Lecture03

The orbital period is approximately 4 days.

It depicts a star system with multiple planets, illustrating the diversity of planetary systems beyond our own.

Approximately 6000 confirmed extrasolar planetary systems have been identified to date.

At least 50% of Sun-like stars are believed to have planets.

The Sun shines by energy released in thermonuclear fusion in its interior.

The Sun contains 99.86% of the mass in the Solar System.

There are eight planets in the Solar System, along with many smaller bodies orbiting the Sun.

The Sun generates energy by thermonuclear fusion of hydrogen (H) into helium (He) in its core.

Brightness and temperature on the main sequence increase sharply with stellar mass; more massive stars are much brighter and have shorter lifespans.

The Sun is currently a 'middle age' star in the main sequence phase, which lasts about 10 billion years.

The Sun formed about 4.6 billion years ago and will maintain a steady luminosity for another 5 billion years before evolving into a red giant and eventually a white dwarf.

After the main sequence phase, the Sun will first become a red giant and then transition into a white dwarf.

The four terrestrial planets are Mercury, Venus, Earth, and Mars.

Terrestrial planets are characterized by their small size and solid, rocky surfaces.

All have an iron-nickel core and a rocky shell.

Venus appears featureless in visible light due to its thick atmosphere composed mostly of carbon dioxide (CO2), which creates a dense cloud cover that obscures surface features.

The age of a sample can be determined by measuring the fraction of radioactive isotope that remains and comparing it to the amount expected to be there after a certain period of time.

The half-life of 238U is 4.47 Gyr, and it decays into 206Pb.

The Earth is estimated to be 4.57 billion years old.

The age of 4.57 billion years for the Earth is based on the dating of meteorites and the oldest materials found in the solar system, which provide a more accurate estimate of the Earth's formation time compared to surface rocks and minerals.

Carbonaceous chondrites are a type of meteorite that contain some of the oldest known material in the Solar System, with an age of 4.57 billion years determined through radiometric dating. They are significant because they provide insights into the early conditions and processes that shaped the Solar System and the formation of Earth.

Asteroids are primarily the source of meteorites, as solid particles, mostly fragments of asteroids, occasionally land on Earth as meteorites. Some asteroids remain largely unaltered since their formation, providing a direct link to the early Solar System.

The Cambrian radiation occurred, marking a period of rapid diversification of life forms.

The surface temperature of Venus is about 670 K, primarily caused by the strong greenhouse effect of its atmosphere, which traps heat.

The Venera-13 lander observed a rocky, orange-brown terrain with several flat, layered rocks scattered across the surface, indicating a geologically diverse landscape.

Mars has a thin atmosphere primarily composed of carbon dioxide (CO2).

The mean surface temperature of Mars is 220 K.

Olympus Mons is the largest volcano in the Solar System, standing at 24 km high. It is an enormous, dead volcano located on Mars.

The four Jovian planets are Jupiter, Saturn, Uranus, and Neptune.

Jovian planets are characterized by their large size and are located in the outer Solar System.

Jupiter has a mass of 318 times that of Earth and 0.001 times that of the Sun.

Jupiter has a radius of 11 times that of Earth and 0.10 times that of the Sun.

Jupiter is primarily composed of gas or liquid.

The Great Red Spot is an anticyclonic storm approximately 20,000 km across and over 300 years old.

Asteroids are rocky and metallic bodies found primarily in the inner Solar System, with a significant concentration in the asteroid belt located between Mars and Jupiter.

Kuiper-Belt Objects are objects made of rock and ice found beyond Neptune in the outer Solar System. They are remnants from the formation of the Solar System.

Pluto is a member of the Kuiper Belt, which consists of various objects that orbit beyond Neptune.

Meteorites are solid particles, primarily fragments of asteroids, that occasionally land on Earth. They are significant because they provide some of the most accurate estimates of the age of the Solar System and Earth.

