Image: Kepler-16b is the first exoplanet disc
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.
Image: An exoplanet passes in front of (or "t
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.
Image: An artist's impression of Gliese 581d,
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.
Credit: David A. Aguilar (CfA)
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.
Image: A cool world some distance from its st
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.
Image: A "hot Jupiter" and its two hypothetic
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.
Credit: Adrian Mann, <a href="http://www.bisb
"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.
Image: An exoplanet being destroyed by X-rays
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.
Image: Artist's impression shows HD 85512b, a
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.
Credit: Adrian Mann, <a href="http://www.bisb
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.
Spanning the gap between large planets and small stars lies an astronomical gray area. This is the domain of brown dwarfs, dim stellar cinders glowing faintly in the darkness. And a binary pair of these stars has just been discovered only 6.5 light-years away, making it the third closest star system to our own.
Star system WISE J104915.57-531906 was announced officially just a few days ago. The tiny star system, orbiting each other once every 25 years, with a separation of 3 AU, was discovered by Kevin Luhman, a researcher at Penn State’s Center for Exoplanets and Habitable Worlds. It is, in fact, the closest star system to be discovered since Barnard’s Star was found in 1916!
Brown dwarfs are the stellar embers that never caught aflame. The reason why? They are simply not massive enough to fuse hydrogen — the lifeblood of any star — in their cores. All fully-fledged stars, from tiny red dwarfs like Proxima Centauri to massive blue supergiants like Eta Carinae, are constantly fusing hydrogen in their cores. Too small to accomplish this, brown dwarfs are, instead, forced to seek easier power sources. They’re fueled by deuterium* fusion, and sometimes lithium fusion too.
In fact, there are a lot of unanswered questions about brown dwarfs. We know that they can form as stars do, and some are known to have planets. Given that some estimates suggest they could comprise up to two thirds of all stars in our neighborhood, there’s a good chance that they may be good places to look for planets. Luhman shares this view, especially given how close this new-found star system is to Earth.
Because they’re so underpowered, brown dwarfs glow like hot coals, rather than shining as their heavier brethren do. They appear brightest in infrared, and the smallest of them emit no visible light at all. This explains why WISE J104915.57-531906 managed to escape our attention for so long. Against the much brighter stars in the plane of the galaxy, these faint objects were simply far too dim to be discerned.
The catalog number WISE J104915.57-531906 (in lieu of any true name, at least for now) shows that the data for this discovery came from NASA’s Wide-field Infrared Survey Explorer (WISE) satellite, which scoured the sky in infrared light from 2009 to 2011. One of the goals of WISE was always to discover the closest star systems to the sun. This latest find, then, is a triumph for the team behind WISE, led by principal investigator Ned Wright.
Luhman managed to spot this diminutive binary in the WISE data by using a fairly nifty little trick. You see, all stars move as they drift through our galaxy, and the closer they are to us here on Earth, the faster they seem to move relative to other stars. This effect is called parallax, and is extremely useful in astronomy.
The apparently speedy motion of this star across the sky was what allowed the pair of dwarfs to be found. Luhman then used the Gemini South observatory in Chile to take some followup observations, discovering that this object is a binary, and checking the spectra of the pair to identify them as brown dwarfs.
“Based on how this star system was moving in the images from the WISE survey, I was able to extrapolate back in time to predict where it should have been located in the older surveys and, sure enough, it was there,” Luhman explains. ”It was a lot of detective work. There are billions of infrared points of light across the sky, and the mystery is which one — if any of them — could be a star that is very close to our solar system.”
* I should clarify, deuterium is an isotope of hydrogen, with one extra neutron in its nucleus. While this means that the two are practically identical chemically, in nuclear physics they’re completely different things!
Image: Artists impression of the binary brown dwarf system WISE J104915.57-531906, with the Sun in the background. Credit: Janella Williams, Penn State University.