13.3 The “Long-Haired” Comets
3 min read•june 12, 2024
are fascinating celestial objects with unique structures and behaviors. They consist of a solid and a gaseous , developing tails as they approach the Sun. The , often described as a "dirty snowball," is a mixture of ice and rocky material.
As comets near the Sun, their ices , forming the coma and tails. The provided valuable insights into composition and behavior. Comets have diverse orbits, ranging from short-period to long-period, and their visibility depends on various factors like proximity and activity level.
Cometary Structure and Composition
Physical features of comets
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- Comets have two main components: nucleus (solid, central part) and coma (fuzzy, gaseous atmosphere surrounding nucleus)
- Comets develop tails as they approach the Sun
- composed of dust particles pushed away from nucleus by radiation pressure
- Appears curved and follows comet's orbit
- composed of ionized gas molecules pushed away from nucleus by
- Appears straight and always points directly away from Sun
- composed of dust particles pushed away from nucleus by radiation pressure
Components of comet nuclei
- Nucleus is solid, icy core of comet
- Composed of mixture of ice (mostly water ice) and rocky material
- Often described as "dirty snowball" due to composition
- Nuclei are typically small, ranging from few hundred meters to few tens of kilometers in diameter
- (visited by Rosetta mission) has nucleus about 4 km in diameter
Behavior of cometary atmospheres
- As comet approaches Sun, nucleus begins to heat up
- Increased temperature causes ices in nucleus to sublimate (change directly from solid to gas)
- Sublimated gases form coma, which can extend up to 100,000 km from nucleus
- Coma grows larger and more active as comet gets closer to Sun
- Dust particles are also released from nucleus as ices sublimate
- These dust particles form dust
- occurs as volatile materials are released from the nucleus, contributing to the formation of the coma and tails
Findings of Rosetta mission
- Rosetta mission, launched by European Space Agency, studied comet 67P/Churyumov-Gerasimenko from 2014 to 2016
- Key findings
- Nucleus has complex, "rubber duck" shape with two distinct lobes
- Surface is covered in variety of terrains, including smooth plains, steep cliffs, and boulder-strewn regions
- Nucleus has low density (about 0.5 g/cm³), indicating high porosity and mixture of ice and dust
- Comet's water has different deuterium-to-hydrogen ratio than Earth's oceans, suggesting comets may not have been primary source of Earth's water
- Organic compounds, including amino acid glycine, were detected in coma, supporting idea that comets may have delivered some of building blocks of life to early Earth
- Evidence of was observed, where internal heat causes icy materials to erupt from the surface
Cometary Orbits and Visibility
Variety of cometary orbits
- Comets can have wide range of orbital periods and shapes
- : orbital periods less than 200 years
- Examples: ###'s_Comet_0### (76 years), (3.3 years)
- : orbital periods greater than 200 years
- Example: (about 2,500 years)
- : orbital periods less than 200 years
- Most comets have highly elliptical orbits
- Spend most of time far from Sun in outer solar system
- Become visible from Earth only when they approach inner solar system near (closest approach to Sun)
- Some comets have
- Not gravitationally bound to Sun
- Will pass through solar system only once and then escape into interstellar space
Comet visibility and origins
- Comet visibility from Earth depends on several factors
- Proximity to Earth and Sun
- Size and activity level of nucleus
- Viewing geometry (position relative to Sun and Earth)
- (reflectivity) of the comet's surface
- Comet is most visible when it is close to both Sun and Earth, has large and active nucleus, and appears in dark sky away from Sun
- Long-period comets often originate from the , a spherical cloud of icy bodies at the outer edge of the solar system
- Short-period comets are typically associated with the , a region of small, icy bodies beyond Neptune's orbit
Key Terms to Review (34)
Albedo: Albedo is the measure of the reflectivity of a surface, specifically the ratio of the amount of light or radiation reflected by a body or surface to the amount of light or radiation incident upon it. It is an important concept in understanding the energy balance and thermal properties of planetary bodies, as well as the behavior of various solar system objects.
