Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William 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 three confirmed planets, all of which were discovered in 2008, and none of which is truly Earth-sized.  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 probably gaseous like Uranus or Neptune, though much lighter.  It is highly unlikely, given their proximity to their parent star, that any has a moon.  All three planets have near circular orbits. 

The Visualization, in the introduction, includes this system as one of its Three Planet Systems. 

HD 40307

HD 40307 b
This planet has a mass of at least 4.2 Earth masses.   It orbits its star at a distance of about 0.047 AU (7,050,000 km) once every 4.3 days. 


HD 40307
c

This planet has a mass of at least 6.8 Earth masses.   It orbits its star at a distance of about 0.081 AU (12,150,000 km) once every 9.6 days. 


HD 40307
d
The largest of the three, this planet has a mass of at least 9.2 Earth masses.   It orbits its star at a distance of about 0.134 AU (20,100,000 km) once every 20.46 days.  
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