SOLAR WIND

The corona, the sun's outer layer, reaches temperatures of up to 2 million degrees Fahrenheit (1.1 million degrees Celsius). At this level, the sun's gravity can't hold on to the rapidly moving particles, and they stream away from the star and thus form the solar winds.

The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma consists of mostly electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV.  Embedded within the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field.

At a distance of more than a few solar radii from the Sun, the solar wind is supersonic and reaches speeds of 250 to 750 kilometers per second. 

Effect on Earth

As the wind travels off the sun, it carries charged particles and magnetic clouds. Emitted in all directions, some of the solar wind is constantly buffeting our planet, with interesting effects.

If the material carried by the solar wind reached a planet's surface, its radiation would do severe damage to any life that might exist. Earth's magnetic field serves as a shield, redirecting the material around the planet so that it streams beyond it. The force of the wind stretches out the magnetic field so that it is smooshed inward on the sun-side and stretched out on the night side.

SUN - ITS ORIGIN AND FATE

It is a G-type main-sequence star (G2V, “yellow dwarf”). This lifespan began 4.6 billion years ago, and will continue for another 4.5 – 5.5 billion years.

The Sun is about half way through the most stable part of its life. During past four billion years, it has remained unchanged. This will continue for another four billion years. After that its hydrogen fuel will be exhausted. The various phases of its life cycles are as follows:

The Birth of the Sun:

According to this theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust. Then, about 4.57 billion years ago, a passing star, or shock waves from a supernova caused gravitational collapse at the center of the cloud.

From this collapse, dust and gas began to collect into denser regions. As the denser regions pulled in more and more matter, conservation of momentum caused it to begin rotating, while due to increasing pressure it heated up. Most of the material came at the center as a ball, while the rest of the matter flattened out into disk that circled around it. While the ball at the center formed the Sun, the rest of the material formed the protoplanetary disc. Eventually, the Sun became a main-sequence star.

The Main Sequence:

The Sun, is on the main sequence stage , during which nuclear fusion reactions in its core fuse hydrogen into helium which began 4.57 billion years ago.

Core Hydrogen Exhaustion:

After 5.4 billion years, Sun hydrogen will be exhausted in the core. Core will heat up and get denser, causing the Sun to grow in size till orbit’s of Mercury, Venus, and even Earth. It will then enter the Red Giant Branch (RGB) phase .

Final Phase and Death:

Sun will have approximately 120 million years of active life left.

In this phase, the core (full of degenerate helium), will ignite violently in a helium flash. The Sun will then shrink to around 10 times its current size and 50 times its luminosity. It will continue to burn helium in its core until it is exhausted. Now, it will be in its Asymptotic-Giant-Branch (AGB) phase, where it will expand again and become more luminous.

Sun will then become unstable and loose its mass. It will become larger each time and increase its luminosity. Eventually half of the Sun’s current mass will remain and its outer envelope will form a nebula.

The final, core temperature will be over 100,000 K, after which the remaining matter will cool to become a white dwarf. It will take trillions of years to fade it to black.

Ultimate Fate of our Sun:

When Sun ran out of hydrogen fuel, it would consume heavier fuel till nickel .

Then, iron would start to build up in the core of the star. When about 1.38 times the mass of the Sun is iron collected at the core, it would implode, releasing energy.

This energy would destroy everything in the Solar System. The energy might be enough to outshine the galaxy, and a new nebula would be visible from nearby star systems. All that would remain would be a rapidly spinning neutron star, or maybe even a stellar black hole. It will eventually collapse into a white star until it burns itself out.

A rapidly spinning neutron star, or maybe a stellar black hole will be remaining. It will eventually collapse into a white star until it burns itself out.

NEBULAR THEORY OF FORMATION OF OUR SOLAR SYSTEM

This theory was proposed by Kant and Laplace. According to this theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust. Then, about 4.57 billion years ago, a passing star, or shock waves from a supernova caused gravitational collapse at the center of the cloud.

From this collapse, dust and gas began to collect into denser regions. As the denser regions pulled in more and more matter, conservation of momentum caused it to begin rotating, while due to increasing pressure it heated up. Most of the material came at the center as a ball, while the rest of the matter flattened out into disk that circled around it. While the ball at the center formed the Sun, the rest of the material formed the protoplanetary disc.

The planets within a critical distance, where temperature was warmer, were rocky (terrestial), while those beyond the critical distance had solid cores and thick, gaseous atmospheres (jovian).

