Our solar system is just one of the billions of solar systems that make up the Milky Way galaxy. The Milky Way is a spiral galaxy and the “arms” of the spiral are active star formation regions. We are located near the Orion Arm, or the Orion Spur. This spur is between two more prominent arms of the spiral, Sagittarius and Perseus.  

Our solar system is made up of many objects, much more than just planets and moons. The most massive thing in our solar system is the Sun, consisting of over 99% of the Solar System’s mass. The last percent is made up of all of the planets, their satellites and rings, comets, asteroids, and dust combined.

What is a Solar System?

A solar system is one or more stars that have a celestial object(s) orbiting and bound to them by gravity. Solar systems don’t all look like ours. Some systems have multiple stars which orbit around their center of mass. Some star systems only have one planet where others may have many more than ours. The planets from star systems other than ours are referred to as exoplanets. Since other stars are so far away, it is hard to observe the nuances of their systems. But scientists are working hard to discover new solar systems, especially ones with planets that might be habitable for humans. 

The Discovery of Our Solar System

Theories about our solar system date back to the ancient civilizations. There were many ideas about what the Solar System contained, how it was structured, the cosmos etc. Some thought that the Sun, planets, and other stars revolved around Earth. This idea is called the geocentric model and was widely accepted as correct in the second century and beyond. It wasn’t until the 16^th century that the correct heliocentric model, where the planets revolved around the Sun, was accepted. 

The discovery of most of the planets in our solar system was rather arbitrary. Obviously, we have known about Earth for some time now. But we have also known about some of the other planets in our solar system for just as long, we just didn’t know they were planets. To the unaided eye, planets are very bright and look like big stars. But if you track them, as the ancient Greeks did, you will find that they don’t behave like stars. Stars “move” according to where our planet is in its orbit, this is why you can see some stars in the winter that you can’t in the summer. The Greeks found that 5 stars in particular were not changing with the season but rather exhibiting some strange behavior. These were called wanderers, along with the Sun and the Moon. Where stars moved uniformly, the wanderers appeared to periodically slow down, stop, and even change direction. They are Mercury, Venus, Mars, Jupiter, and Saturn.

What about Uranus and Neptune? They are the two planets furthest from the Sun which is why they are very difficult to see with the naked eye. The other objects in our solar system are too small to see unaided which is why more of our solar system was discovered after telescopes were invented in 1608. In 1781, Uranus was discovered by Sir William Herschel. In 1801, the asteroid belt was discovered by Giuseppe Piazzi. Then in 1846, Neptune was discovered by John Couch Adams. 

Origin of Our Solar System

The formation of the members of our solar system started about 4.5 billion years ago. Everything in the Solar System formed from the solar nebula which originally was a spherical cloud of dust and gas. The solar nebula was composed mostly of hydrogen and helium, which are now the two most bountiful elements in our solar system. The nebula collapsed into a spinning disk which then condensed to form the Solar System.

Most of the nebula condensed to form the Sun but the outer ring did not and revolved around the new star. As the nebula cooled, the cores of the outer four planets started to form as well as many other much smaller cores in the inner Solar System. These smaller cores chaotically collided with each other to form the inner four planets. The inner planets were messy, jagged fragments of collided rock until the gravity they developed pulled these imperfections into a spherical shape.

The remaining pieces of these cosmic rocks had two main fates. One fate was being propelled into the cosmos. Many of these pieces stayed within the orbit of the Sun and formed the spherical Oort Cloud at the edges of our solar system. Some pieces, however, were ejected from our solar system altogether. The other fate was finding a stable orbit around the Sun. One such orbit is located between Mars and Jupiter and is known as the asteroid belt. Another stable orbit is beyond Neptune and is named the Kuiper belt. 

The Planets

There are 8 planets in our solar system: Mercury, Venus, Earth, Mars, Saturn, Jupiter, Uranus, and Neptune. We can classify all planets, including our own, into a few different categories but, for now, we’ll just focus on the inner planets and outer planets of our solar system.

The inner 4 planets are also known as the terrestrial planets. These planets have a heavy-metal core, a solid surface, and are rather dense. Their surfaces can be impacted and shaped by collisions and they have varying levels of atmosphere depending on their size. The inner planets have very few moons in comparison to the outer planets.

The outer planets are somewhat separated into two categories, gas giant and ice giant. The two gas giants are Jupiter and Saturn. They have a low density considering their colossal size and are constructed mostly of their atmosphere. Their cores are theorized to be rocky but, because of the immense pressure that such a massive atmosphere creates, the rock is most likely not in a solid form. Gas giants are composed of the same elements as stars and are sometimes called failed stars because of it. Saturn famously has dazzling bright rings, but Jupiter also has rings, albeit they are faint.

