solar system – Neville’s Phantastic Physics Phun

You may have heard people describe our sun as ordinary or not special. In comparison to other stars in the universe that may be true, but I submit that to those of us in our solar system the sun is quite special. Let us take a closer look at our sun and then decide if you think it is special or not. Our sun is the only star in our solar system. Eight major planets orbit the sun which is at the center of our solar system. The average distance between the earth and sun is 149,668,992 km or 93 million miles. Astronomers use this average distance as a unit of distance called astronomical units or AU. The distances in our solar system, galaxy, and beyond are so vast that it is easier to calculate distances using astronomical units than it is to use miles or kilometers. The sun sits at the center of our solar system and makes up more than 99% of the mass of the entire solar system. The diameter of our sun is 1.4 million kilometers (865 thousand miles), over one million earths could fit inside the sun. The sun produces heat and light which is needed for life on Earth. Without the sun the planet would freeze and life as we know it, would not exist.

What is Our Sun Made of and What Makes it a Star

Our sun is a G-class star that was formed some 4.6 billion years ago and is expected to last another 5 billion years. Stars form in a stellar nursery known as a nebula. A nebula is “… an enormous cloud of dust and gas occupying the space between stars and acting as a nursery for new stars (spacecenter.org) The sun, like all stars, is a hot ball of ionized gas. Our sun does not have a solid surface nor a solid core. The sun is 73.4% hydrogen and 25% helium by mass. The sun also contains trace amounts of carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron (ucf.edu).

What makes our sun, or any other star a star? The object must be massive enough that nuclear fusion of elements can occur in the core due to the immense pressure inside the object. The smallest stars that exist are approximately 10 percent the mass of our sun while “high mass” stars are classified as stars having more than three times the mass of our sun. UY Scuti is the largest star ever observed and it has a radius that is 1700 times larger than our sun and it has a mass 7-10 times the mass of our star. 5 billion suns could fit into a sphere with the volume of UY Scuti.

The Layers of the Sun

The structure of the sun contains several different layers. The core of the sun is where nuclear fusion occurs as the sun fuses hydrogen into helium through a process called the proton-proton chain. This is a three-step process that results in fusing of hydrogen to produce helium. According to NASA “In the first step two protons collide to produce deuterium, a positron, and a neutrino. In the second step a proton collides with the deuterium to produce a helium-3 nucleus and a gamma ray. In the third step two helium-3s collide to produce a normal helium-4 nucleus with the release of two protons.” A byproduct of the nuclear reactions that occur in the core is the production of elementary particles called neutrinos. Neutrinos, according to scientificamerican.com are subatomic particles that is remarkably similar to an electron but has no electrical charge and a ridiculously small mass, which might even be zero. Neutrinos are one of the most abundant particles in the universe. These reactions are what produce the heat and light that we receive on Earth. The core of the sun extends about a quarter of the distance from the center of our star. The temperature within the core is over 15 million Kelvin.

The radiative zone is the next layer after the core. This region is where energy is carried outwards via radiation. The energy is carried through the radiative zone by photons. These photons, which travel at the speed of light, collide with other particles during their journey to the surface. According to suntoday.org, it takes “several hundred thousand years for radiation to make its way from the core to the top of the radiative zone.”

The convection zone is the outer most layer of the interior of the sun. This zone is much cooler than the core with temperatures of 2,000,000 C at the base of this zone while it is only 5,700 C at the top of the zone. This large temperature difference results in a phenomenon called convection. By definition, convection is “the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat.” The convective motion in this zone results in “the generation of electric currents and solar magnetic fields (cora.nwra.com)

The photosphere is the first layer of the sun we can directly observe. This layer is 100 km thick and has a temperature range of 6500 K at the bottom and 4000 K at the top of the photosphere. This region is where sunspots, faculae, and granules are observed.

The chromosphere is an irregular area located above the photosphere. Temperatures range from 6000 C to 20,000 C. In the chromosphere activity such as prominences, solar flares, filament eruptions can be observed. The reddish color seen in prominences is a result of the light given off from hydrogen at the higher temperatures.

The outermost layer of the sun, often called the solar atmosphere, is the corona. This portion of the sun is visible during solar eclipses as the whitish edge of the sun. The corona features things such as loops, streamers and plumes that may be visible during a solar eclipse. The temperature of the corona is 1 million C. This is 1000 times hotter than the photosphere despite it being further from the core of the sun. In 1942 Swedish scientist Hannes Alfvén proposed a theory to explain this temperature anomaly. According to earthsky.org he “theorized that magnetized waves of plasma could carry huge amounts of energy along the sun’s magnetic field from its interior to the corona. The energy bypasses the photosphere before exploding with heat in the sun’s upper atmosphere.”

