After two decades of one surprising exoplanet discovery after another, planet hunting astronomers have learned that when it comes to the discovery of alien worlds, they should definitely expect the unexpected. In June 2014, a team of astronomers announced their amazing discovery of a rocky world weighing-in at 17 times more than our Earth--and this hefty planet is also twice Earth's diameter.
The planet, dubbed Kepler-10c, has presented quite a challenge to planet formation theorists in their attempts to explain how such a weighty, rocky world could have formed.
Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, led the analysis using information originally gathered by NASA's extremely successful Kepler Space Telescope.
Kepler-10c had an earlier measured diameter of 2 to 3 times that of Earth, but its mass was unknown--until now. The team of astronomers used the HARPS-North instrument on the Telescopio Nazionale Galileo in the Canary Islands to conduct follow-up observations in order to obtain a mass measurement of the rocky giant planet.
Exoplanets In Search Of Another Earth
In search of another Earth we've discovered an extraordinary zoo of planetary nightmares outside our own solar system, all of them truly wild worlds, a collection of monsters.
It was previously thought that such worlds could not form because the immense gravitational force of such a heavy body would accrete a gas envelope during formation. This would cause the planet to blow up like a balloon into a gas giant the size of Neptune--or even Jupiter. In our own Solar System, Jupiter and the beautiful ringed planet Saturn, are gas giants, while Uranus and Neptune are classified as ice giants. All four gas-laden denizens of the outer regions of our Solar System are extremely large when compared to the four small rocky terrestrial planets that orbit closer to our Sun--Mercury, Venus, Earth, and Mars. However, Jupiter and Saturn are considerably larger than Uranus and Neptune, and possess much heavier gaseous envelopes. However, Uranus and Neptune have arger cores--composed of rock and ice--than Jupiter and Saturn. Indeed, Jupiter and Saturn may not possess solid cores at all beneath their immense, thick and very complicated shrouds.
Hefty Kepler-10c, however, is believed not to be a gaseous world at all--but is instead solid, composed primarily of rock.
"Just when you think you've got it all figured out, nature gives you a huge surprise--in this case, literally," commented Dr. Natalie Batalha on June 2, 2014. Dr. Batalha is a Kepler mission scientist at NASA's Ames Research Center in Moffett Field, California. She added: "Isn't science marvelous?"
For a generation now, astronomers have been continually developing new strategies to help them bag their exoplanet quarries. About 2000 exoplanets have been detected beyond our own Solar System, and about 1790 of them are situated in 1110 planetary systems that include approximately 460 systems containing more than one planet--at least, as of May 2014.
Kepler discovers exoplanets by using the transit method, searching for a star that dims slightly when an orbiting planet passes in front of its glaring face. By measuring the amount of dimming, astronomers can calculate the planet's physical size or diameter.
There are thought to be about 100 billion planets dancing around in our large, glowing, barred-spiral Milky Way Galaxy, with at least one planet per star. Our Milky Way also likely contains literally trillions of rogue planets, which are the sad orphans of the planet community, and are not members of the family of any star at all. These unfortunate worlds travel through interstellar Space, after having been ejected from the families of their stellar parents, as the result of gravitational interactions with sibling worlds.
Approximately one in five stars that are similar to our Sun are thought to sport "Earth-sized" planets, dwelling in the habitable zones around their stars. The habitable zone of a star is that comfortable region where the temperatures are such that liquid water can exist. Where liquid water exists, life as we know it has the potential to develop. However, not all planets in the habitable zones of their stars are friendly abodes for life. For example, in our own Solar System, Venus--like our Earth--dwells in the Sun's habitable zone. However, Venus, the tragic victim of a runaway greenhouse effect, has a surface that is so broiling-hot that it could melt lead. There is no liquid water on Venus--and it is clearly not a life-friendly world. In fact, it is an almost-Earth-sized, cloud-cloaked, ball of hell.
Scientists and philosophers have contemplated the possibility of life on distant worlds for centuries. However, until late in the twentieth century, they had no way to truly detect them, or of calculating their frequency.
The first discovery of exoplanets came in 1992, and these bizarre worlds did not circle a Sun-like star. In fact, they circled a type of stellar corpse called a pulsar, which is a rapidly spinning neutron star that emits lighthouse-like beacons into space at regular intervals. Pulsars are all that remains of a star that died an explosive supernova death after it had exhausted its necessary supply of "life"-sustaining nuclear fuel. The pulsar planets are far from hospitable worlds, being constantly showered with deadly radiation that is spewed out by their ghostly stellar host.
|Kepler-10 Stellar Properties|
Kepler-10c orbits its Sun-like star every 45 days. This makes it far too toasty for life as we know it to evolve there. It is located approximately 560 light-years from Earth in the constellation Draco. Kepler-10c sports a diameter of about 18,000 miles, which originally suggested to astronomers that it falls into a category of exoplanets called mini-Neptunes, which are blanketed by thick, gaseous envelopes. However, Kepler-10c's hefty weight showed that it had to have a very dense composition composed of rocks and other solids.
"Kepler-10c didn't lose its atmosphere over time. It's massive enough to have held on to one if it ever had it. It must have formed the way we see it now," Dr. Dumusque said in a June 2, 2014 CfA Press Release.
The discovery that Kepler-10c is a rocky, enormous, Earth-like world has profound implications for the history of the Universe--and the possibility of life. The Kepler-10 system is approximately 11 billion years old--this means that it took shape less that 3 billion years after the Big Bang birth of the Universe itself 13.8 billion years ago.
The ancient Universe knew only the two lightest atomic elements--hydrogen and helium--which were born in the Big Bang (Big Bang nucleosynthesis). The heavier atomic elements so necessary to cook up rocky planets--such as silicon and iron--had to be brewed up in the hot cauldrons of the first generation of stars (stellar nucleosynthesis). When those first ancient stars went supernova, they violently hurled these important ingredients throughout Space--where they could then be incorporated into later generations of sparkling new baby stars.
This process should have taken billions of years. However, the existence of Kepler-10c suggests that the Universe was able to give birth to such immense rocks even during that very ancient era when such heavy atomic elements were rare.
This research indicates that astronomers shouldn't rule out old stars when they hunt for Earth-like worlds. And if old stars can host rocky Earths too, then those who search for them have a better chance of spotting potentially habitable worlds in our own Cosmic neighborhood.
CfA researcher, Dr. Dimitar Sasselov, director of the Harvard Origins of Life Initiative, said at a June 2, 2014 press conference at the AAS meeting that "Finding Kepler-10c tells us that rocky planets could form much earlier than we thought. And if you can make rocks, you can make life."
Information & Resources:
NASA's Kepler Discovers First Earth-Size Planet In The 'Habitable Zone' of Another Star
American Astronomical Society
Telescopio Nazionale Galileo
Harvard-Smithsonian Center for Astrophysics
Harvard Origins of Life Initiative
Kepler Space Telescope
Nasa Kepler telescope discovers planet believed to be most Earth-like yet found
NASA Exoplanet Archive A service of NASA Exoplanet Science Institute
About the Author Judith E. Braffman-Miller
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various newspapers, magazines, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, "Wisps, Ashes, and Smoke," will be published soon.