Alien World Drives its Star Into Early Retirement
A nearby star is not acting its age, thanks to the influence of a massive exoplanet.
A nearby star is not acting its age, thanks to the influence of a massive exoplanet.
The close-orbiting alien planet, known as WASP-18b, is apparently disrupting the magnetic field of its host star so much that the object is behaving like a much older star, researchers said.
"WASP-18b is an extreme exoplanet," study lead author Ignazio Pillitteri, of the Instituto Nazionale di Astrofisica (INAF)-Osservatorio Astronomico di Palermo in Italy, said in a statement. "It is one of the most massive hot Jupiters known and one of the closest to its host star, and these characteristics lead to unexpected behavior. The planet is causing its host star to act old before its time." [The Strangest Alien Planets]
The star WASP-18, which lies about 330 light-years away, is about as massive as our own sun. The gas giant WASP-18b weighs in at more than 10 times the mass of Jupiter and completes one orbit around the star in less than 23 hours, leading scientists to classify it as a "hot Jupiter."
WASP-18b's tight orbit has led scientists to estimate that it may have only one million years of life or so remaining before it's destroyed by the parent star.
Pillitteri's team targeted WASP-18 with NASA's Chandra X-ray Observatory and found it to be relatively quiet - a characteristic of older stars. Young stars tend to be more active, with stronger magnetic fields, larger flares and more intense X-ray emission. Stellar activity is connected to rotation, a process that slows with age.
Observations of WASP-18 using Chandra revealed no X-ray emission. This by itself would suggest that the star has an age similar to the sun's 5 billion years, researchers said. However, Pillitteri and his team used other data as well as theoretical models to calculate that WASP-18 is actually just 500 million to 2 billion years old, and thus approximately 100 times less active than a star its age should be.
The difference, the researchers determined, is due to the planet.
"We think the planet is aging the star by wreaking havoc on its innards," said co-author Scott Wolk, of the Harvard-Smithsonian Center for Astrophysics in Massachusetts.
WASP-18b's strong gravitational pull may be disrupting the star's magnetic field, researchers said. The planet's tug exerts forces similar to those imposed on Earth's tides by the moon, but on a much larger scale.
The strength of a star's magnetic field depends on how much the hot gases within the star stir up its interior, a process known as convection. WASP-18 has a convection zone narrower than most stars, making it more vulnerable to the massive tidal forces exerted by WASP-18b, researchers said.
"The planet's gravity may cause motions of gas in the interior of the star that weaken the convection," said co-author Salvatore Sciortino, also of INAF-Osservatorio Astronomico di Palermo. "This has a domino effect that results in the magnetic field becoming weaker and the star to age prematurely."
The results were published in the July issue of the journal Astronomy and Astrophysics.
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Artist's concept depicting the giant alien planet WASP-18b and its star, which are about 330 light-years away.
Exquisite Exoplanetary Art
Sept. 19, 2011 --
They're alien worlds orbiting distant stars far out of reach of detailed imaging by even our most advanced telescopes. And yet, day after day, we see vivid imaginings of these extrasolar planets with the help of the most talented space artists. The definition of an extrasolar planet -- or "exoplanet" -- is simply a planetary body orbiting a star beyond our solar system, and nearly 700 of these extrasolar worlds have been discovered so far (plus hundreds more "candidate" worlds). With the help of NASA's Kepler space telescope, the ESO's High Accuracy Radial velocity Planet Searcher (HARPS), French COROT space telescope and various other advanced exoplanet-hunting observatories, we are getting very good at detecting these worlds, but to glean some of the detail, we depend on artist's interpretations of fuzzy astronomical images and spectral analyses. That's the way it will be until we build a vast telescope that can directly image an exoplanet's atmosphere or physically travel to an alien star system. So, with the flurry of recent exoplanet discoveries, Discovery News has collected a few of the dazzling pieces of art born from one of the most profound searches mankind has ever carried out: the search for alien worlds orbiting other stars; a journey that may ultimately turn up a true "Earth-like" world.
As an exoplanet passes in front of its star as viewed from Earth, a very slight dip in starlight brightness is detected. Observatories such as NASA's Kepler space telescope use this "transit method" to great effect, constantly detecting new worlds.
Some exoplanets orbit close to their parent stars. Due to their close proximity and generally large size, worlds known as "hot Jupiters" are easier to spot than their smaller, more distant-orbiting cousins.
The primary thrust of exoplanet hunting is to find small, rocky worlds that orbit within their stars' "habitable zones." The habitable zone, also known as the "Goldilocks zone," is the region surrounding a star that is neither too hot nor too cold. At this sweet spot, liquid water may exist on the exoplanet's surface. Where there's water, there's the potential for life.
Usually, exoplanet hunters look for the slight dimming of a star or a star's "wobble" to detect the presence of an exoplanet. However, in the case of Kepler-19c, its presence has been detected by analyzing its gravitational pull on another exoplanet, Kepler-19b. Kepler-19c is therefore the Phantom Menace of the exoplanet world.
The habitable zone seems to be the pinnacle of extraterrestrial living. If you're an alien with similar needs to life on Earth, then you'll need liquid water. If your planet exists outside your star's habitable zone, well, you're in trouble. Either your world will be frozen like a block of ice, or boiling like a kettle. But say if your world had the ability to extend your star's habitable zone? There may be some atmospheric factors that might keep water in a comfy liquid state. Even better, if you like deserts, a dry world could even be oddly beneficial.
Planets with a global magnetic field, like Earth, have some dazzling interactions with the winds emanating from their stars. The high-energy particles bombard the planet's atmosphere after being channeled by the magnetism. A wonderful auroral lightshow ensues. But say if there's an exoplanet, with a magnetosphere, orbiting really close to its star? Well, stand back! The entire world would become engulfed in a dancing show, 100-1000 times brighter than anything we see on Earth.
"Candidate" exoplanets are often mentioned, especially when talking about detections by the Kepler space telescope. But what does this mean? As a world passes in front of its star, slightly dimming the starlight, this isn't considered a "confirmed" exoplanet detection. To make sure that signal is real, more orbital passes of the exoplanet need to be logged before a bona fide discovery can be announced. Until then, these preliminary detections are called exoplanet candidates.
Angry Suns, Naked Planets
Exoplanets come in all sizes and all states of chaos. Some might have wonky orbits, others might be getting naked. Other times, they're simply being ripped apart by X-rays blasted from their parent star. Bummer.
Super-Earths get a lot of press. Mainly because "Earth" is mentioned. Sadly, most of these worlds are likely completely different to anything we'd call "Earth." And you can forget calling the vast majority of them "Earth-like." It's simply a size thing -- they're bigger than Earth, yet a lot smaller than Jupiter, hence their name, "super-Earth." Easy.
For now, we have to make do with artist's renditions of exoplanets for us to visualize how they may look in their alien star systems. However, plans are afoot to send an unmanned probe to an interstellar destination. Although these plans may be several decades off, seeing close-up photographs of these truly alien worlds will be well worth the wait.