Taking a Closer Look at Alpha Centauri's Exoplanets
A low-cost mission could soon be launched to directly observe the exoplanetary system in orbit around Alpha Centauri, one of the solar system's nearest stellar neighbors.
While we think of stars as being very distant, there is one star system that is relatively close - Alpha Centauri, just 4.3 light-years away. In 2012, astronomers discovered a planet in that system; it orbited way too close to its parent star to be considered habitable, but it got a lot of attention because the exoplanet was so close to Earth.
Although the existence of Alpha Centauri Bb has been recently put into doubt, astronomers are still looking toward the neighboring star system in the hope of finding some hidden exoplanetary treasures.
Now, three years after the initial "discovery" of Alpha Centauri Bb, a research team led by Eduardo Bendek, a researcher with the astrophysics branch of NASA, hopes to get a better look at the star system to find habitable, Earth-size planets. Their plan is to launch a telescope that would look at Alpha Centauri for several months in hopes of seeing a small planet pass across the face of its parent star.
"The aim of my research is to develop the technology and a mission concept that will allow us to take the first direct image of an earth like planet around our closest star system, Alpha Centauri," wrote Bendek in an e-mail to Discovery News.
The mission (which is not funded right now) is called Alpha Centauri Exoplanet Satellite, or ACESat, and it would work differently than the famed Kepler telescope that has found more than 1,000 confirmed planets. Kepler looks for planets passing across the face of a star. ACESat would look for planets that are orbiting nearby.
The telescope his group proposes would be a first. It would include a coronograph (a device that blocks out direct light from the star) that makes it easier to spot a star than any one flown before. According to Bendek, it will let researchers see a tiny planet next to a star that is 10 billion times brighter.
Even if the researchers don't catch a planet during the two-year mission, they could still see signs of a debris disk. But if they do see planets, the lengthy observing time could help them characterize aspects such as the planets' size, mass and orbits.
Researchers point to the small size of the telescope mirror (as small as 25 centimeters) and its according relatively low cost to launch due to the small weight (less than $175 million) as reasons to give the design a shot. Its primary mission is very narrow, just looking at one star system, but in a proposed one-year extension the telescope would slew to several other bright, relatively nearby stars to look for more planets.
Bendek adds his team feels there is a good chance of spotting something. "Both stars are sun-analogs, making their environment more likely to be habitable than around brown and red dwarfs that are more unstable," he said.
ACESat was up for a call for proposals in October 2014 for NASA's small explorer program, but did not make the cut for the next stages of development. Nevertheless, Bendek said there is a path forward developing - although it isn't quite time to release what is going on yet, he said.
Artist’s impression of Alpha Centauri Bb, announced in 2012.
Cowboys & Aliens are Coming!
July 29, 2011 --
If aliens are going out of their way to kick up dust in the Wild West, as they do in the upcoming movie "Cowboys & Aliens," they must be coming from somewhere. Life could take root on a moon or a meteorite. But to nurture the kind of life that could destroy our saloons and harass our livestock, a planet might be the most suitable. So far, Kepler, a NASA orbiting telescope that searches for planets beyond our solar system, has detected over 1,200 exoplanets. Surely there must be a few candidates among this group that could meet some of the most basic requirements to host life? Explore some far-out worlds that could support aliens, be they cattle-rustling characters or a more peaceful people.
First, let's lay out some basic criteria. Kepler hasn't identified many rocky worlds and a solid surface is essential for life to take root. Size matters: The mass of the planet helps astrophysicists infer what it's made of. Some planets are Earth-sized. Others are several times the size of our planet. And then there are gas giants, which can range from "Neptune sized" to "super-Jupiters." Orbit: To support life, a planet must be in a stable orbit around its star -- no planets with wonky orbits that will eventually dump them into their star for a fiery death. Goldilocks Zone: This is a region not too hot or too cold that gives the planet enough distance from its parent star to have liquid water, key for life. Loner Stars: Single stars make better parents. In 2010, a pair of closely orbiting binary stars was spotted surrounded by what could be the debris of former planets. Unknowns: Some factors for life can't be confirmed one way or the other from the data available about extrasolar planets. These include: water, chemical compounds such as ammonia; a nitrogen-rich atmosphere; a magnetic field to repel solar and cosmic radiation; and more. BUT, some planets do have a head-start, beginning with Gliese 581D.
