Researchers have detected the first "exomoon" candidate -- a moon orbiting a planet that lies outside our solar system.
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.
For the first time, astronomers may have spotted a moon circling an alien planet -- though they'll probably never know for sure exactly what they've found.
A team of scientists detected a pair of faraway objects that could be a giant Jupiter-like alien planet and a rocky exomoon flying freely through space, or a small dim star hosting a planet about 18 times more massive than Earth.
The astronomers used a technique called gravitational microlensing, watching what happens a big foreground object passes in front of a star from our perspective on Earth. The nearby body's gravitational field bends and magnifies the light from the distant star, acting like a lens. [The Strangest Alien Planets Ever (Gallery)]
Analyzing lensing events can reveal a great deal about the foreground object — for example, in the case of a star, whether it hosts a planet and, if so, how massive that world is compared to the star.
In the new study, the team observed one intriguing lensing event using telescopes in New Zealand and the Australian state of Tasmania. They determined that the foreground object has an orbiting companion about 0.05 percent as massive as itself.
"One possibility is for the lensing system to be a planet and its moon, which if true, would be a spectacular discovery of a totally new type of system," Wes Traub, chief scientist for NASA's Exoplanet Exploration Program office at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement.
"The researchers' models point to the moon solution, but if you simply look at what scenario is more likely in nature, the star solution wins," added Traub, who was not involved in the study.
The team could solve the mystery if they knew how far away from Earth the lensing system, called MOA-2011-BLG-262, lies. If it's relatively nearby, MOA-2011-BLG-262 is probably a starless "rogue planet" and moon; a distant system would have to be as massive as a star to produce the same lensing effects, researchers said.
Unfortunately, the true identity of MOA-2011-BLG-262 will probably remain a mystery forever. Microlensing events are random encounters, so there will be no follow-up observations.
"We won't have a chance to observe the exomoon candidate again," study lead author David Bennett, of the University of Notre Dame, said in a statement. "But we can expect more unexpected finds like this."
And astronomers may be able to measure distances during future microlensing events using the principle of parallax, which describes how the position of an object appears to change when viewed from two different locations.
This strategy could work if observers manage to observe a lensing event with two widely spaced telescopes on Earth, or a ground-based scope and an instrument in orbit, such as NASA's Spitzer or Kepler space telescopes, researchers said.
Astronomers have discovered more than 1,700 alien planets to date, but they're still looking for their first confirmed exomoon.
The new study was led by the joint Japan-New Zealand-American Microlensing Observations in Astrophysics (MOA) and the Probing Lensing Anomalies NETwork (PLANET) programs. It appears in the Astrophysical Journal.
More from SPACE.com:
9 Exoplanets That Could Host Alien Life
Gallery: First Earth-Size Alien Planets Discovered
7 Ways to Discover Alien Planets