How a sunset comet came to be

Mar 18, 2013
Credit: NASA

(Phys.org) —For a comet, visiting the sun is risky business. Fierce solar heat vaporizes gases long frozen in the fragile nucleus, breaking up some comets and completely destroying others.

That's why astronomers weren't sure what would happen in early March when Pan-STARRS, a first-time visitor to the inner solar system, dipped inside the orbit of Mercury. On March 10th, NASA's STEREO-B spacecraft watched as the comet made its closest approach to the sun only 28 million miles away. At that distance, the sun loomed 3 times wider and felt more than 10 times hotter than it does on Earth.

The comet survived.

Still intact, Comet Pan-STARRS is emerging from the Sun's glare into the sunset skies of the . Solar heating has caused the comet to glow brighter than a first magnitude star. Bright twilight sharply reduces visibility, but it is still an easy target for binoculars and small telescopes 1 and 2 hours after sunset. As of March 15th, people are beginning to report that they can see the comet with the unaided eye.

This video is not supported by your browser at this time.
NASA's STEREO-B spacecraft photographed "wild striations" in the tail of Comet Pan-STARRS as it passed by the sun.

Discovered in June 2011 by astronomers using the Pan-STARRS survey telescope atop the Haleakala volcano in Hawaii, the comet is paying its first visit to the . It hails from the Oort cloud, a deep space reservoir of comets far beyond the orbit of Pluto. Because Comet PanSTARRs is a newcomer, its potential brightness and ability to withstand was unknown.

Now we know. "It is a gorgeous comet—one of the brightest in years," says astronomer Matthew Knight of the Lowell Observatory.

Comet specialist Emmanuel Jehin of the has been monitoring Pan-STARRS using a remote-controlled telescope in Chile. Based on his data, Knight concludes that "Comet Pan-STARRS seems to be producing quite a bit of dust compared to an average comet. This is very good for its visibility, because the extra dust is reflecting sunlight and making Pan-STARRS appear brighter than it would otherwise."

The amount of dust and gas spewing from the comet implies a nucleus on the order of 1 km in diameter—in other words, neither unusually large nor small. Size-wise, it is a fairly typical comet.

The comet's tail is anything but typical. STEREO-B images processed by Karl Battams of the Naval Research Lab in Washington DC reveal many wild and ragged striations in the cloud of dust trailing behind Pan-STARRS. "Wow!" says Battams. "The fine-structure is breathtaking. We think this is caused by some fairly complex interaction between the solar wind and the comet's rotating nucleus. It's going to take computer models to figure this one out."

The comet is now receding from Earth. It will slowly dim as it heads back into deep space. Ironically, though, its visibility will improve for a while as it heads into darker skies away from the sun. In the last weeks of March it could become an easy naked-eye object.

Step outside after sunset, face west, and take a look.

Explore further: Mysteries of space dust revealed

Related Stories

A possible naked-eye comet in March

Feb 09, 2013

Far beyond the orbits of Neptune and Pluto, where the sun is a pinprick of light not much brighter than other stars, a vast swarm of icy bodies circles the solar system. Astronomers call it the "Oort Cloud," ...

Comet posing beside crescent moon in cool photo op

Mar 11, 2013

Now's your chance to see the comet that passed within 100 million miles of Earth last week. Twilight on Tuesday will provide the best photo op for the comet called Pan-STARRS. It will be visible in the Northern ...

Comet Pan-STARRS: How bright will it get?

Sep 06, 2012

Early next year, a comet will come fairly close to Earth and the Sun—traveling within the orbit of Mercury—and it has the potential to be visible to the naked eye. Amateur and professional astronomers ...

Comet Pan-STARRS holds promise for stargazers

Mar 06, 2013

A rare bright comet shows up in the northern hemisphere this week, cruising past Earth with promise of spectacular naked-eye viewings of the giant ball of ice and dust streaking the twilight sky with a blazing ...

Recommended for you

Mysteries of space dust revealed

Aug 29, 2014

The first analysis of space dust collected by a special collector onboard NASA's Stardust mission and sent back to Earth for study in 2006 suggests the tiny specks open a door to studying the origins of the ...

A guide to the 2014 Neptune opposition season

Aug 29, 2014

Never seen Neptune? Now is a good time to try, as the outermost ice giant world reaches opposition this weekend at 14:00 Universal Time (UT) or 10:00 AM EDT on Friday, August 29th. This means that the distant ...

Informing NASA's Asteroid Initiative: A citizen forum

Aug 28, 2014

In its history, the Earth has been repeatedly struck by asteroids, large chunks of rock from space that can cause considerable damage in a collision. Can we—or should we—try to protect Earth from potentially ...

Image: Rosetta's comet looms

Aug 28, 2014

Wow! Rosetta is getting ever-closer to its target comet by the day. This navigation camera shot from Aug. 23 shows that the spacecraft is so close to Comet 67P/Churyumov-Gerasimenko that it's difficult to ...

User comments : 0