The Nebular Hypothesis

Currently, the most commonly accepted theory is the Nebular Hypothesis. This theory states that the objects in our Solar System, like the stars and the planets, were formed from nebulous material over 4.5 billion years ago. ⁶ The theory of the Solar System emerging from a nebula was originally proposed by Swedish scientist Emanuel Swedenborg in 1734. Soon after, Immanuel Kant built off of Swedenborg’s work to develop the theory further and published the Nebular Hypothesis in his Universal Natural History and Theory of the Heavens (1755).⁶ In his disquisition, Kant argued that gaseous clouds rotate slowly, eventually collapsing and flattening due to both gravity and the forming stars and planets. Despite this theory being published in the mid seventeen hundreds, the theory is still considered the most widely accepted, even today.

An In-Depth Look at the Nebular Hypothesis

The Nebular Hypothesis is currently the most commonly accepted theory for the origin of the Solar System.⁷ According to the Nebular Hypothesis, the sun and planets in our Solar System started out as a giant, dense cloud of molecular hydrogen. These clouds are gravitationally unstable and as a result, they collapse easily. Approximately 4.57 billion years ago, something occurred that caused this cloud to collapse.⁷ It’s possible this collapse could have been triggered by a passing star, or even shock waves from a SupernovaA star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.. Nevertheless, the result was the same: a gravitational collapse at the cloud’s center. After this collapse, clusters of dust and gas began collecting in denser areas. These denser regions pulled in more matter and the conservation of momentum caused this matter to rotate. In addition to this, increasing pressure causes the matter to heat up.^{6, 7}

The majority of material ended up in the center, while the remaining matter flattened out and circled around it. The matter in the middle would eventually turn into the Sun, while the material surrounding the Sun would form into the protoplanetary disc. The planets of our Solar System would later form through dust and gas accretion.⁷

As a result of high boiling points, only materials such as metal and rock could exist as a solid near the Sun. Hence, the planets of Mercury, Venus, Earth, and Mars reside closest to the Sun. In contrast, Jupiter, Saturn, Uranus, and Neptune form beyond the Frost Linea location cool enough for frozen, volatile compounds to remain solid., a location cool enough for frozen, volatile compounds to remain solid. In a nutshell, this is the Nebular Hypothesis.⁷

Clair Cameron Patterson

Clair Cameron Patterson was responsible for determining the current estimated age of the Solar System. For hundreds of years, the age of the solar system was always being debated and changed. These dates were all incorrect but they stood the test of time until Clair Cameron Patterson showed up on the scene.

Flash forward to 1947. Clair Patterson is a chemist Ph.D. student at the University of Chicago. He is being mentored by Harrison Brown (a nuclear chemist). Brown tasks Patterson with determining the age of the Earth by determining the ratio of uranium to lead in an old rock, such as a meteorite fragment. Brown had worked up a mathematical equation that could determine the age of the Earth but in order to do so, he would need to analyze rock samples 1000 times smaller than anyone had measured before. In order to do this, a mass spectrometer would need to be used.⁴ A mass spectrometer produces charged particles (ions) from the chemical substances that are to be analyzed; it then uses electric and magnetic fields to measure the mass (weight) of the charged particles. Brown gave this task to Patterson because he had experience using a mass spectrometer.⁴

In 1953, Patterson followed Brown to the California Institute of Technology where he then built the world’s cleanest laboratory. He was able to prepare the samples that would be put into the mass spectrometer. When the samples were ready, he took them to the Argonne National Laboratory to use the mass spectrometer to be tested. The machine divulged numbers that Patterson put into Brown’s calculation. He was then able to estimate that the age of the Earth is roughly 4.6 billion years old.^{4, 5}

When we compare that age to the age of the universe and place them on a cosmic calendar⁸ (figure 4), we can see that while everything in the universe’s history happened somewhat far apart, our Sun and planets formed in quick succession. This, in turn, also proves that the Nebular Hypothesis is most likely the proper hypothesis that states how the Solar System was formed.

Apollo missions

Apollo 11 and 12

During the first two apollo missions set out by NASA in the late 1960’s and early 1970s, humanity had their first opportunity to collect samples from a foreign terrestrial body known as our satellite, the moon.⁹ This material was then brought back to Earth. Some of this debris was from impacts of asteroids colliding into the moon.  It was then tested for various reasons. Scientists first studied whether these rock specimens would be harmful to plants, bugs or animals before they were directly in contact with the specimens themselves. According to the second Apollo mission (Apollo 12), a rock called Rock 13, was carbon dated back to 4.6 million years of age providing insight that the solar system could at least be that old. This dates back to what is believed to be the formation of the Solar System when it was still a protoplanetary disk.

