Keck Helps in Discovery of First Earth-Sized, Rocky Exoplanet

Astronomers have found the first Earth-sized planet outside of our solar system that also has a rocky composition.

The exoplanet, as such bodies outside of our solar system are known, is located so close to its star that it completes an orbit every 8.5 hours.

That makes its orbit only about a million miles from its star, leaving the planet much too hot to support life.

For comparison, Mercury, the planet closest to our own sun, is located about 36 million miles from its sun, completes its orbit in 88 Earth days and has a daytime surface temperature of 800 degrees.

The planet known as Kepler-78b was first observed using the Kepler Space Telescope and then further analyzed using the Keck Observatory atop Mauna Kea.

Its star is slightly smaller than our sun and located about 400 light years from Earth in the constellation Cygnus.

As is typical with the discovery of exoplanets, Kepler-78b was found by studying data that showed dimming of the star as it passed in front of it.

A team led by Andrew Howard of the University of Hawaii’s Institute for Astronomy then used a high-resolution spectrometer called HIRES on the Keck I telescope to measure the planet’s mass by measuring the amount of wobble its orbit caused in the star.

The find was another example of cooperation between the observatory and the Kepler Space Telescope survey, which has identified more than 3,000 potential exoplanets, Keck officials said in a statement issued today.

The team of astronomers determined that Kepler-78b has a radius about 1.2 times that of Earth and a mass equal to about 1.7 greater than Earth’s, which suggests it is also made primarily of rock and iron.

The results of the research are being published in the journal Nature.

Kepler-78b is the first of a new class of “ultrashort period” planets identified by Kepler observations to have its mass measured.

These planets all orbit their stars in a period of less than 12 hours, and scientists are still trying to determine how these planets formed and how they came to be so close to their host stars.

A companion study of the same planet done by Francesco Pepe of the University of Geneva which found similar results is being published in the same issue of Nature.

Howard said it was gratifying to have validation of the research so soon.

“The gold standard in science is having your findings reproduced by other researchers,” Howard said in the statement.

Howard’s research team included two graduate students from the University of Hawaii’s Institute or Astronomy, Benjamin Fulton and Evan Sinukoff, and scientists from the Massachusetts Institute of Technology, Harvard, Yale, the University of California at Berkeley and UC-Santa Cruz.