The Strange Case Of The Searing-Hot, Light-Eating Planet
By Judith E Braffman-Miller
There are some very weird “oddball” planets that dwell within the distant families of stars beyond our Sun–and they are mysterious and enchanting Wonderland worlds that are unlike the familiar major planets that circle our own Star. WASP-12b is just such a strange alien world. Searing-hot and as black as fresh asphalt, this faraway world is twice the size of any planet in our own Solar System–including the banded, behemoth Jupiter, that is two-and-a-half times more massive than all of the other major planets in our Sun’s family combined. In September 2017, astronomers using NASA’s Hubble Space Telescope (HST), announced their new findings that WASP-12b has the never-before-seen ability to capture at least 94 percent of the visible starlight that is flowing down into its atmosphere from its fiery parent-star. Furthermore, this broiling, black-as-pitch, light-eating planet, is a member of a class of so-called hot Jupiters–which are giant, gaseous planets that hug their parent-star fast and close in roasting orbits and, as a result, are broiled by this stellar heat to reach extreme temperatures.
WASP-12b‘s atmosphere is so extraordinarily hot that most molecules cannot survive on its roasting day side, where the temperature soars to 4,600 degrees Fahrenheit. As a result, clouds are probably unable to form to reflect light back into space. Instead, incoming starlight dives down deep into the planet’s atmosphere where it is ultimately absorbed by hydrogen atoms and changed into heat energy.
“We did not expect to find such a dark exoplanet. Most hot-Jupiters reflect about 40 percent of starlight,” noted Dr. Taylor Bell in a September 14, 2017 Hubblesite Press Release. Dr. Bell is of McGill University and the Institute for Research on Exoplanets in Montreal, Quebec, Canada.
The toasty, pitch-black planet, WASP-12b, orbits the star WASP-12. It was detected by the Super-WASP planetary transit survey, and its discovery was announced on April 1, 2008. Because of its extremely close orbit around its parent star, WASP-12b possesses one of the lowest densities of any known exoplanet. This is because it has been “inflated” by the flux of energy from its star. The distant world takes only a little over one day to circle its stellar parent, in contrast to Earth’s 365 day orbit around our own Star. Its distance from WASP-12 is approximately 2,115,000 miles, which is only one forty fourth of the Earth-Sun separation. WASP-12 b’s eccentricity is about the same as Jupiter’s. On December 3, 2013, astronomers working with HST announced that they had detected water in the atmosphere of this exoplanet.
WASP-12b clings to its parent-star so closely that the star’s tidal forces distort it into an egg shape, and it is also pulling the planet’s atmosphere at a rate of approximately 189 quadrillion tons per year. Both the tidal heating and the close proximity of this planet to its glaring, roiling star, combine together to cause WASP-12b’s surface temperature to skyrocket.
On May 20, 2010, the HST revealed that WASP-12b is being devoured by its parent-star. Astronomers were already aware that stars could consume their planetary offspring; however, this was the first time that such a tragic event had been observed so clearly. NASA has estimated that WASP-12b has only about 10 million more years left to “live”.
The HST observed the planet by using its Cosmic Origins Spectrograph (COS). The observations confirmed predictions that had been published in the journal Nature in February 2009 by Peking University’s Dr. Shu-lin Li. The planet’s atmosphere has expanded to become almost three times the radius of Jupiter. However, the exoplanet itself has about 40% less mass than Jupiter.
In addition, WASP-12b shows an enhanced carbon-to-oxygen ratio–which is considerably higher than that of our Sun. This means that it is a carbon-rich gas giant. Some astronomers think that with more carbon than oxygen, a planet like WASP-12b could form rocks composed of pure carbon, such as diamond or graphite.
The published study notes: “Although carbon-rich giant planets like WASP-12b have not been observed, theory predicts myriad compositions for carbon-dominated solid planets. Terrestrial-sized carbon planets, for instance, could be dominated by graphite or diamond interiors, as opposed to the silicate compositions of Earth.”
