Solar System and Exoplanets

Key Concepts:
  - The exploration and detection of exoplanets (planets outside our solar system) are challenging due to the faintness of these planets compared to their host stars.
  - The brightness of stars can be about 10^9 times brighter than the planets orbiting them, making it significantly difficult to observe them directly.
  - This is akin to trying to view a candle flickering in front of a set of full beam headlights, magnified further by a factor of 1,000,000.

Visibility Comparison:
- Earth-size planets are often obscured by their host stars' intense light, particularly under visible spectra.
- When UV light is filtered out, detecting planets becomes easier.

Dust Disks as Indicators of Planet Formation:
  - The formation of the solar system is theorized to originate from a massive spinning disk of dust and gas.
  - Dust disks are common and are present around virtually all newly born stars, serving as prime locations for planet formation.
  - Modern techniques can image these disks directly, allowing researchers to observe the environments where planets could form.

Case Study: Beta Pictoris
- The dust disk surrounding Beta Pictoris is observed edge-on.
- The observed warping of the dust disk suggests gravitational influence, likely from a nearby massive planet that distorts the disk's shape.

Challenges of Direct Detection:
  - For over 50 years, astronomers have faced the challenge of detecting planets orbiting other stars due to their faintness, at least 100,000,000 times less bright than stars.
  - Various indirect methods are employed to detect exoplanets:
    1. Astrometric: Observing positional wobble of stars due to gravitational influences.
    2. Spectroscopic: Analyzing shifts in absorption lines due to the Doppler effect (redshift/blueshift).
    3. Photometric: Detecting transits, where a planet passes in front of a star and temporarily blocks light.
    4. Timing Phenomena: Using pulsar timing to infer planet presence.
    5. Gravitational Lensing: Observing how the light of background stars is bent by the gravity of foreground stars/planets.
    6. Imaging: Capturing direct images of planets, generally possible for the most massive and brightest ones.

Barycenter Definition:
  - The barycenter is the center of mass around which two bodies orbit.
  - Examples of barycentric systems:
    - Pluto-Charon system: External barycenter due to the mass difference.
    - Earth-Moon system: Internal barycenter demonstrated by the system's dynamics.
    - Sun-Jupiter system: The barycenter lies outside of the Sun due to Jupiter's mass.

Principle of Measurement:
- Uses the wobble of a star (the star's reflex motion) to detect planets, particularly massive ones like Jupiter due to their higher gravitational influence.
- For instance, the reflex motion of the Sun, caused by Jupiter, is about 13 meters/second.

Hot Jupiters:
- Jupiter-mass planets that orbit extremely close to their stars, e.g., 51 Peg, which has an orbital period of just 4 days (0.05 AU).

Transit Detection Explained:
- During a transit, a planet blocks a portion of starlight, which can be measured as a dimming in brightness.
- This dimming is used to infer the presence and size of the planet relative to the host star.

Use of Pulsars as Timing Tools:
- Pulsars are extremely regular and precise, allowing for precise timing measurements of their signals.
- For example, PSR B1257+12 has three known planets with masses of 0.02, 4.3, and 3.9 Earth masses.

Mechanism of Gravitational Lensing:
- If a planet or a star moves directly in front of background stars, it magnifies their brightness significantly due to gravitational lensing effects.
- However, this method only provides transient glimpses; once the event passes, the planet is not observable for further data.

Indications of Complex Wobbles:
- Detection of multiple planets is indicated by complex wobbles in a star’s motion.
- Upsilon Andromedae serves as an example of a star system with multiple planets.

Kepler Space Telescope:
- Focused on a region in the Cygnus-Lyra area to monitor 100,000 main-sequence stars for exoplanets.
- The mission had a lifetime of 3.5 years, extendable up to 6 years, successfully launched on March 6, 2009.

Relative Size Comparison:
- Jupiter: occupies 1% of the area of the Sun.
- Earth or Venus: occupies only 0.01% of the area of the Sun, or 1/10,000.

Transiting Exoplanet Survey Satellite (TESS):
- Launched on April 18, 2018, aims to find exoplanets that block part of the light from their host stars (transit events).
- TESS will survey 200,000 of the brightest stars near the sun and is expected to provide extensive data on exoplanets and their potential to support life.

Kepler Discoveries:
- Multiple exoplanets identified in the habitable zone where liquid water could exist, such as Kepler-452b.
- Planet characteristics include being within the habitable zones and potentially rocky composition.

Gliese 667 System:
- Contains three stars and hosts potentially habitable planets including Gliese 667C e and f, and c.
- Notable for its configuration wherein all three planets reside in the habitable zone, making them candidates for life.
TRAPPIST-1 System:
- Notable for containing at least three planets within the habitable zone, indicating more potential for discovering life-supporting conditions.