Phys 214. Planets and Life

Transcription

1 Phys 214. Planets and Life Dr. Cristina Buzea Department of Physics Room (Please use PHYS214 in subject) Lecture 8. The scale of time and nature of worlds (Page 64-74) January 23

2 Contents Textbook: Pages The scale of time - the cosmic calendar The Observable Universe The nature of worlds How do other worlds in the Solar System compare to Earth Acknowledgment: images NASA, ESA, Hubble, NOAO, AURA, NSF

3 The cosmic calendar The Universe is 14 billion years old. 14,000,000,000 How do we grasp the meaning of this number? Let s imagine we compress the entire history of the Universe, from the Big Bang to present, into a single year THE COSMIC CALENDAR

4 Jan 1 The Big Bang Feb The Milky Way Many generations of stars lived and died in the subsequent months, enriching the galaxy with heavier elements. Sept Solar System & Earth (about 4.5 billion years ago) Sept 22 early life on Earth (more than 3.5 billion years ago) living organisms remained microscopic in size until Dec 17. The cosmic calendar The Big Bang is on Jan 1st, and the present is the stroke of midnight on Dec 31. Each month is a little more than one billion years, each day ~ 40 million years, each second more than 400 years.

5 The cosmic calendar Dec 17 Cambrian explosion (545 million years ago) Incredible animal diversity Dec 26 Rise of dinosaurs Dec 30 Dinosaurs extinction (65 million years ago) The death of dinosaurs allowed other species to evolve. Dec 31, 9 pm early hominids (human ancestors) 60 million years later after dinosaurs extinction

6 The cosmic calendar Dec 31, 11:58 pm Modern humans evolve The entire history of human civilization fits into just the last half-minute!

7 The scale of time The fact that the Universe is so much older than Earth means that could be many worlds that had plenty of time for life to arise and evolve. These worlds might have had civilizations millions or billions of years ago. The scale of time holds sobering lessons for our own future. Species have come and gone in the months of the cosmic calendar, and there is no reason to think that our fate should be different.

8 How big is the Universe? The Universe could be infinite, and contain an infinite number of galaxies. The age of the universe poses some limitations on the portion of the universe that we can observe with telescopes, due to the limited value of the speed of light. When we look to great distances, we are also looking far back into the past.

9 The observable Universe Andromeda (M31) Andromeda located 2.5 million light-years away. The photo shows the galaxy as it was 2.5 million years ago, long before modern humans existed. It takes 200 million years to rotate once. Probably looks similar today. However, at much greater distances we begin to see back to a time when the universe looks different than today.

10 The observable Universe FAR: We see a galaxy 7 billions light-years away as it was 7 billion years ago, when the Universe was half its current age of 14 billions years old. FARTHER: : We see a galaxy 12 billions light- years away as it was 12 billion years ago, when the Universe was about 2 billions years old. The limit of our observable universe: Light from nearly 14 billion light-years away shows the universe as it looked shortly after the Big Bang, before galaxies existed. Beyond the observable universe: We cannot see anything farther away than 14 billions light-years away, because its light has not had enough time to reach us.

11 The observable Universe Our observable universe - the portion of the entire universe that we can potentially observe lie within 14 billion light-years of Earth. Implications: 1) We cannot observe anything more that 14 billion light-years away. This does not mean that nothing exists beyond that distance or that the universe might not be infinite. 2) We are the center of our observable universe, since it is defined by a light-travel distance in all directions from us. This does not implies we are the center of the Universe. Every observer in another part of the universe must be at the center of his observable universe.

12 Movie Hubble 15 years of discovery Chapter 9. Looking to the end of time (9 minutes + credits ~15 min)

13 Number of galaxies in the observable universe Because the observable universe has a finite size, it must contain a finite number of galaxies. We do not know how many, because there are too many to count and some galaxies are too faint to be observed. By counting the galaxies in the photo, the observable universe has an estimate of about 100 billion galaxies. Hubble Ultra-Deep Field. More than 10 days of exposure, it shows galaxies some at more than 12 billion light-years away.

14 Number of stars in the observable universe The Universe has an estimate of 100 billion galaxies. Milky Way has an estimate of 100 billion stars. 100 billion x 100 billion = 10,000,000,000,000,000,000,000= stars The number of stars in the observable Universe is comparable to the number of grains of sand on every beach on Earth. Due to the incredible size of the universe, our search for extraterrestrial life will probably be limited to within our Milky Way.

