At the beginning of the week, star gazers were surprised to witness a green glow in the night’s sky sometime during the late hours of July 2.
The commotion was triggered by a celestial object known as PANSTARRS (C/2017 S3) — a very unusual comet that astronomers say “exploded in brightness.”
While there was no actual explosion to speak of, comet C/2017 S3 did get an unexpected boost in glow, becoming 16 times brighter than its normal glare.
Dubbed “the incredible Hulk” comet, as noted by the Daily Mail, C/2017 S3 is a true rarity. Discovered last September by the PanSTARRS telescope at Haleakala Observatory in Hawaii, the comet is unique in more ways than one.
Coming all the way from the Oort Cloud — “a big, thick bubble around our solar system” filled with icy comets, explains NASA — the comet is falling toward the sun from high above the solar system’s plane.
This close proximity to the sun is heating up its nucleus, causing the comet’s ice to evaporate into gas and making C/2017 S3 shine brighter than usual, reports CBC. During a short time frame of just 24 hours, the comet increased its brightness 16-fold, expanding its green atmosphere to roughly twice the size of Jupiter.
According to Sky & Telescope, the comet went from a magnitude of 12.5 to almost 9.5 overnight, becoming visible on July 2 “as a dense, tailless cotton ball about 3′ across.” Warmed by the solar radiation, the comet was photographed “casting out an eerie green tail” by Austrian amateur astronomer Michael Jager, notes the Central Telegraph.
Jager was keeping watch when the comet “exploded” in the sky on July 2 and jumped at the opportunity to snag a photo of C/2017 S3, which is now enveloped by a giant cloud of gas measuring 161,556 miles (or 260,000 kilometers) in diameter.
This was the first time that C/2017 S3 was seen in the sky. The comet is likely on its first trip to our solar system and, therefore, virtually unknown.
“Ones like this have never visited the inner solar system before,” said Robert Weryk, a Canadian scientist who was part of the PanSTARRS that detected the comet.
“We don’t really know what the surface is, but it certainly can go through brightening like this.”
Those who missed the chance to see the comet with their telescopes will get another opportunity soon enough, as C/2017 S3 is moving closer and closer to the sun and is expected to reach perihelion in mid-August.
After a voyage of roughly 186 billion miles (300 billion kilometers), the comet will make its closest approach to the sun on August 15-16, becoming even brighter than before.
This will bring it within the orbit of Mercury, from where we might get a chance to see it with the unaided eye — although looking at C/2017 S3 through binoculars and telescopes will surely make for a more spectacular view.
“Comet C/2017 S3 may reach magnitude 3 or 4 as it speeds sun-ward in the morning sky en route to an August 16th perihelion,” notes Sky & Telescope, advising sky watchers to keep an eye out for this rare comet and “expect the unexpected.”
This is because the immense outburst that’s making the comet so luminous could even end up disintegrating it — maybe even under our very eyes.
Whether C/2017 S3 will survive its dive toward the sun remains to be seen. If it manages to get away unscathed, the comet will bounce back to the outer solar system and only pop by again in another 200 years.