Comets: where do they come from?

Look for Halley's Comet on May 6
Halley’s Comet, a comet visible from Earth every 75-76 years

A comet is made of a nucleus (inner core), coma (cloudy envelope around the nucleus), and then a tail. Where exactly do these beautiful, fast-moving cosmic snowballs come from? Scientists are able to trace comets that we see in the inner solar system by retracing their orbits. Through this, scientists believe that comets come from two distinct reservoirs: long-period comets from the Oort Cloud and short-period comets from Kuiper Belt. (A long-period comet is one that takes more than 200 years to complete an orbit around the sun and a short-period comet is one that takes less than 200 years).

The Oort cloud is a theoretical gigantic cloud – found at the outer edges of the solar system beyond Pluto – made of icy planetesimals. Scientists have stated that there could be more than a trillion comets within this cloud. Because of this, it may make up a significant portion of our solar system’s mass. Furthermore, we do not have direct evidence that this cloud exists because it is so far away. Our fastest space probe, Voyager 1, will reach the cloud in ~300 years and it will take another 30,000 years to travel through it!

The second home of comets, the Kuiper belt, is a circumstellar disc that is past the orbit of Neptune. Pluto was actually the first object that was discovered in the Kuiper Belt! The belt contains a vast number of icy bodies which become comets. It is far away, but the Oort Cloud is even further!

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How Life Could Start and Exist on Europa

Although our understanding of the evolutionary process is deep, the exact time and process through which the first life forms on Earth arose is still not entirely clear. The panspermia hypothesis speculates that life exists throughout the universe and is distributed through asteroids, comets, and space dust, and that life on Earth was brought from somewhere else. Though this is nearly impossible to prove, the presence of organic compounds on asteroids and interstellar dust show that at the very least, these building blocks could have been brought to Earth from outer space. The prevailing theory, however, is abiogenesis; how we transitioned from organic compounds to life that is self-replicating. In 1952, Stanley Miller and Harold Urey ran an experiment in which a spark (serving as lightning) was conducted through simulated conditions thought to be present on the early Earth. This resulted in 11 (later found to be 20) amino acids were formed through this process, showing that complex molecules can spontaneously form through the addition of external energy.

Artist’s rendition of the top layers of Jupiter’s moon Europa. Chloride salts bubble up from the liquid ocean through the frozen surface, where they are bombarded with volcanic sulfur from Io. This image can be found here.

We already know that extremophiles can be found deep in Antarctica’s lakes, which is the nearest comparison to Europa’s 100-km deep liquid ocean that we can find on Earth. If there are already organisms that exists on this moon (and are possibly similar to the archaea on Earth), how could angiogenesis be possible? Since there is no atmosphere on Europa, the same electric energy simulated by the spark would not be possible – or could it? Jupiter’s electric field is so large that it reaches its moons, and Europa displays a frozen record of strikes by Jupiter’s thunderbolts in the recent past. The gas giant’s thunderbolts prefer to run across the surface of its moon rather than through the near-vacuum of space. Additionally, research from 2000 found that sparks ran through conditions that simulate Europa yield adenine and guanine, as well as a simple set of amino acids dominated by glycine. We are far away from sending a probe into the liquid ocean of Europa, but hopefully when we do, at least some microorganisms will be waiting for us.

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How Big Can a Planet Get?

Jupiter is big. Not only is it the biggest planet in our solar system, but it is large enough to fit all the other planets in the solar system inside of it. However, Jupiter is not as dense as Earth, and even though it can fit about 1,300 Earths inside of it, it is approximately 318 times as massive as Earth. Is Jupiter’s size – or more importantly its mass – pushing the boundary for what is considered a planet? This question is complicated. Scientists believe that the mass requirement for deuterium fusion, in which a deuterium nucleus (a hydrogen nucleus with a neutron) and a proton combine to form a helium-3 nucleus, is about 13 times the mass of Jupiter. Celestial objects that are this large are classified as “brown dwarfs,” and are unable to sustain nuclear fusion of ordinary hydrogen to helium in their cores. For this to occur, a star must have a mass 65-75 times that of Jupiter.

