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Course: American Museum of Natural History > Unit 2
Lesson 1: Planets- The Pluto Controversy: What's a Planet, Anyway?
- How Was Our Solar System Formed?
- Features of Planets
- The Search for Life
- Curiosity: Searching for Carbon
- Seeing Planets Like Never Before
- Solar System Glossary
- Quiz: Planets
- Exploration Questions: Planets
- Answers to Exploration Questions: Planets
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The Search for Life
In the search for life, we have barely scratched the surface of other planets in our solar system. And we have studied only a tiny fraction of planetary systems around other stars. No life has been found, but the potential for life is widespread. The chemical building blocks for life on Earth exist in the interstellar clouds that give birth to stars. Many stars have planets. There could be billions of habitable planets in our galaxy. Yet we do not know how life arises, or if it can easily evolve to intelligence. Life may be plentiful - the only way to find out is to search.
How Do We Find Other Planets?
For life in the universe to be abundant, planets must be abundant. But planets are hard to detect because they are small, and much fainter than the stars they orbit.
How Does Life Begin?
Scientists do not yet know how the first living things arose on Earth. The geological record shows that life appeared on Earth almost as soon as the young planet was cool and stable enough for living things to survive. This suggests that life may exist wherever conditions allow it.
The chemical building blocks of life, such as amino acids, are easily made by supplying energy to a mixture of the molecules most abundant in the solar system.
But these molecular substances are nowhere nearly as complex as the simplest life-form. We have not yet discovered how aggregations of these building blocks acquire life's capacity to grow, reproduce, and adapt.
Astronomers also observe organic molecules in meteorites, comets, and the giant interstellar clouds of gas and dust where stars and planets are born.
What Conditions Does Life Need?
Life on Earth’s surface derives its energy from the Sun. Another realm of life thrives around seafloor hot springs and in fluid-filled cracks deep below the surface, utilizing the chemical energy of those environments. The chemistry that builds and sustains life requires a fluid medium in which atoms and molecules can react. For all known forms of life, liquid water provides that environment. Carbon atoms are ideally suited to form complex molecules. Carbon is the structural backbone of all the building blocks and material for life, including proteins and DNA.
Want to join the conversation?
Is their life on any other planets except for Earth?(5 votes)
As of right now, scientists do not know of life on any other planets. Recent surveys of Mars have, however, shown that there may have at one point been life on the Red Planet.
These surveys have shown that there may have been streams and rivers on Mars at some point. There's no other easy explanation for how some features there have been formed. Since Mars's conditions seem to have been at one point very similar to Earth's own, and water is necessary for life as we know it, there is a possibility there may have once been life on Mars. It seems unlikely there would still be any.
The real answer for now is we don't know. The universe is a big place, and somewhere it's possible there could be life.(7 votes)
is it possible that on other planets supposed life wouldn't require sunlight or water or O2 or anything like us? They could possibly breathe hydrogen gas, right?(3 votes)
Sunlight is only in our solar system. Other systems have whatever-star-name-they-have light.(2 votes)
What if we were just tiny bacterial beings on a tiny dust particle of someone or something else's world doing the exact thing were doing in a different dimension.(3 votes)- Has anybody heard of Kapteyn b, an earth
like exoplanet 12.8 light years away that might be only a few billion years younger than the universe? and it could also support life! also read sad kapteyn, a short story that was released shortly after it's discovery.(3 votes) 
is there at least one way to survive on the moon for one half of a year(2 votes)- yes, if you had a pressurized artificial habitat sort of thing with food and oxygen to last for that long you could. the problem really is cost. you would have to send multiple rockets and other thing with supplies of oxygen and water and food because you can't send it all up at once in one rocket there would be too much weight. so, we could but there is no practical purpose there is no real need to stay there that long there isn't much more we can learn about the moon. the real action right now is on Mars, not the moon(3 votes)
- if scientist now what form's a planet how cant they tell how the first people got here(1 vote)
- They didn't "get" here. We have evolved from other simpler organisms.
For more information, please look at this article: http://en.wikipedia.org/wiki/Timeline_of_human_evolution(4 votes)
Can extraterrestrial life be made up of things other than cells, even though a living organism on Earth must "have one or more cells" in order to be classified as an organism?(2 votes)
how many galaxies are there(2 votes)
At least one hundred billion, or 100,000,000,000 galaxies! If each of these has as many stars as the Milky Way Galaxy (which has 100 billion stars), then there are 100,000,000,000^2 stars in this universe! That comes out to 10,000,000,000,000,000,000,000 stars, which is 10 septillion. Considering that there are many, many light years away from each other...(2 votes)
life on earth's surface derives its energy from the sun(2 votes)- What is the name of the theory that says we come from fish then amphibians then reptiles then mammals from there to monkeys then to apes to the homogeneous species of the human race?(2 votes)