Did Jupiter Collide with a Massive Planet?

The Cosmic Companion
Aug 15 · 6 min read

A planet 10 times larger than the Earth may have collided with Jupiter as planets were first taking shape, a new computer simulation reveals. This impact, happening 4.5 billion years ago, would have stirred the young core of Jupiter, altering the largest planet of the Solar System until our own time.

Unexpected readings from the Juno spacecraft, studying the massive planet since 2016, found the core of the gas giant is both larger, and less dense, than calculations had predicted, altering what we thought of about the inner structure of Jupiter. This observation sparked researchers to investigate the mystery.

“This is puzzling. It suggests that something happened that stirred up the core, and that’s where the giant impact comes into play,” Andrea Isella, astronomer at Rice University, explains.

A young Jupiter is struck by a planetary body 10 times more massive than Earth, in this artist’s conception. Illustration by K. Suda & Y. Akimoto/Mabuchi Design Office, courtesy of Astrobiology Center, Japan

Jupiter’s Accidental Encounter

Theories of planet formation suggest that Jupiter started as a dense, frozen, rocky world. This body collected vast quantities of gas over time from the primordial disk forming the Solar System. The core, deep beneath the clouds, was thought to have a smooth surface, the result of enormous gravity and pressure.

Juno measured the gravitational field around Jupiter, revealing a different model.

“Instead of a small compact core as we previously assumed, Jupiter’s core is ‘fuzzy.’ This means that the core is likely not made of only rocks and ices but is also mixed with hydrogen and helium and there is a gradual transition as opposed to a sharp boundary between the core and the envelope,” explains Ravit Helled, professor at the University of Zürich, and team member on the Juno mission.

The idea of a massive impact between Jupiter and a large body could explain the observations, researchers concluded. A direct impact between Jupiter and a body of 10 Earth masses would have mixed dense layers deep in the core with less-dense material sitting closer to the surface.

A rendering of an impact between a fledgling Jupiter and a body of 10 Earth masses, 4.5 billion years ago. Illustration by Shang-Fei Liu/Sun Yat-sen University.

“[A] sufficiently energetic head-on collision (giant impact) between a large planetary embryo and the proto-Jupiter could have shattered its primordial compact core and mixed the heavy elements with the inner envelope,” researchers describe in an article published in the journal Nature.

Such an impact would take “many, many billions of years” to recover, Isella describes.


Getting to the Core of What Happened

A team of researchers at Rice University directed a series of virtual simulations, attempting to understand how such a collision could produce a core similar to that revealed by Juno.

Impacts which grazed Jupiter at an angle were caught in the gravitational field of Jupiter and swallowed, while bodies the size of Earth disintegrated in the atmosphere of the massive world.

Andrea Isella is an assistant professor of physics and astronomy and of Earth, environmental and planetary sciences at Rice University and a co-investigator on the NASA-funded CLEVER Planets project. (Photo by Jeff Fitlow/Rice University)

The model found an impact could have resulted in the core we see today, but it would have required an impact with a body 10 times larger than the Earth, in a head-on collision with Jupiter.

“Because it’s dense, and it comes in with a lot of energy, the impactor would be like a bullet that goes through the atmosphere and hits the core head-on. Before impact, you have a very dense core, surrounded by atmosphere. The head-on impact spreads things out, diluting the core,” Isella said.

The gravitational influence of Jupiter would have altered the course of small planetary embryos in the early Solar System, drawing them toward the rapidly-growing world. The tremendous mass of the world would also focus incoming bodies, greatly increasing the frequency of head-on collisions, the model determined.

A study published in March concluded that Jupiter formed in the outer reaches of the Solar System, and migrated inward, closer to the Sun.


An artist’s conception of the Juno spacecraft at Jupiter. Image credit: NASA/JPL-Caltech

Juno has Long Eyes

Juno launched on August 5, 2011, and arrived at Jupiter on July 4, 2016. The mission was originally scheduled to orbit the massive world once every 14 days. However, concerns about valves in the spacecraft’s fuel system caused mission engineers to raise its orbit to a point where the spacecraft takes 53 days to complete a single orbit. This change in orbit slows down data collection, extending the total length of the mission by 41 months. This extended mission could reveal new data about, and images of, the largest planet in the Solar System.

Juno produces amazing images — as well as research, like this image of the Great Red Spot. The elongated orbit brings Juno as close as 5,000 km (3,000 miles) from Jupiter.

While in orbit around Jupiter, Juno will measure the amount of water in the Jovian atmosphere, providing data on the formation of that world. The spacecraft will analyse the atmosphere, and the magnetic and gravitational fields of the massive gas giant. And Juno will observe aurora — northern and southern lights — that put those seen on Earth to shame. This study will provide significant data on how the magnetic field of Jupiter reacts with the atmosphere of that giant world.

Aurora on Jupiter, seen by the Hubble Space Telescope. Image credit: NASA, ESA, and J. Nichols (University of Leicester)

Juno will orbit Jupiter until July 2021, when the spacecraft will dive into the atmosphere of the gas giant, destroying the vehicle. This terminal command to Juno will ensure any microbes which may have hitched a ride to Jupiter aboard the spacecraft will never land on one of the dozens of moons of Jupiter.


An artist’s conception of a young star system, much like our own would have looked in the ancient past. Image credit: NASA/JPL-Caltech

Looking to the Future

Astronomers are currently bathing in new discoveries of worlds around other stars. Since 1992, we have learned of more than 4,000 planets in alien solar systems. Most of these worlds are large, as these worlds (and those close to their parent stars) are the easiest to find.

The TESS spacecraft, launched in April 2018, is now embarking on an ambitious plan to discover thousands of worlds so far unseen.

“We must believe then, that as from hence we see Saturn and Jupiter; if we were in either of the Two, we should discover a great many Worlds which we perceive not; and that the Universe extends so in infinitum.”

— Cyrano de Bergerac

The data collected by Juno at Jupiter could assist astronomers seeking to understand conditions on these far-flung worlds.

One unusual feature seen around a fraction of alien stars are diffuse “flashes” of infrared light, which shine a few years before fading away. These may be debris of planets colliding with each other, Rice researchers suggest.

Data collected by spacecraft, combined with computer modeling and artificial intelligence, is opening up the secrets of worlds beyond our Solar System.

In Greek and Roman mythology, Jupiter would wrap himself in clouds to hide his misdeeds. His wife, the Goddess Juno, would peer through the clouds to reveal her husband’s deepest secrets. Today, Juno the spacecraft, together with computer modeling, is revealing ancient secrets hiding deep within the history of Jupiter.


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The Cosmic Companion

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Written by

James Maynard is the author of two books, and thousands of articles about space and science. E-mail: thecosmiccompanion@gmail.com

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

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