Artist's impression of Kepler-11, one of the many multi-planetary systems discovered by NASA's Kepler space telescope.
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 hasn’t given up on resurrecting its planet-hunting Kepler space telescope, but even if the observatory can’t be saved, scientists expect it already has accomplished its goal of finding a habitable, Earth-like planet. They just don’t know it yet.
“We have quite a bit of data that needs to be fully processed,” said William Borucki, lead Kepler scientist at NASA’s Ames Research Center in Moffett Field, Calif.
“With what we’ve seen -- so many Earth-size planets and a number of planets in the habitable zone already, we’re really pretty positive that we will get the Earth-sized planets in the habitable zone around stars like the sun. I’m very optimistic that the data we have will allow us to accomplish that,” Borucki said.
After four years in orbit, Kepler’s hunt for planets beyond the solar system was suspended last week due to a problem with the telescope’s steering system. The spacecraft uses spinning wheels to keep itself steady enough to capture slight changes in the amount of light coming from distant target stars, some of which may be due to a planet passing by relative to the telescope’s line of sight.
Kepler needs at least three so-called reaction wheels to have a steady enough gaze for planet-hunting. Two have failed.
Engineers are mulling options for reviving the telescope, which so far has found 132 confirmed planets and identified another 2,700 contenders. Scientists are most interested in planets about the same size of Earth that orbit their parent stars about where Earth circles the sun. At that distance, surface temperatures likely would be suitable for liquid water, if any exists. Water is believed to be necessary for life.
“There are planets that we believe are (in the data) that we haven’t found yet,” Borucki said, estimating that the analysis and follow-up confirmations will keep the Kepler team busy for at least two years.
In a conference call with reporters last week, NASA managers said there was a reasonable chance Kepler could be revived.
Options include trying to coax one or both of the failed wheels back into service by running them backwards, for example. If that were successful, Kepler would need to fight the destabilizing pressure of sunlight on the observatory by firing its maneuvering thrusters occasionally, limiting its mission lifetime.
“Like with any stuck wheel ... we could try jiggling it, we could try commanding it back and forth in both directions, we can try forcing it through whatever the resistance is that’s holding it up,” said deputy project manager Charles Sobeck, who is also with Ames.
NASA expects it will take a few weeks to assess the options and decide what recovery attempts to make.
Not everyone was so optimistic, however.
"I think ‘The mission is not over’ means ‘the mission is over.’ Might be other things it can do. But, kids, I think the mission is over,” astronomer Mike Brown, with the California Institute of Technology, wrote on Twitter.
Just before Kepler’s shutdown, another team of astronomers unveiled a new method to comb through Kepler data for planets that uses quirky aspects of Einstein’s theory of relativity.
Though precise and repeated measurement of a star’s light is still needed, the new technique looks for a slight brightening of light from target stars. Kepler data typically is analyzed for light dips as planets pass across the face of their parent stars, relative to Kepler’s line of sight.
The brightening is a manifestation of a planet tugging on its parent star, which causes photons of light to squeeze together, concentrating the energy and temporarily brightening the star. The technique does not require a planet to transit its parent star’s face, but the effects may be too subtle for hunting for anything other than massive planets orbiting close to their parent stars.