Comet ISON is currently diving through the inner solar system, soon to make a close approach with the sun on Nov. 28. Known as a "sungrazer comet," ISON will dive deep into the sun's corona, enduring the intense multi-million degree plasma and powerful solar energy. Since the "pristine" comet was discovered in September 2012, ground-based observatories, space probes and space telescopes alike have been trying to grab a glimpse of what could be the "Comet of the Century" should it survive its solar close approach. Although many of the space missions were not designed to take snapshots of comets, it hasn't stopped many from trying and contributing valuable science as we continue to track ISON's progress. With the help ofthe NASA Comet ISON Observing Campaign
, nine space missions are listed as providing observations of Comet ISON. More will inevitably join the fun, but here's the story so far.PHOTOS: Comet ISON: 5 Things You Should Know
On Jan. 17-18, 2013, NASA's Deep Impact spacecraft imaged Comet ISON during its deep space sojourn from a distance of nearly 500 million miles. From this early observation mission scientists were able to deduce the comet tail was already more than 40,000 miles long, despite the fact it was around the orbit of Jupiter.ANALYSIS: NASA Probe Spies Incoming Comet ISON
Shortly after NASA's Deep Impact (EPOXI) mission imaged ISON, mission managers of NASA's Swift space observatory commanded the mission to take a look. Although Swift is not designed to observe comets (it is, after all a gamma-ray observatory!), it used its Ultraviolet/Optical Telescope (UVOT) to gain a valuable insight to the comet and its growing coma and tail.
NASA's Spitzer Space Telescope is more at home taking snapshots of the infrared emissions of distant star-forming regions, but that doesn't mean it can't be used to observe comets. Seen here, Comet ISON was observed in two infrared wavelengths on June 13
NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Of all the space observatories, the Hubble Space Telescope is able to take some of the most spectacular images of the incoming comet, monitoring ISON as it approaches the sun, watching for any sign of breaking up.
On Oct. 8, 2013, NASA's Mars Reconnaissance Orbiter was commanded to slew away from it's Mars-facing orientation and direct its HiRISE camera at ISON. Although the comet was exhibiting little activity, HiRISE managed to pick it out of the dark.
During close approach with Mars, it wasn't only the MRO that snapped Comet ISON. The veteran Solar and Heliospheric Observatory (SoHO) was able to detect the comet with its wide-angle Solar Wind ANisotropies, or SWAN, instrument.
On Oct. 28, 2013, Comet ISON drifted into the field of view of one of NASA's twin solar observatories, STEREO B. One of two solar satellites, STEREO B is following Earth in its orbit (while STEREO A is leading) with a unique view from the far side of the sun.
On Nov. 4, NASA's Chandra X-Ray Observatory got in on the ISON imaging act, analyzing the structure of the comet. Overall, ISON's X-ray revealed it's a pretty typical comet, shedding 16 Olympic-sized swimming pools worth of water per day.
On Nov. 18 and 19 it wasn't only Comet ISON that passed the orbit of Mercury, Comet Encke did the inner solar system dash, too. Earlier in the month, NASA's Mercury orbiter MESSENGER was able to image ISON and Encke as they approached, reminding us there is usually more than one comet flying through the solar system at any given time.ANALYSIS: Fly With ISON In Stunning Comet Simulation
When Russian astronomers detected the ‘virgin’ Comet ISON in September 2012, the world was hoping for something a little bit special. But no comet is the same and the nature of ‘dirty snowballs’ is rarely predictable.
In a NASA Comet ISON Observing Campaign (CIOC) blog update, astronomer Padma Yanamandra-Fisher (of the Space Science Institute) remarked on the unpredictable nature of ISON, saying: “this comet has decided to march to its own drummer.” In other words, even for a comet, ISON is its own beast, underlining the fact that comets still have many surprises up their icy sleeves.
So, as ISON made its solar close-pass (an event in its orbit known as ‘perihelion’) on Nov. 28, few would have been able to guess what was going to happen next.
Living up to its celebrity status, ISON put on a dramatic show on Thanksgiving Day, first fading from the view of solar observatories as it seemed to succumb to extreme solar heating. All seemed to be lost when the Solar and Heliospheric Observatory (SoHO) spotted a wisp of what seemed to be ISON’s ‘ashes’ re-emerge from the sun’s lower atmosphere — few would have doubted that ISON was toast; it had disintegrated.
Comet ISON-watchers were crestfallen — was this the end of ISON’s voyage through the inner solar system?
Just as the U.S. gave up hope and went back to the Thanksgiving Day wine, confused messages from astronomers studying data from the armada of solar observatories started to pour out. There was something in the debris stream; a possible chunk of Comet ISON had survived the extreme lower coronal environment a mere million miles from the sun’s “surface” (the photosphere). And it was brightening.
Now, around 24 hours post-perihelion, astronomers are tracking ISON once more as it continues its trek through the inner solar system. It obviously didn’t get away from its solar close encounter unscathed, but there is definitely a significant mass of comet material that made it though the solar roasting.
Comet ISON’s violent solar encounter may have caused a significant shedding of mass from ISON, perhaps exposing more primordial icy material (that formed during the early evolution of our solar system) to the sun’s heating. This is likely causing the brightening, but it seems unlikely that ISON will become the Comet of the Century. But it is without doubt one of the most fascinating objects to visit our solar system for some time and may help to rewrite the our understanding of sungrazing comets.
Image: Composite of SoHO LASCO observations of Comet ISON as it approached the sun and completed perihelion, creating a fan-like comet tail structure as it zoomed back out into interplanetary space. Credit: NASA/ESA