What’s the Deal with Low-Mass Stars, Brown Dwarfs, and Planets? Kelle Cruz American Museum of Natural History

People Care About Planets

Low-Mass Stars, BDs, & Jupiter All about same size as Jupiter All about same size as Jupiter L dwarfs can be either a stellar or sub-stellar. L dwarfs can be either a stellar or sub-stellar. Both planets and brown dwarfs cool over time Both planets and brown dwarfs cool over time Jupiter was a T dwarf in youth

Definition of Planet In the Solar System (low mass) In the Solar System (low mass) Sphericity Sphericity Pluto Diameter Pluto Diameter Only 9 Only 9 Discard altogether Discard altogether Terrestrials, Jovians, etc. Terrestrials, Jovians, etc. Outside the Solar System (high mass) Outside the Solar System (high mass) Orbits another body Formed in circumstellar disk rather than grav. collapse Difficult to observe Deuterium Burning 13 M Jupiter cutoff

Kuiper Belt Objects Xena (2003 UB313) Xena (2003 UB313) Larger Larger than Pluto (10 th Planet?) Has a moon 2003 EL EL61 Has two moons Has two moons 2005 FY FY9 Both very bright and ¾ Pluto’s size. Both very bright and ¾ Pluto’s size. From Mike Brown’s website.

GQ Lup B Primary Primary T Tauri (young Sun) T Tauri (young Sun) Secondary (“Planet”) Secondary (“Planet”) Spectral type: M9-L4 Spectral type: M9-L4 Mass: 1-42 M Jupiter Mass: 1-42 M Jupiter

2M 1207B Primary: Primary: young (8 Myr), active young (8 Myr), active brown dwarf (M8) brown dwarf (M8) Secondary: Secondary: 5 M Jupiter, L5-L9.5 5 M Jupiter, L5-L9.5 Too wide and too massive to have formed in a circumstellar disk. Too wide and too massive to have formed in a circumstellar disk.

In Closing What the heck is a planet? What the heck is a planet? None of the proposed definitions take care of both mass ends at the same time. None of the proposed definitions take care of both mass ends at the same time. Personally, I think time will tell but in the meantime, enjoy the spectacle! Personally, I think time will tell but in the meantime, enjoy the spectacle! Provides a great way to engage the public Provides a great way to engage the public Signifies an exciting time in astronomy. Signifies an exciting time in astronomy.