| Gas giant or Terrestrial | |
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Ryag Han Micrometeorite
Number of posts : 14 Age : 31 Location : Romania Registration date : 2009-11-24
| Subject: Gas giant or Terrestrial 23rd December 2009, 1:46 pm | |
| There are over 400 planets discovered so far. About what percent of them are gas giants and what percent are terrestrial planets? So far,the gas giants outnumber the terrestrials,but it is the opposite actually. | |
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Sirius_Alpha Admin
Number of posts : 4320 Location : Earth Registration date : 2008-04-06
| Subject: Re: Gas giant or Terrestrial 23rd December 2009, 8:36 pm | |
| Not counting our solar system...
28 Terrestiral + SuperEarths are known. (Though for most of them, we have only minimum masses)
Out of 415 known exoplanet candidates, that comes out to about 0.067% terrestrial, 99.933% Jovian. _________________ Caps Lock: Cruise control for 'Cool'!
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Lazarus dF star
Number of posts : 3337 Registration date : 2008-06-12
| Subject: Re: Gas giant or Terrestrial 24th December 2009, 10:22 am | |
| What do you mean by "terrestrial"?
Silicate/iron planets or worlds that aren't gas giants?
(For that matter thanks to the IAU, dwarf planets are not planets, so presumably planets that aren't giant planets are subgiant planets? Hmmm...) | |
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Ryag Han Micrometeorite
Number of posts : 14 Age : 31 Location : Romania Registration date : 2009-11-24
| Subject: Re: Gas giant or Terrestrial 24th December 2009, 11:13 am | |
| terrestrial= any planet not made primary out of gas (this dose not includes dwarf planets indeed) for that matter,we have yet to fiend dwarf planets outside this solar system. | |
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Sirius_Alpha Admin
Number of posts : 4320 Location : Earth Registration date : 2008-04-06
| Subject: Re: Gas giant or Terrestrial 24th December 2009, 12:13 pm | |
| If PSR B1257+12 D exists (which does not seem likely), it would probably be a dwarf planet. _________________ Caps Lock: Cruise control for 'Cool'!
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Ryag Han Micrometeorite
Number of posts : 14 Age : 31 Location : Romania Registration date : 2009-11-24
| Subject: Re: Gas giant or Terrestrial 24th December 2009, 1:34 pm | |
| i have doubts that we could detect a planet so small,especially when it orbits a pulsar. i have even higher doubts that a planet so small could be detected in the first place so far away without direct contact. | |
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Sirius_Alpha Admin
Number of posts : 4320 Location : Earth Registration date : 2008-04-06
| Subject: Re: Gas giant or Terrestrial 24th December 2009, 1:36 pm | |
| Detecting bodies around pulsars is actually extremely easy. Pulsars emit pulses in predictable intervals. Timing of these pulses allows the accuracy necessary to find even lunar-mass bodies (i.e. PSR B1257+12 A). _________________ Caps Lock: Cruise control for 'Cool'!
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Ryag Han Micrometeorite
Number of posts : 14 Age : 31 Location : Romania Registration date : 2009-11-24
| Subject: Re: Gas giant or Terrestrial 24th December 2009, 6:31 pm | |
| and how do you do that? i read about pulsar planets but i don't understand how they detected them! | |
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Sirius_Alpha Admin
Number of posts : 4320 Location : Earth Registration date : 2008-04-06
| Subject: Re: Gas giant or Terrestrial 24th December 2009, 7:12 pm | |
| A planet orbiting a star will cause the star to wobble around its barycenter. The star will be closer or farther from Earth, depending on which side of the barycenter the star is on. Pretty much like with radial velocity.
When the pulsar is on the far side of the barycenter, the pulses take time to cross that extra distance to reach earth, causing an apparent delay in the pulses. Over the course of the pulsars orbit about the barycenter, the pulses seem to lag behind, then speed up, then lag behind, then speed up, etc.
Monitoring these pulsar timing variations yield the presence of orbiting bodies. _________________ Caps Lock: Cruise control for 'Cool'!
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Ryag Han Micrometeorite
Number of posts : 14 Age : 31 Location : Romania Registration date : 2009-11-24
| Subject: Re: Gas giant or Terrestrial 25th December 2009, 9:56 am | |
| so its basically the same way 51 Pegasi and most exo planets were detected ? i thought pulsar planets would take more than that! | |
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Sirius_Alpha Admin
Number of posts : 4320 Location : Earth Registration date : 2008-04-06
| Subject: Re: Gas giant or Terrestrial 25th December 2009, 5:21 pm | |
| Yeah, almost the same way. The differences between the two is that pulsar timing relies in light travel delay, and radial velocity depends on the doppler shifting of absorption lines.
Both have the inclination degeneracy, and both yield only minimum masses. _________________ Caps Lock: Cruise control for 'Cool'!
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Lazarus dF star
Number of posts : 3337 Registration date : 2008-06-12
| Subject: Re: Gas giant or Terrestrial 27th December 2009, 8:04 am | |
| Key thing to note is that timing methods rely on the light travel time effects associated position of the star relative to the centre of mass, while RV uses the velocity (obviously).
Thus the inherent biases are different: timing favours worlds on wide orbits, RV favours worlds on close-in orbits (which give higher velocities). Also the form of the degeneracy is different: for RV, the representation m*sin(i) is an approximation that holds only where the planet mass is significantly less than the star mass. For timing, the quantity you get is m*sin(i). | |
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| Subject: Re: Gas giant or Terrestrial | |
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| Gas giant or Terrestrial | |
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