Us residents of the Earth take our atmosphere for granted. We constantly bombard it with harmful chemicals and pollute it with manmade substances that can permanently damage our “forcefield” around Earth. After all, it is responsible from keeping us safe against the harmful rays of the sun and provides us with the oxygen we need to live.
So, how did our shield in the sky come about? When Earth first formed, it was giant rock floating in space. Because of its mass and density, gravity caused the core of Earth to grow hot and this molten core created volcanoes. Such volcanoes emitted H20, C02, and N2, known as volcanic degassing, into the air, creating our initial atmosphere.
So how did we get to where we are today? Sometime and somewhere, life formed on Earth as a simple bacteria in the oceans. As the heavy CO2 sunk and was absorbed by the ocean, this bacteria (precursor to modern plants) was able to live off it and produce the O2 we know and love today as a waste product. Over time, this O2 accumulated and the atmosphere we have today was finally formed.
Images from NASA’s Hubble Space Telescope show changing seasons on the gas giant, Saturn. Saturn has a slower orbit than Earth (29 years to orbit the sun!), which makes each “season” on the planet over 7 years long. Similar to Earth, Saturn is tilted on an axis, which affects the intensity of sunlight on sides of the planet, causing seasons and other atmospheric changes. Saturn’s long seasons produce small changes in photographs of Saturn’s bands taken in consecutive years:
Saturn in 2018 (left), 2019 (center), and 2020 (right) taken by NASA’s Hubble
From 2018 to 2020, the equator grew almost 10% brighter, and wind speeds near the equator have gotten significantly higher in the last decade (now about 1,600 kilometers per hour).
Saturn’s northern hemisphere is approaching Fall, so polar and equatorial regions are changing. Differences can be seen in color, winds, and cloud height, according to Amy Simon, a scientist at NASA’s Goddard Space Flight Center.
Over a longer timescale, more significant changes will be visible on Saturn, thanks to Hubble.
It is no secret that space travel is a risky and dangerous endeavor for all involved. As of 2021, 19 astronauts (including cosmonauts) have died in in-flight accidents. Only one accident, however, occurred in space—over 100 kilometers above the Earth.
Three Soviets (called cosmonauts) were aboard the Soyuz 11 in June of 1971, which was docked to space station Salyut I. For 23 days, the cosmonauts carried out experiments on the ship, keeping precise records and logs of all results, particularly about weather on Earth. On the last day, one of the cosmonauts undocked Soyuz 11 as planned, and notified officials on Earth that they were on their descent back to Earth. At some point during the ship’s descent, the cosmonauts stopped responding to ground control’s messages. The ship landed on Earth in Kazakhstan, and the three cosmonauts were discovered dead with no signs of struggle.
While the official statement read that a seal failure caused a rapid decrease in pressure in the ship, many other theories for the accident were debated by experts. Some thought that humans could simply not survive prolonged time in space, that it caused heart problems. Others thought that a toxic substance had been released. Regardless of the reason, the deaths caused concern among Americans preparing for the launch of Apollo 15.
There is now a memorial where the ship landed, commemorating the tragic deaths of Georgy Dobrovolsky, Viktor Patsayev, and Vladislav Volkov.
An artistic rendition of the Parker Solar Probe (via NASA)
Kevin Durant, a two-time NBA champion, once tweeted: “I’m wondering how do these people kno what’s goin on on the the sun.. ain’t nobody ever been.” Like his tweet from 2010, I too wondered how humans have been able to study the Sun’s surface and what discoveries have been made to determine the surface’s characteristics.
Astronomers since Galileo have used telescopes and, more recently, satellites to view the surface of our Sun, known as the photosphere. Using filters, they could observe the surface to discover that the Sun does not have a solid surface like Earth. Instead, the Sun has a massive plasma sphere that has a temperature of 5500 degrees Celsius. Underneath the gaseous photosphere, scientists in the 1970s began to use helioseismology which is a method that could be used to investigate the structure of the Sun and discover its interior features. Using helioseismology, astronomers study oscillations of particles under the surface, allowing them to understand the Sun’s dense where nuclear reactions produce the star’s fuel.
