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So they thought it would be a good idea to answer that question right off the bat, and to make a video about it.
For those who are familiar with the night sky, you already know the answer because you’ve already looked at the projected trajectory of ISON and read many blog posts about it. For you guys, I don’t think it comes as any surprise when I say the short answer to the question of ‘Will ISON hit us?’ is no.
But c’mon, don’t you want to know why?
A comet’s journey through the solar system is perilous and violent. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars — at some 230 million miles away from the sun — the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether.
Predicted hour-by-hour position of Comet ISON in various instruments on one of NASA’s Solar Terrestrial Relations Observatory spacecraft between 1 a.m. EST on Nov. 26, 2013, and 7 p.m. EST on Nov. 29, 2013. The blue field of view is from the outer coronagraph and green from the inner coronagraph.
Right now, Comet ISON is making that journey. It began its trip from the Oort cloud region of our solar system and is now travelling 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.
Cataloged as C/2012 S1, Comet ISON was first spotted 585 million miles away in September 2012. This is its very first trip around the sun, which means it is still made of pristine matter from the earliest days of the solar system’s formation, its top layers never having been lost by a trip near the sun. Scientists will point as many ground-based observatories as they can and at least 15 space-based assets towards the comet along the way, in order to learn more about this time capsule from when the solar system first formed.
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.
NASA has initiated a Comet ISON Observing Campaign to facilitate a massive global observation campaign incorporating both space-based and ground-based telescopes and encouraging citizen scientists and both professional and amateur astronomers to participate.
Read on for a timeline of observations expected of Comet ISON on its perilous journey.
10,000 years ago
The comet began its journey from the Oort cloud, a swath of icy objects that orbit far beyond Neptune. This is Comet ISON’s first trip through the inner solar system.
September 2012
Comet ISON was first discovered by Russian astronomers, Vitali Nevski and Artyom Novichonok, using the International Scientific Optical Network in Kislovodsk, Russia.
From early June through late-August, ISON was almost directly behind the sun as viewed from Earth, and thus could not be observed from the ground.
BRRISON will observe ISON in the near-infrared, near-ultraviolet and visible wavelength ranges, and will measure the ratio of carbon dioxide to water emissions from the comet. This ratio will be a vital diagnostic of the comet’s origins. These emissions are blocked by Earth’s atmosphere and cannot be measured from the ground.
BRRISON is an unprecedented quick-reaction project to take advantage of the opportunity presented by the discovery of comet ISON, and is the first NASA Planetary Science Division balloon mission to observe a comet.
Comet ISON will be close enough to the sun, as of Oct. 10 that it will be visible by an instrument with an extremely wide view on one of the solar observatories: the HI 2 instrument on one of NASA’s Solar Terrestrial Relations Observatories, STEREO-A. At that point the comet will be around 94.5 million miles away from the sun.
Additional Hubble observations are planned to provide new estimates on nucleus size and composition as well as to search for any fragments that have broken off.
November 2013
Observations of Comet ISON with NASA’s Chandra X-ray Observatory will be used to study particles streaming away from the sun in the solar wind. These particles from the sun interact with Comet ISON to generate X-rays that are detected by Chandra. The first of two sets of observations is planned for early November, when Comet ISON will be passing through the hot wind produced by regions along the sun’s equator.
Once the comet passes Mercury, it will be on the most perilous part of its journey. The intense radiation of the sun causes material to evaporate quickly off the comet. Moreover the very pressure of the solar particles on the comet can cause it to break up. A slew of space and ground-based telescopes will watch the comet as it makes its slingshot around the sun.
All of these observatories will have different views. STEREO-A will be the only one that sees the comet transit across the face of the sun. In SDO’s view, the comet will appear to travel above the sun.
The exact dates of view for these observatories is as follows:
Nov 21–28: STEREO-A HI1 sees comet
Nov 26-29: STEREO-B coronagraphs sees comet
Nov 27-30: SOHO sees comet in coronagraphs
Nov 28-29: STEREO-A coronagraphs sees comet
Nov 28: SDO sees comet (for a few hours)
In addition, ground-based solar telescopes – observing in optical, infrared and radio wavelengths – will all be able to observe the comet during perihelion. Such observations will provide additional information about the composition of the comet and how material evaporates off it, fueling the dusty cloud that surrounds the nucleus.
One last solar effect could impact the comet at this stage in its journey. If the sun coincidentally sends out a giant cloud of solar particles, known as a coronal mass ejection, at the right time and direction to pass the comet, it could pull the comet’s tail right off.
A second set of Chandra observations is planned for the middle of December to early January, when ISON will be passing through a transition region in the solar wind, where the hot wind from the Sun’s sun’s equator is mixed with a cooler wind produced by regions near the poles of the sun.
Comet ISON Interactive Orbital Diagram:
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=ison;orb=1;cov=0;log=0;cad=0#orb
When you play around with the orbital diagram viewpoint controls, you can zoom in and rotate it and adjust the view angle above or below the elliptic. You can also change the date and animate the view.
Comet ISON trajectory:
http://www.youtube.com/watch?v=TULT9QUevnQ