<p>While solving astronomy problems dealing with exoplanets, I always see that the question asks for minimum mass instead of the mass. Why is that so and why is the calculated mass minimum mass?</p>
<p>example problem:
&quot;A 0.7 solar mass star 35.8 pc away from us is known to have an exo-planet with an orbital
period of 2.82 days around the star. If this produces a radial velocity of 64 m/s about the
center of mass of the star, estimate the minimum mass of the exo-planet (in terms of the
solar mass).&quot;</p>

CC BY-SA 4.0
2022-07-05T23:10:49.047Z
Correct. Radial velocity is only the velocity in direction to-from (radial) observer so need to take component.
TazAstroSpacial
CC BY-SA 4.0
2022-05-05T19:22:25.790Z
It's a projection effect that is fundamental to the radial velocity method - you're measuring $\rm m\, \sin i$, where $\rm i$ is the inclination of the planetary orbital plane w.r.t the observer, and not $\rm m$.
AtmosphericPrisonEscape
<star><exoplanet><mass>
Why do we estimate the Minimum mass when we are dealing with exoplanets?
Hardek A.
# Why do we estimate the Minimum mass when we are dealing with exoplanets?

(Asked by: username_0 on 2022-05-05)

While solving astronomy problems dealing with exoplanets, I always see that the question asks for minimum mass instead of the mass. Why is that so and why is the calculated mass minimum mass?

example problem:
"A 0.7 solar mass star 35.8 pc away from us is known to have an exo-planet with an orbital
period of 2.82 days around the star. If this produces a radial velocity of 64 m/s about the
center of mass of the star, estimate the minimum mass of the exo-planet (in terms of the
solar mass)."

**Tags:** star, exoplanet, mass
> **Comments:**
> **username_2**: It's a projection effect that is fundamental to the radial velocity method - you're measuring $\rm m\, \sin i$, where $\rm i$ is the inclination of the planetary orbital plane w.r.t the observer, and not $\rm m$.  
> **username_1**: Correct. Radial velocity is only the velocity in direction to-from (radial) observer so need to take component.  

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## 0 answers

