Exoplanet Count Blasts Through the 1,000 Barrier
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.
Hunting for signs of extrasolar planets — or exoplanets — is hard, but counting them can also prove tricky. Today, however, our historic era of exoplanetary discovery has turned into a red letter day; the first 1,000 exoplanets to be confirmed have been added to the Europe-based Extrasolar Planets Encyclopaedia.
For the last few weeks, astronomers (and the science media) have been waiting with bated breath as the confirmed exoplanet count tallied closer and closer to the 1,000 mark. Then, with the help of the Super Wide Angle Search for Planets (SuperWASP) collaboration, the number jumped from 999 to 1,010 overnight.
The 11 new additions may be noteworthy as breaking the 1,000 barrier, but they’re certainly not noteworthy as being anything remotely habitable. All 11 scoot around their parent stars with periods of between 8 and less than 2 days — making all of these new confirmed worlds “hot-Jupiters.”
Keeping a tally of exoplanets isn’t as easy as it seems. Although the Extrasolar Planets Encyclopaedia has been updated, it may be some time until other exoplanetary lists are updated. For example, NASA’s Jet Propulsion Laboratory keeps its own record called the Exoplanet Archive which currently lists the tally at 919. Why the discrepancy? One reason, according to New Scientist, is that the Extrasolar Planets Encyclopaedia lists exoplanets as soon as their confirmation is announced at conferences. The NASA list, however, only lists them once they’ve been published in a scientific journal. The NASA list will therefore always lag its European counterpart.
Also, some of the 1,000 exoplanets in the list are subject to intense scrutiny as there are some very massive worlds with stellar characteristics. After further study, some may be characterized as brown dwarfs, or “failed stars,” bumping them from being true planetary bodies.
1,000 exoplanets may seem like a big number, but the now defunct NASA Kepler Space Telescope suggests that there are thousands of candidate exoplanetary signals in its transit data awaiting confirmation by other surveys. But even if we end up confirming thousands more over the coming years, that number will pale into insignificance considering there are an estimated 100 billion alien worlds orbiting other stars in our galaxy. Our quest to find habitable exoplanets has only just begun.
But for now, welcome the newest 11 confirmed exoplanets:
WASP-76 b — 0.92 Jupiter masses, orbital period: 1.8 days
WASP-82 b — 1.24 Jupiters, 2.7 days
WASP-84 b — 0.694 Jupiters, 8.5 days