At the border of the solar system, where gravitational forces were weak, the icy bodies walked in eccentric orbits and formed asteroids, and when they get close to the sun, they formed comets.

Eventually, the Sun became a main-sequence star. Solar wind from the Sun created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space.

                                        solar nebular

                                    cloud collapse

                                        pancake

                               planet building

Difference between a nebula and galaxy

Nebula is a cloud of interstellar dust and other ionized gasses particularly helium and hydrogen. A galaxy on the other hand is a huge collection of stars that are held together by gravitational attraction. A galaxy contains star systems, star clusters along with interstellar dust.

DETERMINATION OF MASS OF PLANETS WITH RESPECT TO EARTH

The only way we can measure a planet's mass is through its gravity. The most commonly used technique is to observe a body orbiting or passing close to the planet and see how its path is affected by the planet's gravity.

For example, if we see a moon orbiting a planet at certain distance from it, the orbital period of the moon at that particular distance will mainly depend on the planet's mass. The more massive the planet, the more strongly it attracts the moon and faster the moon moves. It is easy for astronomers to calculate the planet's mass after we have observed the motion of one of its moons for a while.

After knowing the distance between the planet and the moon and the time it takes to complete one revolution is calculated, the weight of the planet can be calculated easily.

Mercury and Venus have no moons,  the only way to measure their gravity was to see how they affect other planets' orbits. Astronomers would measure very small changes in, Earth's orbit, that were caused by the attraction of Venus. So,it was hard to get the exact mass of Venus by this technique. But once spacecraft were launched to Venus and they flew close to it, scientists could easily measure its mass by tracking how these probes were deflected while passing by Venus. The same technique was used for Mercury when the Mariner 10 spacecraft flew by it in 1974.

DETERMINATION OF MASS OF EARTH

Newton, Galileo, Henry Cavendish, and Eratosthenes contributed a lot in this calculation

The mass of the Earth may be determined using Newton's law of gravitation. Newton's law of gravity formulates the gravitational force that two masses exert on each other and is given by

F = GmM/r²

                                                           where,  M and m are the masses  

                                                                        r is the separation between them

                                                                        G is universal gravitational constant                                      

                                                                                  (6.67 × 10⁻¹¹ m³/(kg sec²))

If we assumed that M is the mass of the Earth, and m is the mass of an object on the surface of the Earth, we can solve for M by equating Newton's Law of Gravity with his second law of motion

F = ma

We have:

F = GmM/r² = ma → GM/r² = a

Solving for M, the mass of the Earth,

a = 9.8 m/s²,
r = 6.38 × 10⁶ m, and
G = 6.67 × 10⁻¹¹ m³/(kg sec²)

we obtain:

M = ar²/G = 5.98 × 10²⁴ kg.

BODE'S LAW

Previous year papers questions related to Bode’s Law

1. Write a note on Bode’s law of Planetary position.                                  (2009-10,5 marks)

2. Define and state the Bode’s law with all its mathematical calculations? (2016-17, 15 mar)

3. What is Bode’s law? Which planet do not fit in Bode’s law and why? (2017-18,10 marks)

BODE’S LAW

The Titius-Bode Law is rough rule that predicts the spacing of the planets in the Solar System. The relationship was first pointed out by Johann Titius in 1766 and was formulated as a mathematical expression by J.E. Bode in 1778.The hypothesis correctly predicted the orbits of Ceres (in the asteroid belt) and Uranus, but failed as a predictor of Neptune's orbit.

The law relates the mean distances of the planets from the sun to a simple mathematics progression of numbers. It relates the semi major axis a of each planet outward from Sun :

  a = 4 + x

where x = 0,

3,

6,

12,

24,

48,

96,

192,

384

With the exception of the first two, the others are simple twice the value of the preceding number.

Add 4 to each number:

4

7

10

16

28

52

100

196

388

Then divide by 10:

0.4	0.7	1.0	1.6	2.8	5.2	10.0	19.6	38.8

The resulting sequence is very close to the distribution of mean distances of the planets from the Sun:

Body	Actual distance (A.U.)	Bode's Law prediction
Mercury	0.39	0.4
Venus	0.72	0.7
Earth	1.00	1.0
Mars	1.52	1.6
Asteroid Belt	2.7	2.8
Jupiter	5.20	5.2
Saturn	9.54	10.0
Uranus	19.19	19.6
Neptune	30.1	38.8
Pluto	39.5	77.2

       

When it was initially published, it was found that this law correctly predicts the distances of all known planets from Mercury to Saturn. It also correctly predicted the (then unknown) locations of the asteroid belt and Uranus, but not for Neptune or Pluto .It is now thought to be a mathematical coincidence rather than an actual physical law since it fails to apply to the outermost planets in our solar system. It is suggested that this relation is a mathematical result of orbital resonances and gravitational interactions within multi-body planetary systems.

