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Tuesday, July 21, 2020


NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) mission discovered the icy visitor on March 27, 2020, using its two infrared channels, which are sensitive to the heat signatures given off by the object as the Sun started to turn up the heat.
GUEST BLOG / By Ashley Strickland, CNN Science Writer--Stargazers in the Northern Hemisphere should enjoy every opportunity to see the new Comet NEOWISE as it streaks across the evening sky for the rest of July.

Once it disappears from view, the comet will not be visible in Earth's skies for another 6,800 years, according to NASA.

While July began with the comet visible low on the horizon in the early morning sky, NEOWISE has now transitioned to become an evening comet, perfectly visible as the skies darken.

It's named after NASA's Near-Earth Object Wide-field Infrared Survey Explorer, otherwise known as the NEOWISE mission, which discovered it in late March.

You may be able to see it with the naked eye, but grab a pair of binoculars or peer through a small telescope, if you have either, for a better view.
If you live in an urban area with a lot of light pollution, you may want to find a spot to watch the sky that has less light and obstructions, like tall buildings.

After the sun sets, look for the Big Dipper constellation in the northwestern sky, according to NASA. Just below it, you'll see the comet. It looks a bit like a fuzzy star with a tail.

The comet will continue to rise higher above the northwestern horizon for the rest of this month. It will come closest to Earth on July 22 -- just 64 million miles away.

While comets are unpredictable and can disappear from view at any time, astronomers predict that we should be able to see it for the rest of the month.

And Comet NEOWISE is a survivor. It recently made its closest approach to the sun without breaking apart, which suggests it could have a sturdy structure, rather than a crumbly interior like some comets. The Hubble Space Telescope witnessed Comet ATLAS, discovered in December 2019, break apart into pieces in April.

Comets are really just made up of ice and dust, with some organic material. Many of the comets with long orbits, like NEOWISE, only venture through the inner solar system and close to the sun for a short time.

Scientists compare it to coming out of "cold storage" for the comet because the outer solar system where they originate is so much colder. The warmth of the sun and the inner solar system causes the ice to melt, although astronomers aren't sure why ATLAS broke apart.

After its closest approach to Earth, Comet NEOWISE will continue on its very long orbit to the edge of the solar system, stretching out 715 astronomical units from our sun. (As a comparison, Earth is one astronomical unit from the sun.)

This is why we won't see the comet again in our lifetimes -- it takes thousands of years to travel the outer solar system before returning to the inner solar system.

But, scientists point out, this means the comet isn't exactly new, only new to us, because it previously passed through Earth's skies when humans were present about 6,800 years ago.

Discovering Comet NEOWISE
While Comet NEOWISE was spotted on March 27 by NASA's Near-Earth Object Wide-field Infrared Survey Explorer, the mission didn't start out to find comets.

Ten years ago, the mission was launched as WISE and it was designed to do an all-sky map in infrared light.

But the team realized that it was also pretty useful for observing asteroids and comets and measuring their sizes and how reflective they were, said Amy Mainzer, the NEOWISE principal investigator at the University of Arizona, in a NASA press conference this week. The NEOWISE mission has found a couple dozen comets so far.
The WISE mission was only designed to last for about seven months, but NASA asked the team to reactivate it after its prime mission concluded in 2013, and they've been using NEOWISE to watch the skies ever since, Mainzer said. The team estimated that the NEOWISE mission only has about one year left.

Comet NEOWISE captured on July 6, 2020, above the northeast horizon just before sunrise in Tucson.  Depending on weather conditions the comet will be viewable after sunset this summer.
PHOTO CREDIT: Vishnu Reddy

A new comet is now visible with the naked eye
"We're excited it's still able to find spectacular things like this comet," Mainzer said.

The team spotted Comet NEOWISE by its infrared emissions, meaning they could pick out its heat signature. In late March, the scientists determined it was a comet and when it would pass close to the sun -- and they've been tracking it ever since.

By observing the comet, the researchers have learned that it's about three miles in diameter, the average size for a comet with a long orbit. And it's incredibly bright, even if it's not as spectacular as Comet Hale-Bopp as witnessed in 1997.

Scientists get first look inside comet from outside our solar system
Sometimes when comets that have a lot of mass, like NEOWISE, they can blow apart when they come close to the sun. Their ice becomes heated so quickly that it shreds and destroys the comet, Mainzer said. Because this comet survived, it tells astronomers there is something unique about its structural strength.

The comets in our solar system formed at its very beginning. Gas and dust formed in clumps orbiting in a disk around our young sun, and those clumps became planets, asteroids and comets. The comets were kicked out to the edge of the solar system, so their ice remains pristine.

NASA scientists and the NEOWISE team will continue observing the comet with various instruments and cameras to see how it progresses, said Emily Kramer, co-investigator on the NEOWISE science team at NASA's Jet Propulsion Laboratory in Pasadena, California.

The ingredients for life on Earth may have been delivered by comets, study says
Because the comet is so bright, the scientists expect to get better data, and much more of it, than they typically do for most comets, Kramer said.

Most comets are so faint that they can only be seen using the most powerful telescopes. Scientists are looking forward to learning the composition of this comet based on the data they gather. That composition could reveal more information about the "ingredients" used to make our solar system.

Although this comet takes a long time to complete one orbit around the sun, some that originate further out in the solar system can take hundreds of millions of years to orbit the sun or even longer, Mainzer said. Meanwhile, some of the closer comets only take about five or six years to complete an orbit. Comet NEOWISE is in the middle, taking about 7,000 years.

"This is coming in from a medium-long distance," Mainzer said. "How it got there is a bit of a mystery. It may have had a more distant orbit that was perturbed to create this current orbit."

For the next few days it will be visible about an hour before sunrise, close to the horizon in the northeastern sky in the United States. Observers might be able to see the comet's central core, or nucleus, with the naked eye in dark skies; using binoculars will give viewers a good look at the fuzzy comet and its long, streaky tail.

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