Ask A Scientist

Do the rest of the planets in the universe have cores made out of iron and nickel?

Asked by: Zachary Tiffany
School: Owego Apalachin Middle School
Grade: 6
Teacher: Chris Mahon
Hobbies/Interests: Bike riding, watching horror movies
Career Interest: Doctor

Answer from E. Jay Sarton Jr.

Adjunct faculty member/grants consultant at Bingha

Research area: K-12 Science, education in physical science and earth science

Family: Wife, Cheri, four children, Chris, Matt, Adam and Kate.

Interests/hobbies: Coaching youth soccer and softball, nature photography and astronomy.

When astronomers study the terrestrial (earthlike) planets in our solar system, they immediately encounter a paradox. Terrestrial planets are composed of significant amounts of iron and nickel, elements that make up 40% of the earth’s composition, but less than 0.1 % of the matter in the universe as a whole. If there is so little iron and nickel, how can terrestrial planets form at all in a universe is made up almost entirely of hydrogen (90%) and helium (9%)? Well, four and a half billion years ago our part of the Milky Way galaxy contained a giant nebula (cloud) that spanned 20-40 billion miles. As the gravity of the cloud forced it to contract, the center of the cloud gradually heated and eventually formed the sun. The solid particles of the cloud near the newly created sun stuck together in clumps and eventually built the terrestrial planets. The only elements that could exist as solids near the sun were elements, like iron, with high melting points. Thus, as iron, nickel, silicon and other solids accreted into planets and asteroids, the more abundant hydrogen, helium, and water remained in a gaseous state and did little to build the inner planets. . Though the process is poorly understood at this time, astronomers speculate that the gravity of the cores of Jupiter and the other gas planets trapped the hydrogen, helium and water to create the giant planets. Astronomers reckon that, if our solar system is typical, many other solar systems should include iron-nickel terrestrial planets near, and Jupiter-like planets far, from their local sun. To date about 130 extra solar planets have been discovered around nearby stars, and the number is growing monthly. All planets discovered so far, however, are Jupiter-like. Our instruments are just not sensitive enough today to detect Earth-like planets around other stars. The next generation of massive telescopes should be able to detect terrestrial planets in the upcoming decade or two. If terrestrial planets do turn out to be abundant in space, the chances for detecting the evidence for intelligent life increase significantly. Stay tuned…

Last Updated: 9/18/13