Xena Has A Moon! Gabrielle Options

[Decepticon]

http://us.cnn.com/2005/TECH/space/10/01/ne...n.ap/index.html

Holy Cow.


More articles... http://www.leadingthecharge.com/stories/news-0080088.html
and http://www.usatoday.com/tech/science/space...anet-moon_x.htm

[alan]

From the CNN article
"The moon was first spotted by a 10-meter telescope at the W.M. Keck Observatory in Hawaii on September 10. Scientists expect to learn more about the moon's composition during further observations with the Hubble Space Telescope in November."
A few weeks ago I saw 2003 UB313 B mentioned in a observation log for the Spitzer Space Telescope dated 26 August.
http://ssc.spitzer.caltech.edu/approvdprog...lan/week092.txt
I'm surprised it didn't leak like 2003 EL61.

[dilo]

This is a great new! At this point, we will soon have a precise mass estimation, and the comparison with Pluto mass will probably re-ignite the ongoing debate!
There is someone wo want to guess the Xena mass? (I bet is at leaast 30% higher than Pluto... )

[tfisher]

Michael Brown, lead of the Caltech team studying 2003 UB313 (and arguably its discoverer) has this page of info on the moon.

Here's an image:

[dilo]

Thanks tfisher, great image and very interesting article!
It seems they do not have mass estimation for the moment, due to the unavailability of Laser Adaptive Optics system at Keck caused by huge observetion requests from other researcher ... I hope other groups/observatoires will join the investigation and we will know something more before the January of 2006 date indicated at the end of article!

A couple of interesting phrases from linked article:
"based on how much light it reflects... the planet-moon system appears similar to the Earth-Moon system: Xena is about 5 times smaller than the Earth [2500Km]. Gabrielle is about 8 times smaller than the Moon [450 Km]. And the two are separated by a distance that is about 10 times smaller than the Earth-Moon separation [40000 Km]".
"is quite surprising the 3 of the 4 largest objects in the Kuiper belt (2003 UB313, Pluto, and 2003 EL61) all have moons"...

[Decepticon]

Wow nice image. I didn't expect it to be seen so clear.

[SFJCody]

http://www2.keck.hawaii.edu/optics/staff/mvandam/gabrielle

appears to have an orbital period of about 14 days

If the orbital period is 14 days and the semi major axis 40,000km the total mass of the system is ~2.6X10^22 kg, about twice that of Pluto.

[Guest_Myran_*]

dilo quoted:

"is quite surprising the 3 of the 4 largest objects in the Kuiper belt (2003 UB313, Pluto, and 2003 EL61) all have moons"

To some degree its surprising, if our current theories about moon formation are correct. They are created by 'bull eye' impacts where the ejecta collect in orbit to form a moon.
Seeing these moons simply confirms that all these Kupier objects have been trough the most violent part of solar system history and so are planetary formation building blocks themselves.

[abalone]

dilo quoted:

"is quite surprising the 3 of the 4 largest objects in the Kuiper belt (2003 UB313, Pluto, and 2003 EL61) all have moons"

To some degree its surprising, if our current theories about moon formation are correct. They are created by 'bull eye' impacts where the ejecta collect in orbit to form a moon.
Seeing these moons simply confirms that all these Kupier objects have been trough the most violent part of solar system history and so are planetary formation building blocks themselves.

It is not really that surprising, the further out you go the slower become the relative motion between solar orbiting objects and therefore the larger is the sphere of influence where their gravity exceeds that of the sun's.

[Guest_Richard Trigaux_*]

dilo quoted:

"is quite surprising the 3 of the 4 largest objects in the Kuiper belt (2003 UB313, Pluto, and 2003 EL61) all have moons"

To some degree its surprising, if our current theories about moon formation are correct. They are created by 'bull eye' impacts where the ejecta collect in orbit to form a moon.

The impact theory is not the only one, and it is raher a fashion than a theory accepted after fact testing.

I recall that the most common (and ancient) theory is that planets, like stars, are formed from the collapse of an accretion disk, exactly like the stars. And, exactly like stars have planets, planets have moons. both have the same origin, only a scale difference makes that stars have (are expected to have) many plantes, while small planets usually have few moons. Large planets usually have many mooms, like a mini-solar systems. In fact systems like Earth-Moon, Pluto-Charon etc rather ressemble double stars, and may have formed in the same way: an accretion disk has too much momentum to completelly collapse, and it forms double (or multiple) bodies, or a central body with a planets (or moons) system. This theory explains very well the formation of stars, planets, moons, etc with all their features including chemical differences (the accretion disk containing materials of different origins, which only partially mix together).



