# Tag Info

14

Just because a planet is in the "Habitable zone" doesn't mean it is habitable. A planet is said to be in the habitable zone if it is possible for liquid water to exist on the surface. A planet may be in the habitable zone, and yet not be habitable if, for instance, it's atmospheric pressure is too low (like Mars) or too high (like Venus), both of which are ...

9

From your first link, the definition is: "The circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.[1][2][3][4][5] The bounds of the CHZ are based on Earth's position in the Solar System and the amount of ...

8

It's a pretty straight forward calculation of 3 factors. Distance from the sun, apparent size and albedo. I'm going to compare Jupiter to our full moon, since we're all familiar with that. Jupiter averages between 4.95 and 5.45 AU from the sun. That puts it, in comparison with our full moon (about 1.02 AU on average), that means individual square ...

6

In the real universe, stars that go supernova are very large stars that are short lived, or, they could be white dwarfs that accrue matter and overcome the Chandrasekhar limit. Very large stars, 8 solar masses or more - about the minimum size for a star that goes supernova, the life span of that star is too short for a planet to form, cool and develop life....

5

The Kepler space telescope had a field of view along the so called Orion arm, or spur, of the galaxy. The same structure which we ourselves are inside. It basically looks along a line where the star density is the greatest within the distance that it could detect transiting planets. Less than 3% of the galactic diameter, I think. Note that the illustration ...

5

First it will be important to consider the term 'relativistic speed'. If by that you mean something like 0.1c, it will only change the colour of the stars as you mentioned in the bounty description. However, if it means something with higher Lorentz Gammas (like 0.9c or 0.99c), all other relativistic effects come into play. There's relativistic beaming and ...

5

It's actually the opposite. Venus, Mars and I'll include the Earth as well, are likely getting more solar energy per square meter, not less, over time, even as they slowly move away from the sun. 1.5 cm per year, from the Rob Jeffries' answer to the 2nd question you linked is too slow to make much difference. That's 1 km every 66,000 years and about 70,...

5

Yes and yes. Transit detection is only effective for that (small) fraction of planets that pass between the star and our line of sight. Most planets will go undetected by this method. Also correct. The detection of multiple transits is required to find planets. Even then the dips can be caused by other things (e.g. grazing eclipse binary star systems). This ...

4

This is based purely on Stellarium's simulation, so may not be accurate. From Europa, full Jupiter has a magnitude of almost -17 and an angular diameter of 12 degrees: This makes it about 56 times brighter and 24 times larger (in diameter, not area-- it's about 600 times larger in area) than our full moon (magnitude -12.3), more than good enough for ...

4

My kneejerk reaction is that your only option is to remove a chunk of mass from the outer part of the Sun. The Sun will respond (on a Kelvin-Helmholtz timescale), by contracting and becoming less luminous because the core temperature is lower in a less massive star. This will extend its main sequence lifetime, because only the central parts of the star are ...

4

The possibility of exploring exoplanets is so remote it is not a factor. We are interested in Earth-like planets as there is only one type of planet that we know can support life, and that is the Earth-like ones. We are interested in Earth-like planets as they may provide a habitat for alien life. The question of "does extra-terrestial life exist" is of ...

3

Assume you have a spherical blackbody. The solar flux at the radius of the Earth is given to a good approximation by $L/4\pi d^2$, where $d = 1$ au. This is $f=1367.5$ W/m$^2$ (though note the distance between the Earth and the Sun has an average of 1 au). If it is a blackbody sphere it absorbs all radiation incident upon it. Assuming this is just the ...

3

I agree with David Hammen. Hyperphysics is mostly a very good site but they dropped the ball on that page IMHO. Hope you don't mind a partially speculative answer, but here goes: Why does it matter if there are some areas of a planet with extreme temperatures, as long as there are other spots on the planet that are not extreme? It shouldn't ...

3

For those who haven't seen it: Some human explorers land on a planet orbiting a black hole. The black hole is surrounded by a large accretion disk. The planet orbits at a distance such that going any closer to the black hole will mean that your odds of getting out are slim; it's also composed of water. Finally, time dilation from the black hole means that ...

