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article imageEssential Science: Did Jupiter wander away from the Sun?

By Tim Sandle     Mar 21, 2016 in Science
Astronomers have long wondered why there are no planets closer to the Sun than Mercury. To have planets closer is common with many stars. The answer might be due to Jupiter having once been located closer to our star, suggests a new theory.
The new theory runs that if Jupiter formed close to the sun and then wandered out, this may well explain why there are no planets interior to Mercury’s orbit. The shifting giant planet may also account for why Mercury, the innermost planet in the solar system, is relatively tiny.
Data supplied by NASA’s Kepler space telescope has found frequent examples of planets, mostly farther than Earth, situated in orbits smaller than Mercury’s.
Jupiter is the fifth planet from the Sun. It is colossal, being the largest planet in the Solar System, two and a half times that of all the other planets in the Solar System combined. While the planet has a rocky core, it is composed of hydrogen with a quarter of its mass being helium.
A new science paper suggests that Jupiter’s core could have formed close to the Sun. After drifting loose, the planet could then have wandered through a rocky planet construction zone, in what is known as the Grand Tack Hypothesis, These rocks could have formed planets closer to our Sun than where Mercury currently orbits.
As Jupiter moved, the paper suggests, it may have absorbed some planet-building material and pushed the rest away. This could have led not only to no further planets forming but also leading to the inner planets — Mercury, Venus, Earth and Mars — being smaller than they should have been because they had fewer rocks. In addition to the remaining rocks forming the inner planets, Jupiter might have sent an earlier generation of rocky worlds into the Sun to their doom, clearing the way for the current planets to form.
Artist s depiction of Jupiter-like exoplanet in a solar system far far away.
Artist's depiction of Jupiter-like exoplanet in a solar system far far away.
Latitude0116 / Wikimedia Commons
This idea has been proposed by scientists from the Laboratory of Astrophysics of Bordeaux in Floirac, France. The lead researcher, Sean Raymond, explained, in an interview with Science News, why he was initially dismissive of his own theory: “When I first came up with it, I thought it was ridiculous. This model is kind of crazy, but it holds up.”
Dr. Raymond's work builds upon previous studies that indicate that the inner planets of our solar system formed 4.6 billion years ago. The planets were formed from the belt of interstellar debris that stretched between the current orbits of Venus and Earth. Moreover, information captured by the Kepler telescope suggests many multiplanet systems discovered were formed from interplanetary collisions; in addition, many live on the edge of stability.
Using this, Dr. Raymond ran computer models, predicting what could have happened if a body with three times the mass of Earth started inside Mercury’s orbit and then moved away from the sun.
The model suggested such a body could, if the speed fell within a certain range, could drag large amounts of rock and, at the same time, leave sufficient debris to allow the inner rocky planets — including Earth — to form.
It is also possible that Jupiter had two cores, and that, having moved sufficiently away from the Sun. released the second core. The second core could have then become the basis of Saturn. Other debris could have been pulled, from Jupiter, to construct the asteroid belt.
Whether this theory is plausible is one for astronomical debate. Certainly it cannot be proven and, as it stands, is based on a computer model.
The part that is hardest to square is the notion of a wandering Jupiter. It is possible for the Sun's gravitational waves to draw in or to push out objects, but for Jupiter to have acted in this way would require a very special set of circumstances.
The new paper is published in the journal Monthly Notices of the Royal Astronomical Society, and it is titled " Did Jupiter's core form in the innermost parts of the Sun's protoplanetary disk?"
This article is one of Digital Journal's Essential Science columns. Each week we explore a topical and important scientific issue. Last week a possible connection between viral and bacterial pathogens and the neurodegenerative disorder Alzheimer's disease was discussed. The previous week, we looked at how neurologists have been considering if our brains could cope with being scrambled and reassembled, in the theoretical process of teleportation.
More about Jupiter, Solar system, Planets, Earth, Mercury
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