Hat-P-7b – A Hard Rain’s A-Gonna Fall
By Judith E Braffman-Miller
The hunt for distant planets in orbit around alien stars beyond our own Sun has yielded an overwhelming treasure chest filled with Wonderland worlds–some exotic, some eerily familiar, some weird, and all wonderful. One of the most exotic, weird, and wonderful distant planets circling a faraway star is Hat-P-7b. Discovered in 2008, this strange exoplanet closely hugs its parent-star, Hat-P-7, in a roasting-hot orbit, and it is both more massive and larger than our own Solar System’s resident behemoth, the gas-giant planet Jupiter–and 500 times more massive than Earth. In December 2016, scientists announced that they had managed to detect the bizarre weather patterns of Hat-P-7b–making it the very first gas-giant world beyond our own Solar System to reveal its strange weather to the curious eyes of astronomers. Clouds on this Wonderland world could be composed of the mineral corundum. Corundum forms sapphires and rubies, that fall like a hard rain down on the surface of this giant world that is 1,040 light-years away.
Corundum is a crystalline form of aluminium oxide, and it usually contains small amounts of iron, titanium, vanadium and chromium. Corundum is a rock-forming mineral that is naturally transparent. However it can display different colors when it contains impurities. These transparent specimens are true gems–rubies, if red, and padparadscha if pink-orange. All of the other hues are sapphires.
When the winds of HAT-P-7b are rushing and roaring at their fastest, they powerfully push vast amounts of cloud across this truly alien, distant world. The clouds themselves would be visually astonishing–marvelous, amazing, and fabulous. However, this Wonderland world could never host living creatures. This is because of its extremely violent weather systems, and searing-hot temperatures, from where it broils under the merciless, roiling glare of its parent-star. One side of HAT-P-7b constantly faces its star because it is tidally locked, and that side is perpetually hotter–much, much hotter–than the other, darker side. The day side temperature on HAT-P-7b is predicted to be about 2730 Kelvins.
Signs of these violent and powerful changing winds that thrash this distant world–that is 16 times larger than Earth–were spotted by a team of astronomers led by Dr. David Armstrong of the University of Warwick’s Astrophysics Group. The astronomers found that this gigantic gaseous world is affected by large-scale changes in the strong winds that rush across the planet–and these winds probably trigger catastrophic storms. The University of Warwick is in Coventry, England.
The distant solar system is within the field of view of NASA’s Kepler Mission spacecraft, which confirmed its orbital properties and transit with improved confidence–and observed occultation and light curve characteristics indicating a strongly absorbing atmosphere with limited advection to the night side. In testing its own abilities on Hat-P-7b, Kepler proved itself to be sensitive enough to spot Earth-like planets dwelling in the families of distant stars beyond our own Sun.
NASA’s Kepler Space Telescope was launched on March 2, 2009 from Cape Canaveral, Florida. The spacecraft’s original 3.5-year mission had the objective of determining how frequently Earth-like planets occur within our own Milky Way Galaxy–and it proved to be highly successful. However, Kepler’s original mission came to a premature conclusion when the second of four reaction wheels used to stabilize the spacecraft failed. The spacecraft requires at least three functioning reaction wheels in order to be pointed as accurately as necessary. This is because it needs to keep a steady stare as it hunts for distant Earth-like worlds inhabiting the families of faraway stars beyond our Sun.
However, rumors of Kepler’s untimely demise were premature. Like the Phoenix Bird of Greek mythology, that was given a second chance at life when it rose majestically from the ashes of its own funeral pyre, Kepler was reborn–despite the crippling malfunction that ended its original primary mission in May 2013. Newly renamed the K2 Mission, the spacecraft was ingeniously resurrected, and it is performing very well gathering data during its “second life”.
Beginning in 1988, and as of December 2016, there have been 3,545 exoplanets in 2,660 planetary systems and 597 multiple planetary systems confirmed. Since 2009, the Kepler Space Telescope has spotted a few thousand candidate exoplanets, of which about 11% may be false positives. On average, there is at least one planet per star in our Milky Way Galaxy, with a percentage hosting multiple planets. Approximately 1 in 5 stars are circled by an “Earth-sized” planet situated in its parent star’s habitable zone. The habitable zone is that Goldilocks region surrounding a star where the temperature is not too hot, not too cold, but just right for water to exist in its life-sustaining liquid state. If there are 200 billion stars dancing around in our Galaxy, this would mean that there could be 11 billion potentially habitable Earth-sized worlds in our Galaxy alone. If red dwarf stars are included in this hypothesis, the number would rise to as many as 40 billion potentially habitable exoplanets in our Milky Way. Red dwarf stars are both the smallest and most abundant true stars.
History Of A Planetary Treasure Hunt
Astronomers announced in August 2009 that Hat-P-7b may sport a retrograde orbit around its star, that is 50% more massive, and twice as large, as our own Sun. This observation was based on the Rossiter-McLaughlin effect, which is a spectroscopic phenomenon observed when either an eclipsing binary’s secondary star or an exoplanet is observed to transit across the glaring face of its parent-star. As the main star rotates on its axis, one quadrant of the photosphere appears to be traveling towards the observer, while the other visible quadrant appears to be traveling away. The announcement of Hat-P-7b’s retrograde orbit came only a day after the announcement of the very first exoplanet discovered to also possess such an orbit–WASP-17b.
In January 2010, astronomers announced that ellipsoidal light variations were detected for HAT-P-7b, the first detection ever made of such a phenomenon. This method analyzes the brightness variations resulting from the rotation of a star as its shape is tidally distorted by its orbiting planet. Also, on July 4, 2011, HAT-P-7b became the Hubble Space Telescope’s (HST’s) one millionth science observation.
HAT-P-7b–A Hard Rain’s A-Gonna Fall
The discovery of HAT-P-7b’s weird weather was made by a team of astronomers from the University of Warwick in the UK, Queens University Belfast, Dublin City University, and University College London, when they monitored the light reflected from its atmosphere, and detected changes in this light. Their observations revealed that the brightest point of the planet shifts its position. This shift is the result of an equatorial jet with dramatically changing wind-speeds–which, at their most powerful, shove the clouds across the planet.
“Using the NASA Kepler satellite we were able to study light reflected from HAT-P-7b’s atmosphere, finding that the atmosphere was changing over time. HAT-P-7b is a tidally locked planet, with the same side always facing its star. We expect clouds to form on the cold night side of the planet, but they would evaporate quickly on the hot day side,” Dr. Armstrong explained in a December 2016 University of Warwick Press Release.
“These results show that strong winds circle the planet, transporting clouds from the night side to the day side. The winds change speed dramatically, leading to huge cloud formations building up then dying away. This is the first detection of weather on a gas giant planet outside the solar system,” he added.
Thanks to this pioneering research, astrophysicists can now start exploring how weather systems on other alien planets, far beyond our own Solar System, change over time.
The paper describing this research is titled, Variability in the Atmosphere of the Hot Jupiter HAT-P-7b, and it is published in the first issue of Nature Astronomy (January 2017).
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various journals, magazines, and newspapers. Although she has written on a variety of topics, she particularly loves writing about astronomy, because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.