Sun Grazing Comets as Solar Probes

Watch this video on the Goddard YouTube channel. A comet's journey through the solar syste is perilous and violent. Before it reaches Mars - at some 230 million miles away from the sun - the radiation of the sun begins to cook off the frozen water ice directly into gas. This is called sublimation. It is the first step toward breaking the comet apart. If it survives this, the intense radiation and pressure closer to the sun could destroy it altogether.Animators at NASA's Goddard Space Flight Center in Greenbelt, Md. created this short movie showing how the sun can cook a comet. Such a journey is currently being made by Comet ISON. It began its trip from the Oort cloud region of our solar system and is now traveling toward the sun. The comet will reach its closest approach to the sun on Thanksgiving Day — Nov. 28, 2013 — skimming just 730,000 miles above the sun’s surface. If it comes around the sun without breaking up, the comet will be visible in the Northern Hemisphere with the naked eye, and from what we see now, ISON is predicted to be a particularly bright and beautiful comet. Even if the comet does not survive, tracking its journey will help scientists understand what the comet is made of, how it reacts to its environment, and what this explains about the origins of the solar system. Closer to the sun, watching how the comet and its tail interact with the vast solar atmosphere can teach scientists more about the sun itself. Related pages

Short, narrated video about sungrazing comets.Watch this video on the NASAexplorer YouTube channel.For complete transcript, click here. Sungrazing comets are a special class of comets that come very close to the sun at their nearest approach, a point called perihelion. To be considered a sungrazer, a comet needs to get within about 850,000 miles from the sun at perihelion. Many come even closer, even to within a few thousand miles. Being so close to the sun is very hard on comets for many reasons. They are subjected to a lot of solar radiation which boils off their water or other volatiles. The physical push of the radiation and the solar wind also helps form the tails. And as they get closer to the sun, the comets experience extremely strong tidal forces, or gravitational stress. In this hostile environment, many sungrazers do not survive their trip around the sun. Although they don't actually crash into the solar surface, the sun is able to destroy them anyway. Many sungrazing comets follow a similar orbit, called the Kreutz Path, and collectively belong to a population called the Kreutz Group. In fact, close to 85% of the sungrazers seen by the SOHO satellite are on this orbital highway. Scientists think one extremely large sungrazing comet broke up hundreds, or even thousands, of years ago, and the current comets on the Kreutz Path are the leftover fragments of it. As clumps of remnants make their way back around the sun, we experience a sharp increase in sungrazing comets, which appears to be going on now. Comet Lovejoy, which reached perihelion on December 15, 2011 is the best known recent Kreutz-group sungrazer. And so far, it is the only one that NASA's solar-observing fleet has seen survive its trip around the sun. Comet ISON, an upcoming sungrazer with a perihelion of 730,000 miles on November 28, 2013, is not on the Kreutz Path. In fact, ISON's orbit suggests that it may gain enough momentum to escape the solar system entirely, and never return. Before it does so, it will pass within about 40 million miles from Earth on December 26th. Assuming it survives its trip around the sun. For More InformationSee [http://www.nasa.gov/content/goddard/timeline-of-comet-ison-s-dangerous-journey/](http://www.nasa.gov/content/goddard/timeline-of-comet-ison-s-dangerous-journey/) Related pages

