Mars-sized exoplanet is smallest to have its mass measured
![Kepler 138 system](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2015/06/ticker_artistImpressionSETI-PSU.jpg?fit=860%2C460&ssl=1)
WEIGHING WORLDS Subtle deviations in how three planets orbit the star Kepler 138 (illustrated) allowed researchers to measure the masses of those worlds.
Danielle Futselaar/SETI Institute
WEIGHING WORLDS Subtle deviations in how three planets orbit the star Kepler 138 (illustrated) allowed researchers to measure the masses of those worlds.
Danielle Futselaar/SETI Institute