Life on other planets has to have unmasking signs

When astronomers create catalogs of thousands of planets outside our solar system, they ask a question whether life on these planets is possible, and whether they are manned. Very few people thought of it more seriously, than Victoria Meadows, the astrobiologist from the Washington university. She is engaged in computer modeling of the atmospheres and surfaces of planets and is the leading researcher in team of Virtual planetary laboratory of Astrobiological institute of NASA. The main objective of its work — to determine whether there were exoplanets ever manned, whether there is on them life now, and whether it can appear in the future. Meadows plays with colleagues in Space test kitchen to study results of various biological and geological conditions (“Let’s say I have a model recreating Earth. I clean its star – the yellow dwarf, the Sun, and I replace, say, with the red dwarf. What will happen to the terrestrial atmosphere?”)

Nautilus has a talk with Midouz about what the live world can issue itself.

Nautilus: If newcomers from space tried to find out us what they would look for? On what signs they could claim that on Earth there is life?

Victoria Midouz: They could do the same that is done now by us. We begin with studying of information available to us on basic physical properties and on a planet orbit. We look for answers to two main questions. First, whether this planet concerns to terrestrial group? If whether on it a firm surface on which the ocean is placed? Secondly, whether there is a planet at suitable distance from a star. We call a manned zone this space in which on the surface of the zemlepodobny planet there can be water in liquid state though there are no guarantees that water is there.

One more field of our work — studying of evolution of the planet and its star during the long period of time to try to understand what it can be similar at the moment to. It is important because stars pass through the sequence of evolutionary processes. The main difference of these little children, red dwarfs, that they have a period when they decrease in sizes and become very bright. Any planet created in a manned zone of such young superbright star in an interval of time when it returns to the normal level of brightness, is affected by high radiation. From heat of a star oceans that in the theory can lead to very high level of content in the atmosphere of either oxygen, or carbon dioxide, as on Venus evaporate. Strictly speaking, it is the planet located in a manned zone, but following the results of the development having a lot of carbon dioxide in the atmosphere to be manned.

— Well, suppose, the planet answers all criteria. What’s next?

— We look for planet habitability signs, biological signatures — the peculiar global changes of the environment which have arisen not because of processes of the planet. As we try to find life at incredibly far distance to the next star, signs of life have to be the global phenomenon. Changes of the environment on the planet have to be rather big that we could see them from long distance.

On Earth there are three main signs of life. One — plentiful oxygen which you breathe right now, it is produced thanks to billions of years of work of cyanobacteria, and also vegetation. You will see the second sign if you look at a range of reflection of Earth — how the planet reflects light in different lengths of waves. You can notice this strange thing at any moment of observations. Longer waves which usually are behind visibility limits become well distinguishable, and it is called a red barrier of vegetation. On lengths of waves out of area of photosynthesis plants have a high reflective ability. It is possible to look for also this phenomenon.

The third sign — annual circulation of carbon dioxide on our planet. Carbon dioxide level grows over time. Fluctuation up and down, seasonally is observed. It is connected with photosynthesis of plants which at first reduce volumes of carbon dioxide, and then again they are increased when perish in the winter. If you watch the planet rotating around a star, you can quite see these fluctuations.

— And much they would learn about our planet?

— Actually, there is a lot of. I would like to look at what is called a reflection. And on all phases of Earth, including a semi-phase and a phase of a sickle. I would measure planet brightness. I would note that, approaching a sickle phase, it becomes abnormally bright in comparison with the average value of brightness observed earlier. “Oh, it is strange” — I would tell. In the environment there has to be something that scatters light. It clouds. They scatter light passing through them. And I would look at a reflection — specular reflection from the ocean consisting of liquid substance. Having seen this aberration, I would solve: “Theoretically, I look at something with liquid water on a surface”.

Speak to me: “You just create models. From where to you know that all indeed?” We had a space device for observation of lunar craters. He studied the Moon and, eventually, has failed on it. But before accident he has given the whole pack of the views of Earth removed from far distance. In one of photos it is possible to see a terrestrial sickle with a reflection from the ocean. Him it is really visible. It has confirmed that our model is right.

Then I would receive results of multiwave photometry. For some time would observe different lengths of waves, different colors of a range. Would watch how under me the planet rotates. If to do observations each hour, then a look every time will be different. You begin to notice that color and brightness of Earth change. These changes on different lengths of waves can be used to make the map of the planet. It is possible to limit such factors as an orbit pole inclination, regardless of whether there are on the planet continents. Also it is possible to look for heterogeneity.

— Coming back to search of extraterrestrial life: how our interpretations of biosignatures have in recent years exchanged?

— Earlier all spoke: “In the atmosphere there is so much O2, it couldn’t appear as a result of geological or photochemical processes in any way. It is the obvious biosignature. You should just look for oxygen. It is ready. Get the Nobel Prize”. However not only life can emit so much oxygen in the atmosphere. My team works on a number of various mechanisms on the basis of a fotoliz — decomposition of molecules light. Fotoliz of water or CO2 releases oxygen from molecules. He can freely be in space or be combined in an O2 gas form. Then there is an oxygen in the atmosphere.

So just to find oxygen insufficiently. It is necessary to understand that it is system of interactions in which one mechanisms can work, and others – No. For example, if you have found the high content of O2 and at the same time methane, it means that on the planet there are very strong streams of both gases, methane is an elementary gas which absorbs O2. Possibly, it is also the biosignature which you look for.

— You should recognize that life in space is similar to us?

— We have concentrated on oxygen because it is the simplest to us to establish his existence, we do the analysis of false operations. As they say, we have plunged into a variety of biosignatures. Would be great to find some unusual molecule.

But we shall understand that it is necessary to be able to interpret what we study. The member of my team Bob Blankenship is engaged in evolution of photosynthesis and its course on Earth to understand whether she is possible and in other planetary systems. In the course of photosynthesis light of a star and carbon dioxide is absorbed, and water decays therefore energy is made. It is a crown capability of vegetable organisms. Photosynthesis works, using energy type most of which of all on the surface of the planet, that is light from a star, and also very widespread molecules of water and carbon dioxide which as we consider, are available on the manned planet much. If evolution works, then imagine an organism with such evolutionary benefit: he would occupy all planet.

And it gives me a sign. I look for the metabolic winners capable to dominate in the environment and to make signals. Oxygen photosynthesis can be one of their advantageous tickets. If evolution works, then something similar gives clear evolutionary advantage, and, therefore, such organisms can be seen in the telescope as a global dominant. Here that it is necessary for me: world supremacy!

— It changes subjects to search?

— Yes. It influences a design of telescopes, in particular, on the range of lengths of the waves used for search of molecules in the atmospheres of planets. It is insufficiently simple to develop the telescope for oxygen search. The telescope by means of which it is possible to observe also a set of other molecules is necessary.

The space telescope of James Webb which is planned to start in 2018 has the big area of interception of energy, and with its help we will be able to study planets in manned zones of red dwarfs in movement. “James Webb” will for the first time give us chance to look for life by means of transmission spectroscopy, studying the upper layers of the atmospheres of these planets. Perhaps, throughout all term of the project we will be able to watch only several purposes. But we will be able really to establish the star light which passed through the atmosphere and changed it. We will see what is in the atmosphere. Hurrah!”

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