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A survey searching for objects in the Kuiper Belt has found two undiscovered moons of Jupiter. Jupiter now has 69 known moons:
Until recently the cataloged satellites totaled 67 in number. But only the innermost 15 of these orbit Jupiter in a prograde sense (in the direction of the planet's spin). The rest are retrograde, and are likely captured objects - other pieces of the solar system's solid inventory that strayed into Jupiter's gravitational grasp.
That population of outer moons is mostly small stuff, only a few are 20-60 kilometers in diameter, most are barely 1-2 kilometers in size, and increasingly difficult to spot. Now astronomers Scott Sheppard, David Tholen, and Chadwick Trujillo have added two more; bringing Jupiter's moon count to 69.
These additions are also about 1-2 km in size, and were spotted in images that were part of a survey for much more distant objects out in the Kuiper Belt. Jupiter just happened to be conveniently close in the sky at the time. The moons are S/2016 J1 and S/2017 J1, and are about 21 million km and 24 million km from Jupiter.
The moons are also known as Jupiter LIV and Jupiter LIX, and are members of the Pasiphae group. They are estimated to be about 3 and 2 km in diameter respectively.
Also at Popular Mechanics.
(Score: 0) by Anonymous Coward on Thursday June 15 2017, @02:43AM (10 children)
Since it has not cleared its orbit. It has more trash than Pluto.
(Score: 2) by butthurt on Thursday June 15 2017, @03:00AM (1 child)
My understanding of the idea of "clearing the neighbourhood" (which has been quantified in several different ways) is weak. On Wikipedia I read that satellites are excluded from the criteria. Whether Charon is counted as a satellite of Pluto for that purpose, I don't know. The barycentre of the Pluto–Charon system is not within Pluto. Neptune is counted as something that wasn't cleared from Pluto's neighbourhood, because of the way their orbits cross. Someone else asked why Neptune is deemed a proper planet in spite of the crossing orbits.
https://en.wikipedia.org/wiki/Clearing_the_neighbourhood [wikipedia.org]
https://en.wikipedia.org/wiki/Barycenter [wikipedia.org]
(Score: 3, Interesting) by takyon on Thursday June 15 2017, @03:07AM
Some other TNOs [wikipedia.org] cross Neptune's orbit (sort 'q' column ascending. Centaurs [wikipedia.org] can cross past Saturn, making their orbits unstable and short-lived.
Huya [wikipedia.org] is a named dwarf planet that crosses Neptune's orbit.
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(Score: 3, Interesting) by AthanasiusKircher on Thursday June 15 2017, @03:01AM (5 children)
Dude, let it go. I can understand why some people feel the new definitions are unnecessary, but I'll never understand this irrational affection for Pluto.
(Score: 0) by Anonymous Coward on Thursday June 15 2017, @03:30AM
GP is Setsuna Meioh.
(Score: 0) by Anonymous Coward on Thursday June 15 2017, @07:36AM (2 children)
Some of us aren't going to give up easily, princess.
(Score: 2) by wonkey_monkey on Thursday June 15 2017, @04:51PM (1 child)
That's obvious, but it doesn't explain why.
systemd is Roko's Basilisk
(Score: 4, Insightful) by bob_super on Thursday June 15 2017, @06:03PM
Because the new definition is silly. It's just designed to point out that 8 planets are traditional, and avoid having to refer to dozen of newer ones in the same breath.
Mercury is smaller than a few moons, Jupiter is its own mini-system, there's maybe a big one hiding pretty far but we'll find it soon, and who knows how many others? What's the cosmological point of having decided that 8 are more equal than the others? How can you put the Earth ans Mars in the same category as Jupiter, when they're more similar to Pluto?
I like the barycenter definition, which simply and mathematically classifies planets vs binary systems vs moons (for gravity-shaped objects).
It's just a name. Why did are we even having this discussion? Who woke up one day and decided something was wrong with calling all the new ones planets? I want a solar system with more planets than I can name!
(Score: 0) by Anonymous Coward on Thursday June 15 2017, @09:50PM
I am still upset they revoked Earth's planetary status, then mis-stated it in the press-release.
(Score: 2) by stormwyrm on Thursday June 15 2017, @03:39AM (1 child)
Have a look at this:
https://arxiv.org/abs/1507.06300 [arxiv.org]
It quantifies what is meant by "clearing the neighbourhood around a planet's orbit". No planet can ever fully clear its orbital zone, because gravitational and radiative interactions are inevitably going to push asteroids and comets and other such similar debris into planet-crossing orbits. If you were going to be that pedantically strict about it then NONE of the planets fit that definition! Tons of asteroids regularly cross the earth's orbit, and the same is true of every other planet in our solar system. But that isn't what the IAU means. They mean something more of dynamical dominance, meaning the planet dominates the orbit in terms of mass and orbital distance.
Numquam ponenda est pluralitas sine necessitate.
(Score: 0) by Anonymous Coward on Thursday June 15 2017, @01:24PM
Yup, as I told my wife when she asked me, "Why is Neptune a planet when Pluto crosses its orbit?"
"Well, the definition is that a planet has cleared the orbit of anything more than 2/3s its own size. So those two cross, but Neptune is huge while Pluto is small, so only Pluto loses out as it is no where near 2/3s of Neptune's size."
(Score: 4, Funny) by AthanasiusKircher on Thursday June 15 2017, @03:11AM
I assume they meant two previously undiscovered moons? Or maybe two previously unknown moons? Or perhaps even just "found two new moons." Whatever they are, I don't think we can call them "undiscovered moons" now. [/pedantry]
(Score: 0) by Anonymous Coward on Thursday June 15 2017, @05:18AM (1 child)
So which is it?
(Score: 2) by takyon on Thursday June 15 2017, @05:22AM
Point your telescope at it.
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(Score: 2) by realDonaldTrump on Thursday June 15 2017, @12:29PM (2 children)
(Score: 2) by bob_super on Thursday June 15 2017, @05:53PM (1 child)
If you'd stopped at 69, who would be doing your job today?
(Score: 2) by realDonaldTrump on Thursday June 15 2017, @07:06PM