plan·​e·​tes·​i·​mal | \ ˌpla-nə-ˈte-sə-məl How to pronounce planetesimal (audio) , -zə-məl\

Definition of planetesimal

: any of numerous small celestial bodies that may have existed at an early stage of the development of the solar system

Examples of planetesimal in a Sentence

Recent Examples on the Web

The team categorizes the object as a planetesimal, because of its relatively small size. Catherine Zuckerman, National Geographic, "Newfound tiny planet may be a glimpse of Earth's ultimate fate," 4 Apr. 2019 That much iron could be supplied if a large planetesimal (or small group of them) had migrated inward until the gravity of RW Aur A tore it apart. John Timmer, Ars Technica, "Star’s dimming and brightening may indicate it’s eating a planet," 20 July 2018 The planet formation process involves the coalescing of this material into larger and larger bodies, ultimately concluding in the production of planetesimals, bodies that range in size from large asteroids up to nearly the size of Mars and Mercury. John Timmer, Ars Technica, "Star’s dimming and brightening may indicate it’s eating a planet," 20 July 2018 Specifically, the disks are seen around nearby young stars and contain gas, dust, and planetesimals which combine to form developing planets. Samantha Mathewson,, "New Planets May Be Forming Around Young Nearby Stars, Dusty Disks Suggest," 12 Apr. 2018 At the same time, Jupiter may have hurled material inward as well, crashing hydrogen-rich asteroids and planetary embryos, or planetesimals, into crowded young terrestrial planets. Nola Taylor Redd, Smithsonian, "How Jupiter May Have Gifted Early Earth With Water," 20 June 2018 Their first line of evidence that the space rock was a chunk of what was originally a large planetesimal came from the size of the diamonds themselves. Deborah Netburn,, "One of the solar system’s early planets didn’t survive, but its diamonds are now on Earth," 17 Apr. 2018 Enough grist to form a massive ring could have only been supplied billions of years ago, when the early solar system was chock full of planetesimals. Paul Voosen, Science | AAAS, "Saturn’s rings are a recent addition to the solar system, Cassini observations show," 12 Dec. 2017 In order for the theory to work, planetesimals had to be huge, and this family was one of the biggest. Andrew Wagner, Science | AAAS, "Watch ‘dark asteroids’ reveal secrets of the early solar system," 3 Aug. 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'planetesimal.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

See More

First Known Use of planetesimal

1903, in the meaning defined above

History and Etymology for planetesimal

planet + -esimal (as in infinitesimal)

Keep scrolling for more

Learn More about planetesimal

Statistics for planetesimal

Last Updated

23 Jun 2019

Look-up Popularity

Time Traveler for planetesimal

The first known use of planetesimal was in 1903

See more words from the same year

More from Merriam-Webster on planetesimal

Rhyming Dictionary: Words that rhyme with planetesimal Encyclopedia article about planetesimal

Comments on planetesimal

What made you want to look up planetesimal? Please tell us where you read or heard it (including the quote, if possible).


appealing forcibly to the mind or reason

Get Word of the Day daily email!

Test Your Vocabulary

Farm Idioms Quiz

  • cow coming home
  • What does 'poke' refer to in the expression 'pig in a poke'?
Name That Thing

Test your visual vocabulary with our 10-question challenge!

Add Diction

Test Your Knowledge - and learn some interesting things along the way.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!