This NASA Hubble Space Telescope image of Comet (C/2012 S1) ISON was photographed on April 10, when the comet was slightly closer than Jupiter’s orbit at a distance of 386 million miles from the Sun (394 million miles from Earth).
Even at that great distance the comet is already active as sunlight warms the surface and causes frozen volatiles to sublimate. A detailed analysis of the dust coma surrounding the solid, icy nucleus reveals a strong, jet blasting dust particles off the sunward-facing side of the comet’s nucleus.
(NASA image)
Preliminary measurements from the Hubble images suggest that the nucleus of ISON is no larger than three or four miles across. This is remarkably small considering the high level of activity observed in the comet so far, said researchers.
The comet’s dusty coma, or head of the comet, is approximately 3,100 miles across, or 1.2 times the width of Australia. A dust tail extends more than 57,000 miles, far beyond Hubble’s field of view.
More careful analysis is currently underway to improve these measurements and to predict the possible outcome of the sungrazing perihelion passage of this comet.
Astronomers from the University of Maryland at College Park (UMCP) 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.
“Comet ISON has the potential to be among the brightest comets of the last 50 years, which gives us a rare opportunity to observe its changes in great detail and over an extended period,” said Lead Investigator Dennis Bodewits, an astronomer at UMCP.
The Jan. 30 UVOT observations reveal that ISON was shedding about 112,000 pounds (51,000 kg) of dust, or about two-thirds the mass of an unfueled space shuttle, every minute. By contrast, the comet was producing only about 130 pounds (60 kg) of water every minute, or about four times the amount flowing out of a residential sprinkler system.
While the water and dust production rates are relatively uncertain because of the comet’s faintness, they can be used to estimate the size of ISON’s icy body. Comparing the amount of gas needed for a normal comet to blow off dust at them rate observed for ISON, the scientists estimate that the nucleus is roughly 3 miles (5 km) across, a typical size for a comet. This assumes that only the fraction of the surface most directly exposed to the sun, about 10 percent of the total, is actively producing jets.
An important question is whether ISON will continue to brighten at the same pace once water evaporation becomes the dominant source for its jets. Will the comet sizzle or fizzle?
“It looks promising, but that’s all we can say for sure now,” said Matthew Knight, an astronomer at Lowell Observatory in Flagstaff, Ariz., and a member of the Swift and CIOC teams. “Past comets have failed to live up to expectations once they reached the inner solar system, and only observations over the next few months will improve our knowledge of how ISON will perform.”
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 perhaps a trillion 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.
Comet Pan-STARRS (C/2011 L4) is now within the orbit of Mercury and is starting to brighten and has a nicely formed tail. Observers in the southern hemisphere have been able to capture Pan-STARRS in a nice variety of shots at Spaceweather.com. Pan-STARRS should make an appearance in the northern hemisphere soon with best viewing after March 10th in the early evening western sky. The best viewing will be away from city lights and look low on the horizon. Having binoculars will greatly enhance the view.
Earthsky.org has an excellent resource to help you find Pan-STARRS in the sky.
NASA Science Video:
Comet ISON (C/2012 S1) continues to approach the sun. Comet ISON will be visible in August or September if you have binoculars and are away from city lights.
A large meteorite blazed over Russia’s Chelyabinsk region early Friday, triggering a powerful shock wave that injured hundreds of people and blew out numerous windows. Official estimate that the meteor was around 10 tons and about the size of a bus, left a long white trail as it entered the Earth’s atmosphere at speeds of 33,000 mph.
Photo Credit: Fed Potapowvia.
It was a once in a decade event, Dr. Neil deGrasse Tyson, an astrophysicist at the American Museum of Natural History, told the TODAY show. The impact was the physics equivalent of hitting a brick wall. “When you hit a brick wall, you basically explode, and that’s what happened here, and it exploded in midair,” Tyson said.
This meteor hit just hours prior to the 150 foot wide Asteroid 2012 DA14 was due to skirt within 17,000 miles of Earth. Scientist have said that there is no chance of an impact from 2012 DA14.
Watch for further updates on this event and Comet c/2012 S1 ISON.
NASA’s Deep Impact spacecraft has captured images of comet C/2012 S1 (ISON). The images were taken by the spacecraft’s Medium-Resolution Imager over a 36-hour period on Jan. 17 and 18, 2013, from a distance of 493 million miles (793 million kilometers). There is great anticipatation that comet ISON could potentially be one of the great comets.
Comets like ISON are thought to come from the solar system’s Oortcloud and many are long period comets. These comets have orbits which are difficult to determine. Some long period comets may not return to the solar system for a million years.
A unique opportunity to view Comet ISON off the Costa Rican coast from December 1-8, 2013 aboard the tall ship Star Flyer. This cruise will be hosted by Steve Kates who hosts the Dr. Sky show. Full details can be found at http://tropicalsails.com/Home_Page.php
An excellent article from space.com on if Comet ISON will survive the approach to the sun.
It is predicted that the comet will come within 800,000 miles of the surface of the sun. If Comet ISON does survive the fly there is still a chance that “…it could be destroyed by tidal forces or solar radidiation as it approaches the sun.”
As Comet ISON approaches we have been asked to explain a litte more about what a comet is.
A comet is a body of ice, mixed with rock dust and many other compounds. Most comets are about the size of a small city, or about 10 miles across. The surface of a comet has cracks and fissures and is porous. While the interior of the comet is hundreds of degrees below zero, sunlight can warm the surface and cause dirty jets of gas and water vapor to erupt from the surface. Free of the nucleus, the dust and gas expand into a bright shell called the coma. Sunlight pushes dust out of the coma, making a dust tail. The gases in the tail become electrically charged by the ultraviolet sunlight, and the solar wind shapes it into a gas tail.
Comet ISON is still more than 371,824,154 miles away but generating a lot of excitement. We still don’t know if Comet ISON will live up to all the news reports that it will be one of the brightest in history.
