The massive volcanic comet 12P/Pons-Brooks, which grows giant horns when it erupts, has exploded for a third time in five months
as it continues to race toward the sun.
© Comet Chasers/Richard MilesThe "devil" comet's distinctive horns were first spotted after a major eruption on July 20.
A volcanic "devil comet" that is racing toward Earth erupted again on Halloween, causing it to regrow its distinctive "horns." The latest outburst, which was the second within a month and the third since July, is a reminder that the comet is becoming more volcanically active as it continues its journey toward the heart of the solar system.
The comet, named 12P/Pons-Brooks
(12P), is a cryovolcanic, or cold volcano, comet. Like other comets
, 12P has a solid nucleus — a hard, icy shell filled with ice, gas and dust — that is surrounded by a fuzzy cloud, or coma made of materials that leak out of the comet's insides.
But unlike non-volcanic comets, radiation from the sun
can superheat 12P's interior, causing pressure to build up until it becomes so intense it cracks the nucleus' shell from the inside and sprays its icy guts into space. These eruptions cause the comet's coma to expand and brighten as it reflects more sunlight toward Earth.
When the comet erupts, its coma forms iconic devil "horns." These occur because 12P's large nucleus, which spans around 10.5 miles (17 kilometers) across, has an unusual "notch" on its surface, which blocks the outflow of cryomagma into space and causes its expanded coma to grow with an irregular shape.