Apollo 15 and 16

During the fifth (1971)  and sixth (1972) manned apollo 15 and 16 NASA missions that landed on the the moon, debris was collected from many craters and basins.^{10, 11} Two of them, can be seen with the naked eye from here on Earth and are called Mare Imbrium and Mare Serenitatis. This debris was collected to later be examined for determining the age of these basins. Through carbon dating from material gathered, off the moon and some from Earth, scientists were able to determine that meteors hit the moon and the four inner terrestrial planets, Mercury, Venus, Earth, and Mars, during a certain time frame.^{12, 14} The moon has no atmosphere so these samples were easier to examine because no erosion occurred. On Earth, there is an active erosion cycle, and tectonic plate system as well as other natural phenomenon that has over time and continually deleted materials that would help in determining catastrophic events from the past.¹² Scientists can not find any geological evidence dating past 3.5 billion years ago. The Earth does have some evidence but the moon is a fresh playing field for astronomers and scientists.

Apollo 17

The seventh and last mission that NASA sent to the moon was Apollo 17 in 1972.¹³ It lasted twelve days, making it the longest of the Apollo missions and the largest sample of lunar rock was collected. This mission was set up to get more samples of the lunar basins material. Mare Imbrium is believed to be the youngest basin on the moon out of the two huge basins explored and it is believed that this impact may have covered the older impacts with new debris. Therefore, apparent ages of previous samples collected could have been “reset” by events occurring after them. The Mare Imbrium basin was formed from an asteroid that collided with the moon roughly 3.9 billion years ago but Mare Serenitatis may be an older basin.

Late Bombardment

According to other theories throughout time, the solar system was formed 4.6 billion years ago. The late heavy bombardment theory is estimated to have happened  3.8 to 4.1 billion years ago.^{12, 14} Due to specimens of rock retrieved during the Apollo Missions, scientists were able to study the debris from two of the biggest basins on the moon and conclude that at one point there was a huge asteroid shower that collided with the four inner terrestrial planets. This is known as the Late Heavy Bombardment or Lunar Cataclysm. Early history of the solar system was an aggressive battlefield among planets and other large protoplanets. This theory gives proof that the solar system was forming or already formed in that time era.

This event is believed to have occurred due to the four giant gaseous planets orbiting the outer portion of our solar system. Jupiter, Saturn, Uranus and Neptune were still chaotic in the sense that they were changing their orbital path around the sun. This caused asteroids and comets from the asteroid and/or the Kuiper belt to propel inward towards the center of our solar system. The four terrestrial planets, as well as the Earth’s moon, became victims of this bombardment.

The moon provided evidence of Lunar Cataclysm. As outlined in the Apollo missions, the moon has many craters and basins but no atmosphere.^{9, 10, 11, 13} This allowed scientists and astronauts with many samples to outline how big, when space debris collided into it, and how old the basins were.

However, this theory has been under scrutiny due to various factors. It was believed that basins on the moon came from a large meteor shower but there is speculation that the youngest known basin, Imbrium, may have covered other basins upon impact (meteor impacting moon).¹⁵ This means that only Imbrium material was collected and analyzed. Older debris would be underneath Imbrium rubble. So the basin Serenitatis may be much older than originally thought and there may not have been a Late Heavy Bombardment theory. If this is true, meteors may have hit the moon over a period of time rather than all at once. Imbrium and Serenitatis may be 50 million years apart and throughout this time period thirty other basins have formed. Therefore, the basin Mare Serenitatis would be older than 4.1 billions years of age.

Protoplanetary Disks

A protoplanetary disk, also known as an accretionThe process of growth or increase, typically by the gradual accumulation of additional layers or matter. disk, is made up of dense gas and dust; this surrounds a newly formed star which is in the centre of the disk.^{6, 7, 16} Proto Planets and planetoids still existed a half a billion years after our solar system formed. These large bodies were believed to still have been colliding with the current planets that can be seen today. Saturn and Jupiter also still had a huge influence on these bodies before 4.1 billion years ago. Planetoids and protoplanets would still be colliding at this point in time. Therefore, some of the planet’s surfaces give evidence to how old the Solar System may be!

Conclusion

Research is never stagnant, always progressing in order to fill the void of persistent discovery. In order for progressive research to enrich, many dedicate a lifetime pursuing a desire to establish a credible theory. That passion is what motivated Clair Patterson to determine the age of the earth from a ratio of uranium to lead using old rock samples. Utilizing rock samples to determine age is common practice. The Apollo missions used a process similar to the way in which Patterson determined the age of the earth. Samples of moon debris were returned to earth and evaluated (using carbon dating), for mineral content to determine the age of the moon. Nebular hypothesis, the most commonly accepted theory for the age of the solar system – was first theorized almost four-hundred years ago. It allowed for knowledge into protoplanetary disks, furthermore researchers believe planets in our solar system have further evidence on their surfaces relating to solar system age.  A discovery like this would not have been possible without the Nebular hypothesis. Vortex theory’s proposition is similar to that of Nebular, as both theories involved condensing matter into formation. From the theories within the article, theoretical advancement is displayed through disproving those which are mistaken and building on theories that are accurate. Allowing progressive understanding to flourish, through reevaluation and reconsideration. Technological advancement will become a vital component as we push the boundaries of our understanding into the age of the solar system.