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An unusually horned comet notable for a series of outbursts, known as the “devil’s comet,” will make its closest approach to Earth on Sunday around 3 a.m. ET.
Although the comet has not been visible to those in the Northern Hemisphere since the first week of May, sky-goers in the Southern Hemisphere have a better chance of seeing the fuzzy object through binoculars or a telescope.
Exactly why the dynamic comet takes a shape that has drawn comparisons to the Millennium Falcon spacecraft from the “Star Wars” movies while being explosively active is still an enigma to scientists. But the celestial object only completes one orbit around the sun every 71 years, like Halley’s comet, making it a once-in-a-lifetime opportunity for close study.
Since the comet will not pass Earth again for years, the collective observations of astronomers could provide important insight into its true nature and behavior.
Officially known as Comet 12P/Pons-Brooks, the celestial object made its closest pass to the sun on April 21, coming within 74.4 million miles (119.7 million kilometers) of our star.
The comet will make its closest pass to Earth on Sunday, but it will be more than 143 million miles (230 million kilometers) from our planet and will not pose a threat. For reference, the sun is 93 million miles (149 million kilometers) away from Earth.
The comet peaked in brightness in late April and has been steadily dimming for three to four weeks, said Dr. Dave Schleicher, an astronomer at the Lowell Observatory in Arizona.
“For people below the equator, the coming weeks and months may be their first chance to see this object since the 1950s,” said astronomer Dr. Teddy Kareta, a postdoctoral associate at Lowell.
Two prolific discoverers, Jean-Louis Pons and William Robert Brooks, independently observed the devil’s comet — Pons in 1812 and Brooks in 1883. But the comet probably made many trips around the sun over thousands of years, long before astronomers thought of comets as nothing more than “something weird in the atmosphere,” Schleicher said.
Astronomers estimate the giant comet to be between 6.2 and 12.4 miles (10 to 20 kilometers) in diameter, Kareta said.
The dwarf visitor has a green appearance typical of most comets because they contain diatomic carbon molecules that absorb sunlight and emit a green color from our perspective, Schleicher said.
A series of cosmic outbreaks
Pons-Brooks recently caught the attention of astronomers after they showed an interesting behavior that made the comet look like a horn as it ascends through our solar system.
The comet has had several outbursts over the past eight months, causing it to eject gas and dust. While such a release is not uncommon in comets and a crescent or Pac-Man shape has been observed in others, it is difficult to say what is normal for Pons-Brooks.
“I would say it’s somewhat unusual in terms of the number of hits he’s making,” Schleicher said. “On the other hand, you don’t seem to have good records from the past to tell you what is normal. And I suspect that, given the relatively large number of outbreaks that have occurred in the last eight months, this is clearly a normal occurrence for Pons-Brooks.”
Comets are blobs of dust, rock and ice, essentially frozen remnants from the formation of the solar system. They also contain frozen elements such as carbon dioxide and carbon monoxide.
Comets heat up and brighten as they approach the sun, and some of the frozen gases stored in comets don’t need to heat up long before they begin to vaporize, Schleicher said.
“We think the ultimate driver is, of course, warming from the sun,” he said. “The comet is coming in; it has been sitting outside in a deep freeze for years. The heat will work its way from the surface down to wherever the carbon dioxide or carbon monoxide ice is located.”
Astronomers suspect that Pons-Brooks eruptions have occurred during the repeated events as heat vaporizes material within the comet, causing pressure to build up and break through the surface. Although a gas explosion wouldn’t be visible in telescopes, the dust it kicks off would create the kind of events observed from Pons-Brooks, Schleicher said.
Scientists have traced the jets of material observed ejecting from the comet during its explosion to two source regions on its surface. Astronomers wonder why “the whole surface isn’t going crazy,” Schleicher said.
The observations suggest that the ice has crusted over most of the surface, or that the ice has evaporated, leaving only dirt behind, but astronomers are “not quite sure of those mechanisms that run the show,” he said.
However, the comet’s outbursts appear to have stopped, and it has not shown any outburst activity since February, Kareta said.
What we can learn from comets
The astronomers are looking at Pons-Brooks in the hope of getting more information about their rotation rate, or the rate at which comets spin as they move through space. Pons-Brooks has a rotation period of 57 hours, which is longer than expected, and astronomers are trying to determine whether jets of material ejected from the comet are speeding up or slowing down.
A series of overlapping events likely contributed to Pons-Brooks’ distinctive appearance, but it could also be due to our perspective of the comet, Kareta said.
“These are three-dimensional objects,” Kareta said. “When we take images of the night sky, we are taking them in a limited range of colors all balanced in two dimensions. This will make things that might make perfect sense to you, if you’re able to go up and walk around and see it in a few different perspectives, they’ll look a lot more complicated than they really are.”
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