• Astronomers: find systems
○ Imaged: like solar system
○ Yet: differ
§ First example: 51 P
□ Planet mass> Jupitar's; orbit < that of Mercury
§ HD40307
□ 3 planets: 4-10* Earth mass; orbit< 50% Mercury's
§ 55 C
□ More than 5 planets
□ MASS:10-10000
□ Orbit: 1/10 mercury's—jupiter's
§ Not sunlike: can orbit themseles
○ Solar system: not the most common
§ 1st discovery: unsunlike
□ PSR1257+12
® Steller corpse: Packs a mass > sun's
® Supernova explosion: violent
◊ No planets can survive
® Radius > 1AU
® Remains: form a disk
◊ Bithing grounds
} e.g. sun
– Material→pancake shape
w Dust and gas :coagulate
® By dectect deviations
◊ Bcz: planets pull on the star
§ No other camparable system
□ Pulsar: PSR 1620
® But orbit too far
◊ Not form in a disk
◊ But captured from another star