Jupiter, the “King of Planets,” was named for the king of the gods in ancient Roman mythology. A magnificent, enormous gas-giant world, this fifth planet from our Star is more than twice as massive as all of the other seven major planets in our Solar System combined! Indeed, Jupiter’s hefty weight is 318 times that of our Earth! Jupiter itself has been known since prehistoric times as a sparkling “wandering star”–the fourth most dazzling object lighting up the sky after our Sun has set. In March 2015, a team of planetary scientists announced their findings that the primordial Jupiter may have rampaged through our ancient Solar System, resulting in the formation of the familiar planetary system that we observe today–which is unlike any other astronomers have yet spotted in our Milky Way Galaxy.
According to this scenario, wandering Jupiter tore through our ancient Solar System, wreaking devastating havoc, as it destroyed a first generation of inner planets–before finally calming down and retreating into its current, peaceful orbit around our Sun. A new study, published in the March 23, 2015 issue of the Proceedings of the National Academy of Sciences, indicates that this scenario helps to explain why our Solar System is so different from the hundreds of other planetary systems that astronomers have discovered so far.
“Now that we can look at our own Solar System in the context of all these other planetary systems, one of the most interesting features is the absence of planets inside the orbit of Mercury. The standard issue planetary system in our Galaxy seems to be a set of super-Earths with alarmingly short orbital periods. Our Solar System is looking increasingly like an oddball,” explained Dr. Gregory Laughlin in a March 23, 2015 University of California at Santa Cruz (UCSC) Press Release. Dr. Laughlin is professor and chair of astronomy and astrophysics at UCSC and co-author of the paper.
Even though super-Earths are an abundant population of exoplanets dwelling in Earth’s local Galactic neighborhood, there are no super-Earths inhabiting our Sun’s family. Super-Earths sport greater masses than our own planet, but have masses considerably below a duo of distant denizens of the outer Solar System, Uranus and Neptune–the two gaseous ice-giants of our Solar System. Uranus and Neptune weigh-in with masses of 15 and 17 Earth-masses, respectively.
Jupiter and Saturn are also inhabitants of our Solar System’s outer limits, but they are considerably more massive than Uranus and Neptune. Jupiter and Saturn are gas-giants, with much smaller solid cores–if they have any–than the two ice-giants, and considerably thicker gaseous envelopes. Saturn has the lowest density of any planet in our Solar System, and some scientists think that it could float in a swimming pool–that is, if one could be found large enough to contain it.
The quartet of giant, gaseous planets inhabiting the outer regions of our Sun’s family are very different from the four much smaller inner, rocky terrestrial planets: Mercury, Venus, Earth, and Mars.
The King’s Mysterious Realm
Jupiter is about 89,000 miles wide at its equator, and is so immense that all of the other planets in our Solar System would fit inside of it! Indeed, 1,000 Earths could be packed inside this banded behemoth world!
Jupiter is like a star in its composition, and if it had been about 80 times more massive than it is, the process of nuclear fusion would have lit its stellar fires, and it would have been a star instead of the immense gas-giant planet that it is.
Jupiter is the fifth planet from our Star, and its mean distance from it is about 5.2 astronomical units (AU). One AU is equivalent to the average distance between Earth and Sun, which is 93,000,000 miles. This means that Jupiter’s distance from our Star is a little more than five times the separation between our planet and the Sun. When seen from Earth, Jupiter is usually the second brightest planet in the night sky–after Venus.
Jupiter rotates faster than any other planet in our Solar System. One day amounts to one rotation–or spin–of a planet. Jupiter’s day is only about 10 Earth-hours in duration, and its orbit is elliptical–meaning that it is out of round. It is also about as big as a giant gaseous planet can be, and still be a planet. Jupiter is about 90% hydrogen and 10% helium–just like our Sun. However, Jupiter also harbors relatively small amounts of rocky material, methane, water, and ammonia. If any more material had been accreted by this enormous world, it would have been squeezed tightly by the force of gravity, while the entire radius would have increased only by a small amount. A star can grow to be much, much larger than Jupiter–and a star possesses its own internal source of fiery, raging heat.