Observing from far away using telescopes and satellites has been adequate to understand the Sun, but astronomers needed a more modern approach to researching the star. The result is a 2018 NASA probe called the Parker Solar Probe that will come closer to the Sun than any other human instrument. Its mission is to use the gravitational pull of Venus to orbit closer and closer to the surface, all while taking detailed measurements of our star. In all, the probe will orbit 24 times around the Sun and will begin its return to Earth in 2025. From telescopes to Sun probes, astronomers have come a long way in their ability to study the Sun’s characteristics.
Trajectory of NASA’s Parker Solar Probe (via Wikipedia)
Radiometric dating, or radioactive dating, is a method astronomers use to study a rock’s age. This method is critical in learning about the Solar System’s formation, as rocks from the Solar System can be studied to find how long ago the rock was formed and how old the Solar System is. When billions of atoms collect into a rock, the chemical composition of the atoms change. At that time, any isotopes in the rock begin decaying into a different isotope with new characteristics. By determining the original isotope and the rate the decaying process occurs within the rock, the rock’s formation’s date can be extrapolated. The rates are typically shown in half-life units, or the time it takes for exactly half of the isotope to decay. For example, if the formation occurred at time 0 with 16 radioactive atoms of a particular isotope, there will be 8 radioactive atoms after one half-life. If there were only one atom left today, we would know that the rock was formed four half-lives ago.
Using this process, the oldest known rock on Earth, Acasta Gneiss (shown above), was found in Canada and determined to be just over 4 billion years old. Others collected from the Moon are close in age to Acasta Gneiss. Some non-terrestrial meteorites such as the Murchison meteorite in Australia have been determined to be over 7 billion years old (older than our Solar System!!). Ultimately, without radiometric dating, none of these discoveries would have been possible, and the history of the Solar System would still be a mystery.
Astronomy is awesome. It lets us make cool observations (e.g., things that inform our understanding of the foundations of the universe, like the Cosmic Microwave Background), helps us ask big questions (e.g., why does the universe exist?), and reminds us that not all questions have answers (e.g., we can’t really expect an answer to the question of why the universe exists according to theoretical physicist Sean Carroll).
Astronomy, however, is not a “self-substantiated” entity: it’s based on an assumption we apply to all our observations. The assumption is called the Cosmological Principle, and it has three parts (according to Weintraub, How Old Is the Universe?, pages 228-229):
-Universality: the laws of physics are the same everywhere
-Isotropy: the universe looks the same in all directions to observers everywhere in the universe
-Homogeneity: the average contents of a large enough chunk of the universe will be the same for any chunk of the universe (i.e., the contents of the universe are relatively similar everywhere over large enough volumes)
From the Cosmological Principle, we can apply our understanding of physics to the rest of the universe: we can make claims about the creation of the universe, the size of the universe, how stars work, whether extraterrestrial life may exist, etc. Virtually all of astronomy is based on the Cosmological Principle; without it, we wouldn’t be able to make sense of our measurements of the universe.
Learning about the Cosmological Principle opened my eyes to how lots of analyses are based on some key assumptions, and I’ve carried that lesson with me as I’ve progressed through coursework for my economics and political science majors.
Economics is based around the assumption that producers and consumers are rational, meaning they “maximiz[e] objectives within constraints” (Conley, Microeconomics for Smarter Students, April 2020 draft version, page 24). In other words, we make some key assumptions that consumers, for example, can rank bundles of goods against each other by preference (e.g., I would rather eat two slices of pizza than one… who wouldn’t?). If consumers were to be irrational, though, we wouldn’t necessarily be able to predict and analyze how they would act. If our underlying assumption of rationality were to fail, so too would our analysis fail.
