Strange New Worlds: Seeking Other Earths
By Inge Heyer - March 17, 2013
Last time, I talked about the search for planets and solar systems around other stars, and the progress astronomers have made in finding them. From knowing only the planets in our own Solar System some 20 years ago, we’re at 861 planets as of two weeks ago. As incredible as this seems, our ultimate goal lies somewhat further, namely finding other earths. It doesn’t necessarily have to be literally planets like Earth, but at a minimum it should be planets that could sustain our kind of life.
So what is “our kind of life”? As pointed out in Star Trek: The Motion Picture, we are “carbon units.” Life on this planet Earth is based on the long molecular chains carbon is able to build. The reason for this lies in the number of bonds an atom can have. Hydrogen can only have one bond, oxygen can have two, but carbon can have four. Therefore, carbon atoms can form much more complex molecular chains, binding other atoms such as oxygen, hydrogen, nitrogen, sulfur, and others together. All organic molecules that are found in living organisms on Earth have backbone chains of carbon atoms.
One other ingredient necessary for life on Earth is liquid water. Therefore, the temperatures have to be such that, at least a majority of the time, water is liquid and accessible. Furthermore, the atmospheric pressure must be sufficient to keep the water liquid, so that it does not flash-evaporate. This is one of the problems on Mars at this time; the Martian atmosphere is far too thin to support liquid water.
Finally, while we have a multitude of species on Earth, for a variety of evolutionary reasons, the dominant species that emerged, humans, are of a particular form to allow upright locomotion, the handling of tools, and a large brain to aid in problem solving. But is this carbon-based, bipedal, and mammalian form the only one that would support intelligence? As one of my students pointed out just this week, our search for planets in a “habitable” zone might be rather prejudiced. Of course, he is quite correct, but lacking both theoretical knowledge and evidence for other forms of life, intelligent or otherwise, we have to start with what we know, and that’s our kind of life. One place where scientists are thinking about just these sorts of issues is the NASA Astrobiology Institute. You can find information about them and their work on their website (see below).
Most of the non-humans we have encountered in the various Star Trek episodes and films were still clearly humanoid. This of course was (and still is) driven by the fact that we have only human actors available to play these parts. As technology has advanced, there have been instances where life forms could be constructed via computer, such as Species 8472 from Star Trek: Voyager. However, for believable appearances and meaningful interaction between characters, I think computer-animated characters still don’t work as well as live actors. Now, if, after first contact, we find another culture that understands the concept of acting, then things could get really interesting. But I digress…
There have been two announcements during the last week, which point us further in the desired direction. We have known for a while now that there once was liquid water on Mars. More recently the Mars Opportunity and Curiosity rovers have been digging into the Martian soil, and Curiosity has found evidence that there were once conditions on Mars suited for ancient life. The little rover drilled material out of a sedimentary rock near an ancient stream stream bed in the Gale crater. When analyzed, the scientists discovered the presence of carbon, oxygen, nitrogen, sulfur, hydrogen, and phosphorus, which, as I outlined above, are some of the key chemical ingredients for life. This now presents us with a very similar scenario that is believed to have existed on the early Earth, and that allowed life to develop on this planet. To quote the NASA press release: "The range of chemical ingredients we have identified in the sample is impressive, and it suggests pairings such as sulfates and sulfides that indicate a possible chemical energy source for micro-organisms," said Paul Mahaffy at NASA's Goddard Space Flight Center in Greenbelt, MD. The rovers will keep digging, and they just might find evidence suggesting more than just a possibility of ancient life.
Figure 2a: This set of images compares rocks seen by NASA's Opportunity rover and Curiosity rover at two different parts of Mars. On the left is " Wopmay" rock, in Endurance Crater, Meridiani Planum, as studied by the Opportunity rover (JPL/NASA).
Figure 2b: This image from NASA's Curiosity rover shows the first sample of powdered rock extracted by the rover's drill (NASA/JPL-Caltech/MSSS).
Figure 2c: An analysis of a drilled rock sample from NASA's Curiosity rover shows the presence of water, carbon dioxide, oxygen, sulfur dioxide, and hydrogen sulfide released on heating. The results analyzing the high temperature water release are consistent with smectite clay minerals (JPL/NASA).
The other announcement comes from the Keck Observatory in Hawaii, telling us that they have found water in the atmosphere of one of the extrasolar planets. Sadly, this is not an Earth-like planet, but a gas giant with a temperature of more than a thousand degrees Fahrenheit. It is one of four gas giants in this system. Unlike most extrasolar planets, because these planets are large and far enough away from their star, the astronomers are able to image them directly, which allows the study of their atmospheres. While it might be disappointing that this is not another Earth (or Vulcan, or Raisa), it does tell us that there are planets elsewhere that have water. “The fact that these giant planets may have formed the same way our own giant planets did is a good sign, as that same process also made the rocky planets close to the Sun,” said Dr. Bruce Macintosh from the Lawrence Livermore National Laboratory.
Figure 1a: Artist’s rendering of the planetary system HR 8799 at an early stage in its evolution, showing the planet HR 8799c, a disk of gas and dust, and interior planets (Keck Observatory).
Figure 1b: One of the discovery images of the system obtained at the Keck II telescope using the adaptive optics system and NIRC2 Near-Infrared Imager. The rectangle indicates the field-of-view of the OSIRIS instrument for planet C (Keck Observatory).
We are making ever more progress in our quest to find other Earths. It won’t be long now, I am firmly convinced. When we find another Earth, our home will no longer be as unique as we have always thought. This may require some adjustment in thinking for us. But until then, our blue marble is in a class of her own.
Here are a few links for you if you’d like to know more about this topic.
The Mars Curiosity announcement on “NASA Rover Finds Conditions Once Suited for Ancient Life on Mars”:
Keck Observatory announcement on “Astronomers Detect Water in Atmosphere of Distant Planet”:
The NASA Astrobiology Institute:
The Extrasolar Planets Encyclopedia (all the details on all extrasolar planets confirmed so far):
If you are interested in hearing more about the latest discoveries in the physical sciences and technology in a fannish setting, come visit us at Shore Leave this coming August. This fan-run convention features over 12 hours of science programming, in addition, of course, to all the usual con activities. For more information please visit http://www.shore-leave.com.
Inge Heyer is an avid Star Trek fan and frequent convention guest. After earning a BA in physics and astronomy, Heyer obtained a master's degree in astronomy at the University of Hawaii. As a senior data analyst at the Space Telescope Science Institute in Baltimore, she worked on images received from the the Hubble Space Telescope's Wide-Field and Planetary Camera 2. Following this she led the outreach education efforts for the Joint Astronomy Centre in Hawaii. More recently, she has obtained her doctorate in Science Education from the University of Wyoming, and is now a visiting assistant professor in astronomy and physics at Loyola University Maryland.
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