Finale – Culminate Post

An artist’s concept of our Solar System. The lines emanating from Earth represent the missions we’ve sent out.
Source: NASA/Jenny Mottar

I learned much more than I thought I would in this course. Before taking this class, all I really knew about our solar system was that there are 8 planets (and Earth is the third one), the asteroid belt is a thing, Jupiter is big, and Saturn is the planet with pretty rings. I didn’t know everything in space was so far apart (even our moon is much farther than I thought it was). I had no idea Venus was such a hot, cloudy, and fascinating hellscape. I didn’t know the asteroid belt was so much calmer than how it’s portrayed in movies. I wasn’t aware that the Kuiper Belt and the Oort Cloud even existed. I didn’t know Jupiter and Saturn were basically the same size/radius (I always thought Jupiter was bigger). I didn’t know comets had two tails. I didn’t know Jupiter has a volcanic moon that spews sulphurous gas into space. I didn’t know Saturn had a moon that spouts geysers of ice into space. There was just so many interesting things this class taught me about all the worlds and objects in our solar system and throughout the rest of space. It all made me excited about the possibility of expanding/improving space travel so we can learn even more about the things farther away from us.

The only reason I regret taking this class this semester is because I liked it so much. I sincerely wish I had more time here to take more astronomy classes and learn more and more about what we know of space and everything in it. At the same time, I’m glad to have taken this class my last semester as an undergraduate because it’s been one of my favorite classes I’ve taken here. I actually learned a lot of interesting things, and this class was fun. It felt like a great way to finish up my time here.

The Fermi Paradox and The Great Filter

A ~6 minute video about the Fermi Paradox. Posted to YouTube by “Kurzgesagt – In a Nutshell”

Simply stated, the Fermi Paradox asks the question, “Where Are All The Aliens?” The life-projecting equations we’ve discussed in class, such as the Drake and Seager Equations, all seem to suggest that thousands, millions, or billions of other forms of life should be out there in the universe. But if that’s the case, why haven’t we found them yet? The Great Filter is a potential solution to this paradox; it suggests that there is some obstacle standing in the way of life reaching out, colonizing, or coming into contact with the rest of the galaxy.

Where it gets interesting to me is the discussion of whether or not humans are past the Great Filter. A lot of the time, people seem to think humans are really special, so it would be easy to assume that we’re ‘the lucky ones,’ and are thus far the only living species that have overcome the Great Filter. On the other hand, there’s the possibility that the Great Filter lies ahead of us, and humans are hurtling headfirst into their own extinction. The Kurzgesagt (a mouthful, I know) video linked above, as well as a few others I will link to below discuss the Fermi Paradox and the Great Filter in a simple, straightforward way using some cutesy visuals and calming background music. I think they provide an easy-to-swallow way of thinking about a looming existential problem.

The Great Filter is honestly a bit scary to think about, but it’s an important thing to consider all the same. Do you think we’re past the filter, or is it still something we’ll have to try and overcome in the future? If it does lie in front of us, will we be able to slip through and survive, or are we heading towards extinction?

Some other Kurzgesagt videos that may be worth checking out if the Fermi Paradox/Great Filter interests you: Fermi Paradox (2/2) and The Great Filter. Also, you could look into the text of the original ‘Great Filter’ essay, written by economist Robin Hanson.


The Surface of Enceladus, captured by the Cassini spacecraft
Source: NASA via Wikipedia

Enceladus is a medium-size moon of Saturn, with a diameter of about 500 km. Its surface temperature is quite chilly, ranging between 32.9 K (-240 degrees Celsius) and 145 K (-128 degrees Celsius); this is partially because of its distance from the Sun, and also because of its highly reflective surface. The entire moon is coated in fresh ice, so it reflects a lot of the sunlight that reaches it. This helps make it cold, and also makes it one of the brightest worlds in the solar system. Despite its small size and its frigid surface temperatures, Enceladus seems to show signs of ongoing geological activity, due to the fact that its orbital resonance with Dione (another of Saturn’s moons) causes tidal heating.