The Death of Our Star

The ultimate fate of a star depends on the star’s mass. High mass stars end their lives by going supernova and becoming a blackhole or a neutron star. Our sun is not massive enough to end its life in such spectacular fashion. When the sun exhausts its fuel, it will “expand into a red giant star, becoming so large that it will engulf Mercury and Venus, and possibly Earth as well (solarsystem.nasa.gov). According to an article published in Nature Astronomy the sun will “… produce a visible, though faint, planetary nebula” (earthsky.org). A planetary nebula is a bit of a misnomer as it is not related to planets. The term was coined by “… William Herschel, who also compiled an astronomical catalog. Herschel had recently discovered the planet Uranus, which has a blue-green tint, and he thought that the new objects resembled the gas giant” (space.com). A planetary nebula, according to Oxford languages is “a ring-shaped nebula formed by an expanding shell of gas around an aging star.” This phase of stellar evolution may last for tens of thousands of years which is a brief period astronomically speaking. Over time the faint planetary nebula will fade, and the sun will cease to shine, and its temperature and pressure will drop. The sun will become a white dwarf about the size of the earth. Is that the end of the cycle? Perhaps not. Astronomers believe that the white dwarf will continue to cool down to a point where it no longer emits light or heat. At this point it will no longer be visible and will be called a black dwarf. This cooling period is thought to take trillions of years so no black dwarfs exist. See my earlier post if you want to learn more about these fascinating objects.

As you probably know Jupiter is the largest planet in our solar system. The mass of Jupiter is approximately 2.5 times the mass of all of the other planets combined. Approximately 1,300 Earth’s could fit inside of the Jovian planet. Jupiter is the fifth planet from our sun and is classified as gas giant. Mercury, Venus, Earth, and Mars are rocky terrestrial planets. Jupiter and Saturn are gas giants while Uranus and Neptune are considered ice giants.

So just what is a gas giant you may ask. According to NASA “A gas giant is a large planet mostly composed of helium and/or hydrogen. These planets, like Jupiter and Saturn in our solar system, don’t have hard surfaces and instead have swirling gases above a solid core. Gas giant exoplanets can be much larger than Jupiter, and much closer to their stars than anything found in our solar system.”… ice giants by comparison “are mostly water, probably in the form of a supercritical fluid; the visible clouds likely consist of ice crystals with different compositions.” (planetary society)” Terrestrial of inner planets are described by Nasa as “… planets (Earth sized and smaller) are rocky worlds, composed of rock, silicate, water and/or carbon.”

So What’s in a Name?

Credit: Britannica.com This image is often used to depict both Jupiter and Zeus

“Jupiter was a sky-god who Romans believed oversaw all aspects of life; he is thought to have originated from the Greek god Zeus.” (national geographic) Jupiter was also known as Jove, and in Latin was referred to as Iuppiter, Iovis, and Diespitter according to Britannica.com. Jupiter is known as god of the sky in Roman mythology. He was believed to be king of the gods and the protector of the Roman people. “He granted supremacy to the Romans over other human being in return for all the respect he got from them. In the Roman Empire, the kings and other ministers swore in his name when they took the oath of office. (DifferenceBetween.com)

Image Credit National Geographic. Ruins of a Roman temple to the god Jupiter

For every DC comic book superhero there is an equivalent Marvel superhero. Think Green Arrow in DC comics and Hawkeye in the Marvel Universe. Zeus is the counterpart to Jupiter in Greek mythology. Zeus is also seen as the god of the sky and king of all the other Greek gods as well as the king of humans. Jupiter and Zeus are both thought to have their names derived from terms meaning bright in the respective cultures of the Romans and Greeks. This is in all likelihood due to the bright appearance of Jupiter in the night sky. Jupiter has an apparent magnitude of -2.2 which makes it the third brightest object in the sky behind Venus and the moon. Many people believe that Jupiter and Zeus are the same god having simply having different names in Roman and Greek mythology.

Just the Facts

Let’s check out some facts about the King of Planets The average distance between Jupiter and the sun is 778 million kilometers or 5.2 astronomical units (AU). One astronomical unit is the average distance between the Earth and Sun, this distance is roughly 93 million miles or 150 million kilometers.

Why is a day on Earth 24 hours and a year 365 days? The Earth rotates about its axis once every 24 hours and the it revolves around the sun approximately once every 365 days. So what would a day and a year be on Jupiter? A Jovian day is about 10 hours long. This is the shortest day of any planet in our solar system. Jupiter is much farther from the sun than is the Earth so as you might expect a “year” on Jupiter is much longer than an Earth year. A Jovian year is equivalent to roughly 12 Earth years. Interestingly enough, Jupiter is so large that it doesn’t actually orbit the Sun in the same way other planets do. The Sun and Jupiter actually orbit a common center of gravity. Jupiter “pulls the center of mass between it and the sun, also known as the barycenter, some 1.07 solar radii from the star’s center which is about 30,000 miles above the sun’s surface.” (businessinsider.com)

The Earth has an axial tilt of 23.5 degrees which accounts for the seasons on our home planet. Jupiter has a tilt of only 3 degrees which means there is very little variation in the planets seasons. That certainly does not mean that there is not a complex weather pattern on this behemoth of a planet.

