With time it was realized that the Earth was just one of the solar planets orbiting the sun, but skepticism that planets existed outside the solar system remained strong.  However, with the advent of new techniques and more power telescopes researchers began to discover extrasolar planets at a rapid pace, starting in the 1988, with the discovery of planets orbiting the star Gamma Cephei.  Meanwhile a large new orbiting body was discovered on the fringes of our own system, while Pluto was downgraded to a mere "Plutoid".

Some of these planets were deemed somewhat Earth-like in that they were smaller than gas giants, might have water, and could be made to be habitable.  Other extrasolar planets were similar in size to Earth, but were way to hot to inhabit with current technologies.

Now European astronomers have continued the run of discoveries of smaller planets with the discovery of a trio of "super-Earths" rotating around the star HD 40307, located 42 light-years from Earth towards the southern Doradus and Pictor constellations.  The new planets have masses of 4.2, 6.7, and 9.4 times the mass of Earth and orbits of 4.3, 9.6, and 20.4 days respectively.

The star they orbit is a normal star, approximately the same size as our sun.  According to Didier Queloz and Michel Mayor, expert planet hunters who led the discovery team, the planets are too hot to support life as we know it.

However, despite this slight disappointment, the discovery raises the intriguing possibility of a so-called "crowded universe" teeming with undiscovered planets.  HD 40307 was long thought to hold no planets -- it is clear now that the discovery was only possible with the advances in detection.  There are likely many smaller planets that have yet to be detected.  In total 270 extrasolar planets have already been found.

Stéphane Udry, a colleague of Mayor, describes the advance stating, "With the advent of much more precise instruments such as the HARPS spectrograph on ESO's 3.6-m telescope at La Silla, we can now discover smaller planets, with masses between 2 and 10 times the Earth's mass."

Mayor who works at the Geneva Observatory states, "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.  Clearly these planets are only the tip of the iceberg.  The analysis of all the stars studied with HARPS shows that about one third of all solar-like stars have either super-Earth or Neptune-like planets with orbital periods shorter than 50 days."

The slowly unfolding picture of a universe full of planets brings two key possibilities.  First, the possibility of expansion and colonization outside the solar system, and secondly, the possibility of extraterrestrial life.