Tara Lefebvre, Mikayla McMechan, Arianna Morin, Meagan Power, Mario Proulx, and Emily Schroeder

Comets and Asteroids: An Introduction

From an early age, many have learned about our Solar System – that of which is comprised of our Sun and eight planets with varying resources, environmental conditions, and a spectrum of colours and sizes. There also exists minor planets, moons, dust, gas, and comets and asteroids – but we are not always as knowledgeable about these objects in our Solar System. The fascination with space begins when one looks up at a dark, cloudless, and unpolluted sky to see the delicate speckling of millions of light sources: either dead long-ago or still producing a glowing luminescence. Comets and asteroids are no different to stars in their allure and intrigue to physicists, astronomers, and passionate observers. These large and looming objects present both fear and wonder to those that view them, for many know very little or nothing at all about their projections throughout the Solar System. This article provides an understanding of comets and asteroids through looking at the origins of these objects, the analyzation of empirical research conducted, and a variety of informative pictures, videos, and charts. Upon building a base comprehension of comets and asteroids, the article will dive into their historical and physical impact upon the Earth and the overall Solar System, their intricate role in the Solar System, and their capabilities toward a sustainable future.


The Solar Nebular Hypothesis ­­­- Where Comets and Asteroids Come From

Comets and asteroids are believed to be the remnants of the materials that formed our Solar System nearly 4.6 billion years ago. It is believed that the Solar System was created when a giant cloud of gas and dust was disturbed by a nearby explosion. The explosion caused the cloud to collapse and form a solar nebula – which is an interstellar cloud of dust, hydrogen, helium, and other ionized gases – which begun spinning faster and faster, ultimately forming a disc.1 Pieces of solid material started sticking together and creating planetesimals – small celestial bodies of rock and ice fused together to form planets – which continued to grow as they collected smaller objects.2 As these planetesimals grew, their gravity began pulling in nearby objects that eventually forming planets and moons.2 As metallic and rocky materials were drawn to the center of the disc, the disc became hotter and formed the Sun.1 Lighter gases and dust were blown to the outside of the disc where it was much cooler creating the Gas planets, including Jupiter, Saturn, Uranus, and Neptune. While Mercury, Venus, Earth, and Mars formed closer to the sun as dense rocky terrestrial planets.

However, not all planetesimals formed planets and moons. In the outer part of the Solar System, planetesimals were too far apart from one another to merge into planets, these are what we know today as comets. There is an area between Mars and Jupiter, called the Asteroid Belt, where asteroids were unable to form planets, likely due to Jupiter’s strong gravitational force.2 Another hypothesis about the Asteroid Belt is that it could have contained a planet at one point that was broken up during a collision.3

Figure 1 Comet, meteor, or meteorite? ©Canadian Space Agency Source: http://www.asc-csa.gc.ca/eng/search/images/watch.asp?id=4565

Figure 2 “Oort Cloud” An illustration of the Kuiper Belt and Oort Cloud in relation to our Solar System. NASA Source: https://solarsystem.jpl.nasa.gov/galleries/oort-cloud

How Comets and Asteroids are Different

Both comets and asteroids are relatively small, inactive objects. Asteroids are composed of rocks and minerals, the same materials that planets closer to the sun are comprised, and orbit the sun in a circular motion inside the Asteroid Belt.2 Comets are made of ice, dust and gases, have the same composition as the outer planets of the Solar System, and orbit the sun in an elliptical motion.2 As a comet nears the sun it will heat up and expel gas and dust which forms a tail that glows in the sunlight; when it travels away from the sun it freezes again and the glowing tail disappears.