The Chelyabinsk Fireball, which occurred in February 2013, was an air burst of a small asteroid approximately 20 meters across. This event illustrates the potential impact of meteorites on Earth, even when they do not result in a direct impact.

The largest known meteorite fragment weighs approximately 650 kg.

The Moon is a natural satellite that orbits the Earth.

Mercury and Venus are the only planets that do not have natural satellites (or moons) orbiting them.

Io is the most volcanically active body in the Solar System, which is surprising given its size and density are comparable to our Moon. This activity suggests Io is not geologically dead and indicates complex geological processes at work.

All planets orbit the Sun on nearly circular orbits, in the same direction, and in almost the same plane as the Sun's equator.

1 Astronomical Unit (AU) is approximately 1.496 × 10^11 meters.

The inner terrestrial planet orbits are within 1.5 AU of the Sun.

The outer giant planets are spaced between 5.2 and 30 AU.

Kant and Laplace hypothesized that the Solar System planets formed in a disk, which explains planets orbiting the Sun in the same direction, orbits lying in almost the same plane as the Sun's equator, and nearly circular orbits.

Protoplanetary disks are rotating disks of dense gas and dust surrounding young stars, where planets can form. They are significant because our Solar System formed in such a disk around the young Sun 4.6 billion years ago, providing the material necessary for planet formation.

Protoplanetary disks are directly associated with young stars, as they are formed from the residual material surrounding these stars. The disks are crucial for the process of planet formation, as they contain the building blocks of planets.

Molecular clouds are parts of the interstellar medium that are cold and dense, primarily composed of hydrogen in molecular form (H2).

The densest parts of molecular clouds can collapse under their own gravity into clumps, which form the cores of protostars.

The material forming the protostar usually has some rotation. As it contracts, it spins faster, leading to the formation of a protoplanetary disk around the protostar.

During the gravitational collapse stage, the material contracts and spins faster, resulting in part of it forming a protoplanetary disk with the protostar at the center.

The 'dark cloud' stage represents the initial phase of star formation where dense regions, known as 'dense cores', begin to form within a nebulous region. This is crucial as it sets the stage for gravitational collapse and subsequent star formation.

During the 'gravitational collapse' stage, a black hole or dense core forms at the center, with gravitational forces pulling material inward. This marks the beginning of the star's formation process, leading to the creation of a protostar.

A T Tauri star is defined by its red color, a protoplanetary disk surrounding it, and the presence of bipolar flow from its poles. This stage indicates that the star is still in the process of forming and has not yet reached the main sequence phase.

In the pre-main-sequence star stage, the planetary debris disk surrounds the red star, indicating the presence of material that may eventually form planets. This stage is crucial for the development of a planetary system around the star.

In the young stellar system stage, a yellow central star has formed, surrounded by orbiting planets, indicating the completion of the star formation process and the establishment of a planetary system.

Dust particles of rocks and metals collided and grew into km-sized bodies called planetesimals.

The final assembly of terrestrial planets could take approximately 10^8 years (0.1 billion years).

The temperature was cold enough for volatiles like water to condense into ice particles, providing additional solid material.

Solid bodies of 10 to 20 Earth masses could be formed rapidly in the outer solar system.

Giant planets formed as solid bodies accreted gas after forming from the available solid material in the cold outer solar system.

Terrestrial planets formed through the following stages:

1. Accretion of Micron-Sized Dust Particles: Dust particles coalesce into km-sized planetesimals.
2. Formation of Planetary Embryos: These planetesimals collide and merge into lunar-sized embryos.
3. Planet Formation: The embryos further collide and grow into full-sized planets.

Accretion Heating from collisions generates sufficient heat to allow for melting and differentiation of the planet's interior.

Denser elements such as iron (Fe) and nickel (Ni), which have higher melting points, tend to sink toward the center of a planet under the influence of gravity. This process contributes to the differentiation of a planet's internal structure, leading to the formation of a metallic core.