Our Solar System emerged about 4.56 billion years ago when a very dense, relatively small blob, embedded within one of the numerous giant, cold, dark molecular clouds that haunt our Galaxy, collapsed under the hefty weight of its own gravity. Billowing, enormous molecular clouds–composed of gas and dust–haunt our Galaxy like phantoms, and they serve as the strange nurseries of baby stars. As the small, dense blob experiences gravitational collapse, most of its material collects at the center and catches fire as the result of nuclear fusion–and a star is born! The remaining material swirls around the fiery protostar, and becomes what is called a protoplanetary accretion disk. This rotating disk of gas and dust circles the new star. Just such a disk whirled around our primordial Sun, and the very tiny particles of “sticky” dust within it bumped into one another and “glued” themselves together to create ever larger and larger objects. Ultimately, a vast population of planetesimals formed, and these were the building blocks of the major planets.
When the planet Jupiter was born, it had the potential to become a star. However, it failed. The energy spewed out by the tumbling material caused Jupiter’s interior to grow searing-hot. The larger Jupiter grew, the hotter it became. Ultimately, when the material snatched up from the ambient, turbulent disk was at long last depleted, Jupiter may have sported the awe-inspiring diameter of over 10 times that which it now has. It also likely possessed a central temperature of a roasting 50,000 Kelvin (the Kelvin scale is an absolute scale of temperature, in which zero is equivalent to -459.4 degrees Fahrenheit), and a sparkling bright luminosity that was about 1% as great as that of our own glaring Sun today.
If Jupiter had been born many times heavier, it would have become hotter and hotter, as it shrunk in size –until its nuclear-fusing stellar furnace ignited, and it became a star. Had this happened, our Sun–like many others of its kind–would have had a binary companion. In this scenario, our Earth and the rest of our Solar System probably could not have formed–and we would not be here today.
It takes the planet Jupiter about 12 Earth-years to complete a single orbit around our Star, and so a year on Jupiter is equivalent to a dozen years on our own planet.
The temperature of the Jovian clouds–that float around at the very top of its atmosphere–is an extremely cold -234 degrees Fahrenheit. The temperature near the planet’s center, however, is quite a bit toastier. Indeed, the temperature of Jupiter’s core may reach 43,000 degrees Fahrenheit. This is even hotter than the surface of our Sun!
If it were possible for a human being to stand on the Jovian clouds–which is, of course, impossible–the force of gravity that she would experience would equal about 2.4 times the force of gravity on the surface of our own planet. This basically means that a person who weighs 100 pounds on Earth would weigh about 240 pounds standing on the clouds of Jupiter.
Winds on Jupiter are ferocious. This very windy planet’s mighty gales roar at between 193 miles per hour to over 400 miles per hour. The surface of Jupiter is banded with extremely thick brown, yellow, red, and white clouds. It is also encircled by a trio of thin gossimer rings, that were first detected back in 1979 by NASA’s Voyager 1 spacecraft–and the rings are primarily composed of extremely fine dust motes.
Jupiter’s magnetic field is very powerful. Deep down under Jupiter’s heavy, dense blanket of impenetrable clouds, there may be an enormous ocean of rare liquid metallic hydrogen. As Jupiter rotates, the swirling, churning liquid metal ocean produces the strongest magnetic field in our entire Solar System. At the tops of the obscuring clouds (tens of thousands of miles higher than where the field is created), Jupiter’s magnetic field is approximately 20 times stronger than Earth’s magnetic field.
Jupiter is circled by 62 known moons. The largest Jovian moons are the quartet of Galilean moons: Io, Europa, Ganymede, and Callisto. The four large moons were named in honor of their discoverer, Galileo Galilei, who, on dark, starlit January nights in 1610, spotted them with one of the first telescopes to be used for astronomical purposes.
The Great Red Spot is considered by many scientists to be Jupiter’s most prominent feature, as it whirls around wildly in the surface layer of Jupiter’s banded atmosphere. It is a swirling anti-cyclonic storm that is larger than the Earth!
Jupiter Sweeps The Primordial Solar System Clean
The new research paper explains not only what is termed the “gaping hole” in the inner region of our Solar System, but also certain characteristics of Earth and the other three inner rocky planets–Mercury, Venus, and Mars. The four inner terrestrial planets could have formed later than the outer four gaseous planets from a depleted source of planet-making material.
