© unknownKepler Space Telescope
A NASA spacecraft has found an unusual three-planet system that consists of one super-Earth and two Neptune-size worlds orbiting a star similar to our sun, a new study reveals.
The
planet-hunting Kepler Space Telescope discovered the three planets around the star Kepler-18, which is only 10 percent larger than the sun and contains 97 percent of the sun's mass, researchers from the University of Texas at Austin said. The alien system could also host more planets than have been found so far, they added.
All three planets, which are designated Kepler-18b, c, and d, orbit much closer to their parent star than Mercury does to the sun. The planet Kepler-18b orbits closest to the star, taking 3.5 days to complete its journey. The planet is about 6.9 times the mass of Earth and is twice the size of our home planet, making planet b a so-called
super-Earth, the researchers said.
Kepler-18c, which takes 7.6 days to orbit the star, is about 5.5 times larger than our planet, and has a mass equivalent to about 17 Earths. Kepler-18d has a 14.9-day orbit and is about seven times the size of Earth, with a mass of about 16 Earths. According to these figures, planets c and d qualify as low-density "Neptune-class" worlds, the researchers said.
The findings were presented Tuesday (Oct. 4) at a joint meeting of the European Planetary Science Congress and the American Astronomical Society's Division of Planetary Science in Nantes, France. The study will be published in a special issue of
The Astrophysical Journal Supplement Series in November.
Scanning the cosmosNASA's
Kepler spacecraft
hunts for exoplanets using the transit method, which looks for periodic dips in a star's brightness over time that could indicate a planet is passing in front of it from the telescope's perspective. The alien worlds around Kepler-18 were found using this method, but the orbits of the planets themselves were a point of interest to the researchers.
Kepler-18c orbits its parent star twice for every one orbit that Kepler-18d makes, explained study leader Bill Cochran of The University of Texas at Austin. But the two planets do not cross the face of their parent star at these same orbital periods.
"One is slightly early when the other one is slightly late, [then] both are on time at the same time, and then vice-versa," Cochran said in a statement.
This suggests that Kepler-18c and Kepler-18d are engaged in something of an orbital dance.
"It means they're interacting with each other," Cochran said. "When they are close to each other ... they exchange energy, pull and tug on each other."
Once Kepler identifies potential exoplanet candidates using the transit method, scientists around the world use ground-based telescopes to collect more data and try to separate real findings from any false positives.
The Kepler-18 systemThe planets around Kepler-18 helped astronomers out because the orbital activity between Kepler-18c and Kepler-18d indicated that they must belong to the same planetary system. But, proving the identity of Kepler-18b, the super-Earth, turned out to be a bit more complicated, Cochran said.
The team of astronomers used a technique called "planet validation," in which they examined the probability that the cosmic body could be something other than a planet. The researchers first analyzed high-resolution images of the space around the Kepler-18 star to see if the transit signal could have been caused by background objects in the vicinity.
"We successively went through every possible type of object that could be there," Cochran said. "There are limits on the sort of objects that can be there at different distances from the star. There's a small possibility that [Kepler-18b] is due to a background object, but we're very confident that it's probably a planet."
In fact, Cochran and his colleagues calculated that it is 700 times more likely that Kepler-18b is a real planet rather than a background object.
Identifying alien planetsThe researchers said that this method of planet validation could play an important role in the
ongoing hunt for habitable alien planets.
"We're trying to prepare the astronomical community and the public for the concept of validation," Cochran said. "The goal of Kepler is to find an
Earth-size planet in the habitable zone [where life could arise], with a one-year orbit. Proving that such an object really is a planet is very difficult [with current technology]. When we find what looks to be a habitable planet, we'll have to use a validation process, rather than a confirmation process. We're going to have to make statistical arguments."
To date,
Kepler has found 1,235 planetary "candidates" that are awaiting confirmation through follow-up observations. Researchers have estimated that at least 80 percent of these will be verified as real planets.
Reader Comments
hkackson,
you are a troll who's been smoking from the wrong bowl..
Perhaps one of our excellent moderators will be so kind as to delete your small minded, and insulting drivel. Thus leaving room for someone to make an inteligent, on topic, coment regarding this article..
Perhaps the neptune comment was a bit sarcastic but I think the one year orbit comment was both inteligent and on topic. Perhaps more lessons are needed on your part as we are all in a different place on the curve.
My major in school is astrophysics and am attending UC Berkeley. My astronomy professors have always taught that one should always explain things in full detail as though they were explaining astronomy and physics to there 90 year old grandmother who may only know basic astronomy information (earth is not flat, orbits the sun, that the sun is a star, we have a moon orbiting us-the basic stuff). Neptune is an ice giant as is Uranus. 'Ice giant' is the common classification for these planets however many people draw a blank when hearing this. Often 'Neptune-class' is used and an acceptable synonym that is used when one wants to quickly move on to the message at hand.
As far as the orbit-that is information that is commonly default provided information or information that would be curious to those in the field. Perhaps one day when there are several thousands of exoplanets we will stop being curious. But right now it is interesting as we are in the infancy of understanding what the norms are for these bodies.
Sent from my iPhone-
With someone at my back nagging at the moment
ugh
Off to bed - I apologize for any typos. Or garbling if any. Been a long day.
-david