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Sean Carroll's Mindscape

326 | Natalie Batalha on What We Know and Will Learn About Exoplanets

72 min episode · 2 min read
·
Natalie Batalha

Episode

72 min

Read time

2 min

Topics

Relationships, Fundraising & VC, Science & Discovery

AI-Generated Summary

Key Takeaways

  • Exoplanet abundance: Kepler data reveals every star in the Milky Way has at least one planet on average, with the nearest potentially habitable planet located approximately 10 light years away, suggesting billions of planets exist throughout our galaxy alone.
  • Super-Earth dominance: The most common planet type orbiting within one astronomical unit are super-Earths or mini-Neptunes, ranging from 1.5 to 2 times Earth's radius. These planets don't exist in our solar system, yet dominate the galaxy's planetary population.
  • Atmospheric detection challenge: Rocky planets orbiting M dwarf stars, which comprise 70 percent of galactic stars, may lack atmospheres due to intense stellar radiation during formation. JWST observations over the next five years will determine if these planets retain atmospheres.
  • Transit spectroscopy method: JWST observes planetary transits at a thousand colors simultaneously, measuring how atmospheric molecules like carbon dioxide absorb specific wavelengths. This reveals chemical compositions by detecting deeper light dips at absorption wavelengths, achieving part-per-million precision.
  • Mass-radius relationship: Combining transit photometry for radius measurements with Doppler spectroscopy for mass measurements yields planetary density. This bulk density distinguishes gas giants at one gram per cubic centimeter from rocky planets at five grams per cubic centimeter, revealing composition.

What It Covers

Natalie Batalha explains how the Kepler and TESS missions discovered thousands of exoplanets through transit photometry, what we've learned about planetary populations, and how JWST studies exoplanet atmospheres to search for habitability.

Key Questions Answered

  • Exoplanet abundance: Kepler data reveals every star in the Milky Way has at least one planet on average, with the nearest potentially habitable planet located approximately 10 light years away, suggesting billions of planets exist throughout our galaxy alone.
  • Super-Earth dominance: The most common planet type orbiting within one astronomical unit are super-Earths or mini-Neptunes, ranging from 1.5 to 2 times Earth's radius. These planets don't exist in our solar system, yet dominate the galaxy's planetary population.
  • Atmospheric detection challenge: Rocky planets orbiting M dwarf stars, which comprise 70 percent of galactic stars, may lack atmospheres due to intense stellar radiation during formation. JWST observations over the next five years will determine if these planets retain atmospheres.
  • Transit spectroscopy method: JWST observes planetary transits at a thousand colors simultaneously, measuring how atmospheric molecules like carbon dioxide absorb specific wavelengths. This reveals chemical compositions by detecting deeper light dips at absorption wavelengths, achieving part-per-million precision.
  • Mass-radius relationship: Combining transit photometry for radius measurements with Doppler spectroscopy for mass measurements yields planetary density. This bulk density distinguishes gas giants at one gram per cubic centimeter from rocky planets at five grams per cubic centimeter, revealing composition.

Notable Moment

Batalha attended the 1995 conference where Michel Mayor announced the first exoplanet discovery orbiting a sun-like star. She was a third-year graduate student sent by her advisor, witnessing the moment that transformed stellar astrophysics into exoplanet science and shaped her career.

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Episode Transcript

If you've used Babbel, you would. Babbel's conversation based techniques teaches you useful words and phrases to get you speaking quickly about the things you actually talk about in the real world. With lessons handcrafted by over 200 language experts and voiced by real native speakers, Babbel is like having a private tutor in your pocket. Start speaking with Babbel today. Get up to 55% off your Babbel subscription right now at babbel.com/wandery, spelled babbel,.com/wandery. Rules and restrictions may apply. Hello, everyone. Welcome to the Mindscape podcast. I'm your host, Sean Carroll. One of the things that I learned back in my undergraduate astronomy major days was when you have a telescope, what the telescope can do is defined in part by the telescope itself, you know, its light collecting power, its field of view, things like that, but very much by the instruments that you put at the other end of the telescope. The light comes in, and then you detect certain features of the light. You could put a camera there. Right? This is the obvious things where you get the pretty pictures from from the Hubble Space Telescope or the James Webb Space Telescope. You could put a spectrograph there. This is a workhorse instrument for real astronomy. You look at the spectrum of light from distant objects. You can detect redshifts using that and chemical compositions, all sorts of interesting things. Or you can just do a photometer. You know, when I was an undergraduate at Villanova, suburbs of Philadelphia, we had a telescope on the roof of the Science Building, and I would spend hours out there collecting data. There weren't enough photons that you could get in that particular environment to do precision spectroscopy or even imaging, but you could do photometry. All you're doing is measuring the brightness of the source at different moments of time. We have filters, so you could do different colors. You could detect the redness, the blueness, etcetera, but not precision spectroscopy in any way. There's an enormous amount that a professional astronomer can squeeze out of the data you get from the photometric light curve of an object. Mostly at Villanova, we did variable stars, binary stars, things like that. But the real amazing work that's been done over the past couple decades has, of course, been in detecting planets around other stars, exoplanets. The simplest, most direct way to find an exoplanet, you can't just take a picture of it. They're too dim, the planets. These days, you're beginning to be able to do it, I I should say. But when you first start detecting these, the simplest thing is just to wait until the planet passes in front of the star, blocking out a little bit of the light. And if you're able to very precisely measure the total amount of light, you can see that dip in brightness that is indicative of a planet being there. This is the method that was used by …

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