Category: Comets

Comets are known as dirty snowballs. As they approach the Sun, the constant solar wind picks away at their snowy exterior, creating the beautiful tail we see trailing behind. But sometimes the solar wind is replaced with a solar hurricane, and in the case of Comet Encke, its graceful tail was completely torn off.

The series of images was captured by NASA’s STEREO spacecraft, which are normally gazing at the Sun from two positions in the Earth’s orbit. This allows them to see objects with 3-d vision.

Scientists have long suspected that the Sun’s solar wind can be a fickle thing. Usually it’s blowing steadily from the Sun, but in the case of a coronal mass ejection, it can become a fierce solar hurricane. When scientists detected a coronal mass ejection on the Sun, they refocused the space observatories on Comet Encke, which was unfortunate enough to be inside the orbit of Mercury, just to see what would happen.

As the giant cloud of magnetized gas struck the comet traveling thousands of kilometres a second, it brightened the tail briefly. And then the tail was ripped right off.

Astronomers think that the comet had a mini magnetic reconnection event, similar to what happens here on Earth when we’re struck by a coronal mass ejection. Oppositely directed magnetic fields around the comet “bumped into each other” by the magnetic fields in the CME. That released a burst of energy, and tore off the tail.

The researchers have stitched together several images into a movie, that shows the whole process happening. Just a warning, the video is 7 MB.

Original source: NASA News Release

The most successful comet hunter is not some dedicated amateur who sacrifices night after night searching for icy bodies from the outer Solar System. It’s not a robotic telescope surveying the heavens. Nope, it’s SOHO – a space telescope staring at the Sun; and it discovers comets as a happy side benefit. But recently it turned up something new, one of Halley’s cousins; a periodic comet.

The object is called P/2007 R5, and it wasn’t the first time SOHO had captured images of it. The satellite had actually seen this rare variety of comet on two separate occasions in the past. Instead of falling into the Sun and being destroyed, or getting flung out into a wild orbit, P/2007 R5 takes a very regular elliptical orbit around the Sun.

So if P/2007 R5 had been seen three times by SOHO, why hadn’t anyone noticed before? SOHO sees a lot of comets on a lot of orbits. German PhD student Sebastian Hoenig did notice. He realized that an object that passed by in 1999 had a very similar orbit to another object that came by in 2003. Hoenig calculated the orbit, and predicted that it would be back on September 11, 2007. His prediction was surprisingly accurate; the comet passed through the field of view again, right on schedule.

With that mystery solved, there’s still something puzzling astronomers. P/2007 R5 doesn’t look like a regular comet. It doesn’t have a tail or coma, and some astronomers initially wondered if they were looking at an asteroid, and not a comet. However, on its most recent pass, astronomers were able to study P/2007 R5 a little better, and saw that it does exhibit some cometary behaviour. When it passed within 7.9 million km of the Sun, it flared slightly, just like a comet should.

It’s possible that P/2007 R5 is actually an extinct comet; an object that lost all its volatile gas and ices to the Sun long ago. Objects like this have been long theorized, but never observed.

Original Source: ESA News Release

Scientists think they might have the solution to a mystery that’s been haunting paleontologists for years: what caused an abrupt period of cooling 13,000 years ago and an extinction of the large mammals. The conventional theory is that when human hunters arrived in North America, they killed off all the tasty large mammals. But there’s evidence that a comet exploded over North America at approximately the same time. This could also cause cooling, and wipe out the animals.

The discovery was made by scientists from the University of California at Santa Barbara. They analyzed more than a dozen archaeological sites across North America, and found they all had high concentrations of iridium. This element is a rare substance on Earth, but known to be in many comets and asteroids. Whenever these objects impact the Earth, they leave a blanket of iridium behind which serves as a marker. As archaeologists dig down through the layers of material, they’re looking back in time, and can accurately date when the object struck.

If this theory is correct, a comet approximately 4 km (2.5 miles) across detonated in the skies above North America, and rained fragments down across the whole region. The extreme temperatures would have ignited wildfires across the continent, destroying the vegetation that the large mammals needed to survive. Their death would then lead to a cascade of deaths by the large predators and the rest of the food chain that relied on them.

The comet might have also destabilized a large portion of the Laurentide ice sheet, causing a high volume of fresh water to flow into the ocean. Climate researchers believe this kind of event can disrupt the normal circulation of the ocean’s flow, and lead to a global cooling event. Ecosystems across the planet would have suffered.

Ancient cultures, such as the Clovis people of North America relied on mammoths and other large mammals for food. They would have been affected by the impact, and this might have caused their culture to die out.

Original Source: NSF News Release