Rebirth of astrobiology

Discussion

Why would someone go all the way to Antarctica just to collect meteorites?

Shergottite

Discussion

Though we have never returned a rock sample from Mars, we are certain that these meteorites came from there. How can we be so sure?

Nakhlites

ALH 84001 history

1. Formed on Mars 4.091 billion years ago2. Fractured by nearby impact 3.9-4.0 billion

years ago3. Spent time under water4. Launched into space 15 million years ago5. Landed in Antarctica 13,000 years ago6. Picked up in 1984

Carbonate globule

Polycyclic aromatic hydrocarbons (PAH)

Formed by decay of dead organisms

Nanobacteria Controversy

1-2 nanometers in size

Self replicate in microbiological culture

Inculpated radio-labeled uridine (component of RNA)

2008

self-propagating mineral-fetuin complexes

i.e. blood proteins.

Discussion

Is this enough evidence to convince you?

Problems

1. Most evidence can be reproduced abiotically

2. Contamination of meteorite

“If all this had been seen in a terrestrial rock, there wouldn’t be this level of skepticism.”

Simon J. ClemettLockheed Martin researcher

Unfairly rigorous level of proof?

Mars Rover

Hematite deposit on Mars

Grey Hematite

Methane

Mars express detected small quantities of methane in the Martian atmosphere

Discussion

Methane oxidizes very easily only lasting a few years in Earth atmosphere. On Mars methane can last only a few hundred years. How does this gas get oxidized on Mars?

Discussion

Why is the discovery of methane on Mars important?

Carbonate and Olivine deposits

Mars Science Laboratory

Mission

To assess whether Mars ever was, or is still today, an environment able to support microbial life, to determine the planet's "habitability."

Curiosity landing site

Moons

Discussion

We can only see one side of the Moon from Earth. Does this mean the Moon does not rotate on an axis like the Earth does?

Newton’s Universal Law of Gravity

• Every mass attracts every other mass through a force called gravity

• The force is directly proportional to the product of their masses

• The force is inversely proportional to the square of the distance between them

221

d

MMGF

Newton’s Universal Law of Gravity

Discussion

The Earth’s gravitational force on the Moon keeps the Moon in orbit around the Earth. Does the Moon exert of force on the Earth? Is this force greater than that exerted by the Earth on the Moon, less than, equal to, or is there no force?

Discussion

Which billiard ball experiences the greatest force from the planet?

Discussion

How do the outer two balls appear to move from the perspective of the center ball? Explain.

Spring Tides and Neap Tides

The Sun also contributes to the Earth’s tides. When the Sun and Moon line up to produce higher tides, this is called spring tides. Neap tides occur when the Moon and Sun Partially cancel each other.

As the Earth rotates, it carries the tidal bulge around with it, but the Moon, which orbits more slowly than a day, tugs on this bulge and slows the rotation of the Earth.

Thus the day is lengthening by about 0.002 seconds per century.

Tidal Friction

Tidal Friction

Discussion

Using the idea of tidal friction, explain why the Moon orbits the Earth synchronously.

Synchronous rotation of the Moon

Just as the Moon raises tides on the Earth, the Earth raises tides on the Moon. But the tides are not raised in water but in the very crust of the Moon. The Earth’s gravity pulling on these tidal bulges slowed the Moon’s rotation period over millions to a period equal to that of the Moon’s orbit.

Discussion

What are Kepler’s laws of planetary motion?

Discussion

In actuality, we can see 59% of the Moon’s surface from the Earth. Explain why this is the case using Kepler’s laws.

Conservation of angular momentum

Any object that is spinning or orbiting has angular momentum which is equal to the mass × velocity × radius.

In the absence of an external torque, or twisting force, the angular momentum will remain constant.

The Earth-Moon system

The Moon exerts a force on the tidal bulges on Earth, trying to twist the tidal bugles back to face the Moon. This torque slows the rotation of the Earth.

Discussion

If the Moon is slowing the Earth’s rotation then the Earth is losing angular momentum. But, if the angular momentum of the Earth-Moon system has to be conserved, where does that angular momentum go?

Orbit of the Moon

Due to conservation of angular momentum, the slowing of Earth’s rotation requires the Moon to move faster in its orbit. Because the force of Earth’s gravity does not change, this means the Moon is getting further away, by about 2 inches per year.

Fate of the Earth Moon System

Over billions of years the length of the month and the length of the day will be the same, about 47 days. The Moon will then be stationary in the sky.

Discussion

Will the Moon still have phases?

Pluto and Charon

Pluto has a large satellite named Charon which orbits Pluto in 6.4 days. Like most satellites in the solar system, Charon rotates synchronously, keeping the same face toward Pluto. In addition, like the future Earth-Moon system, Pluto also rotates in 6.4 days, keeping the same face toward Charon.