16 Dec 15
http://phys.org/news/2015-12-nearby-star-hosts-closest-alien.html
Now we know where the first, well maybe the second, first being AC trinary, but this one has a planet, 4 Earth mass, in the goldilocks zone, the star is a red dwarf.
The problem with red dwarf's and habitability is they make much more violent solar flares than our placid sun. So that planet better have a nice fat magnetic field like Earth or stronger. If not, it will get slammed with ions which would probably strip off the atmosphere and be a large Mars.
16 Dec 15
Originally posted by sonhouseWhat do you mean by 'the first'? It is currently the closest, but certainly not the first planet similar to earth found in the goldilocks zone. And the current shortage is mostly simply because our detection methods work much better for larger closer in planets.
Now we know where the first,
(anywhere from 2% to 25% of stars in our galaxy have at least one earth-like planet in the habitable zone.)
16 Dec 15
Originally posted by twhiteheadI meant the first interstellar probe would likely go to Alpha Centauri since it is only 4 and change light years away. Of course with more definitive information about nearby Earthlike planets, they might find something around 20 ly but definite goldilocks zone planet to be a better choice.
What do you mean by 'the first'? It is currently the closest, but certainly not the first planet similar to earth found in the goldilocks zone. And the current shortage is mostly simply because our detection methods work much better for larger closer in planets.
https://www.youtube.com/watch?v=FSHYpN4Zej8
(anywhere from 2% to 25% of stars in our galaxy have at least one earth-like planet in the habitable zone.)
I would still send probe #1 to AC, you get three stars for the price of one....
17 Dec 15
Originally posted by sonhouseI think we are still a long way from searching all nearby stars for planets, and there are a lot of stars less than 14ly away.
I meant the first interstellar probe would likely go to Alpha Centauri since it is only 4 and change light years away. Of course with more definitive information about nearby Earthlike planets, they might find something around 20 ly but definite goldilocks zone planet to be a better choice.
I would still send probe #1 to AC, you get three stars for the price of one....
17 Dec 15
3 edits
Originally posted by twhiteheadYes, what, 50 or so? But if that planet turns out to have say, an oxygen atmosphere, interest in that place as a destination will overshadow the rest unless another candidate is found closer.
I think we are still a long way from searching all nearby stars for planets, and there are a lot of stars less than 14ly away.
This page says 33 stars within 12.5 Ly, so maybe my guess is right at the 14 ly level.
http://www.atlasoftheuniverse.com/12lys.html
This one shows the number out to 20 LY: 150 stars
http://www.solstation.com/stars/s20ly.htm
I wonder how many of those stars have been analyzed for wobble or transits?
18 Dec 15
Originally posted by sonhouseI am fairly sure that we will several many closer candidates.
Yes, what, 50 or so? But if that planet turns out to have say, an oxygen atmosphere, interest in that place as a destination will overshadow the rest unless another candidate is found closer.
This one shows the number out to 20 LY: 150 stars
Assuming 20% have planets in the habitable zone that makes about 30 other candidates. Of course we won't know for sure until we look.
Keep in mind that one of the best ways of looking is through eclipses and that only works if the planets orbit is edge on from our perspective. Other methods also have preferred orientations.
18 Dec 15
Originally posted by twhiteheadWhen you say eclipses I assume you mean transits - when the brightness of the distant star dips slightly due to one of its exoplanets passing in front of it - rather than an actual eclipse which would involve the star being completely obscured by its planet and, from earth, that is basically impossible for main sequence stars as the exoplanet would pretty much have to be larger than it's star. According to the graph in the Wikipedia page [1] on radii of white dwarfs a white dwarf with 1 solar mass would have a radius of the order of 1% of the sun's current radius. The sun is 109 times the radius of the Earth [2] and will lose significant amounts of mass before becoming a white dwarf. So, if the Earth survives the sun becoming a red giant then in its white dwarf phase the Earth will completely eclipse the sun to interstellar distances.
I am fairly sure that we will several many closer candidates.
[b]This one shows the number out to 20 LY: 150 stars
Assuming 20% have planets in the habitable zone that makes about 30 other candidates. Of course we won't know for sure until we look.
Keep in mind that one of the best ways of looking is through eclipses and that only works if the planets orbit is edge on from our perspective. Other methods also have preferred orientations.[/b]
There's some speculation that a white dwarf would have a habitable zone, but there are a lot of barriers to that (see [1]). As far as potential "Earth twins", or any planets with some chance of harbouring life, are concerned I think we are looking at main-sequence stars.