Coma: The coma is the bright, diffuse, cloud-like region surrounding the nucleus of a comet, formed by the evaporation of ice and other volatile materials as the comet approaches the Sun. It is a key feature that distinguishes comets from other celestial objects, giving them their distinctive 'long-haired' appearance.
Coma cluster: The Coma Cluster is a large cluster of galaxies located in the constellation Coma Berenices. It is one of the richest and most densely populated galaxy clusters known, containing thousands of galaxies.
Comet: A comet is a small celestial body composed primarily of ice, dust, and rocky material that orbits the Sun. When close to the Sun, it displays a visible atmosphere or coma and sometimes a tail.
Comet 67P/Churyumov-Gerasimenko: Comet 67P/Churyumov-Gerasimenko is a periodic comet that orbits the Sun. It is named after the two astronomers who discovered it, Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko, in 1969. This comet is of particular interest in the context of the chapter on 'Long-Haired' Comets, as it has been extensively studied by the European Space Agency's Rosetta mission, which provided unprecedented insights into the composition and behavior of comets.
Comet Churyumov-Gerasimenko: Comet Churyumov-Gerasimenko, also known as 67P, is a periodic comet in the Jupiter family. It was the target of the European Space Agency's Rosetta mission, which orbited and landed a probe on its surface in 2014.
Comet dust: Comet dust consists of microscopic particles ejected from the nucleus of a comet. These particles are primarily composed of silicates, carbonaceous materials, and organic compounds.
Comet Encke: Comet Encke is a periodic comet that has one of the shortest orbital periods of any known comet, completing an orbit around the Sun every 3.3 years. It is named after the German astronomer Johann Franz Encke, who calculated its orbit in 1819. Comet Encke is particularly relevant in the context of the 'Long-Haired' Comets discussed in section 13.3 of the course material.
Comet Hale-Bopp: Comet Hale-Bopp is a large and bright comet that was visible from Earth for over a year in 1997, making it one of the most extensively observed comets in modern history. This comet is significant in the context of understanding orbits in the solar system, the overview of our planetary system, the study of asteroids and planetary defense, as well as the characteristics of long-period comets.
Comet Halley: Comet Halley, also known as Halley's Comet, is a periodic comet visible from Earth every 75–76 years. It is one of the most well-known and bright comets, with its last appearance in 1986 and next expected in 2061.
Comets: Comets are icy celestial bodies that orbit the Sun and exhibit a visible atmosphere or coma and sometimes a tail when they come close to the Sun. They originate from the outer regions of the Solar System, primarily the Kuiper Belt and Oort Cloud.
Cryovolcanism: Cryovolcanism refers to the process of volcanic activity on icy planetary bodies, where the magma or other erupted materials are composed primarily of volatile compounds like water, methane, or ammonia rather than the silicate-based magma found on Earth. This type of volcanism is observed on various moons and dwarf planets in the outer solar system.
Dust Tail: The dust tail of a comet is a long, luminous stream of fine dust particles that are ejected from the comet's nucleus and swept back by the pressure of sunlight. It is a key feature of the 'long-haired' comets that are visible from Earth.
Halley: Halley refers to Halley's Comet, a periodic comet visible from Earth every 75-76 years. It is one of the most famous short-period comets known for its relatively brief return time in comparison to other comets.
Halley's Comet: Halley's Comet is a periodic comet that is visible from Earth approximately every 75-76 years as it orbits the Sun. It is named after the English astronomer Edmond Halley, who calculated its orbit and predicted its return in 1758, making it the first comet whose return was predicted successfully.
Hyperbolic Orbits: Hyperbolic orbits are a type of orbital trajectory in which a celestial body, such as a comet, follows a path that is open-ended and never returns to its starting point. These orbits are characterized by their eccentricity being greater than 1, indicating that the object's velocity is high enough to escape the gravitational pull of the object it is orbiting.
Ion Tail: The ion tail, or plasma tail, of a comet is a stream of ionized gas that is blown away from the comet's nucleus by the solar wind. This glowing, luminous feature is one of the most distinctive and recognizable aspects of a comet's appearance in the night sky.
