Comet Pan-STARRS Marches Across the Sky

NASA's NEOWISE mission captured a series of infrared images of comet C/2012 K1 -- also referred to as comet Pan-STARRS -- as it swept across our skies in May 2014.  Full image and caption

 

NEOWISE Spies Comet Pan-STARRS Against Galaxy Backdrop

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NASA's NEOWISE mission captured a series of pictures of comet C/2012 K1 -- also known as comet Pan-STARRS -- as it swept across our skies in May 2014.

The comet is named after the astronomical survey project called the Panoramic Survey Telescope and Rapid Response System in Hawaii, which discovered the icy visitor in May 2012. 

Comet Pan-STARRS hails from the outer fringes of our solar system, from a vast and distant reservoir of comets called the Oort cloud. 

The comet is relatively close to us -- it was only about 143 million miles (230 million kilometers) from Earth when this picture was taken. It is seen passing a much more distant spiral galaxy, called NGC 3726, which is about 55 million light-years from Earth, or 2 trillion times farther away than the comet.

Two tails can be seen lagging behind the head of the comet. The bigger tail is easy to see and is comprised of gas and smaller particles. A fainter, more southern tail, which is hard to spot in this image, may be comprised of larger, more dispersed grains of dust.

Comet Pan-STARRS is on its way around the sun, with its closest approach to the sun occurring in late August. It was visible to viewers in the northern hemisphere through most of June. In the fall, after the comet swings back around the sun, it may be visible to southern hemisphere viewers using small telescopes.

The image was made from data collected by the two infrared channels on board the NEOWISE spacecraft, with the longer-wavelength channel (centered at 4.5 microns) mapped to red and the shorter-wavelength channel (3.4 microns) mapped to cyan. The comet appears brighter in the longer wavelength band, suggesting that the comet may be producing significant quantities of carbon monoxide or carbon dioxide.

Originally called the Wide-field Infrared Survey Explorer (WISE), the NEOWISE spacecraft was put into hibernation in 2011 after its primary mission was completed. In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects. NEOWISE is also characterizing previously known asteroids and comets to better understand their sizes and compositions.

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the NEOWISE mission for NASA's Near-Earth Object Observation Program of its Planetary Science Division in Washington. The Space Dynamics Laboratory in Logan, Utah, built the science instrument. Ball Aerospace & Technologies Corp. of Boulder, Colorado, built the spacecraft. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information on NEOWISE is online at: http://www.nasa.gov/wise and http://www.jpl.nasa.gov/wise/

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov

Source: JPL-Caltech

NASA's Swift Monitors Departing Comet Garradd

Swift's UVOT acquired this image of Comet Garradd (C/2009 P1) on April 1, 2012, when the comet was 142 million miles away, or 636 times farther than the moon. Red shows sunlight reflected from the comet's dust; violet shows ultraviolet light produced by hydroxyl (OH), a fragment of water. NGC 2895 is a barred spiral galaxy located 400 million miles away in the constellation Ursa Major. The UVOT image (outlined) is placed within a wider visible image of the region from the Digital Sky Survey. Credit: NASA/Swift/D. Bodewits (UMD) and S. Immler (GSFC) and DSS/STScI/AURA. View larger-View unlabeled version

An outbound comet that provided a nice show for skywatchers late last year is the target of an ongoing investigation by NASA's Swift satellite. Formally designated C/2009 P1 (Garradd), the unusually dust-rich comet provides a novel opportunity to characterize how cometary activity changes at ever greater distance from the sun.

A comet is a clump of frozen gases mixed with dust. These "dirty snowballs" cast off gas and dust whenever they venture near the sun. What powers this activity is frozen water transforming from solid ice to gas, a process called sublimation. Jets powered by ice sublimation release dust, which reflects sunlight and brightens the comet. Typically, a comet's water content remains frozen until it comes within about three times Earth's distance to the sun, or 3 astronomical units (AU), so astronomers regard this as the solar system's "snow line."

"Comet Garradd was producing lots of dust and gas well before it reached the snow line, which tells us that the activity was powered by something other than water ice," said Dennis Bodewits, an assistant research scientist at the University of Maryland, College Park, and the study's lead investigator. "We plan to use Swift's unique capabilities to monitor Garradd as it moves beyond the snow line, where few comets are studied."

Comets are known to contain other frozen gases, such as carbon monoxide and dioxide (CO and CO2), which sublimate at colder temperatures and much farther from the sun. These are two of the leading candidates for driving cometary activity beyond the snow line, but phase transitions between different forms of water ice also may come into play.

C/2009 P1 was discovered by Gordon J. Garradd at Siding Spring Observatory, Australia, in August 2009. Astronomers say that the comet is "dynamically new," meaning that this is likely its first trip through the inner solar system since it arrived in the Oort cloud, the cometary cold-storage zone located thousands of AU beyond the sun.

Comet Garradd was closest to the sun on Dec. 23, 2011, and passed within 118 million miles (1.27 AU) of Earth on March 5, 2012. The comet remains observable in small telescopes this month as it moves south though the constellations Ursa Major and Lynx.

Although Swift's prime task is to detect and rapidly locate gamma-ray bursts in the distant universe, novel targets of opportunity allow the mission to show off its versatility. One of Swift's instruments, the Ultraviolet/Optical Telescope (UVOT) is ideally suited for studying comets.

The UVOT grism produces images that separate incoming light from ultraviolet and visible sources by wavelength. Molecules produce separate images at discrete wavelengths: hydroxyl (OH) at 308 nm, just beyond the visual range; CN and C3 produce purple light at 387 and 406 nm, respectively. C2 emission at 500 nm is responsible for the dominant green color that characterizes many comets. Comet dust, which reflects sunlight, instead produces a broad, continuous swath. Credit: NASA/Swift/D. Bodewits (UMD) and S. Immler (GSFC). View larger - View unlabeled version

The instrument includes a prism-like device called a grism, which separates incoming light by its wavelength. While Swift's UVOT cannot detect water directly, the molecule quickly breaks up into hydrogen atoms and hydroxyl (OH) molecules when exposed to ultraviolet sunlight. The UVOT detects light emitted by hydroxyl and other important molecular fragments — such as cyanide (CN), carbon monosulfide (CS) and diatomic and triatomic carbon (C2 and C3, respectively) — as well as the sunlight reflected off of cometary dust.

"Tracking the comet's water and dust production and watching its chemistry change as it moves deeper into the solar system will help us better understand how comets work and where they formed," said Stefan Immler, a researcher and Swift team member at NASA's Goddard Space Flight Center in Greenbelt, Md.

Swift last observed the comet on April 1, when it was 1.53 AU away and just past the orbit of Mars. Although detailed results are not yet available, Bodewits estimates that Comet Garradd was shedding about 400 gallons of water each second -- enough to fill an Olympic-size swimming pool in under 30 minutes.

But the water given off by the comet was only about half of the dust mass it produced. Bodewits estimates that each second, Garradd was losing about 7,500 pounds (3.5 metric tons, or about twice the typical mass of a small car) in the form of dust and icy grains.

Thanks to Garradd's brightness and the UVOT's sensitivity and resolution, researchers can monitor the comet when it is beyond the grasp of most ground-based observatories. Plans call for observations at eight different distances from the sun out to about 5.5 AU, which the comet will reach in April 2013.

Related links:

• Swift’s Comet Tally Highlighted in Observatory Webcast

• NASA's Swift Spies Comet Lulin

• NASA's Swift Looks to Comets for a Cool View

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.