[UPDATED: Dec. 5, 2013 – see note, below] This thrilling, deep space video of comet ISON (aka the newest ‘comet of the Century’) passing Earth and Mercury on its way towards the Sun (see below) comes to us courtesy of the Heliospheric Imager on-board NASA’s STEREO probe.
The time frame of the comet’s path captured in the video is November 20th through November 25th (so, its current path has since progressed closer to the sun than shown here). ISON will round the sun sometime in the next 24 hours. At that point, the comet’s perihelion may be as close as one degree of arc (just over a million km from the Sun’s surface), making it very difficult to observe by both space probes and Earth observers.
Like the polar ice sheet, the amount of light that a comet reflects is referred to as its albedo. ISON — a “baby comet” — has relatively low albedo.
‘C/2012 S1’s brightness will increase less quickly than predicted and it will not become so bright as expected. Recent observations of C/2012 S1 suggest that, even if it remains intact, it may only brighten to about magnitude −6’ [source: wikipedia]
ISON — officially designated C/2012 S1 (the ‘c’ means that it is a non-periodic comet) aka Comet Nevski–Novichonok — was discovered September 21 , 2012 (the ‘S’ in the official name means September, the ‘1’ means it was the first discovered that month). It’s more common name (ISON) comes from the Russia-based International Scientific Optical Network which first discovered it.
The impending close encounter with the Sun could very well signify the end of ISON as solar heat boils away much of it constituent water and ice. In fact, this heat-induced loss of cometary matter began well before ISON crossed Mars’ orbit — more than 230 million miles from the sun. With each kilometer traveled, ISON is subjected to greater concentrations of solar wind-born radiation and increasing gravitational pressure.
There’s a small chance that the “sungrazing comet” (as these are known) will survive its close brush with the Sun, but even it does not survive, space scientists will still be able to accumulate important data — such as what the comet is made of — just from tracking its journey and observing its interaction with the intensifying solar wind (which can be seen emanating from the far right of the video frame). Scientists will also gain valuable data about the Sun itself and maybe even tease out a few clues as to the origin of our solar system.
Note that the video distorts (foreshortens) the perspective here, making it seem that the Earth is closer to the Sun than Mercury.
And, if you view the video on a larger screen, you can see another comet — comet Encke (officially; 2P/Encke, a short period comet with a three year solar orbit cycle) — passing through the frame. The following video of comet ISON was made available through NASA Goddard Space Flight Center (which maintains in own Flickr.com photo/video stream)
UPDATE: Nov. 29, 2013 – “…late Thursday night, images from another sun-watching spacecraft, the Solar and Heliospheric Observatory (SOHO) run by NASA and the European Space Agency, picked up a blip of something rounding the sun in a camera called LASCO C3.” [source: Comet ISON Gets Roasted by Sun and Vanishes, But Did It Survive? – Space.com]
UPDATED: Dec. 4, 2013 – It appears as though ISON is no more…disintegrating just before its closest encounter with the sun…read more: ScienceShot: First-Time Comet Perishes