Descriptive Astronomy: PHY 101

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Here's a study guide for Monday's final exam (1:00-3:00 in Preble 335)

General

Extrasolar Planets: Detection Methods

• • Focus: How have we found over 3000 planets around other stars despite the fact that we haven't literally seen most of them?

  • Read Fraknoi et al., Chapter 21, section 21.4

  • Here are some methods for finding extrasolar planets.

  • The transit method can be used to learn about an exoplanet's atmosphere via the absorption bands produced when light from the parent star passes through that atmosphere

  • The Kepler spacecraft used the transit method to identify over 3000 candidate exoplanets, including dozens in the habitable zone; and follow-up observations have confirmed one even smaller than Mercury

  • It's also possible to detect planets by measuring how their gravitational fields bend the light of a background star: gravitational microlensing

  • The big hope for the future is that direct images of exoplanets will become more common

Extrasolar Planets: Results (so far)

• • Read Fraknoi et al., Chapter 21, section 21.3 and section 21.5

  • Planetary systems form from protoplanetary disks, or "proplyds."  You can tell that they're flattened disks when they happen to be viewed edge-on.

  • Here's a planet, recently identified via the transit method, that orbits a sunlike star within the habitable zone where water could be liquid

  • Here's a diagram showing how the habitable zone can depend on the star's luminosity, the planet's distance from the star, and the planet's mass

  • (Note: the cross-in-a-circle symbol in the diagram means "Earth")

  • Potentially habitable planets can also be found around faint, cool red dwarfs

  • In 2014 we identified the first Earth-sized planet orbiting within the habitable zone (of a red dwarf)

  • The most populous planetary system we know of is this one that may contain nine planets

  • The closest exoplanet was announced in August 2016: Proxima Centauri B

  • We don't yet know Proxima Centauri B's internal composition

  • A few months later a nearby planetary system was announced: the TRAPPIST-1 systme

  • OK, so we find an Earthlike planet with an Earthlike orbit around a Sunlike star: What do we look for to check for life on that planet?

  • Optional:

    • In order to have life, a planet must not only be the right size but also the right distance from the right kind of parent star with the right sort of atmosphere.  That is, different kinds of star have different habitable zones in which life could form -- or at least could most easily form.

Circling Back: Planetary Migration and the Lunar Cataclysm

• • Focus: "Hot Jupiters" around other stars changed their orbits early in their lives, and the four large planets in our own solar system seem to have done some of that as well.  Could this explain the "late heavy bombardment" of the inner solar system 3.9 Ga ago?

  • Read Fraknoi et al., Chapter 21, section 21.6

  • This article discusses the possibility that shifts in the orbits of the outer planets made for a hellish time on the Moon and on Earth -- and perhaps stimulated a wet period on Mars.

  • Optional:

    • Here's another clear description of the planetary migration model for our solar system.

Links from previous weeks are here

Here are the requirements for your final paper

For enlightening fun, take a look at the Astronomy Picture of the Day

Descriptive Astronomy has been brought to you by Chris Magri and The University of Maine at Farmington

Last modified on May 4, 2019

URL: https://sites.google.com/a/maine.edu/magri/phy101