There are two types of comets in the Solar System: the short period and long period comet. Short-period comets originate in the Kuiper Belt – they take less time to complete an orbit around the Sun than a long-period comet, therefore passing through the inner Solar System once or twice in a human lifetime.4 Long-period comets originate in the Oort Cloud that surrounds the outside of the Solar System – they take more than 200 years to orbit the Sun and will likely only pass through the inner Solar System once every thousand years.4

The Discovery of Comets

Sightings of Comets with their bright tails date back to as early as the 23rd Century. These unpredictable “hairy stars” were believed to be messages sent from the gods, either to bring good luck, bad luck or to be warnings. 2 In the 16th century, astronomer Tacho Brache estimated the distance of a comet by measuring the parallax to discover that comets were further away than the moon and did not originate inside the Earth atmosphere. 2 Isaac Newton proved a comet’s elliptical orbit in 1687 when he published his laws of gravity, while a friend of his Edmond Halley predicted a comet’s return. 5 Halley used Newton’s laws of gravity and the orbital data from two recorded comets observed in 1531 and 1607 to discover that the elements were nearly the same. 5 He predicted that the comet observed on these two accounts was actually the same comet. We now know this short-period comet at Halley’s Comet which has an orbit of 74 – 79 years. 5

After the discovery of the telescope, many more comets would be discovered by comet hunters such as Charles Messier. In the 18th century Messier discovered thirteen new comets. 6 He then created a catalogue, which was originally made to be an inventory for himself and other comet hunters – to help distinguish objects in the sky that could be mistaken as comets. His catalogue ended up taking on other very interesting objects such as star clusters and galaxies as well. 6 Today there are thousands of comets have been discovered and continue to be discovered.

The Discovery of Asteroids

Asteroids were discovered in the 18th century by Johann Titius, a German astronomer, who created a mathematical rule for the spacing of the planets in the Solar System, coined as the Titius-Bode Law. This law led him to believe there was a planet missing between Jupiter and Mars, to which we now know as the Asteroid Belt.7

The Titius-Bode Law uses the mean distance of planets from the sun and a progression of numbers to find the mean distances of the planets. The sequence is 0, 3, 6, 12, 24, 48, 96, 192, 384 where the values are added together to create the next number (with an exception of the first 2). 4 is added to each number and then divided by 10: 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10, 19.6, 38.8.7 The sequence in his findings is very close to the mean distances of the planets from the Sun.7

Body Actual Distance (A.U.) Bode’s Law
Mercury 0.39 0.4
Venus 0.72 0.7
Earth 1.00 1.0
Mars 1.52 1.6
Jupiter 5.20 5.2
Saturn 9.54 10.0
Uranus 19.19 19.6
Table 1 Calculations of Solar System distances according to Bode’s Law

Figure 3 “Asteroid Belt” Shows the large gap, the Asteroid Belt, between Mars and Jupiter where Johann Titius believed a planet should be. NASA’s Dawn Mission Art series. Source: https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19380

Based on this sequence, it appears there should be a planet in between Mars and Jupiter. In 1801, Giuseppe Piazzi, an Italian astronomer, found a bright object in the sky between the two planets and seemingly thought he had found the answer.2 Piazzi named this unknown object Ceres, which is now known to be the largest asteroid in the Asteroid Belt. Following this discovery, there were more objects like Ceres found in the area, thus creating a new category in our Solar System called asteroids, which means “Star-like.”2

Discoveries Made from Studying Comets and Asteroids

Because comets and asteroids have not been altered by the planetary process, scientists can learn so much about the formation of the Solar System by studying them.2 Samples from asteroids and comets can help scientists determine the materials they are made from and indicate the materials that make up planets and the state of the solar nebula around the time of the formation of the Universe. The first mission, Star Dust, was launched on February 7, 1999. It flew past and collected particle samples from comet Wild-2 and returned those particles to Earth in a sample return capsule in January 2006.8 These samples indicated that a comet’s rocky matter was created in the inner Solar System at extremely high temperatures, indicating they may have been part of an early Sun.8

