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Exploring Science for the Junior Cycle

Unit 5: Earth and Space


Chapter 36: Comets, Asteroids, and MeteorsMichael O'Callaghan, Pat Doyle, Orla Molamphy, Ger Reilly, Edco

Introduction to Small Celestial Objects

  • The night sky contains more than just the Sun and planets.

  • Includes various cosmic structures previously considered mythical.

  • Understanding their origins and properties is essential.

Comets

Definition and Characteristics

  • Comets are ancient objects in our solar system, potentially holding keys to solar system formation (4.6 billion years ago).

  • Described as "giant dirty snowballs" comprising frozen gases, rocks, and dust.

  • Formed far from the Sun, thus remaining icy.

Origin of Comets

  1. The Kuiper Belt

    • Located beyond Neptune's orbit.

    • Comets formed here: Short-period comets (take about 200 years or less to orbit the Sun).

  2. The Oort Cloud

    • Surrounds the outer limits of the solar system, filled with trillions of comets.

    • Comets from here are Long-period comets (orbits take from 200 years to 30 million years).

Comet Appearance

  • Comets seem solid until near the Sun.

  • Sun's heat evaporates ice, releasing dust and gases, forming a glowing head and long tail.

  • Tails can have two components: one of dust, another of gas, always pointing away from the Sun.

  • Comets do not support life, but may have delivered water and other compounds to Earth.

The Rosetta Mission

Overview

  • Launched on 12 November 2014 by ESA and NASA.

  • Landed Philae on comet 67P/Churyumov-Gerasimenko after traveling 6.4 billion km at 135,000 km/h.

Achievements

  • Philae sent back data improving our knowledge about comets.

  • Mission ended on 30 September 2016 with a farewell tweet from Philae.

Asteroids

Definition and Characteristics

  • Asteroids are rocky bodies without air or atmosphere.

  • Located primarily in the asteroid belt between Mars and Jupiter.

Behavior and Risks

  • Asteroids can collide and be displaced from their belts, leading them close to Earth.

  • Despite millions existing, their collective mass is less than that of Earth's moon.

Historical Context

  • Rare asteroid or comet collisions can cause global destruction.

  • Such events are believed to have contributed to the extinction of the dinosaurs.

Size Variability

  • Asteroids vary in size:

    • Small asteroids (approx. 10 m diameter) are called meteors.

    • Larger structures (approx. 100 km diameter) are known as planetoids.

Importance of Study

  • Understanding asteroids is crucial since they pose potential threats to Earth.

  • NASA's Dawn Mission focuses on studying the largest asteroids, Ceres and Vesta, launched on 27 September 2007.

Ceres

Overview

  • Largest asteroid in the belt, measuring 950 km in diameter.

  • ESA discovered water vapor erupting from Ceres, suggesting it contains water.

  • The Dawn mission began studying Ceres in April 2015.

Vesta

Overview

  • Second largest asteroid, with a diameter of 530 km.

  • Notably reflective, with a surface three times more reflective than the Moon.

  • Vesta is the only asteroid visible from Earth without telescopes.

  • Studied by Dawn Mission from July 2011 to September 2012.