Comet observation from Mars, comets close encounters to Mars in 2013 and 2014 Options

[nprev]

Don't confuse estimates based on constraints with actual measurements. The 50km upper limit was based on early albedo predictions; as the comet gets closer these will be refined based on observations.

In other words, the nucleus didn't shrink from 50km to 1-3km.

[DEChengst]

If Mars ploughs through the coma and/or tail SAM may do some great measurements as well. Would be interesting to see how atmospheric composition changes over time if at all.

[fredk]

Tails/comas are extremely tenuous. I'd be very surprized if a pass would leave any measurable effect, even in Mars's thin atmosphere.

[TheAnt]

If Mars ploughs through the coma and/or tail SAM may do some great measurements as well. Would be interesting to see how atmospheric composition changes over time if at all.

The total amount of gas the comet might add could be a few litres of gas at ordinary atmospheric pressure at Mars - in short any addition will most likely be unmeasurable.
That said without considering the effect on one quite unlikely collision - if that happens the effect could be dramatic - possibly even result in a continuous rewriting of the textbooks for the martian atmosphere over the foreseeable future.

What's interesting is that NASA seem to be looking into the option of having any or perhaps all orbiters having a look at the comet, since the comet might be passing as close as a few 100 000 of kilometres and even closer, this could turn out to be one opportunity to get a comet exploration mission for free. =)

[Cosmic Penguin]

OK I need some expertise about spacecraft methane detection: a recent Indian news report claims that the Indian Mars Orbiter may be delayed from this year's launch window because the comet may affect the operation of one of its science instruments, the methane sensor. It quote an un-named scientist saying that "Most comets have methane, and there is a good chance that our MSN payload (methane sensor) may confuse the methane it detects from the comet as that of Mars and transmit wrong data. Such data will mislead us. Even NASA is wary. "

Somehow I think that this should never been a problem - in fact that little spacecraft is in such a high elliptical orbit that it is in the prime position to make observations of the comet tail, so it seems strange that the Indians think that there's a data contamination problem - they could just delay the instrument's observations if this really is a problem, which again I doubt (or just record the before and after comet passage data for comparison). Hmm.... does that mean something else is going on with the testing of the spacecraft?

Can any expert on trace gases shed some light on the credibility of this claim? Thanks!

[Paolo]

I am not sure but I think that it the comet really was able to deliver methane in the atmosphere, it would be extremely interesting to study its dynamics and the mechanisms that should be quickly destroying it

[Mongo]

New Calculations Effectively Rule Out Comet Impacting Mars in 2014

NASA’s Near-Earth Object Office says that new observations of comet C/2013 A1 (Siding Spring) have allowed further refinements of the comet’s orbit, helping to determine the chances it could hit Mars in October of 2014. Shortly after its discovery in December 2012, astronomers thought there was an outside chance that a newly discovered comet might be on a collision course with Mars.

While the latest orbital plot places the comet’s closest approach to Mars slightly closer than previous estimates, the new data now significantly reduces the probability the comet will impact the Red Planet, JPL said, from about 1 in 8,000 to about 1 in 120,000.

The closest approach is now estimated at about 68,000 miles (110,000 kilometers). The most previous estimates had it whizzing by at 186,000 miles (300,000 kilometers).

[Explorer1]

Even that distance is pretty much a stone's throw, only about four and a half times farther than Deimos' orbit. It should be quite a show!

[Paolo]

and we've never recorded such a close approach by a comet to Earth. the closest a comet came, in 1491 was still 1.4 million kilometers away!

[fredk]

I'll never forget the eerie sight of IRAS–Araki–Alcock gliding past the stars in real time back in '83, and that comet only came as close as just under 5 million km from Earth! But you could only see it's motion in real time through a 'scope.

At 50 km/s relative to Mars and a close-approach distance of 100 000 km, that gives an angular speed of about 1.7 arcmin/sec for 2013 A1 (Siding Spring). So it would take around 17 seconds to cross a half degree (diameter of full moon seen from Earth). So the motion might just be noticeable to the unaided eye in real time, especially if it passed close to a bright star. A farther close approach means smaller angular speed.

I suspect much of the general public thinks comets zoom across the sky, so they wouldn't be impressed by this. But it's exceedingly rare to be able to see solar system motions in real time. Close asteroid passes and eclipses and transits are the only other examples I can think of.

[Explorer1]

Yes, many folks confuse comets and meteor speeds, even people I know. Though it's as great an opportunity as any for education!

[Pertinax]

I was tinkering in the iPad app Luminos with C/2013A1 as it passes by Mars next year using the most ephem., and though I'd pass on the viewing info I put together (at this early date) for MSL:

Comet C/2013 A1 rises on MSL sol 738 at 17:25:58 LT (20:21:39 UTC 19Oct14) at Gale Crater while it is 72,784 km away (from Gale). [Az: 112D 12M 33.1S, Alt: -0D 0M 35.8S] This will likely be behind Mt. Sharp from Curiosity's perspective.

The sun at comet rise is 0D 56M 35.0S above the horizon (Az: 255D 2M 20.0S), preparing to set at 17:35 LT (20:31 UTC)

Closest Aproach to Gale Crater occurs at 17:28:54 LT (20:24:39 UTC) at 72,092 km away [Az: 110D 32M 42.6S, Alt: 8D 27M 28.2S] Luminos calculates the apparant brightness at about -10.5 (FWIW)

The apparent motion since rising to this point has on average been: Az: 0.555D/min, 0.009D/sec; Alt: 2.816D/min, 0.047D/sec; The comet will be traveling across the sky at 0.048D/sec, covering the average angular diameter of the moon (0.528D) as seen from earth in 11 seconds (all times for motion here using earth clock).

One hour (Local Time) after sunset, 18:35 LT (21:32:34 UTC), the comet will be at Az: 331D 16M 12.1S, Alt:81D 47M 16.2S and 239,340 km away from Gale. Luminos calculates the apparant brightness at about -7.0 (again, FWIW. I do not know how Luminos calculated apparent mag.)


-- Pertinax

[Phil Stooke]

Interesting presentation just posted - it will actually happen next week at MEPAG:


Phil

[SteveM]

Powerpoint version (with color) here.

[fredk]

Update (with further links) on the Mars observations of ISON here. About the August hirise attempt:

NASA already planned a test observation for August 20th, and unfortunately (but not unexpectedly), Comet ISON remained just below the detection threshold.