Shadow of a martian robot (APOD 4 Feb 2007)

[RJ Emery]

APOD for February 4, 2007, shows the shadow of the Opportunity Rover on Mars. I was wondering what percent of the Martian days does the sun cast a shadow.

Are there many cloudy days on Mars, and if so, what are the clouds made of that obscure the sun? By what mechanism do these clouds form?

Mars is known for dust clouds, and dust is beginning to cover the solar panels, reducing their efficiency.

In the two years the rovers have explored the planet, did it ever 'rain' or 'snow' upon them, and of what would that precipitation consist?

[tnzkka]

I wonder if round the "head"of the shadow a Heiligenschein is visible.
See: http://www.weather-photography.com/albu ... igenschein and if so, if it is another proof of a martian atmosphere.

THX for any comments

[l3p3r]

very interesting.... I think part of the explanation on the site you linked is relevant though:

This effect is enhanced by the fact that in the antisolar point (the point opposite the sun, i.e. the shadow of one's head), no other shadows are visible, and thus the region looks much brighter because the light and dark details of the surface are integrated by the eye.

[orin stepanek]

http://antwrp.gsfc.nasa.gov/apod/ap070204.html

The shadow kind of reminds me of the big robot in 'The Black Hole'.
Orin

[ta152h0]

the MARS exploration site been quiet for a couiple weeks. Wonder if the robots are stuck ( or one fell into Victoria crater ? )

[BMAONE23]

It looks to me like the image was taken fron INSIDE the crater, given the angle of the view and the fact that the plains arent visible. Has Opportunity driven into Victoria???

[NoelC]

Edit: It's an old image, from Endurance crater on Sol 180, 7/26/2004. See: http://www.jpl.nasa.gov/missions/mer/images.cfm?id=738

Anyone notice the little round light spot in the image, just to the left of the shadow of the rover's "knee"? Could that be the remnant of a geyser, or maybe just where they did some digging?

-Noel

[toejam]

Edit: It's an old image, from Endurance crater on Sol 180, 7/26/2004. See: http://www.jpl.nasa.gov/missions/mer/images.cfm?id=738

Anyone notice the little round light spot in the image, just to the left of the shadow of the rover's "knee"? Could that be the remnant of a geyser, or maybe just where they did some digging?

-Noel

Dunno.

But am waiting for one of our high-flyers to comment on the large "star-wars fort" built of shaped stones at roughly 10 o'clock.

[iamlucky13]

The shadow kind of reminds me of the big robot in 'The Black Hole'.
Orin

Charles: We'd be better off without you and Maximilian trying to knock heads.
V.I.N.CENT: I can handle that thing.


NoelC - My guess is they did a brushing with the rock abrasion tool there. It appears very round, with high edges, which is typical of inspections from the R.A.T. Also notice that the wheel depressions just short of and roughly bracketing the feature that indicate they stopped in front of it, exactly in the right position to reach it with the robotic arm. They couldn't have missed seeing that spot from the Hazcam in that position, and they would've gotten really excited about spotting such a feature. It looks like there might be a lightly covered rock patch there that could've been worth investigating.

[iamlucky13]

the MARS exploration site been quiet for a couiple weeks. Wonder if the robots are stuck ( or one fell into Victoria crater ? )

No worries! The latest pictures (4 days old) show that Opportunity has been continuing to drive counter-clockwise around Victoria, scoping out areas of interest and looking for possible routes into the crater.

Things have quieted down from the rovers as the Reconnaisence Orbiter has gained the spotlight, and outstanding field work has become business as usual for the rover crew. Updates have been occasional for quite some time.


tnzkka - Just to make sure your question doesn't get lost: the presence of a Martian atmosphere is not debated, it's just rather thin. Only about 0.1-0.2 psi. It looks like there may indeed be a Heiligenschein around the shadow from the brightness. I wasn't familiar with this effect. Thanks for sharing.

[aichip]

RJ Emery wrote:

I was wondering what percent of the Martian days does the sun cast a shadow.

In fact, virtually all Martian days have sharp shadows. There is little to obscure them, as opposed to the traditional image of a smoggy, dusty sky. Check the front and rear hazcam images for confirmation of this. Only early mornings when there is fog, or when there is in fact a dust storm, will you see any softening of the shadows. Take note of the fact that no dust storms have been observed since the rovers landed.

RJ Emery wrote:

Are there many cloudy days on Mars, and if so, what are the clouds made of that obscure the sun?

There are quite a few cloudy days on Mars, but the clouds are typically fairly high altitude types, showing wispy structures similar to cirrus or cirrostratus clouds on Earth.

There is little or no obscuration of the Sun due to the thinness of the clouds, but they consist of water in the form of droplets or ice crystals. Hubble polarized light studies of the Martian clouds reveal that roughly half of them do not polarize the light while the other half do. Ice crystal clouds do not polarize light but water droplet clouds do. This shows us that half of the clouds are made of liquid water droplets or mist.

RJ Emery wrote:

By what mechanism do these clouds form?

The mechanisms are identical to those in our own atmosphere. Water evaporates from the ground from brine present in the soil, or sublimates from ice in the soil. This vapor is transported to the upper atmosphere where it nucleates droplets on fine dust or salt crystals, or those same particles nucleate ice crystals in colder circumstances.

In either case, you would be unable to distinguish between Martian clouds and terrestrial ones except for one feature: the very thin air means very little drag, and this places a sharp limit on droplet or crystal size. Thicker air such as we have can support larger droplets or ice crystals. Thinner air, like the Martian atmosphere, can only support very small droplets or crystals, regardless of the weaker gravitation.

RJ Emery wrote:

Mars is known for dust clouds, and dust is beginning to cover the solar panels, reducing their efficiency.