3

If you take a slowly rotating asteroid with a large basin of trapped water, some solved minerals, and may be some gases, close to the asteroid's surface, to get an environment similar to a black smoker by the heat of the sun, I wouldn't call it totally impossible. The formation of such an asteroid is close to the limits of my imagination, might be as a ...

3

I'll be honest. I looked up Galactic Habitable Zone on Wikipedia. The idea was introduced in 1986 and expanded upon in the book "Rare Earth" by Brownlee and Ward. Essentially the idea is that in the bulge there is too much activity (supernovae, etc.) and in the halo of the galaxy there is not enough heavy elements (carbon, etc.) for life to exist. This was ...

3

Of the gas giants, the number of "hot Jupiters" is about the same as the number of "hot Neptunes." A little under 9% of known gas giants are in the habitable zones. An article by John Wenz has the discoveries thus far collated into a chart: The claim, "most of them are "Hot Jupiters", orbiting so close to their stars that the heat causes them to swell up ...

3

I was curious about the figure given in Mick's answer (~9%), so I did some data-crunching of my own. I looked at the NASA Exoplanet Archive, in particular the table of confirmed planets. I was interested in four parameters: $a$, the planet's semi-major axis $M\sin i$, the planet's minimum mass $T$, the temperature of the star $R$, the radius of the star ...

3

To your first question... from this paper, we can see that there are 3 types of atmospheric escape: Jeans Escape: Temperature and escape velocity factors determine the gasses and the amount that's lost. Using the chart provided in the comments, and moving Titan along the x-axis to around below Earth's position, we can see Titan will lose most gasses except ...

3

1st Q: It's been said that an astronomical body can keep it's atmosphere if the escape velocity is more than six times the average speed of the molecules. Gravity isn't the only factor that permits an object to retain an atmosphere. The Moon has gravity yet is virtually a vacuum, Mars has a surface pressure less than 1% of Earth and continues to lose its ...

3

Adding to userLTK's excellent answer, it is possible to have a triple star system where a sun-like star orbits a close binary where one member is a white dwarf and the other becomes a red giant that then triggers a supernova by mass transfer. The sun-like star can orbit suitably far away from the binary to make X-rays from the white dwarf and heating from ...

2

Here's a blog post with an exploration of how many Earth-like planets you could pack into the habitable zone.

2

This question not only makes you think about the temperature, pressure but also the impact of gravity. Not moving away from topic, I must say that the region you are saying about is quite large in the view of metrics but quite short again if we really sense gravity. The distance of a planet from the sun is maintained by gravity, but we must also not forget ...

2

Note: I am self-answering my own question in hope that someone post another answer that beats this one. Earth is near the inner edge of the Sun's habitable zone. And since the Sun is expected to grow and increase it luminance, Earth might be unhihabitable for any life somewhere between 1 or 3 billion years in the future. So, a planet that have longer time ...

2

This is a case where the Southern US phrase might could is appropriate. Intelligent life1 might could arise only on terrestrial planets with just the right axial tilt. Then again, intelligent life might could arise on all kinds of other planets as well. Extrapolating from a sample size of one is always a risky endeavor. The hyperphysics page referenced in ...

2

Most galaxies have enough dust to hide their cores from investigation in visible light. But the jet from an AGN is composed of large amounts of relativistic particles, and is easily powerful enough to clear any dust out of its path. We see in M87 a jet punch 5000 light years from an active nucleus. The dust that hides Sagittarius A* is not localised around ...

2

As you suggest, it might be possible for a habitable corridor to exist along the stationary terminator. But there are ideas around for more than that. The planet might be exposed to tidal forces the volcanism of which warms the far side. It might have a thick stormy ocean or atmosphere which evens out the surface temperature (All but the smallest planets ...

2

The number you need is the bolometric luminosity. This tells you how many Watts per square metre are incident upon the planet. That is true for the Sun and it is true for GL 570. Beyond that, you will need to make assumptions about an atmosphere and an albedo if you are trying to calculate a realistic habitable zone. If you just assume the planet is like ...

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