Measuring the rotational speed was a challenge for scientists because the gas giant does not have surface features to use as a frame of reference. Eventually radio emissions from the magnetic field were used to calculate the rotational speed and period. Different parts of the Jupiter’s atmosphere rotate at different speeds. The speed at the equator rotates faster than at the poles.

Credit NASA In this image you can see different parts of the Jovian atmosphere rotating at different velocities. Also visible is the Great Red Spot.

Jupiter has 53 named moons and and additional 26 moons waiting to be named (nasa.gov) The four largest of the named moons are Io, Ganymede, Callisto, and Europa. These are referred to as Galilean satellites as they were discovered by Galileo Galilei in the year 1610. Each of the Galilean satellites are tidally locked meaning one side of the moon is always facing the giant planet. The Earth’s moon is also tidally locked to our home planet.

Credit NASA Image of the Galilean moons shown from left to right: Io, Europa, Ganymede, and Callisto.

The Great Red Spot

Jupiter’s “Great Red Spot” is a massive storm roughly 10,000 miles wide. This storm has been observed for over 200 years and scientists believe that it has been around for much longer. The Hubble Space Telescope (HST) allowed scientists to determine that the outer ring of the storm is rotating counter clockwise and that wind speeds have increased by 8 percent between 2009-2020. The speeds in this “high speed ring” region of the storm top out at over 400 miles per hour. (EarthSky.org) It appears that the “Great Red Spot” is shrinking and changing in shape according to a study in journal Geophysical Research. Scientists are still trying to determine what is causing the wind speed of the storm to increase on the outside of the storm while decreasing its speed inside. According to planetary.org “Measuring the depth of the GRS would provide some context, but even our best estimates from spacecraft are ambiguous; in 2017 NASA’s Juno found that the Spot is “50 to 100 times deeper than Earth’s oceans,” but we still don’t know exactly where the storm ends.” It appears to be anyone’s best guess as to when or if the Great Red Spot. The storm has been decreasing in size for nearly 150 years but scientists are still not certain as to the fate of the solar system’s most famous storm.

The Composition of Jupiter

Jupiter is 93% hydrogen, 7% helium and contains very small quantities of methane, ammonia, and water vapor. It is believed that Jupiter may posses a rocky core that is more than 12 times the mass of the Earth. This core is surrounded by a large body of liquid metallic hydrogen which is surrounded by gaseous hydrogen.

The King of Planets has a large make up of cloud bands that move up to 240 miles per hour. The differing colors of the cloud bands indicate varying chemical composition within the bands. The temperature of the planet increases as you travel below the clouds toward the core of the Jupiter.

It may surprise you to learn that Saturn is not the only planet in our solar system that has rings. In fact, all of the outer planets have their own set of rings. It is believed that Jupiter has a set of four rings around the planet. The rings were first discovered by the Voyager 1 in 1979. According to nasa.gov the rings are difficult to view because the rings “are so faint and tenuous, they are only visible when viewed from behind Jupiter and are lit by the Sun, or directly viewed in the infrared where they faintly glow.” The rings of Saturn are composed of large ice chunks and rock while Jupiter’s rings are composed of small dust particles. Nasa.gov reports that “Jupiter’s rings are formed from dust particles hurled up by micro-meteor impacts on Jupiter’s small inner moons and captured into orbit” In order for the rings to continue to exist the dust and particles must constantly be replenished with dust from the moons.

How was Jupiter Formed and Why is it Called a Failed Star?

Jupiter was formed the same time as the rest of the solar system some 4.5 billion years ago. Gravity caused swirling gas and dust to coalesce and collapse on itself to form a the planet we now know as Jupiter. Most of the mass and debris left over after the formation of the Sun was taken up by the formation of Jupiter. “Giant planets form really fast, in a few million years,” Kevin Walsh, a researcher at the Southwest Research Institute in Boulder, Colorado.

“Jupiter is often lauded as a shield for Earth, but that may not have always been the case. Recent studies suggest that gas giants speed up the timescale of impacts. Early in the life of the solar system, Jupiter tossed material helter-skelter, raining some of it on the terrestrial planets while hurling some of it completely out of the solar system. In systems without Jupiters, however, the impacts are weaker but continue through a planet’s lifetime. That’s because most of the rocks are stuck in orbit around the sun without a giant planet to boot it aside” (space.com).

According to Scientific American Jupiter is a called a failed star because Jupiter “…is made of the same elements (hydrogen and helium) as is the Sun, but it is not massive enough to have the internal pressure and temperature necessary to cause hydrogen to fuse to helium, the energy source that powers the sun and most other stars.” Jupiter only has about .001 times the mass of the our sun which scientists speculate is the result of the Sun obtaining most of the mass during the formation of our solar system. According to Astronomy.com Jupiter would need to be about 75 times its current mass to be able to ignite nuclear fusion in its core and become a star.