Do you have a citation for this? To the best of my knowledge we've only discovered a handful of earth-type planets (something around the number I could count on the fingers of one hand) as opposed to well over a hundred Jupiter-type planets.
In our solar system perhaps lol......
Recent discoveries bring to 45 the total number of Earth-like planets with an orbital period shorter than 50 days it has discovered, and suggests one in three stars similar to our sun may harbour such planets. This is as far as our pretty caveman like technology will allow us to go. We're basically just venturing out to our mailbox, if that, in terms of discovering "the world" (universe).
Last Updated: Monday, June 16, 2008
European astronomers said Monday they have discovered five "super-Earths" — including three orbiting a single star — which they say suggests Earth-like planets could be very common outside our solar system.
The discoveries, revealed at a conference in France, were made using a spectrograph at the La Silla Observatory in Chile, which is run by the European Organization for Astronomical Research in the Southern Hemisphere, or ESO.
Planet hunter Michel Mayor, best known for discovering the first confirmed planet outside our solar system, said in a statement the finds suggest the search for Earth-like planets has just begun.
"Does every single star harbour planets and, if yes, how many? We may not yet know the answer but we are making huge progress towards it," said Mayor, the principal investigator at the ESO's Geneva Observatory.
The term Earth-like planet is a rather broad definition and includes planets with a mass below 30 Earth masses; in other words, planets smaller than gas giants like Jupiter or Saturn. But because they aren't as easy to spot as gas giants, even the largest of these planets evaded detection until recent years.
These planets are often discovered, but not seen directly, by monitoring the slight changes their gravitational pull have on the velocity of their stars. Occasionally a planet will actually pass in front of the Earth's view of the star and provide an even clearer signal of its presence. But in either case, the more frequently the planet orbits the star, the easier it is to spot.
The star with the three Earth-like planets, called HD 40307, is slightly less massive than our sun and is located 42 light-years, or about 400 trillion kilometres, away from Earth.
The planets have masses 4.2, 6.7 and 9.4 times that of Earth, and orbit the star with periods of 4.3, 9.6, and 20.4 days, respectively.
The astronomers discovered the other two Earth-like planets in two separate star systems. One planet with 7.5 times the mass of the Earth, was discovered orbiting the star HD 181433, a star that is already known to host a Jupiter-like planet. The second system contains a planet with 22 times the mass of Earth.
More than 270 planets have been discovered outside our solar system, but as instruments become more precise, research is increasingly focusing on planets similar to Earth, particularly those at a distance similar to our own planet's distance from the sun.
Astronomers see this as the "sweet spot," since the temperature and conditions might allow for the presence of liquid water, a key ingredient for supporting life.
Posted: March 12, 2008
Alpha Centauri, the closest star system to our Solar System, should harbour detectable Earth-like planets, according to a new study by astronomers at the University of Santa Cruz.
Computer simulations of planet formation were performed to show that terrestrial planets are likely to have formed around one of the three stars in the system, Alpha Centauri B. Moreover, the planets would have formed in the 'habitable zone", where liquid water can exist on the planet's surface. Although many different simulations were performed, starting with a variety of different initial conditions, in every case a system of multiple planets evolved with at least one planet about the size of Earth.
Gliese 581 c generated a lot of interest as it was initially reported to be the first potentially Earth-like planet in the habitable zone of its star, with a temperature right for liquid water on its surface and hence, potentially capable of supporting life as we know it. However, subsequent study that took into account the insolation that gives the planet five times the heat the Earth receives and the greenhouse gas effect of the planet’s atmosphere, with at least five times the greenhouse gases, now appears to make this very unlikely.
Gliese 581 d, the third planet in the Gliese system, is now regarded as more likely to harbor life. The planet is astronomically close, at 20.4 light years (193 trillion km or 119 trillion miles) from Earth in the direction of the constellation of Libra
2 months ago
Sources
www.cbc.ca/technology/story/2008/06/16/e...
www.nasa.com/earthlike/search:2007orbitsearchkey...
