ORBITS AKIMBO: The planetary system of Upsilon Andromedae appears to differ greatly from our own solar system, in which all the planets closely follow a shared orbital plane.
Image: NASA, ESA, and A. Feild (STScI)
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MIAMI—The more we learn about planetary systems throughout the galaxy, the more our own solar system appears to be rather unique. A research group measured the orbital tilt of two large objects circling the star Upsilon Andromedae, some 44 light-years away, finding that the two orbits are out of alignment by about 30 degrees. In contrast, the planets of our own solar system—and especially the massive ones—hew closely to a common orbital plane. The researchers announced their finding, published in the June 1 issue of The Astrophysical Journal, on Monday at the semiannual meeting of the American Astronomical Society being held here this week.
"This is the first time we've measured the inclination of multiple planets in a system, and it's not flat," said lead study author Barbara McArthur, a research scientist at the University of Texas at Austin.
The Upsilon Andromedae system contains at least three planets, the first and smallest of which was discovered in 1996. When the more massive second and third planets were found in 1999, Upsilon Andromedae became the first sunlike star known to host a multiple-planet system. It is the orbits of those two objects, which orbit the star at greater distances than their smaller counterpart, that McArthur and her colleagues were able to measure in the new research. McArthur's group supplemented a wealth of data from ground-based observatories with precision astrometric measurements made by the Hubble Space Telescope. Hubble's astrometry instruments track the position of a star on the sky, and are sensitive enough to detect the deflection of a star induced by the gravitational pull of its orbiting planets.
When combined with ground-based radial velocity measurements, which determine how much the same orbital motion pulls the star closer to and farther from Earth, astrometry produces a fairly complete picture of an object's physical and orbital parameters. In this case, the astrometric measurements of the two objects yielded a few surprises: For instance, what was thought to be the larger of the two planets turned out to be less massive than its neighbor. And what was thought to be the smaller planet turned out to be so massive that, by a strict mass-based definition, it qualifies as a sort of failed star known as a brown dwarf. McArthur said she prefers to think of it as a "super Jupiter," because in all likelihood it formed like a planet, not like a star.
But perhaps the greatest surprise is how a detailed study of a planetary system revealed the same kind of diversity in large-scale structures that astronomers are finding among individual planets. "I'm here to tell you that we're not in Kansas anymore, as far as solar systems go," McArthur said. The implication is that in modeling the dynamics of extrasolar planetary systems, astronomers and planetary scientists can no longer assume that the orbits of multiple planets share a common plane.
McArthur said that the Upsilon Andromedae system could have started out similar to our own solar system, only to be disrupted later on by any number of mechanisms. The dynamical ejection of a former planet from the system might have an effect, as might a close passage by the star's binary companion, Upsilon Andromedae B. Or collisions among protoplanets early in the system's formation may have sent one or more of the objects careening off its original path.
Astrophysicist Philip Armitage of the University of Colorado at Boulder, who did not contribute to the new research, said that individual tilted planets have been found before, but their tilt had only been assessed in relation to the rotation axis of their host star, not in relation to any fellow planets. The finding of misaligned objects possibly resulting from collisions and ejections in the Upsilon Andromedae system, he said, supports the theory that "forming planetary systems are often overcrowded, if you like."
Fritz Benedict, a study co-author and a colleague of McArthur's at the University of Texas, said that although there are not many more known planetary systems close enough for Hubble to examine astrometrically, by surveying all of them astronomers may get a better sense of how typical our solar system really is. "We have four others that we're working on, and those are the only ones that we have a chance at with Hubble," Benedict said. With the addition of the solar system and now Upsilon Andromedae, that makes six planetary systems whose orbital inclinations can conceivably be measured, and Benedict said that data on the rest of the group could be in hand within a year and a half.
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8 Comments
Add CommentIf one of the two largest planets is comparably as massive as the star, the illustration's orbital paths are not likely correct.
Reply | Report Abuse | Link to thisIn a two body system of comparable masses, for example, they will both revolve around the collective center of mass, which will be a point generally located between the two objects.
In the illustration, all objects appear to orbit a central star. This is consistent with our perspective of gravitation that is biased by our knowledge of the central mass Solar system (~99% of total mass is within the Sun).
IMO, the illustration must be misleading, since all objects must orbit the center collective center of mass. While the illustrated smaller planet apparently orbiting the star may be correct, just as the moon orbits the nearby Earth, the other bodies most likely orbit some point in locally contracted spacetime.
The location of that point will appear to move in relation to an external observer, although all of this orbital bodies' locations will be defined in relation to the center of collective mass.
For further reading about how the central mass bias of our gravitational perspective influences our interpretations of other orbital systems, leading to the apparent requirements for compensatory Dark Matter, please review the essay, "Mass Distribution Characteristics Invalidate the Galaxy Rotation Problem" posted at:
Reply | Report Abuse | Link to thishttp://www.sciencewithoutfiction.com/uploads/Mass_Distribution-_Galaxy_Rotation_Problem.pdf
I think that this article just gives more weight to alternative formations from the classic ones..instead of dust, star, planets...maybe more of a dust, planets, stars....
Reply | Report Abuse | Link to thisjtdwyer...nice comments and enjoyed your link....
Wayne Williamson - Thanks for the nice remarks.
Reply | Report Abuse | Link to thisIt's difficult to understand exactly what's going on, since no relative masses or identifications were given for the objects, but the outer planet may be orbiting a binary pair. This might account for the differing orbital alignments, which may vary in time...
Interesting that the a priori assumption that took hold in astronomy a little more than a century ago that our sun, solar system and planet were completely unremarkable is turning out to be completely false. It appears that we are actually quite unique. A large satellite to stabilize earth's axial tilt. A massive gas giant with smaller giants in a pattern to stabilize planetary orbits. A class GV star that is unusually calm and stable with an unusual metallicity.
Reply | Report Abuse | Link to thisAll very interesting.
Just wondering if perhaps that massive Jupiter was on a path to being one of a binary but the other proto-star grew faster and in forming into an actual star the blow out of its excess caused the second proto-star (the massive Jupiter) to lose its mass prior to becoming a star and rendering forever a brown dwarf. That would account for the odd angle orbital between it and the planets formed after the first star's formation and blow-out.
Reply | Report Abuse | Link to thisanthony1king - That seems possible, but I'd guess the early Solar wind would have been more likely to blow off Jupiter's gasses. Jupiter is very large and as I understand the most massive planet, but its average density is lower than water.
Reply | Report Abuse | Link to thisA similar possibility might be that when the Sun expands after its fuel is consumed, Jupiter will capture sufficient additional mass to ignite its own unused fuel. It would still be an extremely small star, I think.
I suspect the massive planet in this planetary system is far denser and more massive than Jupiter. It would have been nice to have been given mass estimates relative to the Sun.
Will we still have to pay taxes?
Reply | Report Abuse | Link to thisI've got some planning to do, and I was curious.