NASA's early afternoon press conference lived up to expectations, announcing two new planetary discoveries in the Neptune-mass range. The planet detected around the star 55 Cancri is one of four now known to orbit there, making 55 Cancri the most complete extra-solar planetary system we've found. Nobody knows whether the new 55 Cancri planet is rocky or gaseous, but its mass -- roughly 18 times that of the Earth -- and its location close to its parent star have many speculating that it formed through the accumulation of smaller rocky bodies. Barbara McArthur of the University of Texas, Austin and colleagues found the planet by studying observations made at the Hobby-Eberly Telescope at McDonald Observatory in West Texas. 55 Cancri continues to loom large among extrasolar planetary systems. To me, the most interesting of its planets is the fourth, a gas giant that orbits roughly at the same distance that Jupiter does from the Sun. With almost 140 extrasolar planets now found, the...

Lots of background on mu Arae's (second) discovered planet in this press release from the European Southern Observatory. The discovery was made possible by the HARPS (High Accuracy Radial Velocity Planet Searcher) spectrograph attached to ESO's 3.6-meter La Silla telescope in Chile. The planet previously discovered at mu Arae is roughly Jupiter-size and orbits the star every 650 days. The new one, much closer in, has the mass of Uranus, and thus straddles the line between rocky and gas giant worlds. To quote the press release (text in bold as given by ESO): The mass of this planet places it at the boundary between the very large earth-like (rocky) planets and giant planets. As current planetary formation models are still far from being able to account for all the amazing diversity observed amongst the extrasolar planets discovered, astronomers can only speculate on the true nature of the present object. In the current paradigm of giant planet formation, a core is formed first through...

Keep your eyes on NASA next Tuesday. SpaceRef.com is carrying a NASA press release that says the agency will announce the 'discovery of a new class of planets' next Tuesday at 1 PM EDT. The press conference will be carried live on NASA television or you can check the Webcast here. Exactly what this is escapes me, but I suspect we're getting into the era of small planet detections, as per the story immediately below. Geoff Marcy and Paul Butler, planet finders extraordinaire, are among those who will appear on the NASA panel.

A planet fourteen times the size of the Earth may not be all that small, but it's tiny compared to the bulk of planets discovered around other stars, most of which are so-called 'hot Jupiters' -- gas giants in tight orbits around their parent star. The European Southern Observatory's La Silla telescope has now found a much smaller planet, and one that may well be rocky, a kind of 'super Earth,' as some researchers have said. But the new planet orbits the star mu Arae (about fifty light years from Earth) so tightly that it completes its orbit in less than ten days, making for temperatures that probably top 1000 degrees Fahrenheit. You can read more about the mu Arae planet at Space.com, whose story quotes Alan Boss of the Carnegie Institution in Washington as saying, "It's much closer to our solar system than anything we've found so far...I'm still somewhat stunned that they have such good data." The star mu Arae is similar in size and brightness to the Sun, and the new planet seems...

Over 135 planets have now been discovered by studying their effects on the star they orbit, which produce a pronounced wobble. But so far, only a few have been found by using the transit method, detecting the periodic dimming of a star as a planet passes between it and the Earth. Now a planet called TrES-1 has been located by the Trans-Atlantic Exoplanet Survey (TrES), which uses small, inexpensive telescopes to find planets around bright stars. You can read about the TrES discovery through this press release from the University Corporation for Atmospheric Research. Obviously, finding planets through the transit method means locating those stars whose orbital plane is lined up properly for the Earth-bound observer to see the crossing (and you have to be careful to eliminate eclipsing binaries). But rare as these may be, the beauty of discovering such planets is that we can now make some direct observations of planetary atmospheres, and we'll get a good reading on the mass and size of...