Free Astronomy Magazine September-October 2016

SPACE CHRONICLES the brightness of the young star V883 Orionis flash heated the inner portion of the disk, pushing the water snow line out to a far greater distance than is normal for a proto- star, and making it possible to ob- serve it for the first time. Young stars are often surrounded by dense, rotating disks of gas and dust, known as protoplanetary disks, from which planets are born. Snow lines are the regions in those disks where the temperature reaches the sublimation point for most of the volatile molecules. In the inner disk regions, inside water snow lines, water is vaporized, while outside these lines, in the outer disk, water is found frozen in the form of snow. These lines are so important that they define the basic architecture of planetary systems like our own and are usually located for a typical solar-type star at around 3 au from the star. In the solar nebula, that line was between the orbits of Mars and Jupiter during the formation of the Solar System, hence the rocky planets Mercury, Venus, Earth and Mars formed within the line, and the gaseous planets Jupiter, Saturn, Uranus and Neptune formed out- side. However, the recent ALMA ob- servations show that the water snow line in V883 Orionis is current- ALMA observes first protoplanetary water snow line thanks to stellar outburst by ALMA Observatory A rtist impression of the water snow line around the young star V883 Ori- onis, as detected with ALMA. [A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO)] N ew observations with the Ata- cama Large Millimeter/sub- millimeter Array (ALMA) have produced the first image of a water snow line within a protoplanetary disk. This line marks where the tem- perature in the disk surrounding a young star drops sufficiently low for snow to form. A dramatic increase in