It turns out that snow is quite important in the formation of planets, and now for the first time we have been able to observe directly where snow forms in a distant star system.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international group of astronomers was able to observe the snow line around V883 Orionis, a young star 1,350 light-years from Earth. The snow line represents the transition between gaseous water and ice around a star.
The snow line (or frost line) is the particular distance from a star where it's cold enough for water to condense into solid ice grain. While this research focuses on the water snow line, other volatile compounds like carbon dioxide, methane, and ammonia have snow lines as well.
For a star like the Sun, the water snow line is about 450 million kilometers (280 million miles) away, beyond the orbit of Mars, but thanks to a sudden increase in brightness the snow line around V883 Orionis is now located 6 billion kilometers (3.7 billion miles) away (about the orbit of Pluto).
The star belongs to the variable star class FU Orionis, which regularly flare up as they accrete more and more mass. V883 Orionis is only 30 percent heavier than the Sun but in its latest outburst (that could last for centuries) it has become 400 times more luminous than our yellow companion.
This image of the planet-forming disk around the young star V883 Orionis was obtained by ALMA. ALMA (ESO/NAOJ/NRAO)/L. Cieza
The research, published this week in Nature, is very significant to understanding planetary formation. Beyond the snow line, ice can coat dust grains forming the seeds of gas giants, while within the snow line only smaller rocky planets might form.
“The ALMA observations came as a surprise to us. Our observations were designed to look for disk fragmentation leading to planet formation,” said lead author Lucas Cieza in a statement.
“We saw none of that; instead, we found what looks like a ring at 40 AU. This illustrates well the transformational power of ALMA, which delivers exciting results even if they are not the ones we were looking for.”
This observation suggests that the snow line might not actually stay in the same place. A snow line that appears to move backward and forward through a stellar system could play a crucial role in the evolution of planets, and the ALMA discovery provides new elements to improve the current planetary formation models.
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