Giant impacts among planetary embryos are crucial for the final assembly of planets. These collisions help to merge smaller bodies into larger ones, facilitating the growth and development of planets, and are also important for understanding events such as the formation of the Moon.

The smaller chemical differences between the Earth's crust and mantle arose from later partial melting processes. This melting allows for the differentiation of materials, leading to variations in composition between these two layers.

They discovered the first extrasolar planet orbiting a Sun-like star, 51 Pegasi.

The graph shows periodic variations in the star's velocity, indicating the presence of an orbiting planet.

The minimum mass is approximately 0.5 M_Jupiter.

Some characteristics of extrasolar planetary systems include:

• Giant planets very close to the stars
• Planets on very eccentric orbits

Approximately 1000 systems have multiple planets.

v Octantis consists of:

• v Oct A: A large yellow subgiant star with a mass of 1.57 solar masses.
• v Oct Ab: A retrograde planet with about twice the mass of Jupiter, orbiting v Oct A.
• v Oct B: A distant white dwarf with a mass of 0.57 solar masses.

The retrograde orbit of v Oct Ab suggests that it may have formed under different conditions compared to typical prograde orbits, possibly indicating interactions with other celestial bodies or a complex formation history.

The distribution of Kepler planet candidates by size is as follows:

The Habitable Zone is the range of distances from a star where liquid water can exist on a planetary surface.

Earth is the only planet clearly in the habitable zone of our Solar System.

Examples include Mars, Europa, and Enceladus, which have had or currently have liquid water despite being outside the habitable zone.

Heavier main-sequence stars are brighter than lighter ones.

The Habitable Zone is located further from the star as the stellar mass increases.

Kepler-186f is notable for being the first Earth-size exoplanet discovered in the habitable zone of its star, which suggests it may have conditions suitable for liquid water and potentially life.

Kepler-186f has a radius of 1.11 times that of Earth, indicating it is slightly larger than our planet.

The mass of the star in the Kepler-186 system is 0.48 times that of the Sun, classifying it as a smaller star compared to our solar system's Sun.

The Kepler-186 system contains 5 planets, including Kepler-186f.

Relative Age refers to the order in which a sequence of past events occurred, indicating which layers or events are older or younger compared to others.

Rock units are laid down in a sequence, with the oldest units at the bottom and the youngest units at the top, allowing geologists to determine their relative ages based on their position.

Numerical Age is the actual time when a specific event occurred or when a specific material was formed or deposited, providing a precise age rather than a comparative one.

Radiometric dating is a method used to determine the numerical age of materials by measuring the radioactive decay of isotopes. It is important because it provides a reliable means to date geological and archaeological samples, helping to establish timelines in Earth's history and human evolution.

During alpha decay, a Uranium-238 atom (with 92 protons) decays into a Thorium-234 atom (with 90 protons), emitting 2 neutrons and 2 protons. This process reduces the atomic number and mass of the original atom, resulting in a different element.

In beta decay, a neutron in an atom emits an electron (which has a negative charge), a proton (which has a positive charge), and a neutrino (which has no charge). This process transforms the neutron into a proton, increasing the atomic number of the element.

During gamma radiation, protons in an atom transition to a lower energy state, emitting a photon. This process does not change the number of protons or neutrons in the nucleus but results in the release of energy.

As the proportion of parent atoms decreases exponentially over time, the proportion of daughter atoms increases exponentially. This is due to the process of radioactive decay, where parent atoms transform into daughter atoms, leading to a complementary relationship between the two curves.

Half-life is the average time it takes for half of a batch of nuclei of the same radioactive isotope to undergo decay. This concept is crucial for understanding the rates of decay and the timing of geological processes.

The half-life of 14C is 5730 years, and it decays into 14N.

The atmosphere became oxygen-rich, which was a crucial development for the evolution of aerobic life.

The Cenozoic era saw the evolution of mammals and humans.

It marks the time when the first life appeared on Earth, following a period of intense meteorite impacts.

Photosynthesis started around 3500 million years ago, which was essential for producing oxygen and supporting life.