Comet ISON is now approaching the inner solar system. Discovered last year, the comet remains unusually active for its distance from the sun. If current trends continue, ISON could rank as one of the brightest comets in decades when it makes its close approach to the sun in late November. This animation shows the comet's approach and departure from the inner solar system from various perspectives. Credit: NASA's Goddard Space Flight Center Scientific Visualization StudioWatch this video on YouTube.For complete transcript, click here. This animation shows two views of comet ISON's path through the inner solar system. The first is a view following the comet along its orbit. The second is a view perpendicular to ISON's orbit.Credit: NASA's Goddard Space Flight Center Scientific Visualization StudioWatch this video on YouTube.For complete transcript, click here. Still of all four views of ISON orbital path. This paper model illustrates the comet's path during its six-month trek in the vicinity of Earth, Venus and Mercury. Track how the relationship between Earth and the comet constantly changes by referring to the dates along both orbits.Download the pdf with instructions here. From now through October, Comet ISON tracks through the constellations Gemini, Cancer and Leo as it falls toward the sun. Credit: NASA's Goddard Space Flight Center/Axel Mellinger, Central Michigan Univ.More of Axel Mellinger's images here. From now through October, Comet ISON tracks through the constellations Gemini, Cancer and Leo as it falls toward the sun. No Labels. Credit: NASA's Goddard Space Flight Center/Axel Mellinger, Central Michigan Univ.More of Axel Mellinger's images here. The Ultraviolet/Optical Telescope aboard NASA's Swift imaged Comet ISON (center) on Jan. 30, when it was located about 3.3 degrees from the bright star Castor in the constellation Gemini. At the time of this 5.5-minute optical exposure, ISON was about 5,000 times fainter than the limit of human vision and was located 375 million miles (604 million km) from Earth and 460 million miles (740 million km) from the sun. Credit: NASA/Swift/D. Bodewits, UMCP The Ultraviolet/Optical Telescope aboard NASA's Swift imaged Comet ISON (center) on Jan. 30, when it was located about 3.3 degrees from the bright star Castor in the constellation Gemini. At the time of this 5.5-minute optical exposure, ISON was about 5,000 times fainter than the limit of human vision and was located 375 million miles (604 million km) from Earth and 460 million miles (740 million km) from the sun. Credit: NASA/Swift/D. Bodewits, UMCP No display group of hyperwall multimedia. Comet C/2012 S1, better known as comet ISON, may become a dazzling sight as it traverses the inner solar system in late 2013. During the weeks before its Nov. 28 close approach to the sun, the comet will be observable with small telescopes, and binoculars. Observatories around the world and in space will track the comet during its fiery trek around the sun. If ISON survives its searing solar passage, which seems likely but is not certain, the comet may be visible to the unaided eye in the pre-dawn sky during December.Watch the animations on this page to visualize ISON's voyage through the inner solar system, or build the paper model of its orbit to track the changing positions of Earth and the comet.Like all comets, ISON is a clump of frozen gases mixed with dust. Often described as "dirty snowballs," comets emit gas and dust whenever they venture near enough to the sun that the icy material transforms from a solid to gas, a process called sublimation. Jets powered by sublimating ice also release dust, which reflects sunlight and brightens the comet. On Nov. 28, ISON will make a sweltering passage around the sun. The comet will approach within about 730,000 miles (1.2 million km) of its visible surface, which classifies ISON as a sungrazing comet. In late November, its icy material will furiously sublimate and release torrents of dust as the surface erodes under the sun's fierce heat, all as sun-monitoring satellites look on. Around this time, the comet may become bright enough to glimpse just by holding up a hand to block the sun's glare.Sungrazing comets often shed large fragments or even completely disrupt following close encounters with the sun, but for ISON neither fate is a forgone conclusion.Following ISON's solar swingby, the comet will depart the sun and move toward Earth, appearing in morning twilight through December. The comet will swing past Earth on Dec. 26, approaching within 39.9 million miles (64.2 million km) or about 167 times farther than the moon.The comet was discovered on Sept 21, 2012, by Russian astronomers Vitali Nevski and Artyom Novichonok using a telescope of the International Scientific Optical Network (ISON) located near Kislovodsk.Learn more about sungrazing comets. For More InformationSee [http://solarsystem.nasa.gov/smallworlds/cometison.cfm](http://solarsystem.nasa.gov/smallworlds/cometison.cfm) Related pages

Full resolution 4Kx4K frames This movie zooms into the location where the comet is visible as it passes in front of the Sun. A small comet evaporates away in its flyby of the Sun. Related pages

This movie zooms in for the comet approach and departure. These are full resolution 4Kx4K images which show the instrument repointing. Comet Lovejoy makes a close pass to the Sun, and survives.The Solar Dynamics Observatory (SDO) is actually repointed to better observe the comet's approach to the Sun. Related pages

Slowed and looped video with music.For complete transcript, click here. One instrument watching for the comet was the Solar Dynamics Observatory (SDO), which adjusted its cameras in order to watch the trajectory. Not only does this help with comet research, but it also helps orient instruments on SDO—since the scientists know where the comet is based on other spacecraft, they can finely determine the position of SDO's mirrors. This first clip from SDO from the evening of Dec 15, 2011 shows Comet Lovejoy moving in toward the sun. Comet Lovejoy survived its encounter with the sun. The second clip shows the comet exiting from behind the right side of the sun, after an hour of travel through its closest approach to the sun. By tracking how the comet interacts with the sun's atmosphere, the corona, and how material from the tail moves along the sun's magnetic field lines, solar scientists hope to learn more about the corona. This movie was filmed by the Solar Dynamics Observatory in 171 angstrom wavelength, which is typically shown in yellow.Credit: NASA/SDO Related pages

Comet Encke Comet Encke data from STEREO Related pages

Comet Encke and Solar magnetic Fields This animation shows how Comet Encke interacts with the Solar Magnetic field and how it's tail is stripped away by a CME. Related pages