The idea of moons originating from impact was launched only some years ago (by NASA scientists if I remember well) to explain the (relatively small) differences in isotopic composition between Earth and the Moon. And, it you properly adjust the parametres, simulations work fine: a Mars sized impactor would left a part of its matter in orbit, forming the Moon.
Impact certainly happened into the asteroids belt, and they rather led to smaller bodies (the asteroid families) than to forming larger bodies. Impacts may have happened elsewhere. But I strongly doubt that all the planet features could be explained this way. With my opinion only large bodies would merge after an impact, small bodies would break in parts, making impossible the growth of planets in this way.

So the existence of many multiple bodies in the Kuyper belt is not astonishing and it may owe nothing to collisions. What is astonishing is that intermediary bodies such as Venus, Mercury and Mars do not have moons. Maybe icy bodies are more prone to Moon formation than rocky bodies.

By the way the hight inclination of Zena explains a mystery: how comets in more or less CIRCULAR orbits in the Kuyper belt and Oort clouds may FALL in VERY ELLIPTIC orbits toward the inner solar system. If here are many bodies with random inclinations, they may impact frequently, and at their low speed this impact would be not very explosive, just breaking them appart in many pieces to form the so many comets.

[Guest_Myran_*]

abalone said: It is not really that surprising, the further out you go the slower become the relative motion between solar orbiting objects and therefore the larger is the sphere of influence where their gravity exceeds that of the sun's.

Insightful reply there.
Yet even without firm numbers to back me up, im a bit hesitant to simply give that a 'yay'.
The very weak gravity of these objects, combined with the enormous distances that separate them, and third: In such distant orbits from from the Sun they move slowly.
Finding my Occams razor in the drawer I end with the simplest solution that it happened during the 'planetary bombardment' age when larger objects had wild orbits and when collisions would have been all the more common.

[Bob Shaw]

Possibly all planets/worlds/worldoids formed with moons, but in the outer solar system the perturbing effect of Jupiter and the other giants was sufficiently slight for orbits to remain stable over very long periods - far more than in the inner solar system.

[SFJCody]

Direct measurement of the size of 2003 UB313

http://www.stsci.edu/cgi-bin/get-proposal-info?10759

We propose observations ito directly measure the size of the newly discovered object 2003 UB313. The observations are identical to those used to
successfully measure the size of the minor planet (50000) Quaoar and have a high chance of obtaining the first concrete size measurement of this
object. Even for an absurdly high albedo of 96% this object is larger than Pluto. For more reasonable albedos the object could be as large as 1.5 times
Pluto. At a distance of 97 AU a Pluto-sized object would subtend 32 milliarcseconds, well within our previously estimate limit of 20 milliarcseconds
for accurate measurement. For a more reasonable Pluto-like albedo the object would subtend 42 millarcseconds, essentially identical to Quaoar,
which was successfully resolved by our team several years ago.

The direct measurement will be the cornerstone of the size measurement of this object, which will also include radiometric observations from Spitzer,
IRAM, and the CSO. We anticipate a single thorough analysis using all available means to get the best true size measurement possible.

[Guest_Richard Trigaux_*]

Possibly all planets/worlds/worldoids formed with moons, but in the outer solar system the perturbing effect of Jupiter and the other giants was sufficiently slight for orbits to remain stable over very long periods - far more than in the inner solar system.

Yes but the effect of neighbouring stars is stronger. Perhaps close encounters with other stars in a distant past completelly reshaped the orbits in the far solar system. But this cannot be the cause for capturing moons.

[Rob Pinnegar]

It is not really that surprising, the further out you go the slower become the relative motion between solar orbiting objects and therefore the larger is the sphere of influence where their gravity exceeds that of the sun's.

This can be determined by calculating the "Hill Sphere" for the planet. If I remember correctly, it works out to about 700,000 kilometres for Pluto. I won't go into a mathematical description here -- you can find the equations on Wikipedia if you're interested.

This leads to the possibility that Pluto might have other small satellites, and this has actually been considered. I vaguely remember reading, a while back, that at least one of the teams that have discovered all those distant satellites of the Jovians in the past few years, did at one time propose doing a similar search for Pluto. Can't remember whether it was carried out, though.

As for the giant impact theory, it was actually first proposed around 1947 by an astronomer named (I think) Benz. This neat idea was promptly forgotten for forty years, until it was independently re-proposed in the 1980s by Hartmann, Cameron and others.