Devil Comet makes closest pass to Earth

  ‘Devil comet’ makes its closest approach of Earth  

An unusual horned comet notable for a series of outbursts, nicknamed the “devil comet,” will make its closest approach of Earth on Sunday. Comet Pons-Brooks, sometimes called the “Devil Comet,” will make its closest pass by Earth during the overnight and early-morning hours on Sunday. Pons-Brooks only flies through our part of the solar system every 71 years, so seeing or studying it is a once-in-a-lifetime opportunity. It’s one of the brightest periodic comets in our solar system, similar to Halley’s Comet which arrives near Earth every 76 years. The giant ball of ice and dust is sometimes called the "Devil Comet" because it has occasional outbursts that create a horseshoe shape which some observers describe as “horns.” Some say it becomes the shape of the Millenium Falcon from the Star Wars films. While the comet hasn’t been visible to those in the Northern Hemisphere since the first week of May, sky-gazers in the Southern Hemisphere have a better chance of glimpsing the fuzzy object through binoculars or a telescope.

Scientists still aren’t certain why the single tail splits into two, but they say it seems to happen as the comet gets closer to the sun, when most comets’ tails begin to form and elongate. Pons-Brooks made its closest pass to the sun (and was at its brightest) in early April, at nearly the same time as the total solar eclipse. At that time, the comet was easily visible with binoculars or a telescope and, with perfect conditions, was faintly visible with the naked eye. Exactly why the dynamic comet takes on a shape that has drawn comparisons to the Millennium Falcon spacecraft from the “Star Wars” films when explosively active is still an enigma to scientists. Given that the comet won’t pass by Earth again for decades, collective observations by astronomers could provide key insights into its true nature and behaviour.

As Pons-Brooks makes its closest approach to Earth, roughly 143 million miles away (about 1.5 times farther away than the sun), it will be much dimmer and observers will need, at least, binoculars to see it. The comet was discovered in 1812 by Jean-Louis Pons, a French astronomer considered to be the best visual comet discoverer in history. He wasn’t all that impressed by it and reportedly said it was, “a shapeless object with no apparent tail.” Officially known as Comet 12P/Pons-Brooks, the celestial object made its closest pass of the sun on April 21, coming within 74.4 million miles (119.7 million km's) of our star. The comet will make its closest pass of Earth on Sunday  and won’t pose a risk. For reference, the sun is 93 million miles (149 million km's) away from Earth. “For folks down below the equator, the coming weeks and months might be their first good chance to see this thing since the 1950s,” said astronomer Dr. Teddy Kareta, a postdoctoral associate at Lowell. The Virtual Telescope Project captured a view of the comet over Manciano, in Italy's Tuscany region, under the darkest sky of the peninsula. The comet peaked in brightness in late April and has been steadily fading for three to four weeks, said Dr. Dave Schleicher, astronomer at Lowell Observatory in Arizona.

Pons-Brooks recently captured the attention of astronomers after exhibiting intriguing behaviour that caused the comet to have a horned appearance and soar through our solar system. The comet has experienced a number of outbursts during the past eight months, causing it to eject gas and dust. While such releases are not uncommon in comets and a crescent or Pac-Man shape has been observed in other ones, it’s difficult to tell what is normal for Pons-Brooks. Comets are chunks 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 warm up much before they begin to turn into vapour, Schleicher said."

"Astronomers suspect Pons-Brooks outbursts have occurred over the course of repeated events as heat vaporizes material inside the comet, which causes pressure to build up and break through the surface. While an explosion of gas wouldn’t be visible in telescopes, the dust it kicks up would create the kind of events observed from Pons-Brooks, Schleicher said. "We think the ultimate driver, of course, is heating from the sun,” he said. “The comet is coming in; it’s been sitting out in a deep freeze for years. The heat is going to be working its way from the surface down to wherever that carbon dioxide or carbon monoxide ice is located.”  Scientists have traced the jets of material observed releasing from the comet during its outburst to two source regions on its surface. Astronomers are puzzled as to why “the whole surface isn’t going off like mad,” Schleicher said. The observations imply that ice has crusted over the majority of the surface, or the ice has been vaporized away, leaving only dirt behind, but astronomers are “not quite sure which of those mechanisms runs the show,” he said. The comet’s outbursts seem to have ceased, however, and it hasn’t shown any outburst activity since February, Kareta said. “These are three-dimensional objects,” Kareta said. “When we take images of the night sky, we’re taking them in a limited range of colours all flattened down 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 couple of different perspectives, look much more complicated than they really are.”

The rare visitor has a green appearance typical of most comets because they contain diatomic carbon molecules which absorb sunlight and emit a colour that appears green from our perspective, Schleicher said. Two prolific discoverers, Jean-Louis Pons and William Robert Brooks, independently observed the devil comet, Pons in 1812 and Brooks in 1883. But the comet has likely made many trips around the sun over thousands of years, long before astronomers thought of comets as anything other than “something weird in the atmosphere,” Schleicher said. Astronomers estimate the massive comet to be between 6.2 to 12.4 miles (10 to 20 km's) in diameter, Kareta said.  “I would say it’s somewhat unusual in the number of outbursts it’s been having,” Schleicher said. “On the other hand, it’s not like you have good records from the past to really let you know what is typical. And I suspect given the fairly large number of outbursts that have happened over the last eight months, that this is very clearly a usual occurrence for Pons-Brooks.  

The comet was rediscovered in 1883 by a British-born American astronomer, William Brooks. They didn’t’ realize it was the same comet until Brooks did the orbital math, and since he was the first to do the precise calculations, the comet gets his name, too. Pons-Brooks will be at its closest point to Earth on Sunday. But there’s a catch for central Ohio stargazers: it’s now only visible in the southern hemisphere. Astronomers have been observing Pons-Brooks in the hopes of uncovering more details about its 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 want to know if the jets of material releasing from the comet are speeding it up or slowing it down."  An overlapping series of events likely has contributed to Pons-Brooks’ distinctive look, but it could also be due to our perspective of the comet, Kareta said.