Political science is based on some similar assumptions, and I’m going to zone in on one specific realm of poli-sci right now: understanding the nature of war. When historians and anthropologists study past civilizations, they collect data about things like cracked skulls, the presence of spears, and battle fortifications – they look for signs of warfare. When political scientists come in, we analyze all that data, and we draw conclusions about warfare in older societies from our analyses. Similar to astronomy and the Cosmological Principle, however, this entire analysis is based on a key assumption: the bits of evidence from different societies are manifestations of the same pattern. Think about it: if different societies made spears for entirely different reasons (e.g., one society did it for war and one did it purely for decoration), the constructions of spears would not be related, so we would be incorrect to claim that all old societies with spears were violent. If our underlying assumption of different societies doing the same things for the same reasons were to fail (i.e., if our assumed pattern were to fail), so too would our analysis fail.
So, just like astronomy, it’s easy to see that other analyses are also dependent on some key assumptions. While astronomy assumes the validity of the Cosmological Principle, economics assumes rationality, and political science’s analysis of warfare assumes independent events are related to each other through patterns.
All this leads to two questions I’d like to pose to you: what are the underlying assumptions serving as the foundations of the belief systems with which you’re familiar, and what would happen if those assumptions were to fail?
Expansion of the universe, a phenomenon we understand as a result of assuming the validity of the Cosmological Principle. Image courtesy of Wikipedia.
With the intimate connection between water and life, the discovery and understanding of water on Mars has been a crucial point of research that is continuing to be updated. Although there is no liquid water on the surface of Mars, there is water in the form of ice in polar caps and glaciers. If all of the ice on Mars were melted, the entire planet could be covered in liquid water 10 meters in depth.1 In addition, it is possible that microscopic life could exist underneath the surface near locations of volcanic heat if there is liquid water.1
While there was previous knowledge of a potential lake underneath Mars’ surface, new information in 2020 not only supported the existence of this lake, but also the existence of three other lakes in the same area. Although the amount of salt necessary to keep water under the surface from freezing could pose an obstacle to life, the existence of liquid water on Mars could demonstrate that life exists on Mars or did exist billions of years ago.
Just this week, sources including The New York Times and The Chicago Tribunehave published news regarding a leading theory on where the water on Mars went. While some of the water was split apart and sent into space (or exists as heavier deuterium that does not escape the planet as easily), most water is trapped in minerals and salts and therefore may still be on Mars (just in a useless form). Previous and current NASA rovers and orbiters found hydrated minerals, and the Perseverance Rover that landed recently will go to a river delta to look for clues regarding previous life that may have existed on the planet. Although Elon Musk joked about using nuclear bombs to thaw out the water and heat the planet, it remains to be seen if Mars will be habitable or if it already is (to other lifeforms).
[1] Bennett, Jeffery, et al. The Cosmic Perspective: The Solar System. 9th ed., Pearson, 2020.
For thousands of years, humans have looked to the sky, and every time we uncover an astronomical surprise, we try to explain it. Today, we use the scientific method to do so; in comparison, older societies frequently created myths. In this blog post, I am going to explore some of the myths surrounding the Northern Lights; please note that all information in this post is from this website.
THE NORSE
Vikings believed the Lights were “earthly manifestations of their gods,” and they celebrated them. In comparison, other Norse people thought the Lights posed a danger to humanity: according to Norse mythology, the events of Ragnarök would bring about the end of the world, and some Nordic people believed the Lights were reflections of the armor of the Norse gods’ warriors, the Valkyries, fighting during Ragnarök’s battles. From their logic, I see why they feared the Lights – if I thought the Lights resulted from presently-occurring battles over the fate of the world, I too would be scared!
THE SÁMI
The Sámi, the indigenous Finno-Ugric people, believed the Lights were dead people’s souls moving through the sky. They feared the souls, so they tried to distance themselves from the Lights as much as possible: “waving, whistling, or singing under them would alert the lights to your presence,” and that would be bad given that they believed the Lights were something to be feared. Some people even thought the Lights could behead living people or steal them away, kidnapping them into the sky… very scary!