Rosetta was launched in 2004 and arrived at Comet 67P/Churyumov-Gerasimenko on August 6, 2014, as the first mission to meet up with a comet and follow its orbit.9 Rosetta was accompanied by the lander Philae. Philae descended onto the comet but the surface was much harder than expected and its harpoons did not stick, causing Philae to bounce and land in the unexpected shade. Philae took as much data as possible before losing power, sending all the information to Rosetta.9 Rosetta collected data and sent it back to Earth.  Even though the Rosetta mission is complete the details are still being observed. The data thus far shows that comets are prehistoric and contain the very building blocks of our Solar System.9 As NASA’s project scientist for Rosetta, Bonnie Buratti said: “With the data presented so far, the comet certainly looks pretty primordial, offering us a glimpse of what the building blocks of the planets and moons may have looked like, 4.6 billion years ago.”10

The Physical and Historical Impact of Comets and Asteroids

Comets and asteroids have an important impact on the Solar System, particularly with regards to helping explain an overall history of the Solar System itself. NASA has coined both comets and asteroids as “time capsules” for their purpose in providing scientists a view into the Solar System’s past.11 An example of this is the craters placed on moons and planets, and how they are indicative to impacts with comets and asteroids in the past.11 These impacts can provide an explanation for the variation in surface density on planets such as Mercury, as impacts remove lighter material from the surface, leaving the denser core behind.2 A giant collision can account for Venus’ retrograde rotation compared to other planets.2 Comet and asteroid impacts provide an explanation for the differences in Mars’ crust between each hemisphere.2

Impacts result in a sudden and intense release of energy – enough energy to compress the surface of a planet, ultimately resulting in a crater. With enough energy, a mountain in the middle of the crater, or a ring of mountains can be formed.2 Loose debris, like water and hot melted rock is also thrown away from the impact site, and becoming what is known as ejecta.2 If this ejecta lands with enough energy it can create secondary craters surrounding the original one.2

Figure 4 “Comet Impacts on Jupiter” Shows impact marks from Shoemaker-Levy 9 when it impacted Jupiter.©NASA Source: https://solarsystem.nasa.gov/planets/pshoemakerlevy9/galleries

The first recorded impact between two cosmic bodies in our Solar System occurred between July 16th and July 22nd, 1994.12 The comet Shoemaker-Levy 9 approached Jupiter and was torn apart by the planet’s gravity.13

The Shoemaker-Levy 9-Jupiter impact was viewed by many Earth-based telescopes, as well as atmospheric and space-based telescopes.12 NASA’s Galileo spacecraft captured the image of fireballs erupting from the surface while still a year-and-a-half away from its destination on Jupiter. NASA’s Voyager 2 spacecraft observed the impact with its ultraviolet spectrometer and planetary radio astronomical instrument while six billion kilometers away.12 NASA’s Deep Space Network and the Ulysses spacecraft also observed radio emissions from Jupiter with the Deep Space Network looking for disturbances in the radiation belt caused by comet dust, and Ulysses observed this using its combined radio wave and plasma wave instruments.12 Finally, NASA’s Hubble spacecraft observed the impact and the scars left on Jupiter using its Wide Field and Planetary Camera 2.12

The Shoemaker-Levy-9-Jupiter comet was first discovered by Carolyn and Gene Shoemaker and David Levy using the 0.4-meter Schmidt telescope stationed at Mt. Palomar in a photograph taken on March 18, 1993.13

Comets and Asteroids and Their Role Within the Solar System

Figure 5 “Asteroid Collision Aftermath” A comet-like asteroid known as P/2010 A2 colliding with a smaller asteroid. NASA. Source: https://solarsystem.nasa.gov/galleries/asteroid-collision-aftermath

The impacts of comets and asteroids are not always detrimental – when the proto-Earth was forming in the nebula that formed the Solar System, conditions were not favourable toward the formation of biomolecules, as the temperature was far too hot, and the Earth was depleted of hydrogen, carbon, nitrogen, and oxygen – all key requirements for these molecules.14 Furthermore, a collision with a Mars-sized proto-planet also further stripped the young Earth of what atmosphere, oceans, and materials it had as resources.14 It is possible that Earth’s organic molecules were replenished over time by impacts with comets and asteroids.14

It was previously thought that the Earth’s water was delivered by impact with comets from the outer reaches of the Solar System, but scientists now believe that this is not the case, as the composition of water on comets and on Earth are not the same. After comparing the amounts of deuterium and hydrogen in comets to the amounts on Earth, scientists realized the amounts did not match that of water on Earth. The deuterium to hydrogen ratio in the tails of comets, or their comae, is approximately twice the ratio in the Earth’s oceans.14 This led them to believe that water on Earth did not come from comets.

