Last week, Australian amateur astronomer Anthony Wesley, and amateur Chris Go in the Philippines, independently video captured the momentary flash of a small object plunging into Jupiter’s atmosphere. Last July, Wesley also saw the sooty aftermath from the explosion of another Jupiter intruder. (Maybe he’s getting tips from the Zeta Reticulans who are using Jupiter for target practice.)
We really don’t know the rate at which Jupiter sucks up asteroids and comets, or for that matter the space debris impact rates across the solar system. This why the latest event is so exciting, it is helping planetary astronomers better calibrate just how frequently space junk smacks into planets. We certainly have a vested interest because something only a few times bigger that the latest Jupiter impactor could flatten a major city if it hit Earth in the right spot.
Jupiter's ability to capture and or deflect small solar system bodies is very relevant to Earth's habitability. “Jupiter has been a slight ‘friend’ shielding us from long-period comets, but also a major ‘foe’ tossing a whole lot of main-belt asteroids our way!” says Barrie Jones of the Open University in Great Britain.
What would life on Earth be like without Jupiter? To make this question even more intriguing let’s not simply take Jupiter away (which is an unlikely architecture in many exoplanet systems). Instead, let’s play planetary musical chairs and place Jupiter so close to the sun that it completes and orbit in just a few days.
This is more than just an esoteric thought experiment. A deep “galactic core sample” by Hubble Space Telescope, and nearby sky survey by groundbased telescopes, show that about 7 percent of the stars in the Milky Way should possess so-called hot Jupiters that complete orbits in a matter of days, or even hours. These giant planets did in fact really play musical chairs by migrating from their place of birth, which is beyond the “frost line” periphery of a star where ices don’t sublimate. This distance allows for massive planet to bulk up easily and quickly on lighter elements.
WIDE ANGLE: The Age of the Exoplanet
Computer models shows that if a giant planet forms in a thick gaseous accretion disk surrounding the star, then viscous drag can make it spiral inward to the inner rim of the circumstellar disk. Modeling shows that migration can leave room for Earthlike planets to form after the Jupiter-mass world has changed zip code.
NASA’s Kepler space observatory could very well turn up examples of Earthlike planets in habitable zones in systems containing a hot Jupiter. This would be an extraordinary discovery.
What really made this idea hit home was a recent analysis of all 79 star systems known to have hot Jupiters that pass in front of their star, or transit. Jones and Nick Sleep, also of the Open University, recently published a study. They conclude that only two systems in the sample could not support an Earthlike planet surviving in a habitable zone. However, the hot Jupiters in the rest of the other systems could not gravitationally knock any bodies out of their habitable zones.
In the system HAT-P-13 the outermost of the two giant planets was too close to the habitable zone. It would have ejected any Earthlike planets. In the second case, HD 80606, a 3.4 Jupiter-mass planet is in an eccentric orbit. This would disrupt the orbits of any terrestrial planets. The authors’ theoretical work supports the notion that there could be many Earthlike planets in hot Jupiter systems.
But what would life on Earth be like if Jupiter had migrated to within a few million miles of the sun?
From the point of observational astronomy Jupiter would be a brilliant “star” that would always be close to the sun. At maximum elongation it would be 3 or 4 degrees from the sun (6 to 8 solar diameters). It would be best seen at sunrise or sunset with a low horizon.
If it were hot enough the giant’s atmosphere would bleed into space creating a superficially looking comet tail that might only be seen during solar eclipses. Jupiter would look like a sungrazer comet! There would be a large body of lore, mythology and superstition about this mysterious companion to the sun-god.
Jupiter would be assumed to be a smaller star until telescopes showed that it went through phases, like Venus and Mercury. An occasional transit of Jupiter across the sun’s face would reveal that it was an opaque body and not self-luminous.
A magnetic flux tube running between Jupiter and the sun would leave a permanent pair of black sunspots that tracked below the orbiting planet, like a dog on a leash. This might completely eliminate the 11-year sunspot cycle of waxing and waning solar flare activity, because the sun’s complex magnetic field would be altered in unknown ways.
The asteroid belt would not exist because its planetesimals were originally stirred up by Jupiter’s gravity. Without Jupiter’s influence the dwarf planet Ceres would have been able to agglomerate the other asteroids and grow to a full sized terrestrial planet. It would have a frozen surface but perhaps a deep subsurface mantle of slushy water ice warmed by radioactive decay.
The big unknown is that Earth might be a parched, arid planet like Star Wars’ Tatooine. Jupiter’s gravity likely deflected water-bearing asteroids to collide with and irrigate Earth with water for oceans. But in our imaginary “parallel universe” solar system the Earth forms after Jupiter migrates. Life might not be totally absent from the Dry Earth, but it certainly would have taken a completed different evolutionary pathway, and intelligence may have never evolved.
Even on a Wet Earth, any change in the frequency of globally devastating impacts could also set evolution on a different trajectory. What if the K-T impact never happenned 65 million years ago and thus the dinosaurs survived to the present epoch?
Tags: Asteroids, Jupiter, Solar System
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