THE FINNISH
The Finnish named the Lights “revontulet,” a literal translation of “fire fox.” They believed foxes ran through the sky during the winter, and when their tails brushed past mountains, they created sparks that illuminated the sky. A slightly different version of the story purports that fire fixes flung snowflakes into the sky when they ran, and the snow catching the moonlight created the Lights. Either way, the Lights were not thought to be a harbinger of doom, contrasting with the Nose and Sámi people’s beliefs.
THE GREEKS AND ROMANS
The Greeks and Romans offered another positive interpretation of the Lights: the goddess Aurora, “the personification of the dawn, and the sister of the sun and the moon” rode her chariot across the sky each morning to warn her brother and sister of the impending dawn. According to the myth, Aurora did not intend to cause harm, so the Greeks and Romans did not fear the Lights.
WHAT DO YOU THINK?
The Nose and Sámi believed the Lights were a bad omen, and the Finnish, Greeks, and Romans believed the Lights were not inherently bad. If you were to have lived in a time before science could explain the Lights, how what would you have thought of them? Would you have feared them (like the Norse and Sámi), or would you have created a positive explanation for them (like the Finnish, Greeks, and Romans)?
Stars take the idea of a “last hurrah” to beautifully explosive level. When a star runs out of energy and collapses, it will condense into a bundle of energy and explode. Supernovas are by far the largest explosion in the universe and can only occur to a star that is truly massive. Supernovas normally occur extremely far away, as not many of the stars close to us are capable of this massive discharge. The closest supernova in years, Supernova 1987A, was still an astonishing 168,000 light years away! However, it isn’t such a bad thing that these supernovas are occurring hundreds of thousands of light years away. For example, a supernova thirty light years away would completely destroy the ozone layer and eradicate all ocean life. In addition, the conditions may cause the nitrogen and oxygen in our atmosphere to combine into the poisonous nitrous oxide. A safe distance for a supernova explosion is at least 100 light years away from us. While these radiant membranes of light may looks spectacular, they can be just as easily destructive.
Unfortunately, the answer is no. However, the story of why the Moon’s surface looks the way it does it still an interesting one and one that helps us understand the solar system as a whole. The surface of the Moon most closely resembles that of Mercury (due to the lack of geological activity that comes with the lack of heat and atmosphere), but is quite unique compared to the other terrestrial planets. The Moon has sections called lunar highlands and sections called lunar maria. The lunar highlands have many craters and the areas of impact are so densely packed that there is a lot of overlap. In contrast, the lunar maria are smooth and have very few craters. This tells us a lot about the history of the Moon and of the terrestrial worlds in regard to age, temperature, and periods of bombardment. Radiometric dating showed us that the highlands are about 4.4 billion years old and the maria are between 3 and 4 billion years old.1 Thus, the relatively few impact craters on the maria reveal that extreme bombardment ended about 4 billion years ago and that the lava flow that filled craters to create the maria must have occurred after the bombardment ended. We were then able to use the above information to find the impact rate for the Moon and other terrestrial worlds. This is a helpful method for figuring out ages in the realm of terrestrials because we can perform this technique based only on the crowding of craters visible in photographs.
Although this is no longer true, the Moon once did have a hot interior. So, when large impacts during bombardment cracked the lithosphere of the Moon and radioactive decay heated the mantle, lava rose through the fractures and filled the craters with basalt (igneous rock with mafic materials). Interestingly, the far-side of the Moon looks quite different from the near-side. The near-side has a lower altitude so the lava flowed toward this side. For this reason, the far side is almost all highlands; most maria is on the near-side of the Moon (the side always facing us).
[1] Bennett, Jeffery, et al. The Cosmic Perspective: The Solar System. 9th ed., Pearson, 2020.
