Discovery of a Super-Neptune Through Transit Search

Astronomers from the Harvard-Smithsonian Center for Astrophysics have made an exciting discovery. They have found a planet called HAT-P-11b that is larger and more massive than Neptune. This planet is located 120 light-years away from Earth. While Neptune is already much bigger than Earth, with a diameter 3.8 times that of our planet and a mass 17 times greater, HAT-P-11b is even larger. It has a diameter 4.7 times that of Earth and a mass equivalent to 25 Earths.The discovery of HAT-P-11b was made possible because it passes directly in front of its parent star, causing a slight dimming of the star’s light. This dimming, which amounts to about 0.4 percent, was detected by a network of small telescopes called “HATNet.” These telescopes are operated by the Center in Arizona and Hawaii. HAT-P-11b is actually the 11th extrasolar planet discovered by HATNet, but it is the smallest one found so far among the various transit search projects happening worldwide.

The detection of transits is particularly valuable for astronomers because it allows them to determine the size of the planet. The amount of dimming observed during a transit provides crucial information about the planet’s dimensions. By combining this transit data with measurements of the star’s radial velocity (its wobble), which are obtained using larger telescopes like Keck, astronomers can also determine the planet’s mass.While there have been other Neptune-like planets discovered through radial velocity searches, HAT-P-11b is only the second one found to transit its star. This unique characteristic enables astronomers to precisely determine both its mass and radius.

The newly found planet revolves very closely around its star, completing one orbit every 4.88 days. Consequently, it is subjected to extreme heat, reaching temperatures of approximately 1100 degrees F. The star itself is about three-fourths the size of our Sun and slightly cooler.There are indications of a second planet within the HAT-P-11 system, but further radial velocity data is required to confirm its existence and determine its characteristics.

Another group of researchers has identified another transiting super-Neptune, named GJ436b, around a different star. Its discovery was initially made through a radial velocity search and later confirmed through transit observations.

“Having two such objects for comparison enables astronomers to test theories regarding planetary structure and formation,” stated Gaspar Bakos, the Harvard astronomer who led the team responsible for this discovery.HAT-P-11 is located in the constellation Cygnus, which places it within the field of view of NASA’s upcoming Kepler spacecraft. Kepler will employ the same transit technique pioneered by ground-based telescopes to search for exoplanets. This mission holds the potential to potentially detect the first Earth-like world orbiting a distant star. “Moreover, we anticipate Kepler to provide detailed measurements of HAT-P-11 with unparalleled precision achievable only from space,” added Robert Noyes, another member of the discovery team.

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