Examples Of Planetesimals

About 4 billion years ago, earth was hit by planetesimals daily.
••• Jupiterimages/Photos.com/Getty Images

Terrestrial planets, gas giants, comets, moons, asteroids: earth’s solar system has numerous types of heavenly bodies. Planetesimals are unusual rocky celestial objects that can be measured in a few meters or many kilometers. They are located in many parts of the solar system, and some astronomers believe they are key to the history of planets and moons. Planetesimal matter such as rock and dust may have combined with gravity to form a number of the masses orbiting the sun.

Planetesimal Particulars

Russian astronomer Viktor Safronov theorized that, when the solar system was forming, the attractive force of gravity pulled bits from nebulae --clouds of dust, gasses and plasma-- together, creating rocky planetesimals of various sizes. If the planetesimals nearest the sun were composed of matter that had high melting points, they may have formed the four terrestrial planets. The outer planets could have come from planetesimals made from different materials that formed dense cores, attracting light gases such as hydrogen and helium. This may have resulted in the four planets known as gas giants.

Pluto's New Category

Pluto was once considered one of the nine planets in earth’s solar system. However, in the latter part of the 20th century, many astronomers believed that Pluto was simply not large enough to be considered a major planet. Some of these scientists began referring to Pluto as a planetesimal. By 2006, most astronomers in the International Astronomical Union generally agreed that Pluto was not a planet, although this was a controversial decision for some scientists and non-scientists. Dropping Pluto from the planetary list was intended as a reclassification rather than a demotion.

A Big Belt

In 1943, Irish astronomer Kenneth Edgeworth suggested that undiscovered objects lay near the outer boundary of the solar system. In 1951, Gerard Kuiper offered further evidence to support this idea. In fact, a ring of icy bodies, now commonly known as the Kuiper belt, orbits the sun beyond Neptune. Some of the larger objects in the belt are considered planetesimals or "super comets." Since 1992, many have been identified. Pluto is the largest body within this grouping. Smaller members in the belt are labeled “comets.”

Many Moons

Many of the moons orbiting planets are considered planetesimals. The largest of Neptune’s 13 moons, Triton, falls into this category. One of Saturn’s 53 moons, Phoebe, is a planetesimal, as well as both of Mars’ moons, Phobos and Deimos. In addition, Jupiter has 50 moons, and several of these match the criteria for planetesimals.

Related Articles

What Does the Solar System Look Like?
The Ordinal Position of the Planets
The Characteristics of Comets, Meteors & Asteroids
Which Is the Primordial Nebula?
Three Main Types of Galaxies
The Difference Between Pluto & Gas Giants
Characteristics of Neptune
Surprise! Jupiter Has 12 More Moons Than We Previously...
What is Earth's Position in the Solar System?
Important Facts About the Outer Planets
Which Planet Has More Rings: Jupiter or Saturn?
What Does the Solar System Look Like?
Jupiter's Core vs. Earth's Core
Three Major Characteristics of the Inner Planets
The Effects of Gravity in the Solar System
What Do the Larger Planets Have in Common?
What Are Some Interesting or Unique Features of Neptune?
Differences Between Dwarf Planets, Comets, Asteroids...
Geology Facts on Neptune
How Do Comets Orbit the Sun?

Dont Go!

We Have More Great Sciencing Articles!