WILLIAM & DEBORAH HILLYARD

Extra Solar Planets

HD 40307, a type K2.5V main sequence star, is about 42 light-years away from Earth.  It weighs about 75% of the Sun's mass, with a radius around 71.6% of the Sun.  Initially, the star was thought to be much younger than the Sun at about 1.5 billion years old, but more recent work suggests it is more like 6.1 1.6 billion years old; rather older than the Sun.  At present, it has six confirmed planets, three of which were discovered in 2008 and three in 2012.  None of the planets is truly Earth-sized, though HD 40307 g is likely within the star's habitable zone, and could have liquid water on its surface.  All the planets are relatively light in the approximate range of 4 to 10 Earth masses.  There is considerable debate among scientists over whether the planets are rocky, like the Earth, or gas giants.  The star is of very low metallicity, so they are all, except HD 40307 g, probably gaseous like Uranus or Neptune, though much lighter.  It is possible that D 40307 g is a rocky, large Earth like planet rather than gaseous.  It is highly unlikely, given their proximity to their parent star, that any of the five inner planets has a moon. 

The Visualization, in the introduction, includes this system as one of its Three Planet Systems; the three outer planets discovered in 2012 have yet to be added. 

HD 40307

Planet Description (in order from the star; all quoted values are approximate)
HD 40307 b The planet's mass is at least 3.3 to 4.8 Earth masses.   It orbits its star at a distance of about 0.047 AU (7,000,000 km) once every 4.3 days.
HD 40307 c The planet's mass is at least 5.6 to 7.7 Earth masses.   It orbits its star at a distance of about 0.08 AU (12,000,000 km) once every 9.6 days. 
HD 40307 d The largest of the three, this planet has a mass of at least 8 to 11.2 Earth masses.   It orbits its star at a distance of about 0.132 AU (19,760,000 km) once every 20.43 days.
HD 40307 e The planet's mass is at least 2.1 to 4.9 Earth masses.   It orbits its star at a distance of about 0.19 AU (28,200,000 km) once every 34.6 days.
HD 40307 f The planet's mass is at least 3.6 to 6.7 Earth masses.   It orbits its star at a distance of about 0.25 AU (37,400,000 km) once every 51.76 days.
HD 40307 g The planet's mass is at least 4.5 to 9.7 Earth masses.   It orbits its star at a distance of about 0.6 AU (90,000,000 km) once every 197.8 days.
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