[1] https://en.wikipedia.org/wiki/White_dwarf
[2] https://en.wikipedia.org/wiki/Sun
18 Dec 15
Originally posted by DeepThoughtI thought there were a lot more red dwarf's and they might tip the balance in favor of habitable planets because there are so many of them,
When you say eclipses I assume you mean transits - when the brightness of the distant star dips slightly due to one of its exoplanets passing in front of it - rather than an actual eclipse which would involve the star being completely obscured by its planet and, from earth, that is basically impossible for main sequence stars as the exoplanet would prett ...[text shortened]... e stars.
[1] https://en.wikipedia.org/wiki/White_dwarf
[2] https://en.wikipedia.org/wiki/Sun
Aren't white dwarf's a bit on the rare side?
18 Dec 15
Originally posted by sonhouseYes, red dwarfs are more numerous than white dwarfs, but they aren't exactly rare either. Red dwarfs are main sequence stars and a lot larger than white dwarfs, which are off the main sequence and believed to be ultra-dense conglomerations of degenerate carbon (or whatever element the star stopped generating heavier elements at), red dwarves are believed to burn hydrogen through the proton-proton chain. An earth sized exoplanet will not eclipse its parent star if the parent is a red dwarf, there'll just be a transit. A white dwarf on the other hand would be eclipsed.
I thought there were a lot more red dwarf's and they might tip the balance in favor of habitable planets because there are so many of them,
Aren't white dwarf's a bit on the rare side?
19 Dec 15
Originally posted by twhitehead1700 white dwarf's, didn't know there were that many in our neck of the stellar woods.
Yes. They are almost the same thing, but I did use the wrong term.
This might interest you:
http://arxiv.org/abs/1410.0052
It suggests that white dwarf eclipses (as viewed from earth) are rare.
But 1% would be 17 eclipses and half that say 8 or so but they haven't claimed to have seen even one so how can they just magically come up with that number?
Right now the number is zero%.
19 Dec 15
Originally posted by sonhouseI only read the abstract, but I'd imagine the argument is statistical. You survey 1,700 objects in a large population looking for a feature. Suppose the feature is rare and occurs with some frequency f, then the probability of finding that none of the objects sampled have the feature is (1 - f)^N. So if one sees no instances of the feature in a sample one can put an upper bound on the frequency. Suppose we require that the probability of it coming about by chance is no worse than one in a million (call this p).
1700 white dwarf's, didn't know there were that many in our neck of the stellar woods.
But 1% would be 17 eclipses and half that say 8 or so but they haven't claimed to have seen even one so how can they just magically come up with that number?
Right now the number is zero%.
p >= (1 - f )^N
ln(p) >= N ln(1 - f) ~ - N*f
Where I've used log (1 - x) = - x - x^2/2 - x^3/3 - ...
f <= - ln(p)/N ~ -ln(0.000001) / 1700 ~ 0.008 < 1%
So the maximum possible frequency is of the order of 1%. The actual frequency will be much lower than this, if we have the chance of the result being by chance as 50% then the maximum frequency comes out to 0.04%. So the upper bound they've given is pretty strict.
19 Dec 15
Originally posted by DeepThoughtI guess the real number will be sussed out when enough white dwarf's are analysed.
I only read the abstract, but I'd imagine the argument is statistical. You survey 1,700 objects in a large population looking for a feature. Suppose the feature is rare and occurs with some frequency f, then the probability of finding that none of the objects sampled have the feature is (1 - f)^N. So if one sees no instances of the feature in a sample ...[text shortened]... en the maximum frequency comes out to 0.04%. So the upper bound they've given is pretty strict.
Using that same logic, I would assume if the number became 2X, 3400 samples the min would go down to something like .02% and 6800, .01% even if no eclipses were discovered. Sooner or later they have to give up on that project i would think. The planet has to be lined up with us and be close enough to eclipse so there could be dozens already in that original sample but never eclipsing.
But getting to the white dwarf stage seems to me to be very violent, so how would a prospective planet survive to be around when the star becomes a white dwarf in the first place? That has to place a real restriction on the possibilities.
19 Dec 15
Originally posted by sonhouse'Our neck of the woods' is relative. Our galaxy has somewhere around 100 billion stars.
1700 white dwarf's, didn't know there were that many in our neck of the stellar woods.
But 1% would be 17 eclipses and half that say 8 or so but they haven't claimed to have seen even one so how can they just magically come up with that number?
The only figure I see in the summary is 0.5% and its an upper limit.
19 Dec 15
Originally posted by twhiteheadDo you think they are factoring in the possible way the orbital plane's of the planets.
'Our neck of the woods' is relative. Our galaxy has somewhere around 100 billion stars.
[b]But 1% would be 17 eclipses and half that say 8 or so but they haven't claimed to have seen even one so how can they just magically come up with that number?
The only figure I see in the summary is 0.5% and its an upper limit.[/b]