Located a mere 20 light-years away, practically our backyard in cosmic terms, Gliese 581d is situated on the "outer fringes" of the Goldilocks zone, orbiting a red dwarf star. The planet may be warm enough and wet enough to support life in much the same manner as Earth. It might also contain a thick carbon atmosphere. If we ever need a new Earth and have the means to get there, Gliese 581d may be our best bet for now.
When it was first detected and reported last year in Astrophysical Journal, Gliese 581g appeared to be the perfect candidate for a true "Earth-like" planet. Located in the same star system as Gliese 581d (and detected earlier), Gliese 581g seemed to be the right size and located within a habitable zone away from its parent star. Gliese 581g was said to have three times the mass of Earth, making it possible for the planet to hold an atmosphere. However, since its discovery, follow-up studies have alleged that Gliese 581g might have been a false alarm. In other words, the planet might not exist at all.
Dubbed a "waterworld" and located a mere 42 light-years from Earth, GJ 1214b orbits near a red dwarf star about one-fifth the size of our sun. What makes this planet unique is that it appears to be primarily composed of water, although GJ 1214b is 6.5 times the mass of Earth and 2.7 times wider, which classifies it as a "super-Earth." This planet also has a steamy atmosphere composed of thick, dense clouds of hydrogen, which, although it might not the case with this planet, could incubate life.
Situated 150 light-years from Earth, HD 209458b is a planet that holds traces of water vapor in its atmosphere, and also contains basic organic compounds that, on Earth, foster the development of life. But there are two factors working against HD 209458b as a suitable habitat. The planet is very hot due to its close proximity to its parents star, and it's a gas giant, so no solid surfaces.
If Kepler-10b were located further from its parent star, it might have had a chance of hosting life. Kepler-10b was the first "iron-clad proof of a rocky planet beyond our solar system" back in 2001. It was even dubbed the "missing link" of extrasolar planetary research. When it comes to the search for life, though, Kepler 10-b is missing a lot of other ingredients -- just minor things like water or an atmosphere.
When venturing to a new star system to explore the possibility of extraterrestrial life, trying a star that has already shown itself to nurture planets -- even if they're not the kind you're looking for -- could be a promising strategy. Project Icarus, an ambitious five-year study into launching an unmanned spacecraft to an interstellar destination, has identified two stars located within 15 light-years that might fit the bill: "epsilon Eridani, a single K star 10.5 light-years away, and the red dwarf GJ 674, 14.8 light-years away." Indirect evidence has also shown that epsilon Eridani may already hold smaller worlds scientists simply haven't detected yet. Also, red dwarf star systems generally may be a safe haven for life.
Are We Alone?
Taking into account the number of exoplanets that have been detected, as well as the vastly greater number that are estimated to be out there, some astrophysicists are convinced that extraterrestrial life is inevitable. After all, the Milky Way may be loaded with as many as 50 billion alien worlds. Some even think we'll find alien life by 2020. Others, however, say it may not exist at all. Recently, astrophysicists David Spiegel of Princeton University and Edwin Turner from the University of Tokyo suggested we might be alone in the universe, based on their interpretation of the Drake equation, a formula meant to determine loosely the probability of the existence of life beyond Earth. According to their analysis, just because life on Earth took shape early, endured and prospered doesn't mean the same process would naturally and inevitably occur elsewhere in the universe. Discovering life elsewhere, however, would be the only means of settling this debate. Unless the aliens find us first, of course.