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.
Astronomers have announced the discovery of Kepler-76b — a “hot Jupiter” that takes only 1.5 days to complete an orbit around its star. Unofficially, however, Kepler-76b has been nicknamed “Einstein’s planet” as it was discovered using a novel method that applies a weird relativistic effect as theorized by Albert Einstein.
Usually, NASA’s Kepler space telescope looks for the very slight dips in starlight brightness as exoplanets orbit in front of their host stars from our perspective. Kepler is revolutionizing exoplanetary studies as it is sensitive to the detection of tiny worlds, which is only possible owing to the mission’s advanced optics.
Now, using Kepler data, astronomers have taken a different tact in the hunt for exoplanets.
Kepler-76b was discovered by looking for the slight brightening of a star as an exoplanet passes in front. How does that work?
Normally, as an exoplanet passes in front of a star’s disk, Kepler will detect a dip in brightness in that star’s “light curve.” The greater the dip, the bigger the planet. But this method only works if the orbital plane of the planet is exactly “edge-on” when viewed from Earth. What if there’s an exoplanetary system with an orbital plane inclined away from our point of view? To put it bluntly, Kepler won’t see those exoplanets — or will it?
In 2003, Avi Loeb of the Harvard-Smithsonian Center for Astrophysics (CfA) and Scott Gaudi (now at Ohio State University) had an idea. By their reckoning, if the optics of a space telescope are sensitive enough, the Einstein “beaming effect” should be observable. And on Monday, it was announced that this strange quirk in physics revealed the presence of Kepler-76b.
So, what is this beaming effect and how can it help in the search for exoplanets?
As Kepler-76b orbits its star, it “tugs” on the stellar body. Indeed, it’s this tugging effect that allows another exoplanet-hunting technique to come in to play. The “radial velocity” method is extensively used by ground-based observatories to detect the wobble of stars — as the exoplanet pulls the star toward us, its electromagnetic spectrum is slightly blue-shifted, as it’s pulled away, the spectrum is slightly red-shifted.
Relativistic beaming works in a similar manner, but there is no requirement to analyze the star’s spectrum.
As Kepler-76b is 25 percent larger than Jupiter and twice as massive, it has a sizable tugging effect on the star. The beaming effect occurs when the orbiting exoplanet tugs its star in our direction — the motion toward us creates a focusing effect on the photons we receive from the star — the photons to “bunch up” in the direction of travel, concentrating their energy, brightening the star.
This is the first time the effect has been applied to exoplanetary detection.
“We are looking for very subtle effects,” said team member David Latham of the CfA. “We needed high quality measurements of stellar brightnesses, accurate to a few parts per million,”
“This was only possible because of the exquisite data NASA is collecting with the Kepler spacecraft,” added lead author Simchon Faigler of Tel Aviv University, Israel.
Impressive as this detection may be, the team also wanted to test out two more very subtle of ways the massive exoplanet may be detected. While tugging on the star, the exoplanet elongates the star into a football shape due to the massive tidal forces exerted it. Therefore, the Kepler light-curve should also detect a slight brightening when it views the star from the side (as the “side” will have a larger surface area to radiate light than the “end”). Also, they wanted to see if they could detect the reflected light from the planet’s atmosphere too — another very faint, but measurable effect. They succeeded on all counts.
As a bonus, they also found observational evidence for violent jet streams in the exoplanet’s atmosphere, generating “hotspots” in the atmosphere, offset from the closest point to the star’s energy. The planet is “tidally locked” with its star (i.e. the same hemisphere always faces the star), so standing jetstreams blast from “high noon” (the location of the star, directly overhead) through the atmosphere, creating hotspots 10,000 miles away from noon.
If you’ve read this far wondering what this has to do with BEER, then I apologize. As much as I’d like to say that the spectroscopic signature of a hoppy chilled beverage has also been discovered in the exoplanet’s atmosphere, sadly, it’s not the case. BEER is the (rather forced) acronym for “relativistic BEaming, Ellipsoidal, and Reflection/emission modulations” — an algorithm designed by the researchers to look for relativistic beaming, tidally warped stars and reflected exoplanetary light.
There may not be beer, but it is a very impressive bit of physics detective work that uncovered an exoplanet Kepler may otherwise have missed.
Image credit: David A. Aguilar (CfA)