95 votes
Accepted

Why is Mars cold?

Firstly, Mars has a mean distance from the Sun of 1.524 AU, so by the inverse square law the energy it gets from the Sun is about 40% of what the Earth gets. But the main reason that Mars is so cold ...
PM 2Ring's user avatar
  • 14.4k
60 votes
Accepted

Is oxygen really the most abundant element on the surface of the Moon?

Yes, that's correct; it's also true for the Earth's crust. The reason is that "rocks" are typically made up of components containing combinations of silicon or one or more metals (e.g., ...
Peter Erwin's user avatar
  • 16.7k
26 votes

Why is Mars cold?

I'm just going to expand and deepen on what the other answers already said. In the following I contrast the atmospheric transmission ($T$) and absorption ($A$, which is $A=1-T$) of Mars and Earth. ...
AtmosphericPrisonEscape's user avatar
23 votes

Is oxygen really the most abundant element on the surface of the Moon?

Note this fact is unsurprising. Oxygen is the third most abundant element in the solar system (by mass and by number) after hydrogen and helium. Planets/moons with the size and escape velocities of ...
ProfRob's user avatar
  • 152k
16 votes

Why is Mars cold?

Mars does have a greenhouse effect, only somewhat weaker than Earth's. Mars' atmosphere is very dilute, with a with a surface pressure only 0.6% of Earth's. So even if 95% of it is CO2, that's not a ...
pela's user avatar
  • 38.2k
15 votes
Accepted

Are these parallel lines I'm seeing in this image a real pattern on the Moon?

They are not real. The images used in the animation use a mosaic of photographs taken by an orbiting satellite, the Clementine orbiter. This satellite has a polar orbit, and so returns images in ...
James K's user avatar
  • 121k
12 votes
Accepted

Strange square-like formation on Mars

I looked at the image and annotated it based on what it most likely is: In black is the formation itself. In blue is a depression underneath it. In grey is part of the boundary of what you believed ...
HDE 226868's user avatar
  • 36.6k
5 votes
Accepted

What are the dark spots in the "face of Mars" picture?

What are the dark spots in the “face of Mars” picture? They are called "bit errors" in the NASA JPL image catalog for PIA01141. The explanation seems a bit handy-wavy to me; so I think we'...
uhoh's user avatar
  • 31.1k
5 votes

Longest line of sight on Mars

Tharsis Tholus. Is one of the steepest shield volcanos with average flank slope of 10 degrees (followed by Ceraunius Tholus which is 10 percent less steep (average flank slope is 9 degrees) than the ...
Kavin Ishwaran's user avatar
5 votes

Are all impact craters circular?

There are elongated craters from grazing impacts, and these can sometimes get rather odd shapes like Schiller on the Moon and Orcus Patera on Mars (the later is a bit contested, it might have formed ...
Anders Sandberg's user avatar
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
  • 24k
4 votes

What might the surface of Jupiter's rocky core look like?

There's not going to be any surface features. First of all, let's assume you could look through a thick soup of metallic hydrogen. This material has densities starting at that of water, going to ...
AtmosphericPrisonEscape's user avatar
4 votes

What colours can rocky planets (or moons) have

I'll begin by saying that for exoplanets, the answer to your question is an active area of research, and currently there are no observational constraints on what rocky exoplanets would look like to ...
Thomas's user avatar
  • 196
3 votes

Why do rocks on other solar system bodies that have an atmosphere seem to be flat?

I don't know what you're talking about. The only one that seems to have mostly flat rocks is Venus. At least based on what little photographs we have from the surface of Venus. Mars Venus
Katie Katie's user avatar
2 votes

Angles of sunrise and sunset viewed from a surface anyway oriented

In other words, at what hour angle $h$ is the Sun's azimuth $\mathtt{Az}_s$ at a right angle to the wall's normal vector (84$^\circ$ or 264$^\circ$)? Using these formulas, which I've checked, from ...
Mike G's user avatar
  • 18.7k
2 votes

Could an impact have resurfaced Venus 300 million years ago?

What about the possibility that Venus (and its former moon) went through a much more rapid evolution then occurs normally? Typically a planet-moon system will undergo the following sequence of events: ...
David F's user avatar
  • 21
2 votes
Accepted

How easy is it to mine water on Ceres?

Comments converted to community wiki Ceres' density (2.08 g/cc) suggests it has abundant water/ice below its presumably mostly dry surface. That and the shiny spot (salts left after subsurface water ...
2 votes

What might the surface of Jupiter's rocky core look like?

An answer to your question is not known at this time. From the Internal Structure section of Jupiter's Wikipedia page, Jupiter is thought to consist of a dense core with a mixture of elements, a ...
Cody's user avatar
  • 1,170
2 votes

At what point does an astronomical body's surface stop being gas giant-like and start being sun-like?

A "star" has significant hydrogen fusion occuring in its core. This energy prevents collapse and allows the star to reach a stable position state. A Brown dwarf does not have significant ...
James K's user avatar
  • 121k
2 votes
Accepted

When were the spiders first observed on Mars?

I have the impression these were first observed in images taken by the Mars Orbiter Camera (MOC) of the Mars Global Surveyor, probably sometime between 1997 (arrival at Mars) and 1999 (when the main ...
Peter Erwin's user avatar
  • 16.7k
1 vote

How to calculate the day/permanently dark/night temperatures of different surfaces for exoplanets?

You Question includes an incorrect assumption. There are no celestial objects that do not rotate faster or slower. Celestial objects are formed when smaller objects collide at speed slow enough that ...
M. A. Golding's user avatar
1 vote

How to calculate the day/permanently dark/night temperatures of different surfaces for exoplanets?

For bodies without surface temperature you can guestimate the average temperature by considering the incoming energy and it being re-radiated into space via its complete surface (not only the surface ...
planetmaker's user avatar
  • 19.4k
1 vote

Are all impact craters circular?

Impact craters are not always circular. They vary based on the angle of incidence. One example is the Wetumpka crater. There is also research on Asymmetric craters on Vesta: Impact on sloping surfaces ...
bandybabboon's user avatar
  • 4,252
1 vote
Accepted

How do we get the angular size of a crater without lens?

Most lunar craters are too small to resolve with the naked eye; I would measure a published photograph. A crater near the limb appears as an ellipse whose minor axis is foreshortened but whose major ...
Mike G's user avatar
  • 18.7k
1 vote

What type of telescope can show cliffs on the moon surface from a city location?

The main things to look for are: Decent optics (nearly anything except those with plastic lenses). A steady mount that points where you want to, and moves smoothly. An altitude-azimuth mount is fine ...
TazAstroSpacial's user avatar
1 vote

What will happen when landing on Jupiter?

It's worth noting that a probe entering Jupiter's atmosphere is NOT hypothetical: The orbiter carried a small probe that became the first to sample the atmosphere of a gas planet. The probe measured ...
giardia's user avatar
  • 2,088

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