Inner zone (0.8-1.3 AU) - Dust was very hot and could not contain any residual water (1000K)
2-5 AU - temp remained low, so volitile organic substances can stay solid (below 500K)
beyond 5 AU - water no longer evapourates (less than 150K) - this water ice will be crusial to form the cores of giant plannets
What are plants outside of the frezing point made from?
Planets outside of the frezing point, at formation, are made mostley of silicates and those mast mars, carbon rich silicates, before those outside of satturen are made from ices
How long does it take to form plannets?
1000-100,000 years, takes longer than expected because the will be some residual turbulence – if there was no turbulence, objects of a few kilometers in diameter would form in very little time
when do planets mature into mid life
after around 100,000 years - we expect the central plane to contain around 100 billion objects of 1-10km in size – as they are rotating round the sun, they have many small collisions and gradually accumalate into larger masses
How do larger planetesimals form?
Inner planets are rocky and stuggle to gapture gas vecuase they have smaller masses
Outer planets have larger masses and a larger gravitational field
After around 1 million years, there will be around 20 objects the size of our moon, which will begin to influence the orbits of other bodies around them
What makes the core of the closest planets?
Iron
What types of planets are produced?
Type 1 - Jovians
Type 2 - Terrestrial
what are the charicteristics of jovians
Jupiter, Uranus, Neptune, Saturn
Hyrdogen and helium
low density
rapid rotation
deep atmouspheres
RINGS
lots of moons
Solid core - rock and ice - can only happen outside the ice line - needs to be > 10x earth mass – the core has the gravitational power to hold the large amounts of gas
What are characteristics of terrestrial planets
Mercury, Venus, Earth, Mars
High density
rock and metal
slow rotation
solid surfaces
no rings
few or no moons
Have a variety of atmoushphere gasses - co2, nitogen, oxygen
What is a comet
mostly ice and dust that comes from the outer solar system towards the sun and creates a tail
Left over from creation of solar system -4.6 b yrs ago
Range in size from few miles to 10s of miles
millions of these objects are in the Oort cloud - about 50,000 AUs away to 1 ly away
or in the Kuiper belt - a ring of icy objects beont the orbit of neptune (30-100AU)
What is an asteroid
small rocky body in the solar system
found mostly in the asteroid belt between mars and jupiter
they range in size gretaly
They used to be thought to be a the remains of a planet that jupiter prevented from forming but there is not enougth material to form a planet
formed 4.6 b yrs ago
different types - almost all contain nickl but classification is based on how much iron is contained
- C - carbonaceous
- S - Silicaceaus
- M - Metatlic
What is a meteroride
Small particle from an asterioid or comet orbiting the sin
what is a meteor
an object observed buring up as it enteres the earths atmoushphere (shooting star)
what is a meteorite
a meteorid that survives its passage throguh earths atmoushere and impacts the surface
What was the Hale-Bopp 1977
A comet which was obserable for 18 months and the brightest and most observable comet in the 20th c
How many astrinomical units make 1 light year
63241.1 AU
How would comets leave the oort cloud of Kuiper belt?
grvaitational pertubation of a nearby star cuases them to change their orbit
- enter a hyperbolic orbic, taking them through the solar system once before escaping completky
- enter an elliptical orbit and remain trapped
What is an elliptical orbit
comet that is orbiting a star in an elliptical shape
what is a hyperbolic orbit
orbit where comet flys through the solar system before escaping completely
Describe the tail of a comet
- increases with decreasing distance to the sun
- pointing away from the sun
- two tails - ion tail and dust tail (curved)
What was comet shoemaker-levy 9 (SL9)
greatest collision seen in the solar system
Collision into the side of jupiter in 1994
Fragmented proir to impact
thought to be a mile wide
What were the impacts of SL9
threw up debris 3000km unot the sky (for one fragement (G))
what are the greek camp and the trojans
asteroids orbiting with jupiter
Tell mne about C type asteroids
Carbonaceous Chondrites
C type
75% of all know asteroids
stony and metalic
need a telescope to see
Tell me about Silicaceous asteroids
S type
17% of asteorids
bright metalic nikel-iron mix with magnesium and iron slicates
Tell me about metallic asteroids
8% of asteroids
made from iron
bright, mostyly pure iron
only detected by telescopeshe
when were most creators produced?
around 3.5 billion yrs ago - see on the moon - earth liklkey suffered similar bombardment but weathered away impacts
what is ceres
largest astroid - diamter of 975 km
Why are asteroids not the remains of a destoyed plannet, as once thought?
because together, they have the mass of less than 1/1000 of earth so too small
What is the Chicxulub crater?
180km diamter
66 million years ago
75% of life extinct
