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99

Pluto is something like magnitude 14. The limit for the human vision is somewhere between magnitude 6 (widely accepted) and 8-ish (highly trained observers with perfect vision in ideal conditions using special techniques - and it's a bit controversial anyway). There's zero chance that was Pluto. It was definitely a fixed star.


37

They do, but due to the ratio of masses being vastly different, they seem like they would not to do so as moon seems to rotate just around (the centre of) Earth. The ratio of Earth and Moon's masses is $\frac{M_{Earth}}{M_{Moon}} = 81.3$ whereas for Pluto and Charon the same ratio is $\frac{M_{Pluto}}{M_{Charon}} = 8.09$. Because the ratio for Pluto and ...


30

It's brighter on Pluto than you think. NASA developed a tool called Pluto time, which tells you when at your place the ambient light conditions are similar to the ones on Pluto. This occurs when the Sun is only 2° below the horizon! That's quite shortly after sunset, and considerably before the end of civil twilight, which is when it's 6° below. All of ...


25

No, Pluto is a so called resonant trans-neptunian object; the orbital period of Pluto is almost exactly 3:2 (1.5) times that of Neptune. This means that every time Pluto nears perihelion and is therefore closest to the Sun and also closest to the orbit of Neptune, Neptune is always at a specific angle (50° according to Wikipedia) in front or behind Pluto. (...


17

Back when New Horizons was preparing for its flyby back int 2015, NASA's website set up a tool to allow you to experience the brightness of light at High Noon on the subsolar point on Pluto. From Space.com: NASA's 'Pluto Time' Shows You How Bright It Is on Dwarf Planet To an observer on Pluto's surface, the sun would be about 1,000 times dimmer than it is ...


16

As Florin correctly stated, it can't have been Pluto. You have probably looked at it and you have even gotten its light in your eyes. That little itty bitty shine just has no chance to make your retina do anything (edit: Interesting link in the comments. Might be that people actually can sense single photons. Doesn't help at all to see Pluto though). ...


14

Yes, but they're not very good and they're amazing. The Wikipedia article for Pluto shows a low-resolution map of the surface, generated from Hubble images: And the Wikipedia article for Pluto's largest moon Charon shows a low-resolution map of the Pluto-facing side of Charon (not to scale): Larger image here. Only the Pluto-facing side is shown because ...


14

On barycentres The Pluto-Charon couple is not qualitatively different to the Earth-Moon couple with regards to orbits. As was pointed out in other answers, in both cases, the two bodies revolve around each other, i.e. they are best described as orbiting around their barycentre. In more physical terms, the referential centred on the barycentre of the Earth-...


14

Pluto will never be a planet. There are a number of technical papers that give more precise meaning to the concept of "clearing the neighborhood". It's not just now, it's can the object in question clear the neighborhood of its path while the Sun is still a star. In the case of Pluto, Ceres, Eris, and a host of other not-quite-planet objects, that will not ...


12

Yes, Pluto is still a dwarf planet. According to the IAU website, it still fits the criteria for a dwarf planet, fails to meet the criteria for a planet, and still carries the "dwarf planet" label, whatever its future status may be. I'm sorry I can't provide a longer or more detailed answer, but this is really a yes-or-no question.


12

No. From 1979 to 1999, Pluto was the eighth planet from the sun. In 1999, it slipped beyond Neptune to become the ninth. But Pluto's 248-year orbit around the sun takes it 17 degrees above and below the plane in which Neptune and the other planets travel. So their paths don't actually cross as they swap positions. Imagine you are the sun in the middle of ...


12

The L1, L2, and L3 points are unstable in any orbital system. (source) The L4 and L5 points of a pair of bodies are only stable if the larger of the bodies is at least 25 times as massive than the smaller (source). The ratio of the Pluto/Charon system is only 8.7. Because of this, none of the Lagrange points are stable, and an object orbiting at any of ...


9

Mathematically, the motion of the Pluto-Charon system can be decomposed into two parts: The motion of Pluto-Charon about the Sun, and the motion of Pluto and Charon about one another. If one sets the reference point to be the center of Pluto, the path the Pluto-Charon system would appear to follow about the Sun would be an epicycle, which is a far more ...


