Charon is fainter than Pluto because it is smaller and, probably, because its surface is covered by water ice whereas Pluto is thought to be covered mainly by the more reflective methane frost or snow.
As indicated in the diagram at the bottom of the photograph, Charon's orbit around Pluto is a circle seen nearly edge on from Earth, with a radius of almost twenty thousand kilometers - a distance equal to approximately one and a half times the diameter of the Earth. At the time of observation, Charon was near its maximum apparent distance from Pluto, so that its angular separation was about nine tenths of an arcsecond.
Because of the peculiar orientation of the Pluto-Charon orbit with respect to our line of sight, Charon approaches to within less than one tenth of an arcsecond of Pluto every three days.
- Pluto - the "double planet".
- Kingdom Living.
- Ein amerikanischer Arzt in der Türkei (German Edition).
Due to the physical proximity of the two planets and the great distance to the system, it is extremely difficult to clearly resolve the pair from the Earth except in exceptional circumstances. The best ground based image of Pluto and Charon ever taken to date is shown in the upper left hand frame in the accompanying photograph.
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This image was taken with the Canada-France-Hawaii telescope in Hawaii. The superior resolution of the FOC image is evident. Further HST observations of Pluto and Charon will be extremely important in elucidating the nature and the origin of this fascinating and frigid world where the average temperature approaches minus degrees centigrade - only 58 degrees above absolute zero. Although the "fog" surrounding the images caused by the spherical aberration of the primary mirror prevents the FOC from resolving surface features, several other critical pieces of information can be extracted from continuing FOC observations of these objects.
reality check - Orbit of a double planet - Worldbuilding Stack Exchange
Detailed analysis of the brightness variations of the two planets will provide a wealth of information on their surfaces and atmospheres which are impossible to obtain from the ground. Precise measurements of the orbital parameters of the Pluto-Charon system are now also possible. This will enable astronomers to measure the individual masses and densities of the two objects - thereby providing important clues to their origins. One possibility is that objects similar to Pluto and Charon were created in great numbers in the outer fringes of the primordial solar nebula, but the majority of,these "planetary embryos" were either expelled from the inner solar system or gobbled up by the giant planets Jupiter, Saturn, Uranus, and Neptune.
Only Pluto 'and Charon survived independently to this day. Continued monitoring of these two fascinating objects at the outer edge of our solar system throughout the lifetime of HST will perhaps help astronomers understand the nebula from which we all originally formed.
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The left image was taken with the Canada-France-Hawaii telescope in Hawaii. However, these simulations often resulted in the planets colliding, typically merging or accreting together into a larger planet and sometimes leaving behind a disk of debris from which a moon could form. Also, in some simulations, the planets collided in a grazing manner at high speeds, resulting in "hit and run" interactions in which the worlds escaped from one another. Still, about one-third of the simulations resulted in binary planets forming.
These involved relatively slow, grazing collisions.
Binary Earth-Size Planets Possible Around Distant Stars
The bodies stay mostly intact, but end in a bound orbit with one another. These binary planets would loom extraordinarily close to one another, separated by a distance of about half the diameter of each of the worlds. Over time, the rate at which both planets spin would fall into lockstep, with each world only turning one face toward its partner.
Such binaries can persist for billions of years, researchers say, provided they form at least half an astronomical unit or more away from their parent stars — far enough away for the star's gravitational pull to not disrupt the binary planet system. One astronomical unit, or AU, is the average distance between the sun and Earth, about 93 million miles, or million kilometers.
Astronomers have confirmed more than planets beyond our own solar system, and the discoveries keep rolling in. How much do you know about these exotic worlds? Start the Quiz 0 of 10 questions complete Alien Planet Quiz: Are You an Exoplanet Expert? The research team's goal from here "is to run more simulations, increase the parameters of the simulations, and work to get a better picture of the probability that a binary planet might form," Ryan said.
Originally published on Space.
Choi is a contributing writer for Space. He covers all things human origins and astronomy as well as physics, animals and general science topics.