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73 votes

Why do Jupiter’s moons have so much water?

tl;dr: They have more water because they captured it as ice, and it’s easier to hold onto ice than water vapor. Planets (and by extension, moons) beyond the frost line were formed with ice as a part ...
Justin T's user avatar
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43 votes

Why is Uranus called a "green planet"?

I think your issue is linguistic not astronomical. The way a language cuts up the space of colours into discrete names is varies strongly from one language to another, and even from one dialect to ...
James K's user avatar
  • 123k
36 votes
Accepted

Why is there so little nitrogen in the Martian and Venusian atmospheres?

Nitrogen, with a molecular mass of 28 atomic mass units, is too light to have remained in Mars's atmosphere. Carbon dioxide, with a molecular mass of 44 amu, could (and does) exist on Mars, but it is ...
David Hammen's user avatar
  • 34.1k
32 votes

Do planets lose energy while rotating?

The energy a rotating planet has is derived from the rotation the initial interstellar cloud of gas and dust had prior to it flattening into a protostellar disk. The rotation of a planet is bound by ...
Fred's user avatar
  • 2,169
32 votes
Accepted

Why is it impossible to infer the surface temperature of Venus by spectroscopy observation from earth?

The important difference is that the word "surface" has a different meaning depending on whether we're talking about the Sun or Venus. When we say "the surface of the Sun," we ...
Tanner Swett's user avatar
24 votes

Are heavy elements equally distributed throughout the Solar System?

Initially, in the protostellar disc, the heavy chemical elements would have been uniformly distributed with radial distance from the Sun, with a mean abundance that is similar to that present in the ...
ProfRob's user avatar
  • 153k
23 votes

Why would rocky earth-like planets be rare around white dwarf stars?

Short answer Most planets of this type may have formed too close to their parent star (the progenitor of the white dwarf) to have avoided being swallowed when it became a red giant. Another ...
ProfRob's user avatar
  • 153k
21 votes

Under which conditions could a planet's massive moon's orbit get closer to the planet?

Yes, it is possible for a moon of a planet to move closer to the planet. If a moon moves close enough to the planet, the moon will eventually reach its Roche limit and shatter or else collide with ...
M. A. Golding's user avatar
20 votes

What are the orbital velocities of the other planets? For objects in a 'Low-Earth-Orbit' around planets other than Earth, e.g.?

The formula for orbital velocity is $\sqrt{GM/r}$ and for a "low" orbit you would mean orbit at, or close to the surface, ie with a radius equal to the radius of the planet. This makes ...
James K's user avatar
  • 123k
18 votes
Accepted

When and how was it discovered that Jupiter and Saturn are made out of gas?

I'm unsure of the "history of science" aspect of this, but an actual deduction that these are gas giants would require Kepler's laws and Newton's law of gravity combined with a modest ...
ProfRob's user avatar
  • 153k
18 votes

Why is it impossible to infer the surface temperature of Venus by spectroscopy observation from earth?

I think the problem is that spectroscopy at visible and infrared wavelengths simply can't penetrate the thick atmosphere of Venus. Thus the information comes from much higher in the atmosphere and not ...
ProfRob's user avatar
  • 153k
17 votes

How scientists find the direction of rotation of planets?

I'll focus first on the question of the title: "how do we find / measure rotation?" The easiest method is the same as everyone else: look and see. Take images some time apart and you will ...
planetmaker's user avatar
  • 19.9k
17 votes

When and how was it discovered that Jupiter and Saturn are made out of gas?

By 1690, Giovanni Cassini was able to estimate the rotation period of the planet and noticed that the atmosphere of Jupiter undergoes differential rotation which confirmed that Jupiter was made of gas ...
Nilay Ghosh's user avatar
  • 4,692
17 votes

Why is Uranus called a "green planet"?

This answer looks into why Uranus is "green" or at least greener compared with Neptune's blue. Both planets have similar atmospheric compositions and would ordinarily be expected to show ...
Oscar Lanzi's user avatar
  • 1,131
15 votes

At what point in history was the idea of planets being spit out by the sun abandoned?

That specific idea doesn't seem familiar to me, and I work in that field. Particularly this idea would only be called 'theory' when making testable predictions. The only thing that comes to mind here ...
AtmosphericPrisonEscape's user avatar
14 votes

Is there a way to tell the difference between earth andesite from Mars

If this is something that you have found (rather than purchased as a meteorite) the chances are very small that it is a meteorite. Even if it is a meteorite, the chances it's a Martian one are even ...
astrosnapper's user avatar
  • 8,357
13 votes

Why is there so little nitrogen in the Martian and Venusian atmospheres?

