Skip to main content
38 votes

Do celestial objects need to be big to have liquid water on their surfaces?

Liquid water can't exist in a vacuum. If there is no pressure, then the boiling point will drop to the freezing point and so there will either be ice or water vapour. And if the world is "small&...
James K's user avatar
  • 125k
23 votes

Are there any planets or moons denser than Earth?

I feel it's a cheap answer but heavy Jupiters can get much denser than Earth because planets with Jupiter's mass stop adding size as they add more mass. A planet with Jupiter's size and 10-12 times ...
userLTK's user avatar
  • 24.1k
15 votes

Do celestial objects need to be big to have liquid water on their surfaces?

Do celestial objects need to be big to have liquid water on their surfaces? Yes. In a nutshell: liquid surface water needs an atmosphere. To sustain an atmosphere, a planet must be sufficiently ...
gerrit's user avatar
  • 2,233
13 votes
Accepted

Why don't we have in-between planets?

Super-Earths and Mini-Neptunes are the "in-between" types of exoplanets you're looking for. A sweeping generalization would put most in the range of $\sim1$-$10M_{\oplus}$ (Earth masses), with some ...
HDE 226868's user avatar
  • 37.3k
9 votes
Accepted

Are there any planets or moons denser than Earth?

From the Wikipedia page on Chthonian planet: Transit-timing variation measurements indicate for example that Kepler-52b, Kepler-52c and Kepler-57b have maximum-masses between 30 and 100 times the ...
sno's user avatar
  • 1,464
9 votes

Do celestial objects need to be big to have liquid water on their surfaces?

gerrit's answer has done an excellent job of showing that (1) there are a narrow set of temperatures and pressures where liquid water exists and (2) a planet has to be pretty big to have enough ...
WaterMolecule's user avatar
8 votes

Why is the Earth's magnetic field stronger than its neighbors?

I've learned that the Earth's core is hot due to decay of radioactive elements. This is unproven, non-standard geophysics. There are several arguments against this. One is that all of the long-lived ...
David Hammen's user avatar
  • 34.1k
8 votes

Which planets, nebula, and other objects can be seen using Celestron Astromaster 130EQ

Okay, so that's a 130 mm newtonian with an f/5 focal ratio. Per the manufacturer's website, it comes with two eyepieces, 10 mm and 20 mm, giving 66x and 33x magnifications respectively. First off, ...
Florin Andrei's user avatar
6 votes

Why don't we have in-between planets?

This is not a characteristic of the solar system. It is a characteristic of the definitions of the names you used. Neptune and Uranus are the bodies you believe to be missing. In fact, with the mass ...
user25972's user avatar
  • 459
5 votes
Accepted

How would water-ammonia oceans behave?

It's a big question, but kind of a favorite subject of mine, thinking about exoplanets, so I can give a ballpark answer, and I invite anyone to give correction or give a more technical answer if they ...
userLTK's user avatar
  • 24.1k
5 votes

Why don't we detect planets around OB stars and no terrestrial planets around A or early F stars?

There are a number of reasons and you will see that my answer is subtly different to HDE226868's. OBA stars are less common than FGK stars, but they are much brighter and any magnitude limited sample ...
ProfRob's user avatar
  • 156k
5 votes

How to know if an exoplanet is terrestrial?

One way of trying to do this is to plot a surface gravity versus mass plot. It's basically difficult for gas giant planets to hang onto a gaseous envelope without having a high surface gravity. This ...
ProfRob's user avatar
  • 156k
4 votes
Accepted

Are there other planetary systems where gas giants are on the inside to rocky planet orbits?

The Kepler-20 system has planets with masses in the following order, going outwards from the star: Kepler 20b: $\approx 10 M_\oplus$ Kepler 20e: $\approx M_\oplus$ Kepler 20c: $\approx 16 M_\oplus$...
Michael Seifert's user avatar
4 votes

What is the gaseous-to-rocky ratio of exoplanets?

> Do other stars have similar gaseous-to-rocky ratios among their planets? For any given stellar system, are there typically as many gaseous planets as there are rocky planets? With the current ...
Adrien Chimay's user avatar
4 votes
Accepted

Is there a clear-cut difference between rocky and gaseous planets?

The currently-detected planets do not show a clear distinction between rocky and gaseous planets. While there seem to be somewhat two ensembles, the rocky planets of Earth-size and "super-earths" and ...
planetmaker's user avatar
  • 19.9k
4 votes

Terrestrial Exoplanet Skies – I've Built a Visual Sky Chart. Is it Accurate?