A comparison of Earth, Jupiter, a typical brown dwarf, a low-mass star, and our Sun. Brown dwarfs are only slightly larger than Jupiter but are much more dense and massive. This image can be found here

Planets that are below brown dwarf size are referred to as sub-brown dwarfs or planetary-mass brown dwarfs. Observationally, it is difficult to distinguish between a sub-brown dwarf and a massive exoplanet (sometimes called a super-Jupiter), but they are formed through different processes; sub-brown dwarfs are formed through the collapse of a gas cloud like brown dwarfs and other stars, while super-Jupiters follow classical gas giant formation. The most massive sub-brown dwarf that has been observed (and is very unlikely to be a brown dwarf) is OTS 44 located 550 light-years away from us. It is eleven and a half times as massive as Jupiter, and likely has a circumstellar disk of dust and particles of rock and ice that is about ten times as massive as Earth. Based on NASA’s exoplanet archive, the largest super-Jupiter observed so far is HD 100546 b, an exoplanet 320 light years away from us who’s radius is 6.9 times that of Jupiter.

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Life on Europa?

When considering the likeliest hosts for extraterrestrial life in our very own system, Europa surely is near the top of possible candidates. One of Jupiter’s 79 (!) moons, it possesses the smoothest surface of any celestial body in the solar system. Because of this and imaging from probes, scientists have hypothesized that Europa has a vast subsurface saltwater ocean about 100km thick covering the entire planet. This has led to discussion about the strong possibility of life evolving here; life could exist in a manner similar to deep sea hydrothermal vents on Earth. Additionally, clay-like minerals have been found on Europa which are strongly connected to the proliferation of organic life. The multiple contributing factors to the possibility of life on Europa have led to countless different theories on the nature of life on Europa. Could it be hydrothermal vent dwelling organisms? Or perhaps plankton-like creatures closer to the surface? Or maybe an entirely new form of life that has arisen from processes extremely different to those on Earth? The exciting possibilities of Europa’s ocean has ensured funding for many missions in the near future, which hopefully will provide us with more answers.

Composite photo of Europa showing its true color, taken by the Galileo probe.
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Why isn’t Pluto a planet?

Contrary to what Jerry Smith says in Rick and Morty, Pluto is not a planet. But why did Pluto lose this designation in 2006? The International Astronomical Union has 3 main criteria to determine what is a planet and what is not. These three criteria are: having an orbit around the sun, having sufficient mass to maintain a hydrostatic equilibrium (creating a round shape), and clearing out the space around its orbit. The main reason why Pluto is now considered a dwarf planet is because Pluto only meets two of the three criteria. While Pluto does orbit around the sun, and has enough mass to assume a spherical shape, it has not cleared out the space around its orbit. To clear out space around a planet, it must become gravitationally dominant. When a planet becomes gravitationally dominant in an area of space, it means that there are no other objects of comparable mass in the area other than a planet’s satellites. In Pluto’s case, there are objects in the Kuiper belt within Pluto’s vicinity called plutinos that are also comparable in mass. Because of the discovery of these plutinos, Pluto was downgraded to the status of dwarf planet.

Picture Source: Business Insider

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Dwarf Perspective

Source: NASA

There are many celestial bodies in the Kuiper Belt. One notable object is a dwarf planet named Makemake. This dwarf planet was one of the objects NASA used to demote Pluto from its previous planet status down to dwarf planet status. NASA wasn’t aware of other bodies that looked like Pluto, and when they found more, they could categorize Pluto and Makemake better. This dwarf planet is reddish in color, lacking of an atmosphere, smaller than Pluto, and has an even smaller moon associated with it. Hopefully we can make more discoveries of bodies within the Kuiper Belt range and further.

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Plasma Bubble Around Uranus

On January 14, 1986, Voyager 2 captured a picture of Uranus, capturing the planet’s chilling-blue color. Although the giant planet was already known for being odd — spinning on its side and having an off-center magnetic field. However, it was also recently identified that the icy planet has a giant magnetic bubble around it made of plasma called a plasmoid. When Voyager 2 originally passed the planet, it picked up a magnetic signal that was so tiny that it went noticed until scientists recently went back to the data and noticed it. This exciting discovery can be used as an explanation for why the planet itself is losing mass. The bubble is estimated to be about at least 127,000 x 250,000 miles across.

Hopefully scientists can send another mission to Uranus in order to study the plasmoid and Uranus other unique features with our newer technologies.

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Would Landing on Europa Make Us Europeans?

As I commented in a previous blog post, one of the most fascinating questions that a person studying the solar system can ask is whether life exists outside of our Earthly home. Within this question lay an abundance of philosophical arguments, all counteracting one another and seeking to define the ‘correct’ answer to this question. Are we self-centered enough to believe that we are the only unique life-carrying planet in the universe? Is that not what makes us special and defines our existence These questions, along with a host of other, could all be answered through the possibility of future exploration of Europa, one of Jupiter’s moons.

