<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Hi, Approximately a year ago my son and I, came across a story with regards to a newly discovered planet. This planet's name began with an "A" and was said to be HUGE and gaseous. If memory serves me correctly, it was pictured as reddish yellow. It was said to be, (again if memory serves), 5xs' larger than Jupiter. My son seemed to think that it was related to the Betelgeuse Constellation so we researched that topic extensively and came up empty. Maybe the connection was possibly the fact that both were discovered at about the same time? If anybody has any information about this mysterious "A" planet that we cannot find at all, I would be so grateful as he is very insistent that we add this planet to his science project. The pc we had at the time we originally read the story and saved pictures of this mysterious planet has since died, otherwise I would not be in this predicament.I will thank any or all who have any information with regards to this, as I am dumbfounded as to why we cannot find any information about this planet anymore. Thank you Donna aka Jeepster99 <br /> Posted by Jeepster99</DIV></p><p>You may be thinking of AB Pictoris
http://www.eso.org/public/outreach/press-rel/pr-2005/pr-12-05.html which is a gas giant several times the mass of jupiter that was detected by direct imaging. The mass for this planet is rather uncertain since it hasn't been directly measured, the only thing that is directly measured for this planet is its flux through several filters and its spectral type. Using these observables it's more or less straightforward to determine the planet's luminosity (assuming a distance which you can estimate based on the observed brightness of the star) and temperature. The mass is inferred from untested models that predict the luminosity/temperature of a planet as a function of its mass and age (again estimated from the star). </p><p>The extra-solar planets that we know the most about are the transiting planets (you can find a list of them in the catalog which starsinmyeyes mentioned:
http://exoplanet.eu/catalog-transit.php ). We can directly measure the masses and radii of these planets, it is also possible to infer chemical compositions for these planets and even make rough surface maps of the planets (see
http://www.spitzer.caltech.edu/Media/releases/ssc2007-09/ssc2007-09a.shtml ). In particular, the planets HD 189733 b, HD 209458 b, TRES-1 b are very well studied. A few other really interesting transiting planets include GJ 436 b (the only transiting hot Neptune known so far), HD 149026 b (a hot saturn-mass planet that has a radius that is quite a bit smaller than saturn which implies that the planet may have a rocky core that could be as much as 70 times the mass of the Earth - that's 70 earths worth of rock in the center of the planet!), XO-3 b (a 13 jupiter mass planet), HAT P-2 b (an 8 jupiter mass planet with a really eccentric orbit), and HD 17156 b (the known transiting planet with the longest period - 21 days, it has a mass that is about 3 times that of jupiter and is also quite eccentric). </p><p>Other really interesting extrasolar planet systems that aren't transiting (so we can't say quite as much about them) include the GJ 581 system (three small planets orbiting an M dwarf including 5 and 8 earth mass planets), 55 Cancri which has 5 planets (it is a wide binary star system, the known planets all orbit one of the stars, that star has 4 ~jupiter sized planets 3 which orbit closer to the star than the earth orbits the sun, and it also has 1 planet, the innermost one, that's a little smaller than Neptune), and upsilon andromedae... just to name a few. </p> <div class="Discussion_UserSignature"> </div>