42 votes
Accepted

Why are most discovered exoplanets heavier than Earth?

There are a number of methods of detecting exoplanets, but all of them favour detection of larger planets over smaller ones, albeit for slightly different definitions of large: Radial velocity ...
Steve Linton's user avatar
  • 10.3k
41 votes
Accepted

Can a tectonically inactive planet retain a long-term atmosphere?

Yes, a tectonically inactive planet can retain a long-term atmosphere. You make the connection that a lack of plate tectonics on a planet indicates a "dead" core and thus said planet has no ...
zephyr's user avatar
  • 15k
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
  • 121k
30 votes
Accepted

Exoplanet dip in transit light curve when the planet passes behind the star

Just before the planet goes behind the star, we see the light directly from the star as well as the light reflected from the planet's surface. When the planet is behind the star, we no longer see the ...
Connor Garcia's user avatar
  • 16.3k
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
  • 2,033
13 votes
Accepted

How is an exoplanet characterised as "Earth-Like"?

There is no unique definition of Earth-like and it depends on what characteristics are important in the context of discussion. The most simple one is to just compare radii and masses. That is ...
planetmaker's user avatar
  • 19.4k
11 votes

What if we are looking for the wrong signs of life on other planets?

What if we are looking for the wrong signs of life on other planets? Are there any fields of astronomy that look beyond the "near-Earth" life comparisons and look for life in other (...
userLTK's user avatar
  • 24k
9 votes
Accepted

Are there any common characteristics of habitable planets?

I think I will answer your question from two vantage points. Firstly, what do we have to measure about a new exoplanet to consider it potentially habitable? Keep in mind that in detecting these 1000 ...
zephyr's user avatar
  • 15k
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

Is there another habitable planet in our galaxy?

what'll happen when we destroy our planet or it becomes none-habitual for human life? Very pessimistic idea. We lack the technology to tell if a planet orbiting another star could be lived on by ...
StephenG - Help Ukraine's user avatar
8 votes
Accepted

Why Venus evolved so differently from Earth?

Venus orbits the Sun at 0.723332 AU. As solar radiation follows an inverse square law, the intensity of the Sun at the top of Venus's atmosphere is almost twice that for the Earth ($\frac1{0.723332}^...
David Hammen's user avatar
6 votes
Accepted

Could a moon orbit an Earth size planet in such a way as to create a solar eclipse lasting for several weeks from start to finish?

Short answer: No, it could not. The moon already has little enough mass relative to the earth so that its orbital period is not much shorter than a satellite with negligible mass. So, any object at ...
Mark Foskey's user avatar
  • 3,916
6 votes

How many quakes have been detected by InSight?

This is the latest catalogue from seismic events recorded by InSight: Mars Seismic Catalogue, InSight Mission; V5 2021-01-04. This report includes seismic events up to October 12, 2020. These ...
Wilhelmroentgen's user avatar
5 votes
Accepted

Could a binary system of two planets with oceans reflect each other?

The surface of the ocean isn't smooth, so there would not an image formed. Look at how the Earth's oceans reflect the sun. (credit: NASA/ESA) Obviously the sun is reflected by the ocean, but the ...
James K's user avatar
  • 121k
5 votes

What if we are looking for the wrong signs of life on other planets?

We only have a sample of 1 - the Earth - for analysis or proposition of potential life-compatible conditions on other planets. Only carbon-based life can exist in this universe. Boron and Silicon are ...
QEDlin Saltum's user avatar
5 votes

Calculate planet's surface temperature by distance from star

Neat and tidy calculations for this aren't possible. The math behind effective temperature of a planet can be found here and that's a straight forward calculation where you can input distance, solar ...
userLTK's user avatar
  • 24k
5 votes
Accepted

Wondering about a horseshoe orbit

A basic orbital rule is Kepler's third law, which states that the closer the moon is to the planet, the quicker is its orbit. A body that is close to the Earth will move in orbit faster than one which ...
James K's user avatar
  • 121k
5 votes
Accepted