In addition, a measurement of the water on the comet 67P/Churyumov-Gerasimenko by ROSINA, the mass spectrometer aboard the European Space Agency’s Rosetta spacecraft, also confirms that comets are not necessarily the source of Earth’s water.15 The ratio measured by ROSINA is actually (5.3 ± 0.7) × 10−4.15 This is more than three times the ratio on Earth, 1.5× 10−4.16 However, overall inconsistent data has led scientists to research this matter further.16

Even if comets and asteroids did not deliver water to the Earth, it is possible that they still assisted life on Earth, and provided new habitats for varying ecosystems. Intra- crater lakes that formed in the craters left from impacts could have enhanced water availability.17 In addition to delivering the organics that could have formed life, energy from comet and asteroid impacts can provide the energy necessary for organic molecules or polymers to form, such as the polymerization of nucleotides.17

The complex relationship between comet and asteroid impacts is summarized by Cockle and Bland:

The energy released during the collision of an asteroid or comet with the Earth is sufficient to cause detrimental biological perturbations from the microsphere to biosphere scale. Because impact events could also threaten human populations, it seems counterintuitive to regard these events as beneficial. However, the energies released during the impact can drive processes that are beneficial to life. The formation of biologically useful bonds at the molecular level, the shock alteration of rocks that makes them better habitats for microorganisms, the improved availability of biologically important nutrients and the clearance of whole ecosystems that enables new species to evolve and radiate are some of the beneficial examples. Future research will no doubt reveal more of these beneficial links between otherwise destructive impact energies and life.17

Sustainability Through Asteroid Mining

There are three types of asteroids in terms of composition: C-type, S-type, and M-type. The C-type asteroids are dark and carbon-rich – these asteroids contain high amounts of water in the form of hydrated clay materials.18 If it were possible to extract the water from the interior of the asteroid it would provide a potential water source for humans if their presence in space were to increase. The water can also be broken down into its components – hydrogen and oxygen – which would allow for the creation of rocket fuel. This could mean that future mining space-crafts can refuel from the surface of the asteroid. Lastly, these asteroids contain plenty of organic material including carbon, phosphorus, and other materials that make good fertilizers for food.

The S-type asteroids are composed of little water but are more useful to us in the economic sense, as they are mostly comprised of metal.18 An asteroid even the size of an average house has the potential to be worth millions of dollars. A 1.5 million-pound asteroid would be comprised of nickel, iron, and cobalt. However, approximately 50 pounds of the asteroid could be made up of gold, platinum, and rhodium.

M-type asteroids are rare but can contain up to ten times more metal materials than the S-type asteroids.18

Currently, we do not know enough about the process of mapping and analyzing asteroids and to mine them in an economical way. The cost has the possibility to be billions of dollars to create a space launch, so the mining of asteroids would have to cut the production costs on Earth to an extreme amount. Some research is being done to better understand the composition of asteroids that could ultimately lead to a future in sustainability mining. In September of 2016, OSIRIS–Rex was launched to follow the asteroid Bennu. The spacecraft will not arrive at the asteroid until 2018. After following, analyzing, and collecting a sample from the asteroid, it still will not arrive back on Earth until 2023.18


While research and the understanding of space is continually growing, there is still a limited understanding of comets and asteroids.  The common misconception is that comets and asteroids are objects whose only purpose is causing mass destruction on Earth and are something to be feared.  The purpose of this article was to provide an understanding of comets and asteroids by studying their origins, the history of their impacts on Earth, the empirical research that has been conducted, and the ways they can contribute to a sustainable future. As previously stated, comets and asteroids provide scientists an in-depth look at the formation of our Solar System because they have not been altered by the planetary process. The research that has been conducted shows that impacts are not always detrimental to Earth; it is possible that such impacts assisted life on Earth and provided new habitats for varying ecosystems.

