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PLANETOLOGY the first survey, con- cluded six months before the start of the second. The aim of the comparison was (and it is) that of spotting un- known objects, pos- sibly having a de- tectable slow prop- er motion, or any- how located within short distances and thus affected by the parallax phenome- non. Those objects had to be found among the 750 mil- lion stars, galaxies and asteroids cap- tured in the WISE images. The results of the first two stud- ies – based on that huge amount of survey data – by Kevin Luhman (Penn State Uni- versity) and a team led by Davy Kirkpatrick (California Institute of Technology, Pasa- dena) were recently published in The As- trophysical Journal . From the total of over 22,000 objects displaying a significant prop- er motion, the researchers, based on their specific requirements, have extracted two different groupings of 762 objects (Luh- man) and 3,525 objects (Kirkpatrick et al.). They are in all cases small stars or brown dwarfs located within a 500 light-years ra- dius from the Sun. Among them, none is nearer than similar previously known ob- jects and, more importantly, none is locat- ed in close proximity of the Oort Cloud or more inside the solar system. Of all the brown dwarfs (overall less than expected), none can be considered in terms of size more similar to a planet than to a star. Taking into account the observational lim- its of WISE, from the results published in the ApJ it can be confidently said that no planet as large as Saturn exists within 10,000 astronomical units from the Sun, no planet as big as Jupiter within 26,000 astro- nomical units and no proportionally larger planet at greater distances. The existence of gas giants below the limits reachable by WISE is however unlikely, and if they exist they cannot certainly have formed at those distances from the Sun in not having ever existed out there enough material for their accretion. The theory of the “tenth” planet, and of all its variants does therefore seem to irreversibly fall apart, and since the exis- tence of that object would not in any case help solving any of the current issues rela- ted to the solar system, is it worth conti- nuing to fantasize about it? T he red and blue circles in this simulation show all the stars closest to the Sun and all the brown dwarfs discover- ed by WISE. None of these latter is located at a dis- tance so close that they can dis- turb the orbits of objects that pop- ulate the Oort Cloud. [NASA/JPL- Caltech] I f at the bound- aries of the solar system there were a sub- stellar object it could appear as WISEA J204027.30 +695924.1; red dot nearly in the centre of this image. This is a tiny star, but its dimensions are similar to those of a brown dwarf. [DSS/NASA/JPL- Caltech] n