Sunday, December 18, 2011

Another Good Omen?

The launch plume from MSL's Atlas-V. The input of water vapor into the normally dry mesosphere (at altitudes of around 80km) causes very high ice-water clouds known as "noctilucent" clouds to form. We contemplate the shapes we see in the sky and like the ancient Romans, trying to read auspices, we hope to glean the relevance to our own future of such ephemeral and changing patterns.

On the morning of November 26, as we were boarding our busses to head to the MSL Launch viewing area near the VAB, the brilliant sunrise lit up the light, misty rain we had passed through on the causeway over towards cape canaveral. The refraction through the particles generated a vivid rainbow which seemed to touch the ground in the general direction of pad 41, where the Atlas-V rocket that MSL would ride on its way to Mars was being prepared for departure. We took it as a good omen, and a few hours later, everything went right with the launch.

On the bus ride back to the parking lot, I had the chance to observe another atmospheric phenomena: noctilucent ("night glow") clouds. Well, actually, since they occurred during the day, these would technically be mesospheric clouds. Such clouds are a relatively rare occurrence since there is very little water vapor at such high altitudes. 80km is not an uncommon height, making noctilucent clouds amongst the highest visible atmospheric phenomena after auroral displays. As you might guess from the name, they are typically seen after sunset when their great height allows them to be illuminated by the sun even after the landscape has fallen into shadow. You can see a similar, but less impressive, version of the same effect if you look at scattered clouds on the western horizon immediately after sunset.

Noctilucent clouds observed in Estonia and photographed by wikipedia user Martin Koitmae. Note that the sun has set sufficiently that the clouds appear to shine by their own light, rather than by reflected twilight.

When such clouds are seen it is often in high-latitude regions where water vapor is available to do the job.  But if there is one surefire way of generating a mesospheric cloud at any latitude or time of year, it is by using a rocket launch to do the job. Since one of the major products of the exhaust will be water vapor (no matter the specific fuel used) and rockets pass through the mesosphere on their way out of the atmosphere, there is no issue with water supply. The displays thus-generated can be spectacular. For instance, here's the launch plume/noctilucent clouds associated with the launch of the Delta-II with the Phoenix lander onboard in 2008:

Noctilucent clouds photographed by Sid Leach from Cocoa Beach in the aftermath of the 2008 launch of the Delta-II carrying the Phoenix Lander. Note that the nighttime launch of Phoenix means that these clouds truly do shine by their own light.

It was not uncommon for us to use a version of this image in our education/public outreach presentations which showed a superimposed bird with a fiery tail:

Phoenix launch noctilucent cloud with a stylized phoenix overlaid. This was used in presentations for the mission, but I don't know who captured the image or who modified it. If you know, please make a comment below and I will update this caption!

What then can make of the MSL image at the top of this post? Recall that MSL hopes to be able to understand the habitability of gale crater past and present. That is to say, we want to know whether Gale could ever have had conditions that would have allowed life to thrive and grow and whether the conditions in the interim would have allowed any traces of such past life to survive to the present. Given that preamble, here's my best guess:

Launch plume from MSL as captured by the author and overlaid with a stylized martian courtesy of Michelle Parsons. Is this representative of what we might find? Only time will tell. But, as I say above, it's a good omen!

No comments:

Post a Comment