The ice giants are Uranus and Neptune. They have an icy, rocky, core which is much larger than that of the gas giants. The atmosphere of these planets is more elementally complex than the gas giants. These two planets also have rings but, like Jupiter, they are faint. All of the outer planets have dozens of moons.

Another planet you may familiar with is Pluto. Pluto is no longer considered a major planet because it is not able to clear its orbit of celestial objects. There are a few other minor planets in our solar system: Ceres, Haumea, Makemake, and Eris. All of these planets are smaller than Earth’s moon yet have up to 5 moons of their own.

Comets and Asteroids

Comets and asteroids are the leftover bits and pieces from the formation of our planets. Nevertheless, they have differences in composition, orbit, and how they interact with our solar system. The compositions of comets and asteroids have been somewhat unchanged chemically or physically since they first formed. This makes them valuable examples of the chemical structure of the building blocks of our solar system.  

Comets are chunks of frozen gas, rock, and dust. Comets mostly come from the Oort Cloud where there is estimated to be around 10 trillion comets. The Kuiper belt is known for ejecting a comet on occasion. Comets begin their journey around the Sun by being thrown from the Oort Cloud or Kuiper Belt. Comets vary in size and can range from a diameter of a few hundred feet to many miles. When comets come close to the Sun in their elliptical orbit, something spectacular happens. 

The Sun heats up the frozen gas letting it flow to form a vibrant tail that stretches for millions of miles. When a comet comes around the Sun in its orbit, it picks up incredible speed that allows it to slingshot back out into the cosmos. There are around 3,600 known comets flying around in our solar system. Scientists expect many more.

Asteroids are rocky lumps that are vast in quantity and live considerably less spectacular lives than comets. Asteroids primarily reside in the main asteroid belt located between Mars and Jupiter. Over a million asteroids can be found in this belt which spans a width of millions of kilometers. The life of an asteroid becomes a little more interesting when it collides with something. When asteroids collide with Earth, we call them meteorites but most of the time they fail to pass through our atmosphere. An asteroid that burned up before making an impact is called a meteor. 

How Big is Our Solar System?

It is sometimes difficult to comprehend just how big our solar system is. It is important to note that we consider the end of our solar system to be the Oort Cloud, not the last planet in the Sun’s orbit, Neptune. On Earth, we measure large distances in feet, miles, meters, and kilometers. We can try to use these same measuring devices with space, but since space is so vast, we have to make some adjustments to keep the numbers from being burdens to work with. 

The kilometer (km) is approximately the length of 9 football fields. We use kilometers to talk about the diameters of planets or asteroids and comets. In the context of space, the next largest measurement is the astronomical unit (AU). One AU is the distance from the Earth to the Sun, which is about 147.1 million kilometers. We use AUs to talk about the distance between planets in our solar system. After AU comes light-years (LY) which is 63,241.1 AU. A light-year is how far light can travel in one Earth year. We use light-years to talk about how far away objects are in our galaxy. 

To measure the distance from the Sun to the Oort Cloud, we will use astronomical units. Since the Oort Cloud is still relatively unexplored, scientists can only estimate how far it is from the Sun. Right now, we think the distance between the Sun and the Oort Cloud is between 2,000 and 100,000 AU. Let’s do some simple math to find that distance in the aforementioned example of football fields. 

A reasonable 50,000 AU, or 0.79 LY, will be used as our distance for this example. 50,000 AU is a whopping 7,500,000,000,000 kilometers, that’s 7.5 trillion kilometers. We said that 1 kilometer was 9 football fields so that’s an incredible 67,000,000,000,000, or 67 trillion, football fields between the Sun and the Oort cloud. This number is just the radius of our solar system. With this estimate, we can say that our solar system is 134 trillion football fields, or 15 trillion km, from edge to edge. Our solar system is undoubtably enormous.

The post The Ultimate Guide to Our Solar System appeared first on Space Tonight.

As one of the most classic scenarios of space science fictions, an asteroid impacting the Earth’s surface could potentially create dramatic changes to those living on our planet. Depending on the size of the asteroid or extraterrestrial object, the resulting impact could be potentially alter the Earth’s current orbit around the sun or create a significant explosion that could level out major cities in a 200-mile (320 km) radius.

By looking at craters on the Earth’s surface, we have evidence that asteroids have impacted the Earth in the planet’s 4.5 billion year history. What are the chances of asteroids hitting the Earth in the near future?

What are the chances of asteroids hitting Earth?

First, it is important understand the importance of Earth’s atmosphere, which is not common to all bodies within our Solar System. Earth’s atmosphere causes a lot of the debris from space to burn up before they hit the Earth’s surface at large sizes.

That’s not to say space debris doesn’t reach the earth’s surface. In fact, that’s far from the truth. Everyday, thousands of tiny debris from space hit the earth — typically the size of a grain of sand or small pebble. So to answer the question about asteroids (defined as any inactive, rocky body orbiting the sun) hitting the earth, the chances are 100% on a daily basis.

