 | | | Subject: Planets around A type stars.
Posted Mar 25, 2001 by Professor Sarah Bellum
| | Posting
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 | | I'm writeing a book about a planet round an A type star and have run into a small problem. I've put question into the H2G2 AS and into the H2G2 AS conversation forum but I haven't had much response at the moment so I thought I put a journel entery here. Any assistance is greatly appriciated (spelling?) and will be rewarded as long as a contact address is left.
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This is what have been discussed so far. Any comments on any part that is helpful will be great.
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I'm writing a book about a planet around an A type star like Sirius. However for the planet to be round the life zone of this star it has to be 474,208,814.8 miles from the star. This is because Sirius is a suitable A type star to model my A type star on and it's 26 brighter, hotter and bigger than the sun and that means that the planet has to be 5.099019514 times further than it would be from the Sun (93,000,000). This means that the length of a year on this planet would be quite long. If the planet were four time further away the year would be eight years with seasons being two years long. However this creates a problem in the book because I ideally need the year to be a similar length to an Earth year. I know if I'd chosen a G type
star there wouldn't have been a problem.
I was thinking of having the planet move round the star faster that would mean if it was moving fast enough the year could be a similar length but the speed a planet moves round a star relative to it's distance from the star is a universal constant like the speed of light. This also wouldn't be possible since the further a planet is from a star the slower it moves. If it moved faster then there is a chance of it escaping the star gravity a spinning of into space as a rouge planet like Pluto will be in about 9,000 years. This means I need to think of other ideas and see if they will work. At the moment the only thing I managed to come up with is that the star is a binary
star with one or more companion stars and that with the orbit it could take round the other stars the year could be longer but it could have seasons lasting three months that run in the order of Winter, Spring, Summer, Autumn and follows this pattern a sure as the Earth does. It would means that there would be several Winters a year and the same for the other seasons but this wouldn't be a problem.
I was wondering if you tell me what you think of that idea an suggest any others that would have same solution.
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I got this reply.
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Why not slow their perception of time down, so that the inhabitants
experience life as if a rotation around Sirius were one year, even
though it is actually 8 years of Earth time? This is similar in some
ways to the perceived notion that insects experience the passage of
time differently to humans, manifested in our difficulty at swatting
or catching flies...
Also Ian M Banks proposed the nice idea of an Orbital, which is an
artificial environment that completely rings a star at the right
distance, and which revolves at a rate that gives equal night and
day. Given sufficient technology and intelligence of the native
population, the space environment would not need to be natural, and
could perhaps be customised perfectly to their needs.
CR
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This was my reply.
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Thanks for the suggestion. I had thought of that and that would have been okay apart from the fact that I want a person from Earth to visit the planet however I suppose his perception of time could be slowed down as well. As with the suggestion of the orbital, the technology for that is much to advanced for the level opf technology that the people are as since they are still hunter's and gatherers.
However I may use the first idea so thanks for it. I also thought that maybe if there is a binary system them the planet may be fried but if there was a close orbit to a White Dwarf like Sirius B then that may solve the problem or the planet could be 93,000,000 miles from the star and have a thick dusk cloud between it and the planet that absobes much of the suns heat, light and radiation. What do you think about those ideas? Thanks again.
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I got this reply.
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Humans evolved with a year that was shorter than ours, 22 or 23 hours I think (proved by people being put in a cave and reverting to a 22 hour day) so there is no reason at all for why the new planet needs to have an Earth length day or year. As live begins to evolve the length of day will naturally be programed into the life system so it's natural day will be 35 hours and it's year 400 days etc. I
agree that there needs to be the correct distance range for the solar radiation to be safe but enough to allow life, for us being 93 million miles
>or the planet could be 93,000,000 miles from the star and
>have a thick dusk cloud between it and the planet that
>absobes much of the suns heat, light and radiation.
Don't really like this suggestion, why would there be this dust cloud? If it were a failed planet like our asteroid belt then there would be large rocks and not dust, and this wouldn't absorb nearly enough light. If it is dust then this would be enveloped either into itself to creat said astroids or collapse towards the star. I'm guessing the idea of 93 M miles is just to give the earth type days and years, yes? It shouldn't need the same conditions as Earth
as they wont be earth people who evolved there, they probably won't have elbows for a start. If a human goes there then were going to have to cope with the shock of living with aliens so never mind the longer days (the aliens will also have to cope with us!).
>year could be longer but it could have seasons
>lasting three months that run in the order of Winter,
>Spring, Summer, Autumn and follows this pattern a sure as
>the Earth does. It would means that there would be several
>Winters a year and the same for the other seasons but this
>wouldn't be a problem.
This couldn't work, I don't think as the planet would need a slight tit and the axis of rotation would need to progress round a number of times each year.
If you /really/ want to have an Earth like environmet I guess you could have a highly elliptical orbit, which would mean that the close approaches would constitute 2 summers and an axis tilt POINTING PARRALELL TO THE CLOSE APPROACH PATH so there would be 2 other summers at the extreams where the tilt caused the summer like on Earth. I guess this has problems as with an elliptical orbit of such a degree the loci of Sirrus would be close to one apex, so the plannet would wave an extreamly short hot period and a long cool period. Get a point where the close approaches gives a summer at the equinoxes and then a large tilt gives a summer again this would give 2 sumemrs per year, for each hemisphere.
OR:
have a binary planet system, with quite a long period, this would mean that there could be a summer every binary orbit, for both planets and there could be enough orbits per long year as you see fit.
OR: (and this is an od one)
So we have a distant plannet in a region to allow life, but with a long year. OK, so if the axis of rotation is somehow in line with it's orbit path... no that won't give a nice length day. Hmm...
Hope that makes some sence.
Yeliab, 32373
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This was my reply.
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The length of day with my problem it not an issue since it isn't related to the planet's distance from the star. However the problem isn't about the visitor noticing anything strange about the year either. Also there's no problem with him seeing aliens. He's on another planet so he has to prepared for that and he may have already seen other aliens (if they're anything like you get in Star Trek they wont be a problem anyway).
To do with the idea of the dust cloud, that was to have Earth length years that was why I suggested 93,000,000 miles. However I was reading a book about terraforming Venus and a dust cloud was suggested to combat Venus being only 67,000,000 miles from the Sun (therefore if it can work for Venus it should work for me, shouldn't it?)
I like the idea of the binary system you mentioned.
>have a binary planet system, with quite a long period,
>this would mean that there could be a summer every binary
>orbit, for both planets and there could be enough orbits
>per long year as you see fit.
If you could tell me more about it that would be great.
I hope you don't think I'm criticizing what you said. I'm just mentioning my thoughts on it. If you can think of any more ideas that would be great but I'm interested on the binary idea and it may work.
The real thing I needs if four seasons in the order of Winter, Spring, Summer and Autumn that last about three Earth months even if the sequence is repeated several times a year. I really do need a solution because this is to do with the central theme of the book.
Any suggestion you have would be great. I may have to have a G type star but I'd like to leave that as a last option. Thanks for any help.
Richard.
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If anyone can help me from this point on. Or has any other ideas please let me know. Thanks.
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