Trisolar syzygy and it's effects on the planet

Is it just for the spoiler? My guess is that the 3 suns aligned create a sufficient gravity field for the outermost parts - less well attached - of the planet (atmosphere, people, buildings) to be ...
J. Chomel's user avatar
  • 1,452
5 votes
Accepted

Can life on earth be supported by only a Red Dwarf star or a White Dwarf(state still hot not cooled enough yet)?(Provided it is near to the star)

Certainly a red-dwarf star can have enough energy for a planet around it to be in the goldilocks zone. There are some difficulties with red-dwarf stars and Earth like planets. The planet would ...
userLTK's user avatar
  • 24k
5 votes

Is there a far away probe that has recorded the light spectrum from Earth as if it were an exoplanet?

TL;DR: (1) we don't need to go very far to measure the spectrum of Earth's reflected light: a satellite in orbit around the Earth could easily do that; however, (2) detecting the reflected light of an ...
Chappo Hasn't Forgotten's user avatar
5 votes

Is there a far away probe that has recorded the light spectrum from Earth as if it were an exoplanet?

As an addendum to Chappo's very good answer, I'll note that people have indeed used satellite and spacecraft observations of the Earth to estimate what a similar exoplanet might look like (assuming we ...
Peter Erwin's user avatar
  • 16.7k
5 votes

Can a planet exist with the same mass as the earth, but have a different diameter?

Yes, a planet can exist with the same mass as Earth, but have a different diameter - if it has a different density. The lower the density, the larger will be the diameter. In terms of an exact formula,...
The_Sympathizer's user avatar
5 votes

For colonization purposes, what is so good about Titan?

There is nowhere in the solar system except for parts of Earth where humans have any hope of surviving without heavy technological support. There is next to no free oxygen anywhere, nowhere has a ...
Steve Linton's user avatar
  • 10.3k
5 votes
Accepted

Crust thick enough to prevent volcanos

It depends on the definition of Earth-like planet. In terms of size, density and gravity Venus is very Earth-like, but in terms of atmospheric and surface conditions and its axis of rotation, and ...
Fred's user avatar
  • 2,169
4 votes

What is the smallest possible planet with same sea level atmospheric pressure as Earth?

In the textbook treatment the pressure decreases exponentially with height as $P(z)=P(0)\exp(-z/H)$ where $H=kT/mg$ is the scale height of the atmosphere. This assumes that the gravity $g$ is constant ...
Anders Sandberg's user avatar
4 votes

Could Planet Nine be a tiny black hole or an exotic compact object such that it escaped detection? What would its bounds be?

I think the answer is included in my answer to Could a black hole pass quiescently through the Oort cloud? The mini black hole would be detected via its accretion from the interplanetary medium, ...
ProfRob's user avatar
  • 152k
4 votes
Accepted

What types of star do we know are hostile to life (like ours)?

We so far have a sample size of 1. We know that a largish star, with a surface temperature at about 4.5 billion years of 5800K can be stable enough to support life for long enough for intelligence to ...
James K's user avatar
  • 121k
4 votes

Trisolar syzygy and it's effects on the planet

In addition to the answer above, passing inside a stars Roche limit would likely cook the planet for anything but the smallest, coldest stars or white dwarfs. Evaporating the planet's oceans and ...
userLTK's user avatar
  • 24k
4 votes

horseshoe orbits

A horseshoe orbit requires a central body (eg a star) a large orbiting body (a planet) and a small co-orbiting body (an asteroid). If the asteroid has too much mass. The orbit "works" because the ...
James K's user avatar
  • 121k
4 votes

Is there another habitable planet in our galaxy?

Is there another habitable planet in our galaxy? What constitutes habitable? Oceans, lakes and rivers, soil to grow plants, oxygen to breath, a magnetic field to help maintain the atmosphere, plate ...
userLTK's user avatar
  • 24k

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