GJ3470b is an exoplanet about 14 times the size of the Earth. Astronomers from NAJO and the University of Tokyo have observed the effects of light passing through the atmosphere of this planet for the first time. They found that the (local) sun was shining all over the globe, without a thick cloud layer like similarly-sized Neptune.
Measuring the radius of planets around other stars is usually accomplished by waiting for that planet to pass in front of its local star. By measuring how much the light from the star is dimmed, astronomers can calculate the approximate size of the planet. Since its discovery in 2012, the radius of GJ3470b has been measured, using this method, to be about 4.3 times the diameter of the Earth.
"Suppose the atmosphere consists of hydrogen and helium, [then] the mass of the atmosphere would be 5 to 20% of the total mass of the planet. Comparing that to the fact that the mass of Earth's atmosphere is about one ten-thousandth of a percent (0.0001%) of the total mass of the Earth, this planet has a considerably thick atmosphere." Akihiko Fukui, of the National Astronomical Observatory of Japan (NAOJ), said.
Taking measurements with four instruments at once, using different wavelengths, the researchers noted that the measured radii differed from each other by up to six percent. This is thought to be a result of the atmosphere of the planet absorbing certain wavelengths and not others.
"If we find any substance, such as water or methane, which becomes ice at low temperatures, it probably means that this planet was originally formed at a distance [a few times further than the Earth from the Sun] from the primary star, where ice could exist, and moved toward the primary star thereafter. In contrast, if such substance cannot be found in the atmosphere, it can be thought to be quite likely that this planet was formed near the primary star. We expect to obtain important clues for figuring out how super-Earths were formed through observations of the atmospheric component of GJ3470b," Fukui said.
The instruments used to make the observations include a 74-inch telescope and three other instruments operated by the Okayama Astrophysical Observatory. The observatories are located on Mount Chikurin-Ji in Okayama.
The star around which the super-Earth revolves, GJ3470, is a small dwarf star, which means that a significant amount of its light is blocked when the planet passes between it and the Earth. The planet also revolves close to its parent star - just 3.35 million miles away, offering astronomers frequent chances to make such measurements. These two qualities of the planet make observations easier than with other star systems. So far, the atmosphere of only two stars has been studied in detail.
Researchers hope to soon measure the composition of the the atmosphere of this world with more accurate measurements using instruments like the 323-inch Subaru telescope on Mauna Kea in Hawaii.