9

The size of the cameras that took the Pluto pictures is easy enough to find: the ACS Wide Field Camera has two 2K by 4K (hence 8 Mega pixel) CCDs, with a field of view of 202×202 arcsec. The high resolution HRC had a square 1 Megapixel camera with a 26×29 arcsec field of view. The reason that the images of Pluto are relatively poor, is that Pluto is small! ...


8

No, their orbits do not cross. They are just tangled, but in no point they coincide.


8

That photograph is a composite of two images taken with different exposure times. To be correct we'd have to say that the exposure of the two photographs is different, i.e. the outer photo was created by absorbing more light. In this case we can assume that the focal ratio (derived from Hubble's lens aperture) and the luminance of the scene (how much light ...


8

These two calcs agree pretty well: The Sun's magnitude from from Pluto is -18.7 m = -18.75 magnitudes That's quite a bit brighter than a full moon, so you'd be able to read by it.


7

This Wikipedia page does a decent job of describing the orbit-clearing criterion, based on the original paper by Stern & Levison (2002), which can be found here (PDF). In order to have cleared its orbit over a period of billions of years, an object needs a "Stern-Levison parameter" $\Lambda$ which is $> 1$; Pluto has $\Lambda \approx 3$-$4 \times 10^{...


7

The implication of the question is that this extra 1000 miles should be added to Pluto's radius. The answer is no. For all of the solid planets, it's that solid surface (or solid+liquid surface in the case of the Earth) that counts, not the outer reaches of the atmosphere. The surface is a clear-cut, non-arbitrary boundary. The atmosphere? They can extend a ...


7

Pluto itself so bright that Charon would not be visible in the image if it were exposed in a way to show the remaining moons. Likewise, the remaining moons as so faint as to not be visible in an image that resolves Charon. Thus, the photo that you see is a composite of two image processing techniques: one designed to showcase Charon and one designed to ...


7

Possible rendezvous with a Kuiper belt object and Voyager type data on the heliosphere: "We should have power until the 2030s, so we can get into the outer part of the heliosphere," says Spencer. "As long as we can continue to get good data—and persuade NASA to pay for it—we will keep getting the data, because we will be in a unique environment that we've ...


7

The question says a few interesting things: The system orbit isn't on the ecliptic The system hasn't cleared its neighbourhood These are not going to change in the next few million years - or ever. Orcus is an interesting counter-example. It is in a similar orbit to Pluto - similar aphelion, perihelion and eccentricity, similar orbital period (to within ...


6

The surface of Pluto is not just young, but very young, and also differentiated. The 'heart', Sputnik Planum, may be currently active, with flowing glaciers, and nitrogen snow. This area may have be resurfaced during Pluto's perihelion. Your theory cannot account for the very young age of the surface. Next capture of a rogue planet is not easy. It would ...


6

Part of the problem here is semantics. The meaning of "planet" was really poorly defined prior to 2006 (and some argue that it still is). In the early 2000's, this started to become an issue. You can blame Mike Brown. In January 2005, Mike Brown's team at CalTech in Pasadena, California, discovered an object we now know as Eris (they nicknamed it Xena ...


5

The orbit of a planet does not in any way depend in its moons, mass or own gravity. The orbit is the same for a grain of dust as for a giant planet. It only depends on the mass on the Sun and the distance to the Sun. The eccentricity of the orbit is then given by the initial angular momentum of the orbiting object. This might explain it a bit better. This ...


5

It was predicted by some, before the images arrived, that Pluto's craters would be much shallower than perhaps on other rocky objects/satellites. The reason is the icy composition and the relatively low impact velocities in the outer solar system (Bray & Schenk 2015). There are indeed reported quotes in recent days that there are no impact craters on ...


5

I'm pretty sure that the stripe is there because the two sections of the image have different contrasts. Pluto and Charon are so bright relative to Nix, Hydra, P4 and P5 that to have one contrast, you'd either (a) not be able to see the smaller four, or (b) totally wash out the image with the light from the brighter two. So we simply superimpose two images ...


5

Geothermal activity can originate from a combination of: Residual heat from planet formation: During the formation of a planet, half of the potential energy of the parent region of dust and gas can be theoretically converted to kinetic energy---this is known as the Virial Theorem. The kinetic energy of the particles translate to a temperature. Internal ...


5

The answer by @mso is very good. Another contributing factor is the exposure time of the camera on New Horizons. The amount of light reflecting from Pluto is greater than that from the background stars. As a result the exposure time is set to achieve a good image for the desired target and detail required. Over the integration time the amount of light ...


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