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23 Nov 2019
<p>Imagine two planets orbiting a star the same mass as our sun with orbits edge-on to the Earth. The peak Doppler shift for each 90 m/s, but one has a period of 9 days and the other has a period of 900 days.<br /><br />Calculate the mass of the shorter period planet.<br /><br />I use M<sub>planet</sub> = M<sub>star</sub> x V<sub>star</sub> x P<sub>planet</sub> / 2π x A<sub>planet</sub>.<br /><br />M=mass<br />V=velocity<br />P=Period in seconds<br />A=Semi major axis in meters<br /><br />I think the problem is I can't figure out the semi major axis. Am I to assume it's 1 AU because of the Earth orbit reference? Can someone help?</p>
<p>Imagine two planets orbiting a star the same mass as our sun with orbits edge-on to the Earth. The peak Doppler shift for each 90 m/s, but one has a period of 9 days and the other has a period of 900 days.<br /><br />Calculate the mass of the shorter period planet.<br /><br />I use M<sub>planet</sub> = M<sub>star</sub> x V<sub>star</sub> x P<sub>planet</sub> / 2π x A<sub>planet</sub>.<br /><br />M=mass<br />V=velocity<br />P=Period in seconds<br />A=Semi major axis in meters<br /><br />I think the problem is I can't figure out the semi major axis. Am I to assume it's 1 AU because of the Earth orbit reference? Can someone help?</p>
