C. Pulliam & D. Aguilar (CfA)
Artist's impression of KOI-314c, with neighboring exoplanet KOI-314b, orbiting their red dwarf star.
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’s Kepler space telescope has discovered a veritable menagerie of alien worlds orbiting other stars, but this most recent exoplanetary find is perhaps one of the strangest. The world is of the approximate mass of the Earth, yet it has a ‘puffed-up’ atmosphere, making it appear 60 percent larger than our planet.
Located 200 light-years away, KOI-314c orbits its dim red dwarf star once every 23 days. The close proximity to its star ensures that it has a rather toasty atmosphere of around 220 degrees Fahrenheit (or 104 degrees Celsius) — a little above the boiling point of water at sea-level (on Earth). Any discussion of the possibility for life as we know it is moot, but this new discovery is notable nonetheless; this is the first Earth-mass exoplanet discovered that had its mass measured by using Transit Timing Variations (TTVs).
The easiest way to gauge an exoplanet’s mass is to watch the ‘wobble’ of its host star as it orbits. This may be an effective tool for the more massive exoplanets, but when it comes to planets of Earth-like masses, their featherweight gravitational fields have a minimal effect on the star, making the wobble difficult to discern. Lacking star ‘wobble’ data (otherwise known as radial velocity data), an international team of astronomers used an ingenious technique to measure KOI-314c’s mass.
KOI-314c has company. This exoplanet exists in a multi-planetary system with at least one other exoplanet. The second exoplanet, called KOI-314b, also travels across the face of its star from our perspective (an event known as a ‘transit’), allowing Kepler to make very precise measurements of both planet’s orbital periods. KOI-314b is around the same size as KOI-314c, but it is a lot more dense, ‘weighing-in’ at 4 times the mass of the Earth.
Like the planets in our solar system — and, indeed, the systems of moons around Saturn and Jupiter — KOI-314b and KOI-314c tug on each other gravitationally. From Kepler’s perspective, this gravitational tugging manifests itself as slight changes in transit timings. TTVs have been used to discover the gravitational presence of undiscovered planets that lurk in unseen multi-planetary systems, tugging on other planets that transit their star.
Fascinatingly, TTVs are also being used in an effort to detect exomoons orbiting transiting exoplanets (as the moons’ gravitational tug should cause their parent exoplanet to wobble very slightly, causing a TTV) and the team of astronomers were actually seeking out exomoons in Kepler TTV data when they serendipitously discovered a unique way of deducing KOI-314c’s mass.
“When we noticed this planet showed transit timing variations, the signature was clearly due to the other planet in the system and not a moon,” said David Kipping of the Harvard-Smithsonian Center for Astrophysics (CfA) and lead author of the discovery. “At first we were disappointed it wasn’t a moon but then we soon realized it was an extraordinary measurement.”
“Rather than looking for a wobbling star, we essentially look for a wobbling planet,” said co-investigator David Nesvorny, of the Southwest Research Institute (SwRI). “Kepler saw two planets transiting in front of the same star over and over again. By measuring the times at which these transits occurred very carefully, we were able to discover that the two planets are locked in an intricate dance of tiny wobbles giving away their masses.”
KOI-314b orbits the star every 13 days, giving it a 5-to-3 resonance with KOI-314c — for every 5 orbits by KOI-314b, KOI-314c orbits 3 times.
Apart from proving that TTVs can be used to gauge the mass of transiting exoplanets, the discovery only adds to the fascinating variety of strange new worlds Kepler is uncovering in our galaxy.
“This planet might have the same mass as Earth, but it is certainly not Earth-like,” said Kipping. “It proves that there is no clear dividing line between rocky worlds like Earth and fluffier planets like water worlds or gas giants.”
Knowing the mass and physical size of KOI-314c, Kipping’s team were able to deduce the exoplanet’s average density — it is only 30 percent more dense than water. Therefore, the astronomers have deduced, the world must be a rocky world which is covered a dense atmosphere of hydrogen and helium, hundreds of miles thick. It seems likely that the world was once a Neptune-like gas giant, but over time, the close proximity to its star boiled off the vast majority of its atmosphere, shrinking it to a more Earth-like mass.
Kipping and his team presented their findings on Monday at the 223rd meeting of the American Astronomical Society in Washington D.C.