Countdown To Comet ISON Mars Flyby

Beauty color photo of Comet ISON taken by astrophotographer Damian Peach on Sept. 24. ISON is a dusty comet. Much of that dust is blown back by light pressure from the sun to form the tail. Click to enlarge.

In just 4 days four Mars probes will focus cameras on Comet ISON as it makes its closest approach to the planet on Oct. 1. NASA’s Mars Reconnaissance Orbiter will study and photograph the comet from orbit on three days: Sept. 29, Oct. 1 and Oct. 2. Europe’s Mars Express orbiter, which began its ISON observing campaign on Sept. 21, will study the coma, the tenuous atmosphere that surrounds the comet’s icy nucleus. The probe will examine and photograph ISON through about October 5. As soon as photos are released, you’ll see them here.

The European Mars Express has already began its studies of Comet ISON from Mars orbit on September 21. The probe is the first European craft to visit another planet. Credit: ESA

Both the Curiosity and Opportunity rovers will also be pressed into service to spy ISON from the ground during the same time. Seen from Mars, the comet should glow about magnitude 2.5-3, plenty bright to see with the naked eye if you could somehow wish yourself there.

Comet ISON will shine at around magnitude 3 low in the northern sky in the constellation Lacerta the Lizard from the Curiosity rover’s location. Maps made with Stellarium

Amateur and professional astronomers have been watching Comet ISON evolve since its discovery on Sept. 21, 2012. It began as a dim 15th magnitude patch of haze and brightened very slowly. Amateurs reported a nice uptick in activity beginning late this summer into early fall. ISON now shines at about magnitude 11.5-12 (still faint and requiring a telescope to see) and sports a short tail pointing to the northwest. I was able to see the tail and brighter coma in my 15-inch (37 cm) scope without difficulty about a week ago in a dark sky just before dawn.

Comet ISON tomorrow morning shortly before the start of dawn. The comet’s moving east near the border of the constellations Cancer and Leo. It’s both physically close to Mars and very near the planet in the sky. Because of glare from the moon, a large amateur telescope is still required to see the comet.

Time exposure photos show a classic beauty of a comet with a bright, compact head and elegant tail. According to NASA’s Comet ISON Observing Campaign site, astronomers consider ISON “somewhat more active” that a typical comet. It’s kicking out a lot of dust right now as the sun’s heat vaporizes ice on the comet’s surface. That’s why we see a substantial tail in recent photos. Any guesses as to exactly how bright ISON will become when it zips nearest the sun on Thanksgiving Day are just that … educated guesses.

Movie made from images taken by NASA’s Deep Impact probe in mid-Jan. 2013

Astronomers use formulas based on comet size, distance and dust production rate to come up with brightness predictions. ISON could rival Venus for a short time on Nov. 28 or be substantially fainter or brighter. If it survives its searingly close passage of 745,000 miles (1.2 million km) from the sun’s surface, it will likely become a beautiful sight for northern hemisphere skywatchers during the first half of December. Southern hemisphere observers will have their best views before closest approach.

Much depends on the the comet’s size, currently estimated at 1.8 miles (3 km), pretty typical for a comet. The bigger the iceball, the better the chance of surviving the sun’s battering. Let’s hope ISON keeps it together.

9 Responses

  1. Bob Crozier

    In the Deep Impact video that you posted (very cool btw!), there seems to be little flashes where the tail brightens slightly. It seems that the same clip gets repeated several times; maybe with different filters or something? And then towards the end of the clip, there is a very brief (maybe just one or two frames?) but very bright flash right behind the comet, probably about as bright as the comet itself. Any ideas what that is (or was)?

  2. Edward M. Boll

    I was going to slip out of work at 7 AM, and take a glance at the Moon. But I got busy and did not even think about it till after sunrise.

    1. astrobob

      Always happens, ever since ancient times, that doom is imminent when a bright comet appears. Check out my old posts on Comet Elenin and the doomsayers, the last portent of the world’s end. You can look them up with keywords Astro Bob and Elenin.

  3. Peter K

    Hey Bob,
    Do you know whether the NASA team will be able to catch ISON with the government shutdown? Such horrible timing!

    1. astrobob

      A welcome update. The rovers and MRO will still be operational – they’re run by JPL, not NASA. See blog entry today.

  4. B.Chandrasekar

    What are the chances of COMET ISON or any other comet or meteor colliding with Earth.
    Are we sufficiently prepared for such an Impact.

    1. astrobob

      There’s 0% chance ISON will collide with Earth. We don’t of any comet or asteroid at this moment that will collide with Earth. A few objects have a very tiny probability for an impact, that’s all. The kilometer-sized and larger objects we have a good handle on, however there are lots of smaller asteroids that have yet to be discovered that potentially could harm. Keep in mind that small objects a few meters across are not harmful since they break apart in our atmosphere to fall to the ground as meteorites. This is a common occurrence with somewhere around a dozen witnessed meteorite falls per year.

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