The Kepler satellite, launched by NASA in March 2009, has started bearing its first fruits. The principal investigators of the space mission searching for planets outside our Solar System announced the first discoveries last Monday, at the annual meeting of the American Astronomical Society, taking place these days in Washington DC, USA.
Five new planets, orbiting stars at distances of more than 100 light-years from our Sun, have been detected during Kepler’s first months of observations. They now join the count of extra-solar planets discovered so far, amounting to over 400. Thanks to advances, obtained only in the past 15 years, astronomers can better understand how planets and planetary systems like our own form around other stars.
The new worlds discovered by Kepler are very different from our planet, being much larger and much hotter than the Earth. Four of them are even larger than Jupiter, the biggest planet in the Sun’s court; only one of them is slightly smaller, with a size similar to that of Neptune, another giant in the Solar System.
Due to their high temperatures of more than 1200 degrees Celsius, it is almost impossible to suppose that these planets host any form of “earth-like” life. However, the goal of the Kepler mission is ambitious: in the upcoming three years of observations it will be very likely that astronomers will detect planets similar to our own, somewhere in our galaxy.
The fact that the first planets to be discovered are giant ones is a sort of “drawback” of the method employed in the search. Kepler makes use of the so-called transit technique: when a planet orbiting a star intervenes between it and us, the star becomes clearly dimmer, as its light is obscured by the planet. Through monitoring hundreds of thousands stars over long time scales, astronomers study how their luminosity varies and can thus reveal the presence of one, or more, planets around them.
The bigger the planet, the more pronounced is its obscuring effect upon the star hence the easier it is to discover. But size isn’t everything, as also the distance from the parent star plays an important role. All five of these worlds lie very close to their sun, and only take a few days to complete an orbit around it. In comparison, the Earth takes a year and Mercury, the closest planet to our Sun, takes about three months to complete a so-called revolution.
The vicinity of these planets to their parent star is indeed another factor in their discoverability: as they orbit so fast around it, they obscure the star very often, thus making it more likely for astronomers to notice over human time scales. A planet that takes months or years to orbit its star is more elusive, although not absolutely impossible to detect.
“It's only a matter of time before more Kepler observations lead to smaller planets with longer-period orbits, coming closer and closer to the discovery of the first Earth analog,” said Jon Morse, director of the Astrophysics Division at NASA Headquarters in Washington.
The discovery of planets located at “reasonable” distances from the star they orbit is a crucial step towards the quest for other worlds that could theoretically host life forms. The so-called “habitable zone” defines the range of distances around a given star where the temperature is such to guarantee liquid water on a planet’s surface. In the case of our Sun, this distance corresponds roughly to Earth’s orbit — closer or farther away, the development of human life “as we know it” couldn’t have been possible.
None of the over 400 planets discovered so far lies in its parent star’s “habitable zone”. However, astronomers believe in Kepler’s capabilities and hope that it will be able to detect some in the upcoming years. Furthermore, the question about the existence of life elsewhere in the universe is not restricted to living forms similar to those inhabiting our own planet. “In other regions of this Universe, everything I can’t even imagine exists,” Bluvertigo (*) sang over ten years ago. Let us be surprised by the unimaginable.
(*) Bluvertigo are an Italian rock band formed in the mid-nineties and still active. The quote refers to the popular song “Altre forme di vita” (translated, “Other forms of life”) from 1997.
The image on top shows Kepler, launched on March 6th, 2009 from Cape Canaveral, Florida, USA. The image below is an artistic representation of one of the newly discovered worlds. Credits: NASA/Kim Shiflett and NASA/JPL-Caltech/T. Pyle (SSC), respectively.
Translated from Il Denaro, 07.01.10
