The Sun is a medium sized star made mostly of hydrogen and helium. Deep in its core, hydrogen nuclei fuse into helium, releasing tremendous energy as light and heat. This energy drives Earth’s climate and supports photosynthesis. The Sun’s gravity also anchors the solar system, keeping planets, asteroids, and comets in orbit.
Comprehension Check
What reaction powers the Sun’s energy output?
Which role of the Sun is described in the passage?
Eight Planets, Two Families
Our solar system has eight planets that fall into two broad groups. The inner planets—Mercury, Venus, Earth, and Mars—are small, rocky worlds with solid surfaces. The outer planets—Jupiter and Saturn, called gas giants, and Uranus and Neptune, called ice giants—are much larger and lack solid surfaces. All planets travel in elliptical orbits around the Sun due to its strong gravitational pull.
Comprehension Check
Which planets are classified as inner rocky worlds?
What mainly keeps planets in their elliptical paths?
Small Bodies: Asteroids, Comets, and Meteors
Beyond the planets are many smaller objects. Asteroids are rocky bodies, most of which orbit in the asteroid belt between Mars and Jupiter. Comets are icy objects that develop glowing comas and long tails when heated by the Sun. Meteoroids are small fragments that can enter Earth’s atmosphere; they heat up from friction and become meteors, and any pieces that reach the ground are called meteorites.
Comprehension Check
Where are most asteroids located?
What is the correct sequence of terms as a space rock approaches Earth?
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