Gravitational interaction, not giant planet, may explain unusual TNO orbits

The unusual orbits of many Trans-Neptunian Objects (TNOs) may have been caused by gravitational interactionsthat jostled them rather than by a hypothesized but as yet undiscovered giant planet, according to a new study presented at the 232nd meeting of the American Astronomical Society (AAS) in Denver, Colorado.

Dwarf planet Sedna and other, smaller TNOs have orbits very different and detached from those of most solar system bodies. Somewhat smaller than Pluto but still large enough to be rounded by its own gravity, Sedna, which is located 8 billion miles from the Sun, takes 11,000 years to complete one solar orbit.

Some scientists have theorized that a planet about 10 times the size of Earth in the outer solar system is responsible for perturbing the TNOs' orbits. However, searches for the planet over the last two years have been unsuccessful.

In the new study, a group of scientists led by Ann-Marie Madigan of the University of Colorado at Boulder's (CU Boulder) Department of Astrophysical and Planetary Sciences (APS), propose the many TNOs in the outer solar system could be jostling one another much like bumper cars do.

"There are so many of these bodies out there. What does their collective gravity do? We can solve a lot of these problems by just taking into account that question," she explained.

Many TNOs have wide, circular orbits that bring them nowhere near any of the solar system's gas giants, leading scientists to question how the former initially got to their current positions without having interacted with a much larger object.

CU Boulder undergraduate Jacob Fleisig conducted computer simulations in an effort to determine how these TNOs got into their current orbits.

"You see a pileup of smaller objects to one side of the Sun. These orbits crash into the bigger body (a large TNO, not a gas giant), and what happens is those interactions will change its orbit from an oval shape to a more circular shape," he said.

This theory matches a 2012 finding showing the larger a detached TNO becomes, the more distant its orbit gets from the Sun.

Repeated interaction cycles among large and small TNOs may be responsible for pushing comets into the inner solar system on regular timescales. One of those comets may have been the impactor responsible for the extinction of Earth's dinosaurs 65 million years ago.

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