EVSN - On Background: The Anatomy of a Comet

0:00It's the 365 days of Astronomy PodGa. Coming in 3, 2, 1. This episode of EVSN is coming to you as the Earth and comet 10P Temple 2 make their closest approach of this orbit. The comet will be observable from various places on Earth for the next several months and is currently visible in large binoculars and small telescopes. If you're watching this on YouTube, that image is one I took with a tiny 30mm C-star telescope. If you missed seeing it, however, don't stress.

1:02This consistently pleasing comet has a 5.4 year orbit and it will be back. Well, it's here. Let's take this moment to consider. What exactly are we seeing when we observe this and our other icy visitors? In this special EVSN on background, we discuss the anatomy of a comet from the nucleus that is the source of everything we see to the complex coma and tails that appear as the comet moves into the inner solar system. We've got a little bit of it all. I am Dr. Pamela Gay, a senior scientist at the Planetary Science Institute and this is Escape Velocity Space News on background, an educational series from the team here at CosmoQuest. At their most fundamental level, comets are blobs of ice, rocks and complex molecules that change over time. As we'll discuss in more detailed and future episodes, they originate in the outer solar

2:04system, either in the hyperbelt which starts near Neptune's orbit and extends outward, or in the much more distant or cloud. These regions of our solar system are so cold that materials we're used to experiencing as gases are able to exist as ice, from carbon dioxide to monoxide to molecular nitrogen. Ice has come in a lot of different forms other than the water ice we're used to. When our solar system was young, these icy materials, as well as some more rocky materials, gravitationally pulled themselves together into objects ranging from meters to thousands of kilometers in diameter. The combination of different materials also included carbon-rich organics ranging from simple molecules like ammonia to more complex organic materials. The diversity of materials in comets is part of why comets can appear so different. The most massive objects in the outer solar system, we recognize as the dwarf planets Pluto

3:07Sedna and Iris. The smaller objects, those a couple hundred kilometers across and smaller, can have their orbits disrupted. This may send them in toward the inner solar system, or even sometimes, eject them out of the solar system. Objects that migrate inwards shape shift from solid icy structures into comets as they experience the increasingly more intense sunlight. In the outer solar system, there's really no difference between a comet core and an always distant icy body like a kuiper belt object. It's in the sunlight power transformation in the inner solar system that a comet becomes a comet. Most comet nuclei are just a few kilometers across and would be too small to see at great distances if they didn't grow a coma. The coma is the first observable comet-specific feature to develop. Sometimes hints might be seen inside of Saturn's orbit as rare, more easily-multed carbon

4:13and nitrogen-related ice-s go from solid to gas. Inward of Jupiter, sunlight is intense enough to sublimate the abundant water ice into gas. The random motions of the escaping gases leads to a spherical build-up of gas. To be fair, build-up is a deceptively strong description. The gas is extremely low-density, resembling more of a vacuum than an atmosphere. Comets are huge, however, with comets of a few kilometers across growing coma that span 10,000 to 100,000 kilometers. This massive size allows small particles to add up to big light from two different sources. Embedded dust reflects back sunlight. At the same time, we see the glow from the excitation of various gases. For instance, Comet 10P-Temple II glows a dramatic teal from the excitation of molecular

5:17carbon. Gas and dust tails that streak out from comets have always been a favorite of observers, artists, and astrophotographers. Made of larger materials, a comet's dust tail is what can often be seen by eyes, a white or yellow streak for larger and closer passing comets. These tails consist of material pushed away from the comet by solar radiation, which is a fancy way of saying they're pushed by light. We also see them thanks to the reflection of that same sunlight, like bubbles caught in the wind. The dust tail's direction is often dominated by the sunlight's push, but also reflects the particle's initial motion as they were blown away from their starting point. This combo of effects leads to the dramatic arcs sometimes captured in astrophotographers' images. Harder to see are comets plasma or ion tails.

6:17Made of much lighter materials, these tails stream straight away from comets under the influence of the solar wind. They glow from their own light, much like a neon sign, is energy excites molecules and atoms that eventually settle back down and give off that energy as light. These specific colors of different materials can make it easier for us to measure the composition of comets. The sun can dramatically affect the plasma tails, just like gusts in the wind can send bubbles on chaotic journeys. Gusts of solar wind and magnetic effects can disrupt comet tails and even strip them off entirely. Punctuating comets journey through the solar system are random outbursts. These can occur at many different distances from the sun and are triggered, we think, from processes as varied as landslides and the sudden sublimation of pockets of ice into gas as jets.

7:19This means that comets that normally wouldn't have a visible coma may get one at the distance of Saturn or a comet near the sun may suddenly appear bigger and brighter. Near the sun, brightening can also be related to a comet breaking into pieces. Comets each make only a brief foray into the inner solar system. The time during which they are big, bright and beautiful can be very brief. Sometimes only a few days in duration. We'll do our best to let you know on social media and Patreon when one is worth viewing. And we advise that you get out and look up as soon as you can. Lots of different factors can end a comet show. It may simply begin its journey back toward the outer solar system in cool or it may fall apart under the influence of the sun or even get too close to the sun as the sun grazer and cease to exist. The highly varied nature of these visitors from beyond is part of what makes them so exciting

8:23to watch and study. On our main news show, we'll bring you updates on newly discovered comets as well as updates on well-known comets as new science is published. This special episode is meant to give you the most basic understanding of the different aspects of comets. In future on background episodes, we'll talk about how you can help identify new comets and take data that scientists can use in future research. We'll also look at major moments in comet history, such as the meteor storm, comet temple tunnel caused in 1833 when the stars were observed to fall on Alabama at a rate of 30,000 meters an hour. If there are other topics you want to learn about, let us know in the comments. For now though, this has been Escape Velocity Space News on background. Good night everyone and remember, go out and look up. Escape Velocity Space News is executive produced and written by Dr. Pamela Gaye.

9:25The U. this week in aerospace segment is written and researched by Eric Madis and Dave Ballard. Audio engineering is provided by Alay Pellfree. Escape Velocity Space News is a production of the Planetary Science Institute, a 501-C3 non-profit dedicated to exploring our solar system and beyond. This special episode of Escape Velocity Space News was funded by the National Science Foundation. This material is based upon work supported by the National Science Foundation under grant AST-2510292. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. Like us, please share us. You never know whose life you can change with a little bit of science. You are listening to the 365 Days of Astronomy Podcast.

10:39The 365 Days of Astronomy Podcast is produced by the Planetary Science Institute. Audio post-production is by me, Richard Drum. The management is by Aviva Yamani and hosting is donated by Libsyn.com. This content is released under a Creative Commons Attribution Non-Commercial 4.0 International License. Please share what you love but don't sell what's free. This show is made possible thanks to the generous donations of people like you. Please consider supporting our show on patreon.com, forward slash CosmoQuestX and get access to bonus content. Without your passion and contribution, we won't be able to share the stories and inspire the worlds. We invite you to join our community of storytellers and share your voice with the listeners worldwide. As we wrap up today's episode, we're looking forward to unraveling more stories from the universe. With every new discovery from ground-based and space-based observatories and each milestone

11:44in space exploration, we come closer to understanding the cosmos and our place within it. Until next time, let the stars guide your curiosity.