15 The nature of worlds - solar system

16 The solar system (1) All the planets orbit within a few degrees of the equatorial plane of the Sun (2) Most of the planets have a rotation axis roughly perpendicular to the plane of the solar system Both Pluto and Uranus have rotations that are highly inclined to the plane of the solar system (3) Planets are divided into rocky (terrestrial), gas giants

17 Two major type of planets Terrestrial planets - small, made mostly of rock & iron with high densities, near the Sun. Jovian planets -large, made mostly of gases and liquids with low densities, far from the Sun

18 Terrestrial planets All are similar in overall composition, however their surface looks quite different. Small, made mostly of rock & iron, high densities, close to the Sun (< 5AU), no rings

19 Jovian planets - gas giants - Large - Made mostly of gases with a rocky core - Low densities - Far from the Sun (> 5AU) - Have rings Jupiter- failed star -miniature solar system many moons

20 Jovian planets - gas giants The pressure inside is so high that the gases are compressed into liquid and metallic phases = large magnetic fields Less likely to be habitable if we assume life needs a solid surface or oceans. When we are looking for habitable planets in other star systems we should look for terrestrial planets.

21 Gas giants - Jupiter

22 Gas giants - Jupiter

23 Gas giants - Saturn

24 Gas giants - Saturn North pole South Pole Saturn dragon eye storm

25 Gas giants - Uranus and Neptune

26 Dwarf planets and small bodies orbiting the Sun True Colours of Pluto The Solar Systems goes beyond Neptune -the outermost of the official planets. Pluto counted as a ninth planet until 2006; orbits at a distance about a third farther from the Sun than Neptune. There are thousands of icy objects sharing Pluto s region. An object larger than Pluto was discovered in 2005 Eris (Xena). Dwarf planet - object large enough for their own gravity to make them round. Small body object low enough in mass to take any other shape than round.

27 Small bodies orbiting the Sun - asteroids Eros (image 12 m across) Gaspra (Galileo spacecraft 1991) Asteroids made mostly of metal and rock. Asteroids resemble a terrestrial planet in composition, but are too small to count as a planet itself.

28 Small bodies orbiting the Sun - asteroids Asteroid Itokawa, copyright ISAS, JAXA Asteroids made mostly of metal and rock. Asteroids resemble a terrestrial planet in composition, but are too small to count as a planet itself..

29 Small bodies orbiting the Sun - comets Comet Neat, 2004 Comets made mostly of rock and ice. Comets grow tail when they come close to the Sun. Comet Machholz

30 Comet Neat, 2004 Small bodies orbiting the Sun - comets Comet Wild 2's Heart Comet C/2002 T7

31 Small bodies orbiting the Sun Most asteroids orbit in the region called the asteroid belt, which lies between the orbits of Mars and Jupiter. Comets come from the Kuiper belt and the Oort could.

32 Small bodies orbiting the Sun The Kuiper belt is immediately beyond the orbit of the planet Neptune. The Oort cloud is ar from the Sun in a spherical cloud surrounding the solar system.

33 Small bodies orbiting the Sun

34 Small bodies orbiting the Sun Pluto is a member of the Kuiper belt, along with many of other moderately large objects. These objects are unusually large comets, having the same composition with smaller comets that occasionally fall inward towards the Sun.

35 Small bodies orbiting the Sun Jupiter role in reducing space debris in the inner solar system - cosmic vacuum cleaner discovered in March 24, 1993 by the Shoemakers and Levy Unlike all other comets, it was orbiting Jupiter rather than the Sun

36 Could dwarf planets or small bodies be habitable? Probably not. They are too far away from the Sun and are too cold for liquid water to exist. They are important to life because they occasionally crash into planets and moons and have a profound effect on the living organisms that inhabit the planet.

37 Moons Terrestrial planets have few moons. Mercury and Venus have no moons at all. Mars has two very small moons, probably captured asteroids. Moons are common for Jovian planets, totalling at least 150 moons together.

38 Moons Jupiter moon Ganymede and Saturn moon Titan are larger than planet Mercury. Saturn s moon Titan (2,575 km) Mercury (2,440 km radius) Jupiter Moons: Ganymede (2,634 km), Callisto (2,403 km), Io (1,821 km), Europa (1,565 km)

39 Moons Io (1,821 km), Europa (1,565 km), Titan (2,575 km) Many moons are planetlike in almost every way except their orbits. Some moons are geologically active, others have water, other atmosphere. Io is the most volcanically active world in the Solar System. Europa has occasionally water or ice floating on its surface. Titan has an atmosphere thicker than the Earth. Large moons around jovian planets offer a second category (after terrestrial planets) of potentially habitable worlds.

40 Next lecture Nebular theory - the formation of the solar system + movie