One of the most fascinating things about Enceladus is that it is believed to have a global subsurface ocean of water beneath its coating of ice. Thanks to tidal heating, Enceladus spews geysers of its ocean material from near its South Pole. The Cassini spacecraft found that these geysers contain mostly water vapor, along with traces of nitrogen, methane, and carbon dioxide. The geysers reach hundreds of miles into space, and the released material makes up most of Saturn’s E ring.

Cassini image of Enceladus, backlit by the Sun. Illustrates how far the geysers reach.
Source: NASA

The presence of liquid water and other compounds have led many to speculate/wonder if Enceladus is capable of sustaining some form of life in its ocean. Programs such as the Breakthrough Initiatives and other proposed missions such as the Enceladus Life Finder seek to find whether life does exist somewhere on Enceladus.

Solar Flare vs Solar Prominence

A short video in which you can see solar flares and solar prominences occurring along the Sun’s surface.

I obviously can’t speak for anyone else, but I whole-heartedly believed that the beautiful loops of material that we sometimes see images and videos of on the Sun were included in the term ‘solar flare.’ As I looked into it, I came to find that solar flares and solar prominences (the ‘loops’) are in fact separate things.

Solar flares are sudden flashes of brightness sometimes observable on the surface of the Sun. They occur when an area of the plasma of the Sun interacts with accelerated charged particles, and the plasma is heated to tens of millions of Kelvin while ions are accelerated to nearly light speed. Flares happen in active regions (near sunspots) and occur when magnetic energy stored in the Sun’s corona is suddenly released. Flares produce electromagnetic radiation, but only some of the energy released is within the range of visible light, meaning that the majority of a solar flare is not actually visible to the naked eye. X-rays and UV rays from solar flares can have effects on Earth’s upper atmosphere, while radio emissions can disrupt Earth’s long-range communications (e.g. radar devices that depend on radio frequencies).

Solar prominences, on the other hand, are essentially loops of relatively cool plasma that form on the Sun’s surface and extend outward into the corona. They form in the magnetic fields generated by sunspots. Prominences can reach up to hundreds of thousands of miles into space and persist for several weeks or months. Some prominences may break apart and result in coronal mass ejections. {A coronal mass ejection (CME) refers to the release of a large amount of plasma and electromagnetic radiation from the solar corona into space. They often follow solar flares or other solar activity and can cause both negative effects (e.g. communications disruptions as aforementioned in the discussion of solar flares) and positive effects (e.g. auroras).}

The Atmosphere of Venus

A true-color image of Venus.
Author/Source: NASA via Wikipedia

Venus’s atmosphere is very, very dense. It is composed of about 96% carbon dioxide, 3.5% nitrogen, and trace amounts of other gases, including sulfur dioxide. Although Earth’s atmosphere is composed of over 75% nitrogen, Venus’s atmosphere is so dense that the 3.5% of its atmosphere that is composed of nitrogen has around 4 times the mass of the nitrogen found in Earth’s atmosphere. The density of the atmosphere on Venus also means that there is about 90 times the atmospheric pressure on Venus’s surface than on Earth’s, which is pressure similar to what would be experienced if you dove about 1000 meters under the surface of one of Earth’s oceans.

The composition of Venus’s atmosphere is also largely responsible for its surface/planetary heat. In the past, the increasing brightness of the early sun, as well as the composition of Venus’s atmosphere (carbon dioxide is a greenhouse gas, which warms the planet), contributed to a runaway greenhouse effect. This effect is essentially a positive feedback loop that caused the planet’s ocean(s) to evaporate and the surface temperature to rise higher and higher. Because of this, Venus’s surface is even hotter than Mercury’s, despite the fact that Mercury is closer to the Sun. The carbon dioxide, sulfur dioxide, and trace amounts of water vapor in Venus’s atmosphere also react with each other to form clouds made up of sulfuric acid, a corrosive compound that can result in severe burns and skin tissue damage; however, acid rain never reaches the surface of Venus since the intense heat evaporates it all before it can reach the surface.

