Sunday, December 16, 2018

Comet 46P/Wirtanen Passes by Earth

An image of Comet 46P/Wirtanen taken by Wouter Van Reeven at ESA’s European Space Astronomy Centre (ESAC) near Madrid, Spain, on December 6, 2018. Credit: ESA / ESAC Astronomy Club / W. Van Reeven

A special visitor is crossing the sky this December: Comet 46P/Wirtanen, sighted with telescopes and binoculars in recent weeks, is on the way to its closest approach to Earth this weekend, when it might become visible to the naked eye.

On Sunday, Dec. 16, 46P/Wirtanen will make one of the 10 closest comet flybys of Earth in 70 years, and you may even be able to see it without a telescope.

Although the approach will be a distant 7.1 million miles (11.4 million kilometers, or 30 lunar distances) from Earth, it's still a fairly rare opportunity.

"This will be the closest comet Wirtanen has come to Earth for centuries and the closest it will come to Earth for centuries," says Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA's Jet Propulsion Laboratory in Pasadena, California. What's more, Chodas said, "This could be one of the brightest comets in years, offering astronomers an important opportunity to study a comet up close with ground-based telescopes, both optical and radar."

Comet Wirtanen has already been visible in larger amateur telescopes, and while the brightness of comets is notoriously difficult to predict, there is the possibility that during its close approach comet Wirtanen could be visible with binoculars or to the naked eye.

Because Comet 46P is passing so close to us, it is very bright and will allow astronomers to observe it with a wide range of telescopes. With these data, they will put together a more complete picture of the comet and what drives its activity.

Las Cumbres Observatory (LCO) is contributing to this effort using a new instrument that was quickly assembled in the LCO headquarters in Goleta and shipped out to and installed on LCO’s 2-meter telescope on Maui. This instrument contains a camera and a number of specialized filters, provided by the European Space Agency, which are tuned to the specific gasses emitted by comets.

“It was a heroic effort by the staff and engineers at LCO to get this instrument built and ready in such a short time for this historic opportunity. These special filters are great to observe a bright comet like 46P, enabling us to separate the gas and dust content of the coma,” says Tim Lister, Staff Scientist at LCO.

46P/Wirtanen had been chosen in the 1990s as the target of ESA’s Rosetta mission

“When we began to study Rosetta, one of the most important tasks was to create a list of comets that could be reached by a spacecraft launched on an Ariane 5 and carrying sufficient payload to study the comet,” says Gerhard Schwehm, who was the ESA Rosetta project scientist at the time.

“It turned out that a mission to Comet 46P/Wirtanen with launch in early 2003 would be one of the best opportunities. This initiated an intensive observation campaign from the ground to prepare for the mission.”

However, a launch delay from 2003 to 2004 meant the spacecraft would not be able to rendezvous with that comet at its closest approach to the Sun in 2013, prompting the Rosetta team to select a new target, the now famed 67P/Churyumov­–Gerasimenko.

“The rest, as they say, is history, but because of the original choice, Comet 46P remains one of the best-observed comets to date,” adds Gerhard.

Astronomer Carl Wirtanen discovered the comet in 1948 at Lick Observatory on Mt. Hamilton in Santa Clara County, California. With a width of 0.7 miles (1.1 kilometers), 46P/Wirtanen orbits the Sun fairly quickly for a comet — once every 5.4 years — making it a short-period comet. (Long-period comets, on the other hand, have orbital periods greater than 200 years.) At the time of closest approach, the comet will appear to be located in the constellation Taurus close to the Pleiades.


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