A year in a day

[[Tycho?]]

http://news.bbc.co.uk/2/hi/science/nature/5407038.stm

 

It uncovered the existence of 16 planets in the category of close orbiters, taking between 0.4 and 3.2 days to go around their respective stars.

 

Yikes! Those planets must be incredibly close to their stars to be able to make such a quick orbit.

 

Well I just tossed out a quick calculation, with a period of 1 day, a planet the mass of 10^27kg (around that of jupiter) around a star of mass 10^30 (around that of the sun) I get a semi major axis of just over 2 million km (!) and an orbital velocity of 27 000m/s (!!).

 

I have to think that planets in such a position much have fairly short life spans, as massive as they are they must be getting a ton of their mass blown off by solar radiation. Or maybe not, what do I know.

[ecoli]

That's insane! Imagine the seasons only being a couple of hours long?

[Martin]

;305635']http://news.bbc.co.uk/2/hi/science/nature/5407038.stm

 

 

 

Yikes! Those planets must be incredibly close to their stars to be able to make such a quick orbit.

 

Well I just tossed out a quick calculation' date=' with a period of 1 day, a planet the mass of 10^27kg (around that of jupiter) around a star of mass 10^30 (around that of the sun) I get a semi major axis of just over 2 million km (!) and an orbital velocity of 27 000m/s (!!).

 

I have to think that planets in such a position much have fairly short life spans, as massive as they are they must be getting a ton of their mass blown off by solar radiation. Or maybe not, what do I know.[/quote']

 

you know a lot.

 

basically right---stuff would be being boiled off into space, blown away by the solar wind, blown by the simple light pressure. It would be a mess.

 

I did a rough back of envelope check of your 2+ million km semimajor axis and it seemed right

 

I was approximating a day to be 10**5 seconds:embarass: so my answer came out larger than yours but still less than 3 million km.

 

IIRC the radius of the sun is about 0.7 million km

 

the "sun" would fill a pretty large angle in the sky, like very roughly around 40 or 50 degrees.

that's a very crude estimate, but anyway it would look big