3.5% of all atmosphere in Venus still accounts for more partial pressure of nitrogen than on Earth. Venus has ~90bar pressure at the surface, 3.5% of them are ~3.2 bar nitrogen. Earth has only 0.8 bar ...
fraxinus's user avatar
  • 2,839
13 votes
Accepted

Do some comets spin? If so, how fast?

Yes, comets spin although measuring it can be tricky due to the coma and outgassing from the nucleus. It's easiest to measure the rotation period when the comet is inactive near aphelion although this ...
astrosnapper's user avatar
  • 8,357
13 votes

Are heavy elements equally distributed throughout the Solar System?

Initially yes(1), but actually not anymore. Initially the chemical composition in the solar nebular was uniform. However a such protoplanetary disc is subject to a radial temperature gradient. Thus ...
planetmaker's user avatar
  • 19.9k
12 votes
Accepted

How fast is Neptune getting brighter? When was was this first noticed and reported?

TL;DR: There was apparent 11% increase of Neptune brightness during 1980 and 2000. This could be due to multiple reasons. Recent observation suggested the reason to be change in the amount and ...
Nilay Ghosh's user avatar
  • 4,692
12 votes
Accepted

At what point in history was the idea of planets being spit out by the sun abandoned?

Between 1965 and 1980 I recall a book from the "Ladybird" series of short non-fiction books for children which included two possibilities for the formation of the planets. One was "...
James K's user avatar
  • 123k
12 votes

Do planets lose energy while rotating?

In addition to the interaction with other bodies (moons, other planets, stars) as described in another answer, you also have gravitational waves produced by spinning body that isn't perfectly ...
BurnNote's user avatar
  • 229
12 votes

Concerning a binary system of stars/planets/black holes could one of them be ejected before eventually merging or colliding?

Not in Newtonian gravity with particles. This situation is soluble with stable elliptical orbits, so any examples would have to depend on either Relativity, or that the bodies are not particles. If ...
James K's user avatar
  • 123k
11 votes

Which JWST instrument modes are compatible with observations of the bright trans-Earth planets Mars, Jupiter, and Saturn? Which aren't?

There are approved proposals for Cycle 1 to point the JWST at The Jovian system Jupiter's great red spot Mars Saturn and its moons and rings In those PDFs, they describe exactly what instruments ...
Gavin S. Yancey's user avatar
10 votes
Accepted

Radio signals between Mercury and the Moon during an eclipse

A total eclipse occurs when a full moon coincides with an orbital node of the moon. That is to say it occurs entirely due to the relative position of the Moon to the Earth and Sun An elongation of ...
James K's user avatar
  • 123k
10 votes

Under which conditions could a planet's massive moon's orbit get closer to the planet?

Under which conditions could a planet's massive moon's orbit get closer to the planet? I'll give the most straightforward condition: The tidal interaction tends to accelerate the orbiting moon in the ...
Sten's user avatar
  • 4,733
9 votes

Do gas giants have a core?

Gas giants are believed to have a solid core. They first formed as icy planets, and were heavy enough to accrete hydrogen and helium from the protoplanetary cloud they were in. Saturn, for instance, ...
usernumber's user avatar
  • 17.5k
9 votes

What is k2, how does it relate to Io's volcanism and how can Juno constrain its value?

It is called Tidal love number. The definition is as follows: In Newtonian gravitational theory, a tidal Love number relates the mass multipole moment created by tidal forces on a spherical body to ...
Nilay Ghosh's user avatar
  • 4,692
9 votes

How do rocky planet break up? Would they fragment into "a gazillion" rocky pieces pieces, or crack open like an egg?

Energy Intro I think any good discussion of planetary destruction should start by talking about energy! Our SI base unit of energy is a Joule, which is defined as $\mathrm{J} = \mathrm{kg} \mathrm{m}^...
Connor Garcia's user avatar
  • 16.3k
9 votes

At what point in history was the idea of planets being spit out by the sun abandoned?

Spit out? In 1955 my parents gave me an illustrated book on Astronomy, which gave two hypotheses: the Kant-Laplace (nebular) hypothesis, and Sir James Jeans' idea that a passing star pulled some ...
Simon Crase's user avatar

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