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25

From the Report of the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements of the Planets and Satellites (2000), section 3: The rotational pole of a planet or satellite which lies on the north side of the invariable plane will be called north, and northern latitudes will be designated as positive. The planetographic longitude of ...


20

Rings are made up of tiny (and not so tiny) pieces of rock and ice that are in some way the bits "left over" from the formation of the planet. The theory involves the Roche limit - and is that particles that are already within this limit can't accrete into a larger body because of the tidal forces involved. Another theory is that they are formed when a moon ...


16

Nasa.gov speculates that the most likely possibility is that an object with a mass close to that of Earth's collided with Uranus, causing it to rotate on its side from then on. A recent test by Space.com suggests that "Planet Uranus Got Sideways Tilt From Multiple Impacts". These findings suggest that two or more smaller collisions probably ...


14

NASA's Neptune fact sheet states that Neptune's irradiance is $1.51 W/m^2$. This is roughly three orders of magnitude less than at Earth (at $1367.6 W/m^2$). This sounds like a lot, and it is quite an attenuation. So much that for example solar panels for interplanetary probes are not worthwile at these distances from the sun. However, if you compare this ...


13

From wikipedia, the rings of uranus The definitive discovery of the Uranian Rings [...] use[d] the occultation of the star SAO 158687[...] The star SAO 158687, also cataloged as HD 128598 is a magnitude 8.7, orange dwarf star in Libra. There seems to be nothing special about the star, except that one day, a planet passed in front of it.


7

The obliquity of Uranus is a tricky one to explain, the issue with keeping the satellites in the equatorial plane is one of the problems. Another issue is that giant impacts would be expected to randomise the rotation, yet Uranus has ended up with a rotation period similar to Neptune despite its tilt. As noted by Morbidelli et al. (2012), tilting Uranus ...


7

As Miranda is a rather small object (only 235km diameter) it may simply have not enough mass to make it matter settle into hydrostatic equilibrium under the influence of its gravity, thus it basically retains the irregular shape most asteroids have. This nice arxiv paper discusses the mass limits necessary for a stellar body to settle into a nice round shape:...


7

The "strength of gravity" (ie gravitational acceleration) is determined by the mass of the planet and the distance between the planet and the moon. The formula is $$GM/r^2.$$ For the Earth (mass= 1 Earth, distance to moon=390000km) the acceleration is $0.003 ms^{-2}$ For Uranus and Titania (mass =14.5 Earth, distance=435000km) the acceleration is $0.03 ms^...


6

Why does Uranus and Neptune have more methane than Jupiter and Saturn? It's a combination of equations of state (EOS), serpentinization, and mixing (rotational and convective) that favors a preference for some reactions (and resulting compounds) over others. See the references below. The giant planets are all mostly hydrogen and helium, but Uranus and ...


6

The high inclination of the Uranus system to its orbit around the Sun has been known since the satellites were discovered. Lassell 1851 shows Ariel and Umbriel moving at least as far north and south of the planet as they do east and west of it. William Herschel probably noticed the same thing about Titania and Oberon in 1787. When Uranus is at an equinox, ...


5

The suspected theory of a giant impact most likely happened during the formation of our Solar System around 3 - 4 billion years ago. It is assumed that an Earth-size or larger proto-planet collided with Uranus. If not all, most of the moons of Uranus were formed after that impact, since such an impact would release a tremendous amount of material into ...


5

The inside of a giant planet is not like regular gas. First of all, it is hot. You are away of how it gets hot inside the Earth (causing volcanos). It is also hot inside Jupiter, but since Jupiter is bigger, it is hotter. It would be hot enough to vaporise rock under "normal conditions". The pressure is immense, and things stop behaving as you are used to ...


4

I have found the answer. I just found that venus has an axial tilt of nearly 180 degrees, so I realised that the >90 degree tilts are due to the fact that they are the planets with retrograde rotation, which is equivalent to an 'upside down' (>90 degrees) counter clockwise, normal, rotation.


