'Trojan' asteroids in far reaches of solar system more common than previously thought

August 29, 2013, University of British Columbia
This image shows the motion of 2011 QF99 over the next 59 kyr. Shown here is the trajectory of 2011 QF99, according to the best fit to the observations. The current position is marked by a red square, and the black line shows the trajectory 59 kyr into the future. L4 and L5 are the triangular Lagrange points, the points in space which Credit: UBC Astronomy

University of British Columbia astronomers have discovered the first Trojan asteroid sharing the orbit of Uranus, and believe 2011 QF99 is part of a larger-than-expected population of transient objects temporarily trapped by the gravitational pull of the Solar System's giant planets.

Trojans are asteroids that share the orbit of a planet, occupying stable positions known as Lagrangian points. Astronomers considered their presence at Uranus unlikely because the gravitational pull of larger neighbouring planets would destabilize and expel any Uranian Trojans over the age of the Solar System.

To determine how the 60 kilometre-wide ball of rock and ice ended up sharing an orbit with Uranus the astronomers created a simulation of the Solar System and its co-orbital objects, including Trojans.

"Surprisingly, our model predicts that at any given time three per cent of scattered objects between Jupiter and Neptune should be co-orbitals of Uranus or Neptune," says Mike Alexandersen, lead author of the study to be published tomorrow in the journal Science. This percentage had never before been computed, and is much higher than previous estimates.

Several temporary Trojans and co-orbitals have been discovered in the Solar System during the past decade. QF99 is one of those temporary objects, only recently (within the last few hundred thousand years) ensnared by Uranus and set to escape the planet's in about a million years.

This is one of three discovery images of 2011 QF99 taken from CFHT on 2011 October 24 (2011 QF99 is inside the green circle). This is the first of three images of the same patch of sky, taken one hour apart, that were then compared to find moving light-sources. Credit: UBC Astronomy

"This tells us something about the current evolution of the Solar System," says Alexandersen. "By studying the process by which Trojans become temporarily captured, one can better understand how objects migrate into the planetary region of the Solar System."

A short-term animation showing the motion of 2011 QF99, as seen from above the north pole of the solar system. Credit: UBC

UBC astronomers Brett Gladman, Sarah Greenstreet and colleagues at the National Research Council of Canada and Observatoire de Besancon in France were part of the research team.

Explore further: Three centaurs follow Uranus through the solar system

More information: "A Uranian Trojan and the Frequency of Temporary Giant-Planet Co-Orbitals," by M. Alexandersen et al. Science, 2013.

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not rated yet Aug 29, 2013
Much would become apparent with a graphic depiction of the gravitational/dynamic equipotential surface tied to the sun/Uranus system. The Lagrange points will show as local minima/saddle points and the equipotential lines would suggest Trojan orbits.
3 / 5 (2) Aug 29, 2013
sick of hearing all this "more/less than we thought"
were still writing the first page on the book earth. we can't even comprehend the first page on the universe. keep the open mind and trek onward. stop with this all too common arrogance throughout our history that we are the most advanced, intelligent generation to grace these lands. we are proving that we are anything but.
5 / 5 (2) Aug 29, 2013
The Lagrange points will show as local minima/saddle points and the equipotential lines would suggest Trojan orbits

lol, the top graphic shows the Trojan orbit; it's the eliptical slinky shaped spiral shown in black. The trojan does a corkscrew behind the planet in this case.

sick of hearing all this "more/less than we thought"... blah blah blah

The whole point of science is rooted in the fact that we don't know anything. Nothing could be less arrogant than basic scientific research like this. You don't even bother doing it if you think you already know.

In a lot of cases, this "more than expected" simply means that it's on the high side of an estimated value, but still within the error bounds, so not really a surprise. News people like to use phrases that get people's attention, such as "Surprising results" or "Unprecedented discovery", but it's usually rather mundane when you start reading past the headline.

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