From Gemini: “A Partly-cloudy Exoplanet”


Gemini Observatory
Gemini Observatory

June 6, 2017

The first exoplanet discovered using the Gemini Planet Imager (GPI) is a young, cool object between 2–10 Jupiter masses. Identified as 51 Eridani b, new research indicates that its color is redder than similar brown dwarfs and might be due to clouds in its atmosphere. The research also hints that the formation of this exoplanet is likely due to the collapse of icy disk materials followed by the accretion of a thick gas atmosphere – much like the process astronomers think probably formed the gas giants in our Solar System.

NOAO Gemini Planet Imager on Gemini South

Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile

GPI images in the K1, K2, LP and MS bands, the emission of host star was blocked. The exoplanet 51 Eri b is indicated by an arrow.

An international team of astronomers led by Abhijith Rajan (School of Earth and Space Exploration, Arizona State University) observed the exoplanet 51 Eri b using GPI spectroscopy and determined that the planet is redder than similar brown dwarfs seen elsewhere. “This might be due to presence of clouds, similar to young L-type planetary mass companions,” said Rajan. “A possible reason for the presence of clouds, is that the planet is still in transitioning from a partially- to patchy-cloudy atmosphere, with lower mean surface temperatures.”

The GPI observations, part of the Gemini Planet Imager Exoplanet Survey (GPIES) was combined with mid-infrared photometry at the W.M. Keck Observatory.

Keck Observatory, Mauna Kea, Hawaii, USA

These data allowed the team to conclude 51 Eri b appears to be one of the only directly imaged planet that is consistent with cold-start scenario. In this scenario 51 Eri b would have formed by core accretion in which a core is formed very early from planetesimal agglomerations while there is enough gas around it to form a gas giant planet. The result is a low temperature and low luminosity planet. This mechanism is also a widely-held hypothesis explaining the formation of the gas giants in our Solar System.

Located about 100 light years from Earth, 51 Eri b is between 2–10 times the mass of Jupiter and orbits the star 51 Eridani A. The host star, 51 Eridani A, has a visual magnitude of 5.2 and visible to the naked eye under ideal conditions and easily visible in a pair of binoculars from most of the Earth’s surface!

More information about GPI and 51 Eri b is available in the October 2015 issue of GeminiFocus (page 3) and in this Gemini Press Release.

The full results are accepted for publication in The Astronomical Journal.

See the full article here .

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Gemini/North telescope at Mauna Kea, Hawaii, USA
Gemini/North telescope at Mauna Kea, Hawaii, USA

Gemini South
Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile


Gemini’s mission is to advance our knowledge of the Universe by providing the international Gemini Community with forefront access to the entire sky.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai’i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.