           The Titius-Bode relation plotted against the actual distances of planets from the Sun.

ASTEROIDS

ASTEROIDS

Asteroids are small, atmosphere-less rocky-metallic objects which range in size from about the size of pebbles to around 600 miles (~1,000 km) across (Ex - Ceres). Although they orbit the Sun, they are too small to be considered planets. Asteroids are thought to be leftover material from the formation of our Solar System. While dust particles came together to form celestial objects through a process called accretion – smaller objects came together with other small objects, creating larger space rocks. Some of these celestial rocks were able to grow large enough to develop their own gravity and became planets. Many others were held back from getting together by Jupiter's gravitation force. These became asteroids.

Because they revolve around the Sun like planets do, asteroids are also sometimes called planetoids or minor planets.

                    an asteroid.

Most are found in the Asteroid Belt, a doughnut-shaped ring which lies between the orbits of Mars and Jupiter and in the Jupiter Trojans. Astronomers have also identified a group of asteroids whose orbits cross Earth's orbit, termed as near-Earth asteroid. Several hundred thousand asteroids are known to exist in our Solar System, and many are yet to be discovered. Most of the undiscovered asteroids are the smaller ones (less than 100 km across) which are more difficult to detect. It is estimated that there are over a million of these smaller asteroids.

                                            Ahead of Jupiter is Greek camp and behind is Trojan Camp.

Depending on the chemical component, which is the carbon content, metal composition and silicate quantity, the asteroids are classified into 3 main groups:

1) C-type or  carbonaceous asteroids  – These are the most common type of asteroids, consisting 75% of known asteroid population, also dominating the outer part of asteroid belt. All carbonaceous asteroids fall under this category. C-type asteroids are extremely dark in their nature with their reflection co-efficient ranging from 0.03 to 0.10.

2) S-type or silicaceous asteroids – The moderately-bright asteroids (albedo/reflection co-efficient- 0.10-0.22) with component mainly including iron and magnesium silicates. These are mainly found in the inner asteroid belt.

3) M-type or metallic asteroids– The asteroids with nickel and iron in its purest form are categorised under M-type. Sometimes these are also found with the presence of stones. Their brightness ranges from 0.1 to 0.2. These are found in the middle of the Asteroid Belt and are much brighter.

All the asteroids are visible by binoculars except for one, Vesta because of the relatively reflective surface. It is only rare that a passing asteroid becomes visible to naked eyes.

  

Meteoroids

Sometimes one asteroid can smash into another. This can cause small pieces of the asteroid to break off. Those pieces are called meteoroids.

                                                                  Meteors

If a meteoroid comes close enough to Earth and enters Earth’s atmosphere, it vaporizes and turns into a meteor: a streak of light in the sky.

Because of their appearance, these streaks of light are sometimes called "shooting stars." But scientists know that meteors are not stars at all—they are just bits of rock!

At certain times of the year, you might be lucky enough to see more meteors in the sky than usual. This is called a meteor shower.  Image credit: NASA/JPL

Because meteors leave streaks of light in the sky, they are sometimes confused with comets. However, these two things are very different.

Comets

Comets orbit the Sun, like asteroids. But comets are made of ice and dust—not rock.

As a comet’s orbit takes it toward the Sun, the ice and dust begin to vaporize. That vaporized ice and dust become the comet’s tail. You can see a comet even when it is very far from Earth. However, when you see a meteor, it’s in our atmosphere.

Meteorites

Sometimes meteoroid rocks don’t vaporize completely in the atmosphere. In fact, sometimes they survive their trip through Earth’s atmosphere and land as rocks on the Earth’s surface. Those rocks are called meteorites.

A scientist investigates a meteorite that landed in Sudan's Nubian Desert in 2008. Image credit: NASA

NASA’s Johnson Space Center has a collection of meteorites that have been collected from many different locations on Earth. The collection acts as a meteorite library for scientists.

Because asteroids formed near at the beginning of our solar system nearly 4.6 billion years ago, meteorites can give scientists information about what the solar system was like way back then!