APOD: Atlas, Daphnis, and Pan (2019 May 18)

[APOD Robot]

Atlas, Daphnis, and Pan

Explanation: Atlas, Daphnis, and Pan are small, inner, ring moons of Saturn. They are shown at the same scale in this montage of images by the Cassini spacecraft that made its grand final orbit of the ringed planet in September 2017. In fact, Daphnis was discovered in Cassini images from 2005. Atlas and Pan were first sighted in images from the Voyager 1 and 2 spacecraft. Flying saucer-shaped Atlas orbits near the outer edge of Saturn's bright A Ring while Daphnis orbits inside the A Ring's narrow Keeler Gap and Pan within the A Ring's larger Encke Gap. The curious equatorial ridges of the small ring moons could be built up by the accumulation of ring material over time. Even diminutive Daphnis makes waves in the ring material as it glides along the edge of the Keeler Gap.

<< Previous APOD

This Day in APOD

Next APOD >>

[BDanielMayfield]

These links:

Explanation: Atlas, Daphnis, and Pan

return 404 page not found errors now.

[gcsunsfan11]

These are not moons, they are captured asteroids. If Pluto is not a planet, these are not moons.

[De58te]

These links:

Explanation: Atlas, Daphnis, and Pan

return 404 page not found errors now.

The active page for that can be found here for example, solarsystem.nasa.gov/moons/saturn-moons/daphnis/in-depth/ (The other moons can be found by clicking on Saturn Moons.)

[Ann]

These are not moons, they are captured asteroids. If Pluto is not a planet, these are not moons.

A captured asteroid that is in orbit around a planet is a moon. I believe that Neptune's giant moon Triton has been captured (and is eventually going to crash into Neptune). I think that the biggest moon of Mars, Phobos, has also been captured and is also going to crash.

Ann

[orin stepanek]

These are not moons, they are captured asteroids. If Pluto is not a planet, these are not moons.

A captured asteroid that is in orbit around a planet is a moon. I believe that Neptune's giant moon Triton has been captured (and is eventually going to crash into Neptune). I think that the biggest moon of Mars, Phobos, has also been captured and is also gong to crash.

Ann

Pluto; the little planet that showed its stuff! It's OK Ann! Pluto is a dwarf; so in my book; Neptune; Uranus; Saturn; and Jupiter aren't planets either: they are giants! So there are only 4 planets! All because scientists didn't want to admit that there are more other planets out there beyond Pluto!!!!!!!!

[orin stepanek]

Atlas, Daphnis, and Pan! Are these mostly water ice?

[Chris Peterson]

These are not moons, they are captured asteroids. If Pluto is not a planet, these are not moons.

Pluto is a planet, as is every body orbiting the Sun, including asteroids. Words have multiple meanings. In the context of standardized scientific definitions, however, Pluto is a subcategory of planet, and any body that orbits a planet, no matter how small, is a moon. Indeed, the term "moon" is even used to refer to a small rock orbiting another small rock.

[Cousin Ricky]

I see people are making up their own rules and definitions. This is not conducive to communication. I’m inclined to trust Chris to be level-headed and know what he’s talking about; and Ann has not contradicted current scientific usage.

Regarding Pluto, I’ll quote Neil deGrasse Tyson: “Get over it!”

And always remember: Atlas, Daphnis, Jupiter, Neptune, Pan, Phobos, Pluto, Saturn, Triton, and Uranus remain Atlas, Daphnis, Jupiter, Neptune, Pan, Phobos, Pluto, Saturn, Triton, and Uranus, respectively, no matter what labels we puny humans apply to them.

[orin stepanek]

Most here know my feelings! I don't like sub categories about planets except for planetoids; (asteroids)! Pluto is; (should be} just concidered a full-fledged planet as well as Sedna; Make Make; etc! The guy on the the Science Chanel says it would be too much for school kids to have to remember! {bah humbug!] Most kids I know would like to have that dwarf tag eliminated!

[JohnD]

Ooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooh!
J.

[Boomer12k]

What type of cleaner do we use on all that "build up"?

Great Images. Interesting.

PS: Science is not our personal opinions...
:---[===] *

[neufer]

These are not moons, they are captured asteroids. If Pluto is not a planet, these are not moons.

Pluto is a planet, as is every body orbiting the Sun, including asteroids. Words have multiple meanings. In the context of standardized scientific definitions, however, Pluto is a subcategory of planet, and any body that orbits a planet, no matter how small, is a moon. Indeed, the term "moon" is even used to refer to a small rock orbiting another small rock.

• Pluto is constantly mooning Neptune and, hence, should be considered a moon of Neptune.

Pluto's 3:2 Resonance with Neptune

---

<<Pluto is locked into a 3:2 resonance with Neptune. For every 3 orbits of the Sun completed by Neptune, Pluto completes 2 orbits. At any given moment, however, the ratio is not exactly 3:2. Sometimes Pluto's period is slightly faster than its average value. Sometimes it is slower.

When Pluto's period is slightly faster than average, the points where its orbit intersects the orbit of Neptune advance with each orbit. But when this intersection gets too close to Neptune, Pluto is accelerated by Neptune's gravity. This causes Pluto to rise into a higher orbit with a longer period. Now orbiting the Sun with a period slightly slower than its average value, the points where Pluto's orbit intersects Neptune's orbit retreat with each orbit. Eventually, it approaches Neptune from the other direction, allowing Neptune's gravity to pull Pluto into a lower orbit with a shorter period. This repeats indefinately, ensuring that Pluto and Neptune never get too close to each other.

The simulation PlutoResonance.gsim shows the orbit of Pluto in a rotating frame whose period matches the period of Neptune. This causes Neptune to appear stationary, exposing this 3:2 resonance. The orbits of Jupiter (purple), Saturn (yellow), and Uranus (green) are also visible.

The starting conditions for this simulation were obtained by JPL's Horizons Ephemeris Computation Service.>>