Hot answers tagged

52 votes
Accepted

How much of the surface of other planets is lit by the sun?

OK, let start with some assumptions: spherical objects and no atmospheric effects. Here's the relevant geometry with the object on the left representing a planet and the object on the right ...
GrapefruitIsAwesome's user avatar
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
29 votes
Accepted

Why did the dust between the planets disappear during the birth of the solar system?

Dust happens in two ways. "Primordial dust" just condenses out of the protostellar material in the disc providing it gets cool enough and dense enough. "Second generation" dust is ...
ProfRob's user avatar
  • 149k
23 votes
Accepted

Could it be possible to detect planets from stars that went supernova through the resulting nebula shape?

The escape speed of a big planet like Jupiter is about 60 km/s. The speed of the ejecta from a supernova explosion is something like $10^4$ km/s. i.e. Jupiter would have little discernable ...
ProfRob's user avatar
  • 149k
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
  • 149k
15 votes
Accepted

How small stars help with planet formation

You need to add some numbers for a definitive answer. Low mass stars, say less than 0.9 times the mass of the Sun, do not make any contribution to enriching the interstellar medium. That is because ...
ProfRob's user avatar
  • 149k
14 votes
Accepted

Can one or more moons orbit around a double planet system?

Yes, it is possible. Pluto and Charon are a double "planet" system, and have moons like Kerberos, Nix and Hydra that orbit the heavier masses. The problem of orbital stability has mostly ...
Anders Sandberg's user avatar
13 votes
Accepted

Why can't a half-illuminated planet support life at all?

The phenomenon you are referring to is called "tidal locking", it occurs when the orbital period or one revolution of the planet is roughly equal to the time it takes to rotate in on its ...
Arjun's user avatar
  • 1,256
12 votes

Why can't a half-illuminated planet support life at all?

Pierrehumbert (2010) modelled the possible climates of Gliese 581g. Although that planet has since been shown to probably not exist, the model of a planet with similar characteristics should still ...
gerrit's user avatar
  • 2,033
11 votes
Accepted

Is there a formula for calculating surface temperature of a rocky world based on atmosphere and solar input?

Guillot et al. 2010 give a comparatively simple solution (their Eqn. 27) for a double-gray purely radiative atmosphere. It reproduces the equilibrium temperature in the optically thin limit. Robinson &...
AtmosphericPrisonEscape's user avatar
10 votes
Accepted

Planet and star rotation through gas in the galaxy

You can account for this friction, but it is totally negligible. The basic reason is that the Sun and planets are very compact, while the distributed gas is very sparse. The density of the ...
ProfRob's user avatar
  • 149k
9 votes

How is a Planet's Moment of Inertia Measured Remotely?

I dug around quite a bit and was unable to find anyone making measurements of the type that would lead one to determine the moment of inertia of Uranus or Neptune without first making assumptions ...
Paul T.'s user avatar
  • 687
9 votes
Accepted

Celestial "orbits"

Physical theories describe how things change in given circumstances (if the theory is right). In practice this means that they are applied in simplified ways, where the simplifications of ...
Anders Sandberg's user avatar
7 votes
Accepted

What is the maximum size for a solid celestial body such that it still can be tunneled down to the core?

Such tunnels might be possible for objects up to a few hundred kilometres in size. Larger objects could be tunnelled if the tunnels are lined with high strength materials. Assuming the centre of the ...
David Bailey's user avatar
7 votes
Accepted

Does the Sun have different unique orbits around barycenters?

There's only one barycenter for the solar system, which includes the impact from every planet, asteroid, comet, and space probe in the solar system. The path the sun takes around that barycenter is ...
Darth Pseudonym's user avatar
7 votes

Difference in results between JPL Horizons and cspice (rust-spice)

The issue is with how you have configured HORIZONS to show the output. You have apparent RA, Dec selected as output columns which includes the precession and nutation, in addition to the light time ...
astrosnapper's user avatar
  • 8,347
6 votes

why does earth have speed?

Just by random chance, every giant cloud of gas and dust has some average rotation. Before the sun was even there, the solar system was just a large cloud of dust and gas like this. When it collapses ...
Mark Foskey's user avatar
  • 3,896
6 votes

Why don't scientists believe Earth's surface water came up from the mantle?

If the question is actually "why don't any geologists believe that Earth's surface and near-surface waters were brought up from the Earth's interior?", then the premise is false since many ...
David Bailey's user avatar
6 votes

Celestial "orbits"

You are right. But you miss a few quirks of reality, or some fine-print of the applicable physics. Yes, the Moon is moving away from Earth as slowing down Earth's spin rotation means that angular ...
planetmaker's user avatar
5 votes

How small stars help with planet formation

All depends on where you put the boundary. According to a Warwick release about a 2020 Nature paper, stars lower than 1.5 solar masses do not contribute to carbon enrichment. But certainly by 2.0 ...
BowlOfRed's user avatar
  • 1,965
5 votes

Trouble seeing Mars and Venus more than specks of light

I've gone ahead and reached out to my local astronomy club and received back an invite to their next event as well as helpful information for more viewing.
BeardedChemist9's user avatar
5 votes
Accepted

Have we observed other habitable planets like Earth?

As others have said, the answer is yes and no. There are quite a few planets (and, as is less often covered, gas-giants able to support moons) that could potentially host life. Planets and moons both ...
Kazon's user avatar
  • 587
5 votes
Accepted

When did Venus reach approximate radiation equilibrium?

If we assume that energy transport in atmospheres happens purely via radiation, then we can estimate a simple adjustment time to an exchange of exterior forcing factors (change in mean solar angle, ...
AtmosphericPrisonEscape's user avatar
5 votes

Why can't a half-illuminated planet support life at all?

I wish to add a couple of comments to the good answer provided by Arjun. A popular fallacy has it that close-in planets are always tidally locked in a 1:1 spin-orbit resonance (SOR), i.e., are always ...
Michael_1812's user avatar
  • 1,231
5 votes

Why can't a half-illuminated planet support life at all?

As several people have indirectly noted, the premise of this question is controversial. There are plenty of studies* suggesting that an Earth-like planet tidally locked to its star can be habitable as ...
Ilmari Karonen's user avatar
4 votes

Have we observed other habitable planets like Earth?

Yes and no. But mostly no. While it is true we have found other planets with atmospheres, experts at NASA (or if you're in Europe, ESA, Japan JAXA, et cetera et cetera) will all tell you that an ...
Deko Revinio's user avatar
4 votes
Accepted

Planets revolving counter clockwise around the Sun

The direction in which planets are supposed to orbit their host star is prograde -- i.e., coincides with the direction of rotation of the star. The reason for this is that the said motions are pre-...
Michael_1812's user avatar
  • 1,231
4 votes

How common for all 7 planets to be above the horizon?

This is definitely dependent on observing location, observing times, atmospheric refraction, and probably a couple other things I didn't think of. But just to get another reasonable estimation: ...
notovny's user avatar
  • 4,770
4 votes
Accepted

When did Venus get as hot as it is now?

According to current models and computer simulations, Venus was a water world many billion years ago but due to the close proximity to it's host star, Sun or Sol, the water was Photocatalytically ...
Arjun's user avatar
  • 1,256
4 votes

Celestial "orbits"

The model of the elliptical orbit is a close approximation of the reality—and even Kepler knew that, when he wrote that “orbits are ellipses.” In reality, gravitational interactions between the Sun, ...
Pierre Paquette's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible