EVSN - On Background: The Anatomy of a Comet

0:00It's the 365 Days of Astronomy podcast, coming in 3, 2, 1.

0:30This 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 30-millimeter Seastar telescope. If you missed seeing it, however, don't stress. This consistently pleasing comet has a 5.4-year orbit, and it will be

1:07back. While 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

1:40on 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 detail in future episodes, they originate in the outer solar system, either in the Kuiper belt, which starts near Neptune's orbit and extends outward, or in the much more distant Oort cloud. These regions of our solar system are so cold that materials we're

2:15used to experiencing as gases are able to exist as ice. From carbon dioxide and monoxide to molecular nitrogen, ices 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

2:50molecules like ammonia to more complex organic materials. And 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, Sedna, and Eris. 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

3:26inwards shapeshift 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 this 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

4:02first observable comet-specific feature to develop. Sometimes hints might be seen inside of Saturn's orbit as rare, more easily melted carbon and nitrogen-related ices 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 buildup of gas. To be fair, buildup is a deceptively strong

4:34description. The gas is extremely low density, resembling more of a vacuum than an atmosphere. Coma are huge, however, with comets 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

5:07the excitation of various gases. For instance, comet 10P-Temple 2 glows a dramatic teal from the excitation of molecular carbon. 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 eye as a white or yellow streak for larger and closer passing comets. These tails

5:40consist 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 tails direction is often dominated by the sunlight's push, but also reflects the particles' 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.

6:11Harder to see are comets' plasma or ion tails. Made 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, as energy excites molecules and atoms that eventually settle back down and give off that energy as light. The 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

6:48gusts 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. This means that comets that normally wouldn't have a visible coma may get one

7:25at 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

8:00different 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 a sun grazer and cease to exist. The highly varied nature of these visitors from beyond is part of what makes them so exciting to 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

8:33episode 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 Tuttle caused in 1833, when the stars were observed to fall on Alabama at a rate of 30,000 meteors an hour. If there are other topics you want to learn about,

9:05let 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.

9:41Exploring 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 he can change with a little

10:13bit of science. You are listening to the 365 Days of Astronomy podcast. Cool.

10:37The 365 Days of Astronomy podcast is produced by the Planetary Science Institute. Audio post-production is by me, Richard Drumm. Project 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

11:12supporting 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 that 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 in space

11:44exploration, we come closer to understanding the cosmos and our place within it. Until next time, let the stars guide your curiosity. ä tand plast.com änt

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