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Author Topic:   New planet(s)!
Sylas
Member (Idle past 5250 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 1 of 2 (228036)
07-31-2005 3:52 AM


This is worth a thread of its own. There is also New Tenth Planet?.
It's been a confusing weekend for people trying to follow events in astronomy. The solar system is growing!
For comparison, I'll review some details of the ninth planet, and some of the other larger bodies in the outer reaches of the solar system.
Michael Brown, a Professor of Planetary Astronomy at CalTech, has a great website with details of these various discoveries; and he leads one of the teams directly involved in the whole matter.
Pluto
Pluto is, on average, around 39.5 Astronomical Units from the Sun. One AU is the distance from the Earth to the Sun. Pluto's orbit is far from circular. The eccentricity is about 0.25, making the orbit a fairly elongated ellipse, and distance ranges from just under 30 AU to almost 50 AU. In fact, Pluto was actually closer to the Sun than Neptune up until Feb 1999, but now it is back to the normal case of being further out than Neptune.
The first eight planets lie in roughly the same plane of the solar system, but Pluto's orbits lines in a different plane, inclined at an angle of about 17 degrees.
Pluto has a diameter of around 2250 km. It also has a large moon, Charon, about 1172 km in diameter.
Sedna
Last year marked discovery of Sedna, also touted as a new planet. Sedna has an extremely elliptical orbit. The eccentricity is a whopping 0.8. Its distance from the Sun ranges from 75 to about 1000 AU, and it has a diameter of roughly 1500 km. The orbit is nothing like any of the other planets; it is more like a giant comet.
It is also too distant to be consider a Kuiper belt object; it could be an Oort cloud object knocked out of its usual orbit, perhaps by a passing star. More accurately; it's an unsolved puzzle, that may yet be able to shed light on planet formation and interactions in the early solar system.
Quaoar, and others
There have been many large bodies found out in the Kuiper belt, a few of which are large enough to be compared with planets. Quaoar is the largest at around 1250 km in diameter, at a distance of around 42 AU, and with an orbit that is quite close to being circular: eccentricity 0.04. A circle has zero eccentricity.
Now for developments this weekend...
2003 EL61
Early on July 28, a team at the Sierra Nevada Observatory in Spain announced their discovery of 2003 EL61. For a couple of hours, this was the largest publically known Kuiper Belt object, unless you count Pluto as Kuiper belt object.
EL61 is about 70% of the diameter of Pluto, around 1500 km; and it also has a small moon. It is probably just a bit bigger than Sedna, but with a much more planet-like orbit. . It is currently about 52 Astronomical Units away, which about as distant as it ever gets; the orbit brings it in to with 31 AU of the Sun; so the orbit is a bit more elongated than that of Pluto. It is in a plane inclined at 28 degrees to the rest of the solar system.
The initial discovery was actually made with photographs made in 2003, but it has since been found in photographic plates going back to 1955. Another group at CalTech also found it, in 2004. There is no question of priority here; the Spanish astronomers have first claim, and Caltech astronomers acknowledge this. Both groups have been waiting before going public in order to accumulate more information and confirmatory sightings.
In a curious insight into how science works, credit for discovery goes to the group that publishes first; not the group that actually finds it first. This is a good system; it prevents people sitting on data for too long. The Spanish team get formal priority by making their publica announcement just a few hours ahead of the Caltech team, led by Mike Brown.
But the Caltech team actually come out ahead, because...
2003 UB313
This is the big one; found by Mike Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University). A name has been proposed to the IAU, but we won't know until it is formally accepted.
UB313 is currently around 97 AU away from the Sun; the furthest such object ever detected. The orbit is inclined at 44 degrees, way off the plane of the solar system, and a high eccentricity of 0.44. This explains why it has not been found before; we don't look for planets that far off the plane of the solar system. It is probably around 2,600 km in diameter; significantly bigger than Pluto. Amateur observers with CCD equipment able to detect 19th magnitude objects should be able to find it themselves; there are co-ordinates available in the sky and telescope report.
My guess is that the major fall out from this is not that we have a new planet, but that we shall lose an old one. Pluto's status as a planet is shaken by these discoveries. I expect that the major consensus will end up recognizing eight planets in our solar system; plus a lot of other objects in orbits off the planetary plane.
Cheers -- Sylas

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Message 2 of 2 (228044)
07-31-2005 8:03 AM


Thread copied to the New planet(s)! thread in the Big Bang and Cosmology forum, this copy of the thread has been closed.

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