Using observations from the High Accuracy Radial velocity Planet Searcher (HARPS), a high-precision spectrograph on ESO’s 3.6-m telescope at La Silla Observatory, astronomers have managed to measure wind velocities on opposite sides of an exoplanet called HD 189733b, the closest hot Jupiter to the Solar System.
HD 189733b is shown here in front of its host star, HD 189733; a belt of wind around the equator of the planet travels at 5,400 mph from the heated day side to the night side. Image credit: Mark A. Garlick / University of Warwick.
HD 189733b is a gas giant planet with a hazy atmosphere mainly composed of hydrogen. It is some 63 light-years away toward the constellation Vulpecula.
The planet was discovered in 2005 by astronomers using two telescopes at the Haute-Provence Observatory.
HD 189733b is only 1.2 times bigger than Jupiter but in very close orbit around its parent star, HD 189733; it orbits the star once every 2.2 days.
About two years ago, a team of astronomers in the United Kingdom determined the true color of HD 189733b. According to the team, the planet has a deep, azure blue color – reminiscent of Earth’s color as seen from space.
Now, another team in UK has measured the velocities on the two sides of the planet and found a strong wind moving at over 5,400 mph blowing from its dayside to its night side.
“Whilst we have previously known of wind on exoplanets, we have never before been able to directly measure and map a weather system,” said team member Tom Louden, of the University of Warwick.
“HD 189733b’s velocity was measured using high resolution spectroscopy of the sodium absorption featured in its atmosphere,” he said. “As parts of HD 189733b’s atmosphere move towards or away from the Earth the Doppler effect changes the wavelength of this feature, which allows the velocity to be measured.”
This image shows the planet HD 189733b with the Sun, Sirius and Alpha Centauri in the background (NASA / ESA / G. Bacon / AURA / STScI)
“The surface of the star is brighter at the centre than it is at the edge, so as the planet moves in front of the star the relative amount of light blocked by different parts of the atmosphere changes,” Louden said.
“For the first time we’ve used this information to measure the velocities on opposite sides of the planet independently, which gives us our velocity map.”
“We are tremendously excited to have found a way to map weather systems on distant planets,” said team member Dr Peter Wheatley, also of the University of Warwick.
“As we develop the technique further we will be able to study wind flows in increasing detail and make weather maps of smaller planets. Ultimately this technique will allow us to image the weather systems on Earth-like planets.”
The findings will be published in the Astrophysical Journal Letters (arXiv.org preprint).
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Tom Louden & Peter J. Wheatley. 2015. Spatially resolved eastward winds and rotation of HD189733b. ApJL, accepted for publication; arXiv: 1511.03689
