Friday, July 7, 2017

Astronomers Discover a Warm, Dusty Giant Planet

The exoplanet HIP 65426b — the first to be seen by the SPHERE instrument on ESO’s Very Large Telescope. The image of the parent star has been removed from the image for clarity, and its position marked with a cross; the circle indicates the orbit of Neptune around the Sun on the same scale. The planet is clearly visible at the lower-left in this remarkable image.  Credit: ESO

An international team of astronomers reports the detection of a warm, dusty giant exoplanet orbiting a young, nearby star. The newly discovered alien world, designated HIP 65426 b, is about the size of Jupiter, but much more massive. The finding was presented in a paper published July 5 on the arXiv pre-print repository.

The discovery was made as part of the SpHere INfrared survey for Exoplanets (SHINE) program, which utilizes the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument installed on the Very Large Telescope (VLT) in Chile. The group of researchers, led by Gaƫl Chauvin of the Grenoble Alps University in France, uses SPHERE to search and characterize new exoworlds around young, nearby stars.

Located some 363 light years away, the 14-million-year-old HIP 65426 is one of such stars. With a radius of about 1.77 solar radii, it is nearly twice as massive as the Sun. The star has a spectral type of A2 and is a member of the Lower Centaurus-Crux association.

Chauvin’s team employed SPHERE to observe HIP 65426 in May and June 2016. They used the instrument’s IRDIS dual-band imager and the IFS integral field spectrograph to acquire high-contrast coronagraphic differential near-infrared images and spectra of this star. These observations allowed the team to detect faint red companion of HIP 65426 and to confirm its planetary status. This is, so far, the first planet discovered by SPHERE.

“The deep coronographic near-infrared observations revealed the presence of a young, warm, and dusty L5-L7 massive Jovian planet, hereafter HIP 65426 b,” the researchers wrote in the paper.

According to the study, HIP 65426 b orbits its parent star at a relatively large distance of approximately 92 AU (Neptune orbits the Sun at 30 AU). However, the authors are uncertain about the planet’s radius and mass. They note that it most likely has a radius between 1.0 to 1.5 Jupiter radii and is several times more massive than the biggest planet of our Solar System (within the range of 6.0 to 12 Jupiter masses). The planet has an effective temperature between 1,300 and 1,600 K.

What is important, the research provided basic information about the atmosphere of HIP 65426 b. The authors argue that the planet has a warm, dusty atmosphere characteristic for young, low surface-gravity L5-L7 brown dwarfs. They also underlined the significance of their findings for our understandings of atmospheres on alien worlds and planetary formation processes.

“It represents a particularly interesting case to study the presence of clouds as a function of particle size, composition, and location in the atmosphere, to search for signatures of non-equilibrium chemistry, and finally to test the theory of planet formation and evolution,” the paper reads.

The scientists call for further observations of HIP 65426 b using instruments like NAOS-CONICA (Nasmyth Adaptive Optics System, Near-Infrared Imager and Spectrograph) at the Paranal Observatory in Chile and NASA’s future James Webb Space Telescope (JWST). Such instruments could allow researchers to explore the young planetary atmosphere of this planet in detail.

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