Lecture 35 - Pluto and Extra Solar Planets

What happens as a star moves towards and away from Earth? Why does this happen? What happens as the frequency of light is shifted?

As a star moves towards and then away from the Earth due to the "wobble" produced by the gravitational pull of its companion, the frequency of light emitted is shifted, much as the pitch of a train whistle changes depending on whether the train is moving towards or away from an observer. Precise measurement of this small change in the frequency of light emitted allows the orbits of the star and planet to be deduced. This provides information on the size of the planet and its distance from the star.

What has a similar structure to Pluto? What are they probably composed of? What is this based on?

Both Triton and Pluto are thought to have similar, differentiated internal structures. Based on their density, these bodies are probably composed of ~50-70% rocky material, with the rest being icy material.

When did we discover the mass of Pluto? How did we discover Pluto's moons?

Direct measurement of Pluto's mass was impossible until it was discovered in 1978 that Pluto has a moon, Charon. In 2005, the Hubble Space Telescope discovered two new small moons of Pluto, Nix and Hydra.

Who discovered Pluto? When? How?

In 1930, a young assistant at the Lowell Observatory discovered Pluto by comparing thousands of photographs taken a week apart and looking for any movement

What elements are present on Pluto and Triton? What are the three layers made of?

In addition to water ice, CO2 and N2 ice are also present. Layer 1: Frozen nitrogen Layer 2: Water ice Later 3: Rock and iron

What happens to Pluto near perihelion?

Near perihelion Pluto develops a thin N2 atmosphere similar to Triton, but this atmosphere may freeze back out during Pluto's long winter as it approaches aphelion.

What do scientists hope for the New Horizons spacecraft?

New Horizons is getting close to Pluto. The spacecraft is in a race against time. Pluto recently passed its perihelion and is now traveling away from the sun. Scientists think that Pluto's atmosphere is a seasonal phenomena-it will begin to freeze onto the surface as Pluto travels further from the sun. Scientists hope that New Horizons can examine the atmosphere before it disappears.

Bearing in mind that our methods for finding exoplanets are more likely to detect large planets and planets that orbit close to their star, what have we learned so far?

One important finding is that "hot Jupiters" are very common. These are giant planets that orbit very close to their star. Current models for planet formation indicate these planets cannot have formed in their current position-they must have formed further from their star and spiraled inward.

Is Pluto unique? What is the largest known Kuiper Belt Object? What is it's diameter?

Pluto is far from unique. Other Kuiper Belt Objects similar in size to Pluto have been discovered. The largest known Kuiper Belt Object is Eris, which has a diameter of ~2300-2400 km.

How do we learn about Pluto? What do we know for sure? Why is it a reddish color?

Pluto is too distant for us to learn much from even the best telescopes. We do know that the surface varies in terms of brightness and color, so distinct terrains are present. Pluto has a reddish color, probably due to organic molecules on the surface that form due to exposure of methane and ammonia ice to UV radiation.

How is Pluto's orbit different from the other planets?

Pluto's orbit is very different from the orbits of the planets. Most of the planets have low-eccentricity orbits (Mercury is an exception with an eccentricity of 0.205). In contrast, Pluto has a highly elliptical orbit, with an eccentricity of 0.25. In addition, Pluto's orbit is tilted relative to the plane of the ecliptic by 17 degrees.

What generates heat on Pluto? Where are these elements concentrated? What is this dependent upon?

Radioactive decay of naturally occurring elements like potassium, uranium, and thorium generates heat. These elements are concentrated in the rocky portions of planets and moons. Depending on the initial thermal structure of Pluto, the heat might be enough to melt a layer of water at the base of Pluto's icy mantle.

How do we look for planets around other stars? Which was the first method to detect extra-solar planets?

Several methods have been developed, including the Doppler method, Transit method, Astrometry, and Direct Imaging. Of these, the Doppler Method was the first to detect extra-solar planets.

What does the Doppler method involve?

The Doppler and astrometry methods involve measuring the "wobble" of a star produced by the gravitational pull of a large orbiting planet. The star and planet orbit around a shared center of mass, causing the star to "wobble". The wobble is like a change in eccentricity or orbit.

When was the New Horizons spacecraft launched? Why is this exciting for us today? What is the New Horizons going to give us? What will it help us determine?

The New Horizons spacecraft was launched in 2006, and will fly past Pluto in 2015. New Horizons will provide much more detailed information about Pluto's surface, structure, atmosphere, and composition. The images and measurements New Horizons makes during it's flyby will help determine whether Pluto has a layer of liquid water beneath its surface.

Why was Pluto demoted?

The large number of objects with similar sizes and orbits to Pluto is one reason that Pluto has been demoted from "planet" to "dwarf planet". If we let Pluto in the club, everyone will want to join.

How did we find Pluto?

The search for Pluto was based on a faulty assumption. They basically thought Neptune's mass was too small for Uranus' orbit to be so awkward, so there MUST be another planet out there!

How can we determine a planet's mass if it has a moon? Why is knowing the mass important?

We can calculate the mass of any given planet using its moon's radial orbit! Physics stuff. Knowing the mass- important bc we'll know more about the composition of the planet as well

If no ocean ever present what does that tell us about the planet?

equatorial bulge should exist from early rapid rotation (like Iapetus) mostly extensional tectonic features present on surface

If there used to be a subsurface ocean, but isn't anymore what does this tell us about the planet?

mixture of compressional and extensional features no equatorial bulge.

If ocean present beneath icy layer what does this tell us about the planet?

no equatorial bulge, mostly compressional surface features (e.g., wrinkle ridges) (melting of ice causes volume contraction, compression)