I think the star,its halo and cloud can't be darker than the sky color even early M type still look blindingly bright orange-red on the sky not dim orange-red. The sky color, if heavier i think it ...
Techodom Boonyasoma's user avatar
4 votes

Terrestrial Exoplanet Skies – I've Built a Visual Sky Chart. Is it Accurate?

Your plots are incorrect in the segments of high pressure as well as of low star temperature. At high pressure the important factor becomes light extinction, which makes the sky yellowish unless there'...
Ruslan's user avatar
  • 967
4 votes
Accepted

Is the material that could have formed a "Super-earth" divided among the four terrestrial planets

I think the answer to your question lies with Jupiter, be it directly or indirectly, the gas giant is now believed to have had a large influence on the way the inner planets formed. Many planetary ...
Dean's user avatar
  • 1,489
4 votes
Accepted

How can we tell the age of a rogue planet?

At the moment there is basically only one way. That is to associate the planetary-sized object with a cluster of stars or moving group of stars of known age. That's basically it. If the planetary-...
ProfRob's user avatar
  • 156k
4 votes
Accepted

Geological/tectonic/thermal/etc. implications of Rayleigh numbers ≥ 100,000,000

(This is more an answer to this part: "If any of these are physically impossible, let me know".) As you mention volcanism, plate tectonics, mountains... I make the assumption that you ...
Jean-Marie Prival's user avatar
3 votes

Which planets, nebula, and other objects can be seen using Celestron Astromaster 130EQ

By lens in this case I presume you mean eyepiece. The magnification you get from an eyepiece is given by dividing the focal length of the mirror (650) by the focal length of the eyepiece. You did not ...
Dave's user avatar
  • 51
3 votes
Accepted

Does terrestrial planets conduct heat from near to far side?

The transfer of heat would be insignificant. Consider the Earth, the core is as hot as the surface of the sun. Some of this heat does get transferred to the surface, but it is only 0.03% of the energy ...
James K's user avatar
  • 125k
3 votes
Accepted

Do celestial bodies actually appear larger along the horizon?

No, it's an illusion. Probably the ancient one. Simple experiment you can do is, set grid on telescope, measure the angle subtended when moon is at horizon and when moon is atop. You will see angle ...
Kartik Chhajed's user avatar
3 votes

Why is the Earth's magnetic field stronger than its neighbors?

There are two main factors that control if planets have magnetic field. There must be a fluid conducting medium (liquid iron for Earth, liquid metallic hydrogen for Jupiter), and the faster the core ...
TazAstroSpacial's user avatar
2 votes
Accepted

Surface conditions of lonely (rogue) planets

Rogue planets have two formation mechanisms: Independent formation and ejection. An independently formed rogue planet would have condensed out of the nebular material by itself and not formed from a ...
Mark Olson's user avatar
  • 7,650
2 votes

Terrestrial Exoplanet Skies – I've Built a Visual Sky Chart. Is it Accurate?

(Some of) These plots are incorrect. Whilst Rayleigh scattering has a steep dependence on wavelength $(\propto \lambda^{-4})$, it cannot scatter what is not there. There is almost no blue light at all ...
ProfRob's user avatar
  • 156k
2 votes

Are there any planets or moons denser than Earth?

From another question on the stack exchange I just found out about an exoplanet with a much higher density than Earth: Kepler-131c. http://www.exoplanetkyoto.org/exohtml/Kepler-131_c.html
user30007's user avatar
  • 1,236
1 vote

Why do Venus, Earth, and Mars have tall volcanoes, but the Moon, Mercury, and Io don't?

Mercury MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) data show that most of Mercury's surface consists of lava plains. However, no volcanoes (mountains built by eruptions)...
Nilay Ghosh's user avatar
  • 4,733
1 vote

Can a terrestrial planet orbit an icy planet (or vice versa)?

Uranus and Neptune would be primary known examples of ice giants. Miranda - Uranus moon. That density suggests a composition of more than 60% water ice. Though it is far rockier than its corresponding ...
Lariliss's user avatar
  • 156
1 vote
Accepted

If a planet gained too many moons could the tidal forces of those moons rip the planet apart?

No. There are two simple arguments, each on its own alone enought to refute such thought: First way: Tidal force is the gradient of the gravitational attraction. Gravitational force goes like $F_g \...
planetmaker's user avatar
  • 19.9k

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