4

The solar perturbations on most of the satellites of Uranus are on a very small scale indeed, which may explain the absence of the instabilities noted in the question. A perturbational effect depends on the scale of the solar perturbing accelerations relative to the ordinary inverse-square attraction of the primary body. The scale factor (often designated ...


4

Herschel, the discoverer of the planet named it Georgium Sidus, "George's star" after his patron, King George III of Great Britain. The name was not popular outside of Great Britain, and there were various other proposals. It was Johann Elert Bode who proposed Uranus, the Latin form of the Greek god of the sky. It fits with the existing planets having the ...


3

A relevant paper is Papaloizou & Melita (2004) "Structuring eccentric-narrow planetary rings" which starts off promisingly with the following: The nature of the dynamical mechanism that maintains the apse alignment of narrow-eccentric planetary rings is one of the most interesting and challenging problems of Celestial Mechanics. According to ...


3

In short, No. Side detail: Uranus and Neptune consist likely of 20% gas and 80% rock, coming from simple density considerations. They have large inner cores with masses around $\rm 12-14 \; m_{earth} $, and something like $\rm 2-3 \; m_{earth} $ of gas on top of them. Jupiter and Saturn are true gas giants. They both have $\rm 5-20 \; m_{earth} $ of solids ...


3

Provided that you are the same distance from the centre and you are on or above the surface then the heavier (more mass) planet will have a greater gravitational attraction. It is still possible that the heavier planet has a lower attraction at the surface since it may be bigger. If you can find the mass and radius then you can use the formula that James ...


3

The Nice model of solar system evolution proposes that both Uranus and Neptune migrated outward from their original orbits due to numerous encounters with planetesimals, stimulated by a temporary 2:1 resonance between Jupiter and Saturn. Simulations going back billions of years can put either Uranus or Neptune initially closer to the Sun. Desch 2007, ...


2

As per the books referred to in comments: Both planets could be resolved as a disk, but no surface features could be observed on either. Spectrograms had been taken, so the general colour of the planets was known. The extreme axial tilt of Uranus was known about. But the relative warmth of Neptune was not.


2

The simple answer is that the composition in terms of elements doesn't matter for the colour, since that is determined by the molecular composition as well as state (pressure and temperature) of the visual layers (which contain a small but significant fraction of other elements than H and He). Given the differences in the giant planets temperature and ...


2

Slipher 1912 and Lowell 1912 used a one-prism spectrograph on the 24-inch refractor at Lowell Observatory in this way. Their 1911 observations of Uranus yielded a period of 10.8 hours, which made sense given the polar flattening previously observed by others. They knew the obliquity of Uranus's satellites' orbits and assumed that its equator was in a ...


2

NASA conducted a study on the Ice Giants in 2016 after recognition as a high-priority flagship mission target in the 2013-2022 Planetary Decadal Survey (overview of the Decadal Survey from The Planetary Society), a community document which helps set priorities and goals. The full report and summary are available from LPI's Ice Giants Mission Planning page ...


1

This is a supplemental answer to @MikeG's excellent answer. I've just plotted Uranus' axis direction versus the direction we view it at, to put those dates into context. The "solstice of 1901-02" is clearly seen in the plot. Plotted using Python script based on Skyfield: import numpy as np import matplotlib.pyplot as plt from skyfield.api import Loader, ...


1

No. The difference in mass is less than 20%, and for astronomers that counts as "basically the same" (for the masses, check wikipedia). Your question implies that more massive planets should form closer to their star. However, there is as yet no definitive theory on the formation of planetary systems - that might come with the next generation of telescopes, ...


1

You could just have Googled this question. Post #5 from the first hit: First off, by "wondering what colors different gas giants can be", you are presumably asking about their light spectra through the visible range of wavelengths (380-720 nm), right?** Light interacts primarily with electrons. It is scattered or absorbed in the presence of ...


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