Russian astronomers, observing a change in the curve of the shine emitted by WASP-12b, saw regular bursts of light. These bursts hinted that WASP-12b has at least one large exomoon in orbit around it. However, this probably is not the case because hot Jupiters are expected to lose large moons within geologically brief timescales.
The Hunt For Distant Worlds
Historically, the quest to detect remote planets, inhabiting the families of alien stars beyond our own Sun, proved to be very difficult. The discovery of the first group of exoplanets more than twenty years ago is certainly one of humanity’s greatest accomplishments. This is because discovering a giant planet, such as our own Jupiter, can be compared to observing light bouncing off a mosquito flying near the 1,000-watt light bulb of a glaring street lamp–when the observer is 10 miles away.
The original successful technique used by astronomers back in 1995, called the Doppler Shift method–sometimes more casually referred to as the “wobble” method–favored the discovery of giant planets circling their parent-stars in roasting, close-in orbits. However, new and improved technologies were soon developed that enabled astronomers to detect ever smaller and smaller exoplanets that resided at greater distances from their stars. Indeed, many astronomers think that exoplanets about the same size as Earth are common denizens in our Galactic neighborhood.
The smaller the exoplanet, the harder it is to discover. For example, if an alien astronomer, belonging to a technologically sophisticated society, went on the hunt for other worlds situated in distant regions of our Milky Way Galaxy, it would have a very difficult time detecting our own tiny, rocky, little blue world. Our Earth would be only a faint speck lost in the powerful glare of the Sun.
The first detection of an exoplanet occurred back in 1988–however, the first confirmed detection came in 1992, with the discovery of some genuinely strange beasts inhabiting the planetary zoo–a batch of bizarre, inhospitable, but completely fascinating worlds in orbit around a dense stellar remnant called a pulsar–the lingering corpse of a massive star that recently ended its hydrogen-burning “life” in the violent, fiery tantrum of an explosive supernova blast, that destroyed the original progenitor star. A team of astronomers detected the first exoplanet in orbit around a still-“living”, hydrogen-burning, Sun-like star in 1995. As of September 2017, there are 3,667 confirmed exoplanets occupying 2,747 systems, with 616 systems containing more than one solitary planet.
Since 2004, the European Southern Observatory’s (ESO’s) High Accuracy Radial velocity Planet Searcher (HARPS) 3.6 meter telescope has successfully discovered about 100 exoplanets, while NASA’s Kepler Space Telescope, since 2009, has found more than two thousand. Kepler has also spotted a few thousand candidate exoplanets still awaiting confirmation. However, it is generally thought that about 11% of these distant worlds may be false-positives. In several instances, multiple planets have been spied circling their parent-star.
Many astronomers think that about 1 in 5 distant Sun-like stars possess an “Earth-sized” planet situated in its habitable zone. The habitable zone surrounding a star is that “Goldilocks” region where the temperatures are not too hot, not too cold, but just right for liquid water to exist. Where liquid water exists, life as we know it could also exist–however, there are other factors to be taken into account, and the location of a planet in its star’s habitable zone does not indicate that it is definitely inhabited. In our own Solar System, the planet Venus is situated in the habitable zone of our Star. Alas, Venus is the tragic victim of a runaway greenhouse effect, making it much hotter than it should be. Any water that may once have pooled on the surface of this inhospitable world would have boiled away long ago.
Assuming that there are 200 billion stars inhabiting our Galaxy, scientists can hypothesize that there are 11 billion potentially habitable Earth-sized exoplanets in our Milky Way, rising to about 40 billion if planets orbiting the very numerous red dwarf stars are included in the tally. Smaller than our own small Sun, red dwarfs are both the most numerous, as well as the longest-lived stars in our Milky Way. In fact, red dwarfs go on burning their necessary supply of hydrogen for trillions of years–and the Universe is only about 13.8 billion years old.
