A Piece of the Planetary Puzzle

A new concept in planetary formation suggests that terrestrial (‘rocky’) planets share a common geological history. Scientists have long wondered what processes led terrestrial bodies — such as Mercury, Venus, Mars and the Moon — to form as we know them today. According to a team of researchers at NASA, Hampton University and University of Hong Kong, a process called heat-pipe cooling is the missing puzzle piece.

The debate surrounding the formation of the planets in our solar system, particularly the terrestrial planets, has been ongoing for many years. At their core, and immediately surrounding it, rocky planets are quite similar. Despite this, their outer shells — known as the lithosphere — look different — so much so that scientists have always thought that the planets formed — through different means.

Yet hints at a shared planetary evolution have been within our own planetary neighborhood all along. The present dynamics of Jupiter’s volcanically active moon, Io, involve heat-pipe cooling. This process occurs when melted magma rises through narrow channels of the lithosphere, creating a thick layer of solid rock. Io oozes lava; it has so many heat-pipes that the its entire surface is covered by material constantly pushed up from below.

Researchers theorized that this process is not unique to Io, but it could point in the direction of a universal model for the early development of terrestrial planets, including early Earth. In order to test their “heat-pipe” hypothesis, the team of scientists surveyed geological and geochemical observations to trace backwards and piece together the most likely scenarios that led to modern day planetary neighbors. The authors reviewed the current models proposed to explain how terrestrial planets came to be. They then discuss the major discrepancies within these models and show how the “heat-pipe” hypothesis can resolve these in a consistent way across all planets.

Rather than supplanting the current paradigm, heat-pipe cooling fills in the gaps that the general theories lacked. “In undergraduate textbooks, they don’t talk about the problems,” Dr. Justin Simon, NASA Planetary Scientist at NASA’s Johnson Space Center in Houston, Texas and co-author of the paper. “We see this addition to our general idea of how planets evolve as strengthening our general understanding of rocky planet formation rather than throwing out everything.”

While heat-pipe cooling provides a coherent framework for understanding planetary evolution through large breadths of time, a few puzzles remain. As we move beyond the confines of our solar system, we open up to the possibility of terrestrial exoplanets. “Many of the planets we observe around other stars, we may be observing them in their heat pipe era,” says Dr. William Moore, professor of atmospheric and planetary sciences at Hampton University and co-author of the paper. “If we assume that they’re behaving more like the planets we know at present, then we may misinterpret the signatures we see as being signals of life. This contribution is really kind of ground work for enabling us to say with some more certainty what it is we’re observing when we look at other planets around other stars.”