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Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ∼20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10-6and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter.

Synthetic triclinic calcium pyrophosphate dihydrate crystals were uniformly trace-labeled with Ytterbium-169 (169Yb), a pure gamma-emitting isotope with a halflife of 31 days. The solubility of the labeled crystals was similar to that of cold synthetic crystals. The clearance rate of labeled sterile crystals, sieved to obtain the desired size, was determined after injection of microgram quantities into 4 arthritic huuman and 3 normal adult rabbit joints and corrected by the observed rate of clearance of free 169Yb. The derived rate constants were then used to calculate the time required for half of the injected dose of CPPD to be cleared from the joint. Crystal clearance was found in all instances. Crystal removal from normal rabbit joints was much more rapid than from the much larger human arthritic joints and was inversely proportional to the size of the crystals injected.