Kuiper belt: The Kuiper Belt is a region of the solar system beyond Neptune, populated with icy bodies and dwarf planets. It is the source of many short-period comets that orbit the Sun in less than 200 years.
Kuiper Belt: The Kuiper Belt is a region of the solar system beyond the orbit of Neptune, containing numerous small icy objects, including dwarf planets like Pluto. This belt of objects orbits the Sun and is considered an important feature in understanding the formation and evolution of the solar system.
Long-Period Comets: Long-period comets are a class of comets with orbital periods greater than 200 years, often taking thousands of years to complete a single orbit around the Sun. These comets originate from the Oort Cloud, a distant reservoir of icy objects at the edge of the Solar System, and are believed to have been perturbed from their stable orbits by the gravitational influence of passing stars or galactic tides.
Nucleus: The nucleus is the central core of an atom, containing protons and neutrons. It is positively charged and holds most of the atom's mass.
Nucleus: The nucleus is the central and most important part of an atom, containing protons and neutrons. It is the core of an atom that holds the majority of its mass and positive charge, and it is the defining feature of an atom's identity and properties.
Oort cloud: The Oort Cloud is a hypothetical, distant region of the Solar System that is believed to surround the Sun with a vast shell of icy bodies. It is thought to be the source of most long-period comets that enter the inner Solar System.
Oort Cloud: The Oort Cloud is a hypothetical spherical cloud of icy objects that is believed to surround the Solar System at a vast distance. It is considered the source of long-period comets that enter the inner Solar System. The Oort Cloud plays a crucial role in our understanding of the formation and evolution of the Solar System, as well as the origin and fate of comets and related objects.
Outgassing: Outgassing refers to the release of gases or vapors from solid or liquid materials, particularly in the context of planetary and cometary bodies. It is a crucial process that shapes the evolution and atmospheres of these celestial objects.
Perihelion: Perihelion is the point in the orbit of a planet, asteroid, or comet where it is closest to the Sun. At this point, the celestial body travels at its maximum orbital velocity due to the gravitational pull of the Sun.
Perihelion: Perihelion is the point in a planet's or comet's orbit when it is closest to the Sun. This is a crucial concept in understanding the motions and behaviors of objects within our solar system.
Rosetta Mission: The Rosetta mission was a landmark European Space Agency (ESA) space probe that was launched in 2004 with the goal of studying the comet 67P/Churyumov–Gerasimenko. It was the first spacecraft to orbit a comet and land a probe on its surface, providing unprecedented insights into the composition and behavior of comets.
Short-Period Comets: Short-period comets are comets with orbital periods of less than 200 years, meaning they regularly return to the inner solar system and can be observed multiple times. These comets have orbits that are typically less elongated than long-period comets, allowing them to be studied more extensively over time.
Solar wind: Solar wind is a continuous stream of charged particles released from the upper atmosphere of the Sun, called the corona. It consists primarily of electrons, protons, and alpha particles.
Solar Wind: The solar wind is a constant stream of charged particles, primarily electrons and protons, that flow outward from the Sun in all directions at high speeds. This solar wind originates from the Sun's upper atmosphere, known as the corona, and interacts with the planetary bodies and interstellar medium throughout the solar system.
Sublimate: Sublimation is the process by which a solid substance transitions directly into a gaseous state, bypassing the liquid phase, when exposed to sufficient heat or reduced pressure. This phenomenon is particularly relevant in the context of comets, where the solid icy components of the comet nucleus can sublimate as the comet approaches the Sun, forming the characteristic comet tail.
Tail: The tail of a comet is a stream of gas and dust particles that extends from the comet's nucleus, often millions of kilometers long. The tail forms when the comet is heated by the Sun, causing material to vaporize and be pushed away by solar wind and radiation pressure.
Whipple: Whipple refers to Fred Lawrence Whipple, an American astronomer who proposed the 'dirty snowball' model for comets. His model describes comets as icy bodies containing dust and other materials that form a glowing coma and tail when near the Sun.