Thursday, March 12, 2009


The itt Peak McMath-Pierce Solar Telescope in Fog

Image Credit:
Yours truly

Clouds are the bane of the ground-based astronomer. The picture above is of the Kitt Peak McMath-Pierce Solar Telescope during an ice fog in January 2004. I was supposed to be observing that night on the Mayall Telescope, and the next, and the night thereafter. Needless to say, we didn't get much observing done. (It did finally clear off for our last night, but it was a long wait in the cold and damp weather.)

Today, it is raining here in Austin. It's our first substantial rain since last fall, and we desperately need the rain to quench a devastating drought in the region. But it is dreary and cloudy. This morning several students were complaining about the rain, and though I found the gray skies depressing, I am very happy to see the rain.

My point is that, on the Earth, clouds can both hide what we'd like to see (the sky and sun) and yet be beneficial (by bringing water). Since we can't have our clouds and see through them, too, we astronomers have learned to deal, such as by patience, using other wavelengths of light, or going above the clouds.

As we search for signs of life on other planets, such as the Earth-like planets that the Kepler mission may find, clouds may pose a challenge. Presumably any surface-dwelling, land-based life on other planets (like alien trees and alien intelligent dinosaurs) will rely on weather similar to that on Earth. But what if the clouds are hiding the surface? Some of the primary biomarkers that astronomers hope to look for, like chlorophyll, would be hidden. Others, like ozone, might well be visible above clouds.

Clouds are hard to model. We understand why they form in atmospheres, but we are surprised by the variety of clouds that we see. On the Earth, cloudiness varies by both location and time, and where there are clouds, there are many different varieties. From many light-years away, though, this wouldn't matter. Aliens looking at the Earth would get occasional glimpses of vegetation through holes in the clouds, and should be able to detect biomarkers.

But other planets and moons in our Solar System would be tougher nuts to crack. Mars is almost (but not quite!) cloud free, and we still argue as to whether life might exist on Mars. Venus is a lot like Earth in size and composition, but it is completely shrouded in clouds. Venus is also likely devoid of life, since its clouds are made of sulfuric acid and the surface is hot enough to melt lead. Saturn's moon Titan has some clouds that come and go, but those clouds are difficult to see under a layer of thick haze and smog. Jupiter has clouds of all shapes, colors, and sizes, but we don't know what many of these clouds (like the Great Red Spot) are made out of! Given this variety in our own Solar System, we can only imagine what clouds may cover an alien planet.

Beyond planets, even some stars (well, okay, "failed" stars) have clouds. At least some brown dwarfs have clouds, and those clouds may even be changing over time. Now that we are finally able to predict weather on Earth reasonably well, we have to start worrying about weather on other planets. Gosh, what bad luck would it be if I were to use Hubble to look at planet Vulcan during a planet-wide dust storm?

1 comment:

  1. Hi Prof,
    That's a really interesting post and got me thinking about some hypothetical scenarios in the far future. From hundreds of parsecs away, here on Earth, we can start to detect, through spectral analysis, the presence of various elements in the atmosphere and infer from that the processes that may be producing those elements from our existing knowledge of biology and chemistry. However, to extrapolate further and find out if these signatures were indicative of complex life forms beyond simple bacterial life, then surely we'd need to make a closer inspection, right? One cannot jump to the conclusion that all complex life has technological capability to transit in the radio frequencies. They could be complex animal life like on Earth and we’d need to get up close to detect such life directly.

    Lets assume, one day, we manage to find signatures of life in a distant Earth like planet that happens to orbit in the habitable zone of its parent star, and develop the technology to send a probe across the vast distances of space to make closer inspections of the planet. This opens up lots of "what if" questions for me. Most notably, how do we know if we're going to interfere or influence the existence of a sentient complex life form that has never encountered an alien race such as Humans? Should our probe remotely monitor from a "safe distance" so as not to be visually detectible? That would limit our ability to make closer inspections. After all, having spent some much time, money and R&D to send the probe so far, surely we would want to see living, breathing, moving life on the surface? If we get closer, for example in to mid or low planetary orbit, how do we know that we're not going to expose technology, as of yet unknown to the complex life forms on the surface and change the course of their history in some way by changing their own beliefs on life beyond their own planet. If you look at Earth, so many people still think god placed us and all other living life on Earth and that we are unique in the known universe, the only sentient, intelligent life anywhere. However, what would happen if WE were visited in a big way one day by a technologically advanced alien life form? How would that affect the sense and sensibilities of our current beliefs, theology and modern perspective of our place in the universe? Flip that on its head and look at it from the perspective of that space probe around that distant planet. How would it affect the inhabitants of that planet if it was detected, all be it from a distance?

    In conclusion, today we're battling with clouds on Earth, which we have countered by observing in other parts of the spectrum and by going above the clouds with our space telescopes. We have started to send probes to other planets to cut through the clouds on Venus, Titan and some other objects, but tomorrow we'll need to look far closer and deeper at those distant planets beyond our solar system as well, to be able to satisfy our scientific curiosity. How do we go about doing this in a mindful, ethical and responsible way? Who would decide on these rules of engagement, encounter and first contact? Scientists? Politicians? Policy makers? Perhaps, a combination of all three and many other groups? How much will all this debate delay the progress of exploration and finally and most importantly, are scientists morally bound to take these things in to consideration before they fulfill their scientific curiosity in ever increasingly invasive ways?