Why search for exoplanets

  1. wolram

    wolram 3,719
    Gold Member

    What is the reason for searching for exoplanets? i can think of many reasons why not, including we will never build a space craft to visit them, when we get there conditions for human life may not be
    suitable for human life, this would mean building a space craft that could return to earth, which would make it extremely expensive.
    So what conditions can be detected before our space explorers set out?
     
  2. jcsd
  3. mfb

    Staff: Mentor

    How can you be sure?
    This will need more research about exoplanets...

    With current telescopes or those under construction: mass, orbital period, average temperature, chemical composition, various properties about the star. The length of a "day" might be possible, too.
    If there is life, sending some messages, we might have a chance to receive them.


    I think even without the option to visit them, it is extremely interesting to see how other planets look like. More than 99% of the known planets do not orbit our own sun.
     
    Last edited: Mar 28, 2013
  4. Because Education is always preferable over Ignorance.
    Because the more we learn about planets, the more we can understad about OUR planet.
    Because there is almost certainly other intrelligent life out there, and the laws of strategy and tactics tell us Offense (whomever contacts the other first) has the initiative and some control over Defense, which is always reactive rather than proactive.
    Because, as Benjamin Franklin was known to ask rhetorically, "What is the use of an infant?"
     
  5. russ_watters

    Staff: Mentor

    None of those reasons qualify as why not unless you condition the search based on a requirement that we send humans there.

    We don't study the sun because we hope to send people there either.
     
  6. Drakkith

    Staff: Mentor

    I personally took a series of images of a star using my own equipment, measured and plotted the amount of light gathered, and was able to "see" the transit of an exoplanet across the star in the form of dips in the light curve. Why did I do this? Because I like it. I find it interesting. And perhaps one day I will help shed light on whether or not life exists elsewhere in this universe.

    You can find it at the Exoplanet Transit Database using the following link: http://var2.astro.cz/EN/tresca/transit-detail.php?id=1338376697
    Main ETD page here: http://var2.astro.cz/ETD/
     
  7. Nice! I always love to see results like this. I'm currently observing variable stars (not stars who vary due to transits yet :biggrin:) but in the future when I'm no longer a poor student I'll maybe starting doing the same as you just did!
     
  8. Drakkith

    Staff: Mentor

    What are you observing with?
     
  9. I'm doing visual observations with my 14" dobsonian.
     
  10. Chronos

    Chronos 9,754
    Science Advisor
    Gold Member

    People are naturally curious. If we ever find another earth, it will be a seminal event in human history. After all, fighting with each other will seem silly when there is an entire planet out there [possibly complete with repulsive natives] in desperate need of conquest and colonization. Space programs are politically motivated. Extrasolar planets fascinate people, making it an attractive means to generate public good will and funding. And, unlike SETI, it even generates short term results, which maintains interest.
     
  11. epenguin

    epenguin 2,121
    Homework Helper
    Gold Member

    Man has observed the stars, some of the nearby planets , meteros and comets for tens of thousands of years! For nearly all this time they were more obvious and familiar than they are now. They have been objects of wonder, speculation, philosophy, and of literature and science ever since there has been anything we can call that. There must have been, there has been, wonder about what they really were and what they were like. Were they anything like here, even with life? After all, they were given the names of mythical personages. And human dramas, sometimes spectacular, sometimes of philosophical and moral import were played out on them in science fiction films and writings.

    Imagine what it felt like to be the first man in all these decakiloyears to have discovered one of them had planets, in that respect resembling where we are. And that was only yesterday - 1995! Or even to discover the hundreth of them like Drakkith here! Perhaps there is life on Europa, or Mars, or there was, perhaps our ancestors even came from there?!

    Science that is! - we try to be scientists. Oh - but we are terribly sober about it. We start at school and instead of fireworks and adventuring onto The Forbidden Planet we find we are measuring densities and specific heats and calculating stoichiometries, pH's, simultaneous equations and sine addition formulas and it doesn't seem so magic after all, even plain boring some would say. But hopefully we stick with it for some higher purpose and become disciplined, and even realise that voltage calculations, thermodynamic relations etc. have their own horrible intrinsic interest of principle after all. We are so disciplined and can risk becoming too much so and turning into a dry academism, making a virtue of our scaled-down interests, hanging like bats in a world of inverted values relative to ordinary untrained and unbrainwashed perceptions.

    So let us not be wet blankets nor let our disciplne make us forget what got some of us and will still get others interested in science in the first place
     
    Last edited: Mar 28, 2013
  12. Astronuc

    Staff: Mentor

    Because they're there, and we can. :biggrin:

    The universe is not as sterile as we thought a several decades ago.
     
