A Quote by David Grinspoon
Venus and Mars are our next of kin: they are the two most Earth-like planets that we know about. They're the only two other very Earth-like planets in our solar system, meaning they orbit close to the sun; they have rocky surfaces and thin atmospheres.
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A major puzzle for which nobody has an answer is this: is there some size at which the planets change their nature from water-rich planets like Neptune, to rocky planets like the Earth? We have found two planets that are the size of the Earth in radius, but they are very close to their host star, so water on the surface would evaporate away.
Discovering that our solar system has many more planets than we ever expected, and that most of them are ice dwarfs rather than like Earth and the other rocky terrestrials, is just another step in the revolution in viewpoint that removed the Earth from the center of the physical universe and makes Earth all the more special.
It will be a long time, if ever, before we get to study Earth-like planets orbiting around other stars, so really, the study of Venus and Mars is the best opportunity that we have, and can imagine having anytime in the future, to understand the evolution of Earth-like planets.
When I grew up as a kid, we didn't know there were any other planets outside of our own solar system. It was widely speculated that planet formation was an incredibly rare event and that it's possible that other planets just don't exist in our galaxy, and it's just this special situation where we happen to have planets around our sun.
There is a project that's underway called the interplanetary Internet. It's in operation between Earth and Mars. It's operating on the International Space Station. It's part of the spacecraft that's in orbit around the Sun that's rendezvoused with two planets.
There's no doubt that the search for planets is motivated by the search for life. Humans are interested in whether or not life evolves on other planets. We'd especially like to find communicating, technological life, and we look around our own solar system, and we see that of all the planets, there's only one that's inhabited.
There are other planets besides the Earth and Mars. I'd like to remind you that studying Venus is vital to understanding life elsewhere.
Most Jupiter-sized planets orbit the mother star in a highly elliptical orbit. This means they will often cross the orbit of any Earth-like planet and fling it into outer space, making life impossible. But our Jupiter travels in a near-perfect circular orbit, preventing a collision with any Earth-like planet, making life possible.
Before 1995, the only planets we knew about were the planets in our solar system.
Maybe the search for life shouldn't restrict attention to planets like Earth. Science fiction writers have other ideas: balloon-like creatures floating in the dense atmospheres of planets such as Jupiter, swarms of intelligent insects, nano-scale robots and more.
Of all the planets apart from Earth in our solar system, Mars is the most hospitable. Yeah. Right. Better keep my visit short. And yet, despite the discomfort, the danger, I love it here. I love coming back for these imaginary vacations. The sights are amazing.
The planets and moons of our solar system are blatantly visible because they reflect sunlight. Without the nearby Sun, these planets would be cryptic and dark on the sky.
But what exceeds all wonders, I have discovered four new planets and observed their proper and particular motions, different among themselves and from the motions of all the other stars; and these new planets move about another very large star [Jupiter] like Venus and Mercury, and perchance the other known planets, move about the Sun. As soon as this tract, which I shall send to all the philosophers and mathematicians as an announcement, is finished, I shall send a copy to the Most Serene Grand Duke, together with an excellent spyglass, so that he can verify all these truths.
Because Alpha Centauri is so close, it is our first stop outside our solar system. There's almost certain to be small, rocky planets around Alpha Centauri A and B.
We know that within the solar system is very unlikely there will be anything more advanced than microbial life, but if we think outside the solar system and then, the distances are, of course, immense, then there could be Earth-like planets with more advanced form of life.
We know there are billions of stars and planets literally out there, and the universe is getting bigger. We know from our fancy telescopes that just in the last two years more than 20 planets have been identified outside our solar system that seem to be far enough away from their suns - - and dense enough - - that they might be able to support some form of life. So it makes it increasing less likely that we're alone. But if we were visited someday, I wouldn't be surprised.
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