Through this research, it is our hope that many will move past their rigid views of comets and asteroids as destructible forces, and advance their awareness toward the positive reinforcements that both comets and asteroids provide. The extraction of metals and minerals on comets and asteroids will be a pivotal moment for Earth’s economic sustainability and longevity. Comets and asteroids do not need to impact our Earth in a violent way, but instead through the lens of economic prosperity and environment. Their origins illustrate both an ever-changing landscape, but also the very beginnings of time itself. Comets and asteroids are therefore considered timeless objects – as they provide a glimpse into the universe’s fossilized past and its resourceful future.


1 Windows to the Universe, Solar System Formation, https://www.windows2universe.org/our_solar_system/formation.html (Accessed May 30, 2017)

2 L. Kay, S. Palen, and G. Blumenthal, 21st Century Astronomy: The Solar System 5th Edition (W.W. Norton & Company, New York, London) Chapter 7, Chapter 8, Chapter 12.

3 National Geographic, Asteroids and Comets, http://www.nationalgeographic.com/science/space/solar-system/asteroids-comets/ (Accessed June 6, 2017)

4 NASA, StarChild Question of the Month for December 2001 – Where do comets come from?, https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question40.html (Accessed June 6, 2017).

5 Wikipedia, Halley’s Comet, https://en.wikipedia.org/wiki/Halley’s_Comet (Accessed June 21, 2017).

6 ESA, History of Comets Part 2 – Testing Gravity: How Comets Helped to Prove Newton Right, http://sci.esa.int/rosetta/54199-testing-gravity-how-comets-helped-to-prove-newton-right/ (Accessed June 21, 2017).

7 Cornell University, Bode’s Law, http://www.astro.cornell.edu/academics/courses/astro201/bodes_law.htm (Accessed June 1, 2017).

8 D.C. Agle, NASA’s Stardust Sample Return was 10 Years Ago Today, https://www.nasa.gov/feature/nasas-stardust-sample-return-was-10-years-ago-today (Accessed May 29, 2017).

9 ESA, The Amazing Adventure of Rosetta and Philae, https://youtu.be/HD2zrF3I_II (Accessed May 29, 2017).

10 ESA, The Surprising Comet, http://www.esa.int/Our_Activities/Space_Science/Rosetta/The_surprising_comet (Accessed May 29, 2017).

11 NASA, Exploring Comets and Asteroids: Time Capsules of the Solar System, https://www.nasa.gov/content/exploring-comets-and-asteroids-time-capsules-of-the-solar-system (Accessed June 3, 2017).

12 Preston Dyches, Looking Back at the Jupiter Crash 20 Years Later, https://www.nasa.gov/jpl/news/shoemaker-levy-9-jupiter-crash-20140715/ (Accessed on June 4, 2017).

13 NASA, P/Shoemaker-Levy 9: In Depth, https://solarsystem.nasa.gov/planets/pshoemakerlevy9/indepth (Accessed June 4, 2017).

14 M. Mumma, Astrobiology 8, 339 (2008).

15 K. Altwegg et al., Science 347, 1261952-1 (2015).

16 A. Yeager, Rosetta casts doubt on comets as Earth’s water providers, https://www.sciencenews.org/article/rosetta-casts-doubt-comets-earth’s-water-providers?mode=magazine&context=1457 (Retrieved June 21, 2017).

17 C. S. Cockell and P. A. Bland, Trends in Ecology and Evolution 20, 175 (2005).

18 W. Steigerwald, New NASA Mission to Help Us Learn How to Mine Asteroids, https://www.nasa.gov/content/goddard/new-nasa-mission-to-help-us-learn-how-to-mine-asteroids (Accessed 8 June 2017).