  13. additional question :
    how can we predict or know that xyz planet is a earth like planet or having a earth like condition, when we are not abl to see it directly (if i am not wrong) ?
     
  14. cepheid

    cepheid 5,194
    Staff Emeritus
    Science Advisor
    Gold Member

    You're not wrong. There are only a handful (literally fewer than 10) of planets that we've been able to image directly (and even then, we can't tell much about them). The rest have been detected by indirect means.

    There are a couple of different indirect methods for detecting exoplanets. One is the Doppler or radial velocity technique, in which a planet tugs on its parent star a bit due to gravity, and we can see this wobble as change in velocity of the star, by means of the Doppler effect. This gives you a lower limit on the mass of the planet (there is some uncertainty due to the orbital inclination).

    The second technique is called the transit technique. If you're lucky, the orbit will be inclined such that, from our point of view, the planet passes in front of its parent star once per orbit (a "transit") and then passes behind it (an "occultation"). The light output from the star that we measure drops a bit when the planet is in front of the star, obscuring a small part of it. By measuring the drop, we can determine how much of the star's surface the planet is covering, and therefore what the radius of the planet is, relative to its parent star.

    If you're lucky enough to have detected a planet *both* by the Doppler technique and by means of a transit, you can get both the mass and the radius. That lets you determine the mean density of the planet, and hence, in a vague sense, what material it is mostly made out of. I.e. is it dense enough to be solid/rocky, or is it mostly liquid water, or is it gaseous? If you have a planet that is a few Earth masses, is similar in size to Earth (maybe a factor of a few larger), then this is already starting to fit the astronomers' definition of "Earth-like."

    Finally, although we can't quite do this yet, if you have a transiting planet, and you do spectroscopy (i.e. measure the spectrum) on the light from the star, you might find that there is a difference in the spectrum when the planet is in front of the star (compared to when it is not) because the star's light is passing through the planet's atmosphere, and so you might see spectral lines in absorption that tell you what the chemical composition of the planet's atmosphere is. You could determine if it contained oxygen and other things that are conducive to life as we know it on Earth. I don't think we can quite do this yet, because our instruments are not yet sensitive enough.
     
    Last edited: Mar 29, 2013
  15. Drakkith

    Staff: Mentor

    We can't predict it without knowing some parameters in advance. We have several techniques to figure out if a planet might be earth like. Most of the techniques we use to find exoplanets allow us to figure out how far out from their parent star their orbit is, and since we can measure the properties of the star we can know whether the exoplanet is in the "habitable" zone or not. Several of the techniques, such as the radial velocity method, allow us to measure the mass of the planet, which further pins down whether it may be earth like.

    Future technologies and improvements in existing techniques should allow us to get spectroscopic measurements of the planets themselves, which allows us to determine what their atmosphere is composed of.
     
  16. The 'reason' for searching is the inborn urge to explore in case something advantageous turns up, which most animals do. But it shouldn't cost too much and I don't see the justification for sending a returnable spacecraft. The performance of our robotic probes on Mars is encouraging.

    I assume that any other life forms out there will follow, and possibly have already followed, the same logic. Human biology is not suitable for space travel, except possibly with suspended animation. We should initially explore space with inanimate tools, which we are getting very good at. Robots offer many advantages including sensory, computation, reliability and physical robustness.

    .
     
  17. @chepied and darkith thanks guys it really helped to improve my knowledge
     
  18. However, when exploring a distant star system, there'd be no hope for two-way communication with Earth due to the extreme distance (unless some surprise breakthrough in physics shows that faster-than-light communication is really possible). So any robot would have to do everything in an artificially-intelligent manner. If it's to match a human operator it might very well need human-level artificial intelligence. If that is achieved, then we might not need humans for exploration at all. I'd imagine by the time we'd gotten both interstellar travel and high artificial intelligence, we would have the ability to make robots that could do everything a human could or even better (e.g. we'd probably have the dexterity problem all worked out, for example).
     
  19. @Hercuflea - Thanks for the links.

    Some very interesting projects! Apart from the technical challenges, the major question relates to cost/risk/benefit. If the cost is so high with high risks and we have to wait decades for an unknown result, if any, where is the motivation for the investment? Probably we need to have a specific destination(s) with a high chance of a payback before going to all this trouble.

    Sounds like a Mars refit would make more sense.

    .
     
    Last edited: Mar 31, 2013
  20. A probe would travel much slower than communications, so I don't see the problem with the light speed of communications.

    Sure we need humans for exploration, but not personally. On Earth we do less and less with our own bodies and brains. We use machines and computers. That's human too.

    .
     
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