Europa’s composition offers the compelling possibility of life / the development of life

Europa offers a compelling case study to scientists of all sorts – biologists, astronomers, etc.—due to its composition and location. Europa is thought to have more liquid water than that in all of Earth’s oceans trapped beneath a thick and icy crust. Under this crust and in these oceans, some scientists have hypothesized that life could develop in a manner similar to that of Earth. While it would require a space probe landing on the surface of Europa and then undertaking a drilling project to even “scratch the surface” of these hypotheses, this project could quite literally change our understanding of the entire universe. However, as a result of not only the ice but Europa’s location around Jupiter renders photosynthesis (one of the key ingredients — nay the key ingredient — to life on Earth) nearly impossible. This point begs the question: are there other forms through which life can be created by a volcanic seafloor’s heat like on Europa or is photosynthesis and the Earth’s marvelous story of life the end all be all? Stay tuned!

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So Close, Yet From So Far ☄️

Comet Atlas, captured on March 16th, 2020 by Steve Pauken

The above image is of Comet Atlas, which is a comet that has been getting closer and much, much brighter over the past few weeks. If it doesn’t fizzle out, Comet Atlas will be able to be seen by the naked eye in as little time as a couple of weeks, at places without much light pollution.

Comets are indeed very pretty to look at in the night sky, but sometimes we ponder the question of where they come from. It turns out that these balls of gas, dust, rock, and ice largely come from an area on the edge of our solar system; the Kuiper Belt and the Oort Cloud. Haven’t heard of these two before? They mostly consist of clouds of small, icy bodies. Sometimes, these objects get gravitationally pulled a little too close to the rest of the solar system, and this changes their orbit slightly which passes by the inner solar system and straight into the Sun, where it’ll never be seen again. However, most of the time, we are able to spot them through binoculars and telescopes or even just our eyes, and we call them comets.

The Kuiper Belt is closer to us than the Oort Cloud, but the Oort Cloud’s existence is based merely on speculation and we don’t really know how big it is, or exactly how far away it lies. However, we believe that long period comets, comets that take 200 years or more to complete one orbit, come from the Oort Cloud, and short period comets mostly come from the Kuiper Belt.

The Kuiper Belt and the Oort Cloud were created when the solar system first formed. The remaining gas, dust, and rocks that didn’t coalese into planets were slingshotted away by gravitational force and formed parts of these spherical clouds. Some material was too far away from any of the planets, but not too far to escape the solar system, so it continues to reside in the Kuiper Belt.

Both the Kuiper Belt and Oort Cloud are constantly changing and even diminishing, since objects continually collide with one another and turn into smaller, dustier fragments, then get blown away by the solar wind. Some comets burn up on their orbit into the inner solar system, and never return. Though we’re not sure of all the details yet, it’s still fascinating to find that beyond the commonly known orbits of our planets, we are surrounded by bits of our solar system’s nursery.

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Solar Winds

Solar winds are arguably one of the most destructive forces in our solar system. As a kid, I never took these forces into account when thinking about space travel. In my mind, as long as you avoided flying your space ship directly into the sun (which I thought was on fire, of course), our star was not to be worried about. Unfortunately, solar winds have to be taken into account when traversing space.

A rendering of solar winds and the sun’s corona

Here on earth, tornadoes and hurricanes are some of mother natures most immediately damaging phenomenon. One of the things that make these occurrences so scary, is that they can seem to appear out of nowhere. Just recently, Nashville was hit by a devastating tornado. There was little to no warning for those that were affected by it. Tornadoes can have wind speeds up to 300 mph, the recent Nashville tornado is estimated to have had 165 mph winds. Comparatively, solar winds can reach speeds up to 500 miles per second. That’s a top speed of 1.8 million mph!

This incredible speed leads to a large transfer of energy into whatever the winds collides with, and luckily for us, we have our magnetosphere to protect us. I mentioned the magnetosphere in my previous post about the northern lights, but there are other things that occur when the wind makes contact with our magnetosphere. The near invisible collisions can cause the magnetosphere to become deformed, leading to turbulence. this turbulence can lead to a number of things, interference in terrestrial communications, satellite malfunctions, and even issues in our power grids. Solar wind is a part of our local space weather, which we need to be conscious of, whether we are traveling in space or living here on Earth.

An awesome photo by NASA on solar wind!
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