Measuring of the Mass-Mars size of Exoplanet - Physics-Astronomy.org

Measuring of the Mass-Mars size of Exoplanet

Determining the size of an Earth-size exo-planet by the quantity of starlight it blocks hundreds of light-years away formerly was the realm of science fiction. Measuring the mass of such a little planet based on its gravity was one more  rank entirely, but astronomers have done just that for an exo-planet 50% the size of Earth.
Re-searchers using NASA's Kepler mission data have measured the mass of a Mars-size exo-planet that is about one 10th  the mass of Earth. Called Kepler-138b, it is the first exo-planet smaller than Earth to contain both its mass and size measured. This considerably extends the range of planets with measured densities
To determine a planet's mass, astronomers classically measure the minuscule movement of the star cause by the gravitational tug of an orbit planet. For planets the mass of Earth detecting such a little tug is particularly challenging with recent technology. Fortunately, when a star hosts multiple planets that orbit closely jointly, scientists have developed another way to get at the planets’ masses.
Measuring of the Mass-Mars size of  Exoplanet
> Daniel Jontof-Hutter, a research associate at the Pennsylvania State University’s Center for Exo-planets and Habitable Worlds, led a team of astronomers in a study to measure the mass of all 3 planets by precisely observe the times each planet passed in front of, or transited, the star Kepler-138.

"Each planet occasionally slows down and accelerates ever so slightly from the gravity of its neighboring planets. The slight change in time between transits allows us to measure the masses of the planets," said Jontof-Hutter.
Both time a planet transits a star it blocks a small fraction of the star's light, allowing astronomers to measure the size of the planet. This is how the Kepler space-craft has  detected  1000 planets around other stars.
By measuring both the mass and size of an exo-planet, scientists can compute the density and infer the bulk composition to determine if a planet is predominantly made of rock, water or gas. Tiny Kepler-138b's density is consistent with a rocky composition like Earth or Mars, but further observations are needed before astronomers can definitively say that it is a rocky world.
Kepler-138b is the innermost of 3 planets that orbit Kepler-138, a star less than half the size of our sun and roughly thirty percent cooler. The Kepler-138 system is located about 200 light-years from Earth in the direction of the constellation Lira
The outer 2  planets, Kepler-138c and Kepler-138d, are approximately the size of Earth. Kepler-138c is likely to be rocky, whereas Kepler-138d is less dense and cannot be made of the similar mix of material as Earth. All three planets orbit too close to their star for liquid water to exist on the surface and support life, as we know it.
"The considerable difference among the density of the two bigger planets tells us that not all planets comparable to Earth in size are rocky," said Jack Lissauer, co-author and planetary scientist at NASA's Ames Research Center in Moffett Field, Calif. "Further study of small planets will help provide more understanding of the diversity that exists in nature, and will help determine if rocky planets like Earth are common or rare."
Much like astronomers in the early 20th century studied a wide variety of stars to characterize and classify different types, astronomers in the 21st century are doing the same to understand the diversity and demographics of planet populations in our Milky Way galaxy.
Scientists are working to use these new measurements of little planets from Kepler and NASA's upcoming Transiting Exoplanet Survey Satellite to identify patterns in the relationship between mass and size. These insights will provide context for understanding the history of Earth and other planets in our own solar system, and tell the next generation planet hunters as they search for life beyond the solar system.
A earlier study had measured the masses of the two external planets. This new study performed a more detailed  psychoanalysis of the Kepler-138 system using additional Kepler data. This enabled the measurement of the mass of the Mars-size inner planet and improved the accurateness of the size and mass measurements for the outer planets. The results will appear in the  issue of the journal Nature.
Ames Research Center in Moffett Field, California, manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

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