On the contrary, if you look at the Moon or Mercury, you can see craters everywhere largely due to their lack of an atmosphere that acts as a buffer between their surfaces and any celestial debris.

Have humans been killed by a meteorite or by the after effects of an impact?

According to NASA, there have been known no humans killed in the past 1,000 years by a meteorite or by a meteorite striking the earth’s surface. There is no record of that happening anywhere on the planet.

However, in Ancient China, there are records of such occurrences. An individual’s chance of getting struck or impacted by a meteorite is very small; however, the risk increases when you deal with regional or global catastrophes that result from objects impacting the surface with a surface area of larger than 1 km².

Predictions on upcoming asteroids entering the Earth’s atmosphere

According to the European Space Agency’s Risk Page, they share a number of objects that have a non-zero probability of impacting the Earth’s surface, with the soonest object expected to fly near-Earth in 2020.

• Object Name: 2018VP1
• Diameter: 2.3 meters
• Date: November 2, 2020
• Link for additional information on 2018VP1

• Object Name: 2009JF1
• Diameter: 13 meters
• Date: May 6, 2022
• Link for additional information on 2009JF1

• Object Name: 2008JL3
• Diameter: 30 meters
• Date: May 1, 2027
• Link for additional information on 2008JL3

• Object Name: 2007KE4
• Diameter: 30 meters
• Date: May 26, 2029
• Link for additional information on 2007KE4

• Object Name: 2012QD8
• Diameter: 90 meters
• Date: March 8, 2047
• Link for additional information on 2012QD8

• Object Name: 99942 Apophis
• Diameter: 375 meters
• Date: April 12, 2068
• Link for additional information on 99942 Apophis

• Object Name: 2000SG344
• Diameter: 30 meters
• Date: September 16, 2071
• Link for additional information on 2000SG344

• Object Name: 2019DS1
• Diameter: 26 meters
• Date: February 26, 2082
• Link for additional information on 2019DS1

• Object Name: 2010RF12
• Diameter: 9 meters
• Date: September 5, 2095
• Link for additional information on 2010RF12

• Object Name: 1979XB
• Diameter: 700 meters
• Date: December 14, 2113
• Link for additional information on 1979XB

How many near-Earth asteroids have been discovered in 2019?

According to NASA, the total number of near-Earth asteroids discovered since the beginning of 2019 was around 19,000. On a given week, NASA expects that 30 new asteroids are discovered, making these near-Earth objects a very common occurrence in the grand scheme of things.

The majority of these space rocks have been found as a result of NASA-funded surveys of the skies, mostly by using ground-based telescopes. In 1998, NASA started to actively catalogue these objects.

Potentially hazardous asteroids (PHA)

The qualification of potentially hazardous asteroids, or PHAs, depend on the size of the asteroids. These asteroids measure at least 460 feet or 140 meters across, which large enough to wipe out an entire US state if they were to hit the earth. At the moment, 8,000 PHAs have been discovered and catalogued.

What can we do about asteroids on the path of collision with Earth?

The field of “asteroid impact avoidance” is associated with a number of methods and approaches that can be deployed to divert the path of an asteroid that is on-track to hitting the Earth’s surface. These “near-Earth objects” are referred by acronym as NEOs.

Generally speaking, the two primary strategies focus on either “destruction” or “diversion.”

Destruction of NEOs

Aptly-named, the destruction of near-Earth objects involve breaking the larger body into harmless fragments that may evaporate as they approach the Earth’s surface. These strategies are typically used against larger objects that may require significant force to re-direct using diversion methods.

• Nuclear explosive devices: Large nuclear explosion set off on or near the asteroid to break up the object.
• Concentrated solar energy: Channeling of solar energy to heat an asteroid and vaporize it. Over the span of long durations, this could provide enough energy to deflect the object.
• Asteroid laser ablation: Similar to concentrated solar energy, a high-powered laser could be used to produce a similar effect.
• Mass driver: A system that would eject material from the asteroid into space, giving steady pushes away from Earth as well as allowing mass to avoid the earth.

Diversion of NEOs

These techniques are responsible for delaying the asteroids path or advancing the asteroids path. Essentially, these are techniques used to ensure that the path of the asteroid does not intersect the path of the earth.

By slowing down the asteroid, we can create asteroid avoidance by allowing the Earth to pass by as our planet is constantly orbiting the sun. In the same way, we could also speed up the asteroid, but this is generally more difficult to accomplish.

• Kinetic impact: Hitting an asteroid with another high-mass object to knock it off course.
• Asteroid tractor: This technique involves adding a small bit of thrust on the asteroid over a long duration to ultimately change its trajectory.
• Ion beam shepherd: Another technique that involves using a low-divergence ion thruster that is pointed at the object from another lighter spacecraft hovering alongside.

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