Apparent Retrograde Motion: what it is, and what it isn’t

One thing that must be said right away: retrograde motion is not the same thing as apparent retrograde motion. Retrograde motion generally denotes ‘backwards’ motion, and the specifics depend on how the term is being used. A retrograde orbit refers to an object orbiting in the opposite direction that the thing it orbits around is spinning (see image below).

An animation depicting retrograde orbit. Author/Source: Anynobody, user on Wikipedia

Retrograde rotation refers to an object rotating on its axis in a direction opposite to the motion of its own orbit. For example, when visualizing the orbit of the planets as seen from above the North Pole of the Sun, the planets all orbit the Sun counterclockwise, and most also rotate on their axes counterclockwise; however, Venus rotates on its axis in a clockwise direction, and thus exhibits retrograde rotation.

Apparent retrograde motion refers to the phenomenon that a planet begins moving backwards (e.g. from east to west, rather than west to east) across the sky, as seen from the surface of Earth.

Apparent Retrograde motion of Mars in 2003.
Author/Source: Eugene Alvin Vilar, via Wikipedia

This occurs because, simply put, the Earth is catching up to and ‘lapping’ the other planet during their orbits. As Earth passes the other planet in its orbit, the other planet appears to move backwards. Retrograde motion is something that is observed over the course of weeks or months, as a planet changes place in the sky in relation to the stars, constellations, and other objects in the night sky (that is to say, it is not at all observable overnight). An important thing to keep in mind is that apparent retrograde motion is only apparent. The planet in the sky is not actually moving ‘backwards’ at any point, it simply appears to be in relation to how Earth itself is moving.

The Size of the Universe, Relative to the Size of a Picnicker

Powers of Ten, the video I discuss below

The video begins with a man and a woman out on a picnic, then begins zooming out farther and farther. They start with a focus image 1 x 1 meter wide, then zoom out to a field of vision 10 times larger every ten seconds. So, the first zoom out brings the image to 10m x 10m, then 100m x 100 m, and so on. At 10 million x 10 million meters, the entire earth is enclosed in the square, then at 1,000 million x 1,000 million meters, the orbit of the moon around earth is encompassed as well. At the 1 million million meters (1012) square, the sun and the four rocky planets are within view, and by the next zoom out (1013), the entire solar system is inside the box (save for a clip of Pluto’s orbit). At 100,000 light years (1021), most of the Milky Way galaxy is in the box. The farthest they zoom out is to 100 million light years (1024), at which point our own Milky Way galaxy cannot be seen. The galaxies and galaxy clusters in view are spread out, barely visible dots on the screen. The rest of the video zooms back in, all the way down to the picnickers, and then farther to a subatomic level.

What struck me about this video is just how small it made me feel. It reminded me of what Dr. Neil deGrasse Tyson spoke of in the foreword of our textbook, about the Hayden Planetarium’s “Passport to the Universe” show. This video is essentially a less encompassing version of what he described there. Having said that, the video is still completely captivating. It’s hard not to be drawn in. As the camera zoomed out, I just felt smaller and smaller, more and more insignificant. While I understand that this could sound a little depressing, I found myself getting more and more excited the smaller I felt. The simplest way to explain my stance is this: The universe is huge, and I am tiny. That means there’s so much for me to learn about and explore in all the vast open space around the miniscule portion that I occupy. Humans are insignificant little specs of stardust in the grand scheme of things, but that just means there’s a lot to discover and we have a lot more exploring to do. Although this class only addresses the confines of our own Solar System, it’s a great starting point for someone like me with no past formal education about anything space related. Suffice to say, it made me all the more excited to keep learning about everything this class has to offer.