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The question Interstellar eavesdropping points out that we have been broadcasting to space for a long time, currently we are approaching a century. This means every star system in within 100 light years has had the opportunity to become aware of Earth.

There are of course technical issues in receiving and translating our broadcasts, particularity across light years, I am allowing those issues to be the subject of different questions. This question focuses on the size and membership of the broadcast sphere.

How many star systems have our broadcasts been exposed to? What will the exposure be as time goes on? (i.e. another 100 or 1,000 years). Of the exoplanets we have discovered so far how many are in our broadcast sphere?

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I believe by "solar systems" you mean "planetary systems". Do you mean confirmed planetary systems or do you want us to assume all star systems are planetary systems? You also ask about the exoplanets we have discovered so far, do you mean initial discovery or confirmed? –  called2voyage Mar 21 at 17:21
@called2voyage Assume all star systems are planetary systems; For exoplanets use initial discovery. Lack of confirmation, does not mean lack of planets. –  James Jenkins Mar 21 at 17:40
For the clarification of readers: In this post, a lone star shall be considered a star system--just like a binary system or a multiple star system of greater number. –  called2voyage Mar 21 at 17:47
It is worth mentioning that this is only going to be an estimate. Distance to a star is a hard figure to nail-down accurately, especially at the distances you're mentioning here. –  john3103 Mar 21 at 18:34
@john3103 Definitely, I think my estimate below is a good exercise in demonstrating how vast the volume we are talking about is. –  called2voyage Mar 21 at 18:36

1 Answer 1

up vote 10 down vote accepted

Within 100 light-years, there are approximately 14,600 stars. Many of these are not even known. It is difficult to determine exactly the number of star systems as opposed to stars.

113 star systems within 100 light-years are confirmed to have exoplanets in them (listed from nearest to furthest):

Alpha Centauri B     → cont'd ↓             → cont'd ↓           → cont'd ↓
Epsilon Eridani      Upsilon Andromedae     Beta Pictoris        HD 142
Gliese 674           47 Ursae Majoris       GJ 3483              HD 16417
Gliese 876           Gamma Cephei           HD 189733            HD 39194
Gliese 832           HIP 79431              HD 192263            HD 96700
82 G. Eridani        HD 136352              7 Canis Majoris      Gliese 439
Gliese 581           HD 176051 B            GJ 3634              23 Librae
Gliese 667 C         HD 38858               HD 217107            HD 30562
Fomalhaut            Gliese 317             Alpha Arietis        HD 134606
61 Virginis          Tau Boötis             HD 24496 A           HD 20367
Gliese 433           Mu Arae                HD 114783            HD 181433
Gliese 785           51 Pegasi              HD 33564             Rho Indi
Gliese 176           HD 113538              HD 97658             HD 204941
HD 102365            Gliese 777             HD 104067            HD 82943
Gliese 849           HD 128311              CFBDS 1448           HD 179949
Gliese 436           Gliese 676 A           16 Cygni B           HD 93083
Pollux               HD 7924                HD 210277            HD 125595
Gliese 649           Iota Horologii         HD 215152            HD 70642
Gliese 86            GJ 3021                HD 45184             HD 13808
54 Piscium           HD 10647               HD 4308              HD 218566
Gliese 370           14 Herculis            HD 164922            HD 52265
HIP 57050            HD 154088              HD 90156             HD 114386
Ross 458             HD 189567              94 Ceti              HD 75289
Gliese 179           Epsilon Reticuli       HIP 12961            HD 101930
55 Cancri            HD 87883               HD 1461              HD 111232
HD 69830             83 Leonis B            HIP 70849            HD 150433
HD 40307             70 Virginis            HD 134060            HD 102195
HD 147513            Pi Mensae              HD 156668            HD 50554
GJ 1214              HD 154345              HD 60532             Kappa Coronae Borealis

Within just 50 light years, 93 exoplanets have been discovered (listed from nearest to furthest):

Alpha Centauri Bb    → cont'd ↓            → cont'd ↓           → cont'd ↓ 
Luhman 16 Ab         Gliese 581 c           Gliese 649 c         HD 40307 f
Epsilon Eridani b    Gliese 581 d           Gliese 649 b         HD 40307 g
Epsilon Eridani d    Gliese 667 Cb          Pollux b             Upsilon Andromedae b
Epsilon Eridani c    Gliese 667 Cc          Gliese 86 b          Upsilon Andromedae c
Epsilon Indi b       Gliese 667 Cf          HIP 57050 b          Upsilon Andromedae d
Tau Ceti b           Gliese 667 Ce          54 Piscium Ac        Upsilon Andromedae e
Tau Ceti c           Gliese 667 Cd          54 Piscium Ab        47 Ursae Majoris b
Tau Ceti d           Gliese 667 Cg          Gliese 370 b         47 Ursae Majoris c
Tau Ceti e           Fomalhaut b            Gliese 179 b         47 Ursae Majoris d
Tau Ceti f           61 Virginis b          55 Cancri e          Gamma Cephei Ab
Teegarden's star b   61 Virginis c          55 Cancri b          HIP 79431 b
Gliese 674 b         61 Virginis d          55 Cancri c          HD 136352 b
Gliese 876 d         Gliese 785 b           55 Cancri f          HD 136352 c
Gliese 876 c         Gliese 785 c           55 Cancri d          HD 136352 d
Gliese 876 b         Gliese 433 b           HD 69830 b           HD 176051 Bb
Gliese 876 e         Gliese 433 c           HD 69830 c           Gliese 163 b
Gliese 832 b         Gliese 849 b           HD 69830 d           Gliese 163 e
VB 10 b              Gliese 849 c           HD 147513 b          Gliese 163 c
82 G. Eridani b      HD 102365 b            GJ 1214 b            Gliese 163 f
82 G. Eridani c      Gliese 176 b           HD 40307 b           Gliese 163 d
82 G. Eridani c      Gliese 436 c           HD 40307 c           Gliese 317 b
Gliese 581 e         Gliese 436 b           HD 40307 d           Gliese 317 c
Gliese 581 b         Gliese 436 d           HD 40307 e           HD 38858 b

Based on the average number of confirmed exoplanets per star system, there are about 140 exoplanets total within 100 light-years in confirmed planetary systems. I won't list the rest of them here.

If we use the same average across our estimated number of stars, we arrive at about 17,500 exoplanets in 100 light-years.

There are also some rogue planets within 100 light-years which aren't even considered in any of these numbers.

As you can see, in another 100-1000 years, there will be practically countless planets in our sphere of broadcast influence.

Even more interesting, eight out of the 93 discovered exoplanets within 50 light-years are potentially habitable. If this same ratio extended out to our 17,500 estimate, that would mean about 1,500 potentially habitable planets within 100 light-years.


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Wikipedia may not be the best of sources in many cases, but the sheer volume of aggregate data that would have to be compiled to duplicate Wikipedia's efforts in this case make Wikipedia a much more practical solution. Also, I think laysources do pretty well at capturing exoplanet discoveries. –  called2voyage Mar 21 at 18:41
WOW, I had no idea the number would be that high. If 1 planet in every 10,000 systems harbors intelligent life.... It boggles the mind to think about it.... –  James Jenkins Mar 21 at 18:45
@JamesJenkins Check out my addition about potentially habitable planets--even more mind-boggling. –  called2voyage Mar 21 at 18:58
@TildalWave Thanks, that makes this answer look prettier. –  called2voyage Mar 21 at 19:11

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