An introduction to exoplanets
An introduction to exoplanets

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An introduction to exoplanets

Week 7: The Special Ones


Last week, you learned what we’ve been able to learn from large exoplanet surveys like Kepler, and how we’ve been able to use our findings to understand the likely population of planets in the Milky Way. You also looked at the Drake equation and efforts to find nearby habitable worlds. This week, you’re going to focus on a few special exoplanets that have been studied in detail. You’ll learn how astronomers are using some pretty nifty science to discover what planets that can’t even be seen are like.

Start by watching the following video with Carole Haswell.

Download this video clip.Video player: boc_exo_1_video_week7_carole_upload.mp4
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Carole Haswell:
So now we know that there are billions of planets in the Milky Way Galaxy. Obviously, we can’t study them all in this course. We can’t even study all of the few thousand confirmed exoplanet discoveries astronomers have made so far.
Instead, I picked out a few particularly interesting ones. These are most of my own personal current favourites, though I’ve saved my absolute favourite for next week. One of the reasons for choosing these particular exoplanets is that they are close by astronomical standards. The closer an object is, the easier it is to study. We can study really dim objects provided they are close enough and we use a big enough telescope.
An important application of studying nearby dim objects is that if we manage to itemise every planet in our own local region of the Galaxy we can form what astronomers call a volume-limited sample. If we then scale up by the total volume of the Galaxy, we can work out the total number of planets in the Galaxy.
And we can apply the same method to other galaxies too. Most of the galaxies in the Universe are dim, dwarf galaxies, like the Magellanic Clouds. We have some idea how many galaxies there are in the observable Universe from a carefully defined sample of all the galaxies we can find in our local Universe.
It’s obviously not that easy to find dim objects, and our volume-limited samples might miss some hard to find objects. It’s good to leave some work for future generations though. Having said that, I think we’re lucky to be alive now. This is the most exciting age of discovery in human history and I hope you’re enjoying being part of it
End transcript
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By the end of this week, you will be able to:

  • have a qualitative appreciation of how transmission spectroscopy tells us which atoms and molecules are present in exoplanet atmospheres
  • appreciate why astronomers can get better measurements when an object is nearby
  • recognise the importance of:
    • HD 189733 b, HD 209458 b and WASP-12 b
    • GJ 1214 b and GJ 1132 b
    • Kepler-1520 b
    • the TRAPPIST-1 system.

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