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.
NASA has selected a $200 million mission to carry out a full-sky survey for exoplanets orbiting nearby stars. The space observatory, called the Transiting Exoplanet Survey Satellite (TESS), is scheduled for a 2017 launch.
Like the currently operational Kepler Space Telescope, TESS will be in the lookout for exoplanets that orbit in front of their host stars, resulting in a slight dip in starlight. This dip is known as a “transit” and Kepler has revolutionized our understanding about planets orbiting other stars in our galaxy by applying this effective technique. As of January 2013, Kepler has spotted 2,740 exoplanetary candidates.
Although Kepler’s powerful optics have allowed astronomers an unprecedented look into multiplanetary systems, identifying worlds as small as Mercury to many times the size of Jupiter, it is restricted to gazing at a small field of view — accounting for a mere 0.28 percent of the sky. Tiny it may be, but 145,000 main sequence stars fill that view, providing us with a gargantuan amount of transit data for hundreds of exoplanets.
But TESS will be surveying the entire sky, supercharging our profound quest to understand how many stars like our own could host worlds, not too dissimilar to Earth, in their habitable zones.
“TESS will carry out the first space-borne all-sky transit survey, covering 400 times as much sky as any previous mission,” said TESS lead scientist George Ricker, of the Massachusetts Institute of Technology (MIT) Kavli Institute for Astrophysics and Space Research (MKI). “It will identify thousands of new planets in the solar neighborhood, with a special focus on planets comparable in size to the Earth.”
“The TESS legacy will be a catalog of the nearest and brightest main-sequence stars hosting transiting exoplanets, which will forever be the most favorable targets for detailed investigations,” added Ricker.
According to a NASA announcement on Friday, “TESS will use an array of telescopes to perform an all-sky survey to discover transiting exoplanets ranging from Earth-sized to gas giants, in orbit around the nearest and brightest stars in the sky. Its goal is to identify terrestrial planets in the habitable zones of nearby stars.”
Kepler was launched in 2009 and recently saw its mission extended to 2016. It is hoped that the space telescope will detect unequivocal evidence for the presence of an Earth-sized world orbiting within its host star’s habitable zone — the region that is not too close and not too far from a star that permits liquid water to exist on a rocky planet’s surface.
Although we are some time off from probing a distant potentially habitable world’s atmosphere for the presence of liquid water or chemical traces of life, Kepler — along with supporting observations by other space- and ground-based instrumentation — is giving us a tantalizing hint of the preponderance of small rocky worlds in the Milky Way. Using Kepler data, astronomers extrapolated an estimated exoplanetary population for the Milky Way earlier this year and arrived at a staggering number: 100 billion. This, in turn, suggests there are many, many multiplanetary systems out there.
TESS will undoubtedly become the “next generation” of exoplanet hunters, revolutionizing our perspective on our cosmic backyard once again.
Submitted as concepts for NASA’s Explorer program, TESS and the $55 million Neutron Star Interior Composition Explorer (NICER) were chosen from four options as they “offer the best scientific value and most feasible development plans.” NICER will be attached to the space station to measure the “variability of cosmic X-ray sources, a process called X-ray timing, to explore the exotic states of matter within neutron stars and reveal their interior and surface compositions,” according to the NASA news release.
NASA’s Explorer program is intended to provide frequent, low-cost science missions. Satellite missions are capped at $200 million, whereas space station missions are capped at $55 million.
Image: Artist’s impression of the Transiting Exoplanet Survey Satellite. Credit: MIT Kavli Institute for Astrophysics and Space Research