Jupiter’s Gravity Prevented Impact With a Captive Asteroid For the Past One-Million Years




For at least a million years, an asteroid orbiting the “wrong” way around the sun has been playing a cosmic game of chicken with giant Jupiter and with about 6,000 other asteroids sharing the giant planet’s space, says a report published in the latest issue of Nature. The asteroid, nicknamed Bee-Zed, is the only one in this solar system that’s known both to have an opposite, retrograde orbit around the sun while at the same time sharing a planet’s orbital space, says researcher and co-author Paul Wiegert of Western Ontario University Physics and Astronomy.

All but 82 of the million or so known asteroids in our solar system travel around the sun in what’s called a prograde motion: that is, counter-clockwise when visualized from above. But asteroid 2015 BZ509 (“Bee-Zed” for short) circles clockwise, in a retrograde motion — moving against the flow of all other asteroids in the giant planet’s orbital entourage.

Put another way, it’s as if Jupiter is a monster truck on a track circling the sun, and the asteroids in Jupiter’s orbit are sub-compact cars all whizzing along in the same direction. Bee-Zed is the rogue — driving around the track in the wrong direction — steering between the 6,000 other cars and swerving around the monster truck. And it does so every single lap, and has done so for thousands of laps for a million years or more.

So how does it avoid colliding with Jupiter? Jupiter’s gravity actually deflects the asteroid’s path at each pass so as to allow both to continue safely on their way, Wiegert says.

Little is known about the asteroid, which was discovered in January, 2015. It has a diameter of about three kilometers and it may have originated from the same place as Halley’s comet, which also has a retrograde orbit. The team hasn’t been able to determine yet if Bee-Zed is an icy comet or a rocky asteroid.

But their analysis — based on complex calculations and on observations through the Large Binocular Camera on the Large Binocular Telescope in Mt. Graham, Arizona, during a span of 300 days — show Bee-Zed is somehow able to maintain a stable orbit even as an outlier.

The calculations conducted by the team show the orbit has been stable for at least a million years and will be stable for at least a million more. Learning more about the asteroid provides another intriguing glimpse into previously unknown and unmapped features of our solar system. “The detective work has just begun,” he said.

Since 1941 many astronomers have thought of Jupiter as a protective big brother for planet Earth -a celestial shield, deflecting asteroids and comets away from the inner Solar System. This long-standing belief that Jupiter acts as a celestial shield, deflecting asteroids and comets away from the inner Solar System, has been challenged by a series of studies evaluating the impact risk to the Earth posed by different groups of object such as the Levy Shoemaker impacts in 1991 and the Pacific-Ocean sized impact of 2009.

Important research by Jarrad Pond (University of Central Florida), and a team from the University of Central Florida and University of California, Santa Cruz aims to help determine the object responsible for the 2009 impact on Jupiter. Without a direct observation of the event, the team used numerical simulations in order to better understand the object responsible for the large disturbance of the Jovian atmosphere.

Using three dimensional hydrodynamics code, the team modeled the impacts of eight simulated impactors. The team used impactors of .5 and 1km, with different densities and compositions (basalt or ice). By using the same impact angle (69 degrees) and impact velocity 61.4 km/sec), the team was able to narrow down the potential size and composition of the object responsible for the July 2009 impact, referred to as the Wesley impact that caused a black spot in the planet’s atmosphere. The spot was similar in area to the planet’s Little Red Spot, approximately the size of the Pacific Ocean.

On 1994 July 16-22, over twenty fragments of comet Shoemaker-Levy 9 (image at top of page) collided with the planet Jupiter. The comet, discovered the previous year by astronomers Carolyn and Eugene Shoemaker and David Levy, was observed by astronomers at hundreds of observatories around the world as it crashed into Jupiter’s southern hemisphere.

In July of 2009, a comet or asteroid ripped another Pacific-Ocean sized hole in Jupiter. By comparing their simulations of the 2009 impact event with simulations of the Shoemaker-Levy 9 events, differences in plume development were revealed. The angle of the 2009 impact appears to have led to a shallower impact depth, as well as a smaller and slower plume. The team’s simulations revealed that the 0.5km impactor events produced smaller and slower plumes, while the 1km impactor events produced larger and faster plumes.

The Daily Galaxy via University of Western Ontario and nature.com


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