Dr. Laughlin and coauthor Dr. Konstantin Batygin, who is an assistant professor in the Division of Geological and Planetary Sciences at the California Institute of Technology (Caltech), in Pasadena, California, explored the implications of a leading scenario for the formation of Jupiter and Saturn. According to this scenario, first proposed by a different team of astronomers in 2011 and called the Grand Tack, Jupiter first migrated inward toward our Star–until the formation of Saturn caused it to change direction and migrate outward to where it now resides. Dr. Batygin, who first collaborated with Dr. Laughlin when he was an undergraduate at UCSC, performed numerical calculations to determine what would occur if a batch of rocky planets, with close-in orbits, had formed before Jupiter made its disastrous invasion into our Solar System’s inner regions.
At the time of the Jovian invasion, it is entirely possible that rocky planets with deep atmospheres could have been forming close to our Star from the dust and gas of the surrounding, swirling protoplanetary accretion disk. This set of planets may well have been on their way to becoming typical super Earths like many of the exoplanets astronomers have found dwelling within the families of other, distant stars in our Galaxy. As Jupiter marched inward, however, gravitational disturbances from the enormous planet would have swept the inner planets (and smaller planetesimals) into close-knit, overlapping orbits, triggering a series of catastrophic collisions that shattered the nascent planets into fragments.
“It’s the same thing we worry about if satellites were to be destroyed in low-Earth orbit. Their fragments would start smashing into other satellites and you’d risk a chain reaction of collisions. Our work indicates that Jupiter would have created just such a collisional cascade in the inner Solar System,” Dr. Laughlin explained in the March 23, 2015 UCSC Press Release.
Debris created as a result of these collisional disasters would have then spiraled into our Sun–under the heavy influence of a strong “headwind” from the dense gas still swirling in the disk around our Star. The inward spiraling material would have shattered any newly-formed super-Earths by chasing them into our glaring, roiling Sun. After this tragedy, a second generation of inner planets would have formed later from the depleted material that was left behind–which is consistent with evidence that our Solar System’s four inner planets (Earth included) are younger than the outer planets. The second-generation of inner planets–Mercury, Venus, Earth, and Mars–are also less massive and sport considerably thinner atmospheres than would otherwise be predicted, Dr. Laughin continued to explain.
“One of the predictions of our theory is that truly Earth-like planets, with solid surfaces and modest atmospheric pressures, are rare,” he added.
Astronomers on the hunt for exoplanets have discovered well over a thousand of these alien worlds orbiting stars in our Galaxy–including almost 500 systems with multiple planets. These observations indicate that the “typical” planetary system in our Galaxy consists of a few planets sporting masses several times larger than Earth’s (super-Earths) circling much closer to their parent-stars than Mercury’s distance from our Sun. In systems with giant planets akin to Jupiter, these enormous alien worlds also tend to be considerably closer to their parent-stars than the giant planets in our Sun’s familiar family. The quartet of rocky, inner planets dwelling in our Solar System, with relatively low masses and thin atmospheres, may turn out to be rather anomalous.
Dr. Laughlin explained to the press on March 23, 2015 that the formation of enormous gaseous worlds like Jupiter is somewhat rare. When it does occur, the huge world frequently migrates inward towards its parent-star, and winds up at an orbital distance similar to that of Earth’s from our Sun. But in our own Sun’s family, the formation of Saturn pulled Jupiter back out and allowed Mercury, Venus, Earth, and Mars to be born. Hence, another prediction of the research paper is that systems with giant planets at orbital periods of more than about 100 days would be unlikely to host multiple close-in planets.
Dr. Laughlin continued to note that “This kind of theory, where first this happened and then that happened, is almost always wrong, so I was initially skeptical. But it actually involves generic processes that have been extensively studied by other researchers. There is a lot of evidence that supports the idea of Jupiter’s inward and then outward migration. Our work looks at the consequences of that Jupiter’s ‘Grand Tack’ that may well have been a ‘Grand Attack’ on the original inner Solar System.”
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