Collinder 153

Collinder 153 is a small, intermediate-age open star cluster in the constellation Puppis, also known as Cr 153 and NGC 2423. It lies about 1.3° north of Messier 47 (Collinder 152) and a little over 2° from Messier 46, forming a trio of clusters in the same field. Its distance is 2,500 to 3,000 light-years. It spans about 12 arcminutes (around 9 light-years), with 50 to 100 stars. It stands out because one of its red giants, NGC 2423-3, was reported in 2007 to host a planet of about 10.6 Jupiter masses (NGC 2423-3 b), one of the first planets found in an open cluster. The same team later found that the signal could come from stellar activity or pulsations, so the planet may not exist. The cluster is much older than M47: Gaia-based estimates of 1.0 to 1.4 billion years from student analyses.