Comet ISON Survives

Comet ISON, or some part of it, has survived its close encounter with the Sun, but, as noted yesterday, it seems to have fizzled as a great comet. This animation of still from SOHO shows it orbiting around the sun on 28 November. ISON appears much smaller as it moves away, but its nucleus may still be intact.ison-survives_0Video Credit: NASA

Comet ISON

ison-19_NOVAt the time this picture was made, Comet ISON was some 70 million km from the sun, 128 million km from Earth, and moving at around 220,000 km/h. Comet ISON will pass very close to the Sun on Thanksgiving Day. If it survives that close encounter, it should provide a spectacular show for observers in the Northern Hemisphere for several days afterward.

This picture was taken just before sunrise yesterday morning at Marshall Space Flight Center in Huntsville, Alabama using a 14-in telescope.

Image Credit: NASA

Comet ISON is Coming

comet_ison_25OctAt this time of this picture was made, Comet ISON was located in the constellation of Leo the Lion, about 212 million km from Earth and heading toward the sun at a bit over 140,000 km/h.

For now, the comet is still too dim to be seen with the naked eye or even small binoculars, but it is a reasonable target for a small telescope. This picture was made using a 14 in telescope at Marshall Space Flight Center in Huntsville, Alabama, just before sunrise on 25 October. The comet shows a faint green color near the center of the image. The diagonal streak was caused by a satellite passing though the field of view.

Image Credit: NASA / Aaron Kingery

Comet ISON Update

comet-ison_9Oct_HubbleThis new picture taken by the Hubble Space Telescope on 9 October of Comet ISON indicates that the comet is intact despite some suggestions that its icy nucleus might disintegrate as the sun warms it. The comet will pass closest to the sun on Thanksgiving Day. The comet’s solid nucleus is unresolved because it is so small. If the nucleus had broken apart, Hubble probably would have seen evidence of the fragments. The coma or head surrounding the comet’s nucleus appears smooth and symmetrical. That would likely not be the case if it were a cluster of fragments. A polar jet of dust first seen in Hubble images taken in April is no longer visible.

When this picture was taken, the comet was inside Mars’s orbit and about 280 million km from Earth. Comet ISON should make its closest approach to Earth on 26 December, roughly 64 million km away.

Image Credit: NASA

Comet ISON


Video Credit: NASA

Comet ISON is presently hurtling toward the Sun at over 77,000 km/h. Its motion is captured in this time-lapse movie made from pictures taken during a 43-minute interval on 8 May, 2013, by the Hubble Space Telescope when the comet between the orbits of Mars and Jupiter, roughly 640 million km from Earth. In the movie about 55,000 km of motion is compressed into five seconds.

The comet’s tail is a stream of gas and dust from its icy nucleus, which is surrounded by a bright star-like-looking coma. The pressure of the solar wind sweeps the material into a tail, like a wind on Earth blowing a flag. The comet is very cold now. As it warms up closer to the Sun, its rate of sublimation (the process of a solid changing directly to a gas) will increase. The comet will get brighter and its tail will grow longer as it nears the Sun. The comet should be visible to the naked eye in late November and may even be visible during the day on Thanksgiving Day.

The comet is named after the organization that discovered it, the Russia-based International Scientific Optical Network.

Incoming Comet ISON

ISON_HubbleThis Hubble Space Telescope image of Comet ISON (C/2012 S1) was photographed earlier this month when the comet was just inside Jupiter’s orbit at a distance of around 620 million km from the Sun (635 million km from Earth).

Even that far out, the comet is already becoming active as sunlight warms the surface and frozen volatiles sublimate. Analysis of the dust coma surrounding the solid, icy nucleus shows a strong stream of dust particles coming off the Sun-facing side of the comet.

Preliminary measurements from Hubble images suggest that the ISON’s nucleus isn’t much more than than 5 or 6 km across. That’s tiny considering the high level of activity observed thus far. Astronomers are measuring the activity level of this comet now in order to predict the comet’s activity when it skims a bit more than 1,000,000 km above the sun’s surface on Thanksgiving.

The comet’s dusty coma, the head of the comet, is approximately 5,000 km across, and its dust tail stretches more than 90,000 km, which is wider than Hubble’s field of view.

This image was taken in visible light. The blue false color was added to highlight details in the comet structure.

Image Credit: NASA

Comet ISON

Astronomers from the University of Maryland at College Park and Lowell Observatory have used NASA’s Swift satellite to check out comet C/2012 S1 (ISON), which may become one of the most dazzling in decades when it rounds the sun later this year. Using images acquired over the last two months from Swift‘s Ultraviolet/Optical Telescope (UVOT), the team has made initial estimates of the comet’s water and dust production and used them to infer the size of its icy nucleus.Swift_ISONThe UVOT imaged comet ISON (center) at the end of January, when it was located about 3.3 degrees from the bright star Castor in the constellation Gemini. When this 5.5 min time exposure was taken, the comet was about 5,000 times fainter than the limit of human vision.

Based on ISON’s orbit, astronomers think the comet is making its first-ever trip through the inner solar system. Before beginning its long fall toward the Sun, the comet resided in the Oort comet cloud, a vast shell of icy bodies that extends from the outer reaches of the planetary system to about a third of the distance to the star nearest the Sun.

On 1 October, the inbound comet passes about 10.8 million km from Mars. During this close encounter, NASA and ESA spacecraft now orbiting Mars may be able to observe the comet. It may also have its picture taken by the Curiosity rover from the surface of Mars.

On 28 November, ISON will swing around around the sun. The comet will approach within about 1.2 million km of the Sun’s visible surface, which classifies it as a sungrazing comet. In late November, icy material will furiously sublimate and torrents of dust will be released as the ISON’s surface erodes because of the Sun’s fierce heat—as sun-monitoring satellites look on. Around this time, the comet may become bright enough to be seen from Earth just by holding up a hand to block the Sun’s glare.

Following ISON’s solar encounter, the comet will move toward Earth, appearing in evening twilight through December. It will swing past Earth on the day after Christmas, coming within 64.2 million km or about 167 times farther than the moon.

Image and Video Credit: NASA