True enough, but we have not yet seen any of these ubiquitous dust clouds since the rovers landed. The deposition of dust is actually quite slow, which provides us with a good amount of data on how little dust there really is in the Martian atmosphere.

If the amounts were anything like NASA seems to protray, then the solar panels would have been useless within a few weeks. As it is, we see that the dust is taking three years in the case of Spirit to cover the panels. Again, we see how sharp the shadows are, and when we combine this with the fact that it takes years to cover the solar panels, then we know that there is nowhere near the level of dust that is officially proclamed. The "red skies" are pretty much a myth, supported by using the L2 infrared filter as "red" in the official versions of the images. If you use L4 as reality dictates, the skies turn out a bland white, gray or blue.

RJ Emery wrote:

In the two years the rovers have explored the planet, did it ever 'rain' or 'snow' upon them, and of what would that precipitation consist?

While there is little evidence of precipitation per se (except for a dusting of frost or snow during the winter months on occasion), there have been numerous incidents for Opportunity that NASA refers to as "Martian car wash". In my opinion this is when the eruption of geyser spray washes off the dust. We have no images of this for the following reasons: first, the eruptions would most likely occur early in the morning, perhaps before sunrise when air pressure is lowest and therefore the differential pressure from underground would be highest. Second, without a light source on the rovers, we cannot get images of the process as it happens, so no images are taken at the times when the eruptions would be most likely to occur.

Dust devils have sometimes been hypothesized as the cleaning agent, but again, no such event has been imaged, and if you think about it, a dust devil is just as likely to deposit the dust, not remove it.

So technically, precipitation does occur on Mars, but it is probably nearly all ice crystals or snow. However, fog does sometimes form and this has been imaged. A condensate forming on the solar panels could in fact be sufficient to wash them clean, in a manner similar to dew forming on your car. However, we would expect to see some evidence of droplet patterns on the panels when imaged by the microscopic imager. This has so far not been seen.

Could it rain on Mars? Perhaps, but not much. I think it is far more likely that the evidence of erosion that we presently see is from geyser activity. Have a look at this set of microscopic images showing a badly eroded rover track.

http://marsrovers.jpl.nasa.gov/gallery/ ... _m510.html
The markings are identical to those left by raindrops driven into soil, and the erosion shows spherules on pedestals, identical to those formed in a rain on Earth. Again, I doubt that rain did this, and feel it is far more likely to be from groundwater erupting in a spray. This explains the erosion as well as the solar panels being cleaned. Compare the eroded images to these fresh rover tracks:
http://marsrovers.jpl.nasa.gov/gallery/ ... _m023.html

The conclusion is that the weather on Mars is as dependent on water as it is on Earth. Water can carry the latent heat of evaporation and through the change of state provide the thermal energy and expansion and contraction that is needed. That is of course powered by the Sun.

[RJ Emery]

aichip,

I much appreciate the detailed and factual response. Thank you.

[aichip]

You are welcome.

[iamlucky13]

If the amounts were anything like NASA seems to protray, then the solar panels would have been useless within a few weeks.

As I understand, the Martian weather has been relatively calm since the rovers arrived. There was a fairly large dust storm that was subsiding as they touched down, and a short-lived, minor one later, but little activity since. This is nothing compared to the storm that enveloped the whole planet in 2001 after the MGS arrived in orbit. Remember Pathfinder (1999?) only lasted 3 months.

Was what you were saying about the dust devils that none has been pictured in the act of cleaning? They certainly have been pictured in the distance, but I couldn't imagine a picture of the panels while one was passing over would be identifiable, much less likely given the tiny fraction of the time pictures are actually being taken.

I looked at those rover track pictures and did not see any thing that appeared to me like rain or geyser drops. The different image sets are on different types of soil, and I suspect we're not seeing water eroded wheel tracks, but wind-eroded, firm soil that has been slightly depressed by the wheels. Then again, I'm sure we could debate this pretty heavily and not come to agreement on it, so I'll just leave it at stating my opinion.

[RJ Emery]

Remember Pathfinder (1999?) only lasted 3 months.

IIRC, Pathfinder was the delivery and communications relay vehicle while Sojourner was the robot vehicle. The mission was to have lasted one month, but continued for three months.

Pathfinder failed I think for reasons still unknown, not necessarily due to dust accumulating on its solar panels, but at the time its failure, Sojourner itself was not incapacitated.

Please correct me if I am mistaken, but kindly cite your information source.

[iamlucky13]

No, it turns out you're correct about the failure, according to wikipedia. The batteries, which kept the Pathfinder's electronics warm overnight, could only handle about 40 charge/discharge cycles. NASA wanted 30 days. They got over 80. At that point, something in the electronics probably failed due to the temperature cycling. I recall Spirit and Opportunity actually have a small amount of Plutonium on board to keep the electronics warm overnight, as well as a different battery type.

However, here's my source for the dust storms. I don't have a specific source newer than 2003 handy, but I paid close attention to the MER website for a couple years, and dust storm activity levels were frequently mentioned, both because it affected their operations and because mission scientists have been using the rovers to study the weather on Mars, in addition to the geology.

[ta152h0]

Bet a capacitor on one of the circuit boards went kablooye and shorted out. had one do that when I was working in my previous life and put a hole the size of a dollar on the board.

[RJ Emery]

Bet a capacitor on one of the circuit boards went kablooye and shorted out. had one do that when I was working in my previous life and put a hole the size of a dollar on the board.

Someday, man will actually get to Mars, and no doubt the wreckage and/or remains of all the probes will be forensically examined when mission time then permits.

Who would have ever thought in 1912 that the Titanic would have been examined in detail starting 73 years later?

[ta152h0]

By the time a human astrnaut gets there, it will be like finding the Antikitera mechanism, noone will know what it did