Watching two suns over Tatooine's sky in the original Star Wars movie was a breathtaking experience, particularly given where most science fiction films were at the time. Here was an attempt to convey a truly alien landscape. But a second thought quickly came unbidden. Was this planet not in an extremely unstable orbit, moving around both stars simultaneously in an obvious habitable zone? The suspicion was that a planet could orbit one or the other members of a binary system, but surely not both unless its orbit were extended so far out into the planetary nether regions as to make life doubtful. Image: The twin suns of Tatooine. Are planetary orbits like this possible? Credit: © Lucasfilm Ltd. & TM. All Rights Reserved. That was back in the 1970s, of course, but take a look at the situation today. The 'hot Jupiter' in the triple system HD 188753 is interesting, but the planet in question orbits but one of the stars. The early discussion of HD 188753 Ab was quick to raise the Tatooine...

We're still arguing about how giant planets form around Sun-like stars, but terrestrial planets seem to be less controversial. Assuming the model is right, we start with a swarm of planetesimals in the range of one kilometer in size. As these objects grow, out to a range of at least 2 AU, the largest bodies at some point go through a runaway period of chaotic growth marked by collisions. Emerging from the debris should be terrestrial worlds, some in Earth-like orbits. Add to this the fact that gas and dust disks seem to be relatively routine outcomes of star formation and you have an indication that small rocky planets may be widespread. The problem with all this is that theory has to be matched with observation. On that score, new work by Mike Meyer (University of Arizona) and colleagues Lynne Hillenbrand and John Carpenter (California Institute of Technology) is instructive. The researchers chose to look at mid-range infrared emissions at the 24 micron level, a range chosen because...

The closest we've come so far to identifying Earth-like planets around other stars is in the identification of so-called 'super Earths.' Calculations designed to model the composition of such planets say that worlds up to about ten Earth masses are rocky rather than gaseous. Some of these, as we have in the case of Gliese 581, have even excited interest in their possible habitability. We'd like to find ways beyond the now conventional radial velocity and transit studies to identify more such worlds. Now a new planet may have been found around GJ 436, a red dwarf already known to host a Neptune-mass planet in a tight 2.6 day orbit. This is interesting work because of the methods used. Ignasi Ribas (Institut de Ciències de l'Espai, Spain) and team have taken a close look at the known planet and are arguing it is possible to identify a second world, a super-Earth, through the telltale variations in the transit duration of GJ 436b, the already known 'hot Neptune.' Giving the game away is...

Planets around other stars are too faint to be imaged directly, and although claims have been made for such detections (2M1207b is a case in point), it's safe to say that our current techniques need significant upgrading to achieve reliable images of such distant worlds. But studying terrestrial planets is a long-term objective and numerous studies have gone into concepts like Terrestrial Planet Finder and Darwin. One day and with some instrument we will indeed be looking at an exoplanet as small as the Earth, working with estimates of surface temperatures and checking its atmosphere for biomarkers that flag the presence of life. So let's suppose that in fifteen years or so we're looking at actual reflected light from a terrestrial world. What else can we learn about the place? The brightness of a planet like this can be affected by many things, including the presence of deserts on the surface or bright clouds above it. An active weather pattern would indicate the presence of a...