The least massive known exoplanet has been dubbed Draugr, and it is approximately twice the mass of Earth’s Moon. In marked contrast, the most massive known exoplanet is DENIS-P J082303.11-491201 b, and it is about 29 times the mass of Jupiter. However, according to some definitions of what constitutes a “planet”, this jumbo distant world is too massive to be designated a “planet”, and it may more precisely be considered a type of failed star called a brown dwarf. Brown dwarfs are objects that are likely born the same way as true stars–as the result of the collapse of a dense pocket embedded within the swirling folds of a cold, dark, giant molecular cloud–but have not attained sufficient mass to light their nuclear-fusing stellar fires.
There are explanets that cling to their parent-star in such close, broiling orbits that they take only a few hours to circle it–and there are others that are so far from their star that it is a challenge for astronomers to determine whether they truly are gravitationally bound to it. Almost all of the distant alien worlds, that belong to the families of stars beyond our own Sun, are inhabitants of our Milky Way Galaxy. However, there have also been discoveries of a few fascinating potential extragalactic exoplanets. The nearest exoplanet to our Earth is Proxima Centauri b, which dances around its star, Proxima Centauri, at “only” 4.2 light-years away from us. Proxima Centauri is the closest stellar inhabitant to our Sun.
Numerous rogue planets also dwell in our Galaxy, and these solitary worlds do not belong to the family of any star at all, but wander through interstellar space without a stellar family to call their own. Alas, these solitary planets probably once belonged to the family of a distant star, but were heartlessly booted out as the result of destructive gravitational interactions with sibling planets, or as the result of a passing star that closely brushed past their own star–with disastrous consequences for the rudely evicted rogue planet.
The discovery of so many faraway exoplanets has stimulated significant scientific interest in the quest to find life beyond Earth–with special attention being paid to planets that orbit their stellar-parent within its habitable zone.
The Strange Case Of The Searing-Hot, Light-Eating Planet
Even though hot Jupiters reflect 40 percent of starlight, WASP-12b’s nighttime side is different. This strange planet has both a fixed day side and a fixed night side, because it hugs it parent-star so closely that it is tidally locked. The nighttime side is more than 2,000 degrees Fahrenheit cooler than the day side, and this allows water vapor and clouds to form. Earlier HST observations of the day/night boundary spotted evidence of water vapor, as well as the possibility of clouds and hazes in the atmosphere. WASP-12b is approximately 2 million miles away from its parent-star and it finishes a complete orbit once a day.
“This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters. You can have planets like WASP-12b that are 4,600 degrees Fahrenheit and some that are 2,200 degrees Fahrenheit, and they’re both called hot Jupiters. Past observations of hot Jupiters indicate that the temperature difference between the day and night sides of the planet increases with hotter day sides. This previous research suggests that more heat is being pumped into the day side of the planet, but the processes, such as winds, that carry the heat to the night side of the planet don’t keep up the pace,” Dr. Bell explained in the September 14, 2017 Hubblesite Press Release.
The astronomers found out about the planet’s light-eating habits by using HST’S Imaging Spectrograph to search in mostly visible light for a very small drop in starlight as the planet floated directly behind its star. The amount of dimming reveals to astronomers how much reflected light is being given off by the planet. However, the observations did not detect reflected light at all, and this hinted that the daytime side of WASP-12b is absorbing almost all of the starlight flowing to it from its star.
Since its discovery, several telescopes have observed this pitch black, seething hot exoplanet, including HST, NASA’s Spitzer Space Telescope, and NASA’s Chandra X-ray Observatory. Earlier observations by astronomers, using HST‘s Cosmic Origins Spactrograph (COS), revealed that WASP-12b may be in the process of losing some of its material. COS spotted material originating from the planet’s super-heated atmosphere pouring onto its glaring parent-star.
The results of this study appear in the September 14, 2017 issue of The Astrophysical Journal Letters.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, newspapers, and journals. 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.
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