Contents
What are comets made of?
The solid part of a comet is called the nucleus, which consists of ice, dust, and rock bonded together.
Data from the Rosetta spacecraft shows that the comet nucleus:
- Has a highly porous structure.
- Has a lower density than water.
- Contains more dust than ice.
This has led to the familiar "dirty snowball" model being replaced by a more accurate image: a clump of dust with ice interspersed throughout.
Why do comets have tails?
As they approach the Sun, the ice in the nucleus begins to sublimate into gas, dragging dust out into space.
This process creates:
- Coma, the layer of gas and dust surrounding the nucleus.
- Ion tail, narrow and straight, shaped by the solar wind.
- Dust tail, wider and more curved.
Interestingly, a comet's tail always points away from the Sun, not necessarily trailing behind the direction of motion.
Where do comets come from?
Scattered disc and Kuiper Belt
This is the source of most short-period comets.
These celestial bodies reside beyond the orbit of Neptune and are occasionally perturbed by gravity, pushing them into the inner Solar System.
Oort cloud
Long-period comets are thought to originate from the Oort cloud, a hypothetical region of celestial bodies located far beyond the Solar System.
To date, the Oort cloud has not been directly observed but is inferred from the orbits of comets.
The fate of a comet
Each time a comet passes near the Sun, it loses a portion of its material.
Eventually, they may:
- Deplete their ice and become inactive.
- Break into many pieces due to gravitational forces.
- Collide with a planet or the Sun.
The dust left behind in the orbit creates meteor showers when Earth passes through it.
Did comets bring water to Earth?
This remains a subject of ongoing research.
Measurements show that the water composition of many comets is not exactly the same as water in Earth's oceans, so most of the water on our planet likely came from carbon-rich asteroids.
However, it has been confirmed that comets contain many complex organic molecules, so they may have contributed to bringing essential chemical ingredients to the early Earth.
☄️ The greatest scientific value of comets lies not in their glowing tails, but in the fact that they are nearly pristine objects from the time the Solar System was born, helping scientists study the most ancient materials still existing in our vicinity.
Further reading
References
- [1]Prebiotic chemicals — amino acid and phosphorus — in the coma of comet 67P/Churyumov–Gerasimenko — Science Advances 2, e1600285 (2016)
- [2]On the nucleus structure and activity of comet 67P/Churyumov–Gerasimenko — Science 347, aaa1044 (2015)
- [3]Dust measurements in the coma of comet 67P/Churyumov–Gerasimenko inbound to the Sun — Science 347, aaa3905 (2015)
- [4]67P/Churyumov–Gerasimenko, a Jupiter family comet with a high D/H ratio — Science 347, 1261952 (2015)
- [5]Ocean-like water in the Jupiter-family comet 103P/Hartley 2 — Nature 478, 218 (2011)
- [6]Activity in Geminid Parent (3200) Phaethon — The Astronomical Journal 140, 1519 (2010)
- [7]Cometary glycine detected in samples returned by Stardust — Meteoritics & Planetary Science 44, 1323 (2009)
- [8]The comet 17P/Holmes 2007 outburst: the early motion of the outburst material — Astronomy & Astrophysics 479, L45 (2008)
- [9]Identification of comet Hyakutake's extremely long ion tail from magnetic field signatures — Nature 404, 574 (2000)
- [10]A Scattered Comet Disk and the Origin of Jupiter Family Comets — Science 276, 1670 (1997)
- [11]First Halley Multicolour Camera imaging results from Giotto — Nature 321, 320 (1986)
- [12]The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin — Bulletin of the Astronomical Institutes of the Netherlands 11, 91 (1950)
- [13]Meteor Shower Calendar — thời gian hoạt động, cực điểm và thiên thể mẹ — International Meteor Organization (2026)
- [14]Danh mục sao chổi, vật thể liên sao và quy tắc đặt tên của IAU — IAU Minor Planet Center (2026)
- [15]Small-Body Database — phần tử quỹ đạo và chu kỳ của 1P/Halley và 2P/Encke — NASA Jet Propulsion Laboratory (2026)
- [16]Comet Shoemaker–Levy 9 Collision with Jupiter — NASA Science (2024)
- [17]Sao chổi: nguồn gốc và đặc điểm — Thiên văn Việt Nam (VACA) — Trần Quốc Việt (2015)
- [18]Comets: A Chronological History of Observation, Science, Myth, and Folklore — ghi chép Trung Quốc năm 240 TCN và dự báo của Halley — Wiley / NASA Science (1991)
Image: ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0 — Wikimedia Commons, CC BY-SA 3.0 igo.
