Summary lecture notes to go along with Chapter 1

These notes are merely to high light the points we focused on during class from this and future chapters. They are a supplement to, not a replacement of, the text book.

If you are considering making a printed copy of these notes, I recommend NOT printing these notes until we have completed this section in class, since I will update them as we go through the material. For printing them you may want to reduce the font size on your browser to reduce the number of pages to print.

Tips:

- Take notes from the blackboard, not everything is in these notes. I will use the board to further explain concepts and occasionally in answering your questions.

- look at the various appendices in the book. You will find:

• Various useful numbers and physical constants.

• The most important formulae we use in this class. A refresher on scientific units, notation, and working with units (essential since we are dealing with large or small numbers with many zeros!)
  A review of how ratios make it easy to compare differences between physical quantities

• Tables with properties of planets

• Glossary of terms and index, useful for quick reference.

Intro - Some wonders of astronomy

What we'd like to find
Maybe not a bad place to start
We look around these objects

This one is easier to find around other stars
And so is this one
While these can only be found in our solar system thus far
There are a lot of places to look

The Milky Way over Hawaii
And a lot of interesting stuff along the way
Wow, a nursery here
A nearby galaxy pair

The astounding number of galaxies in the Universe, here is a tiny section of the sky, imaged with the Hubble Space Telescope

And let's not forget our vehicle!

But, other galaxies are so far away we cannot currently look for other planets etc. there, we have our hands full with stuff in our Milky Way.

Know: what is the difference between planets and stars?

Know: what is the Milky Way?

What are we searching for?

Apparently, 50% of the people in the US believe that we have already been visited by aliens. However, we can not go by beliefs; in this course we treat the question of whether any life may exist outside Earth in a scientific way so we will only consider actual evidence. And unfortunately "eye witness accounts" tend to not be very valuable as scientific evidence and we demand a higher standard of proof.

So what do we look for? Well, we would consider any life form, from the most primitive bacteria to more advanced life forms as evidence, but it has to be solid evidence. We look for planets that resemble our Earth in key characteristics around suitable stars, we study properties of all planets in our Solar System to see where life might be, what life is and what it takes for life to flourish, and we will discuss the search for intelligent life and space travel.

Some key discoveries related to the search for life:

• The universe is not infinitely old (nor very young). There is strong evidence that it was formed in the "Big Bang" as we now refer to it. We know when this happened, and we know which chemical elements were formed right after the Big Bang, and where the other elements in the periodic table were formed.

• Conditions outside Earth in our Solar System are not hospitable to advanced life but we have not searched very deeply for primitive life forms.

• We have discovered planets around other stars in the last twenty years. So far it is easier to find planets that are larger and/or more massive than Earth, but the search is continuing and major discoveries are happening continuously.

• The building blocks of life are now well understood; our genetic material and the living tissue in our bodies is made of the same atoms we find elsewhere in the universe, on our Sun and planets, and on other stars and gas between the stars. Thus, from this perspective, life could have formed elsewhere too, if it happened on earth.

• Biology has taught us that life can evolve over time from primitive to more advanced forms and that it may arise spontaneously. We have evidence for microbial life on Earth dating back 3 to 4 billion years, indicating that life formed early in Earth's history.

• We find life on Earth in extreme environments in conditions thought impossible to sustain life, yet it exists; life seems very capable of surviving extreme conditions.

The nature of the search

"Locally" in our solar system, we can send spacecraft to study in detail the surfaces and atmospheres of the terrestrial planets and moons. We can put landers on the surface and possibly bring back samples to look for life forms. Eventually, we will be able to put astronauts there to explore in more detail.

The text book discusses three different approaches to the Search for Life: the Astronomical, the Planetary, and the Biological. Each has its own unique qualities and focus. Astronomy provides the "Big Picture View", our place in the cosmos and the origin and formation of objects we find in it, the Planetary approach focuses on properties of planets, in and outside our solar system and how they may provide a habitat for life, the Biological approach focuses on the "Life" aspect, how it may form and evolve and what characteristics it may have. All three are essential in our quest.

Know: What is the difference between planets and moons?

On larger scales, we can explore distant planets and search for terrestrial analogs around other stars with telescopes and special detectors. We can detect signatures of the planets' atmospheres and look for evidence of life (molecular oxygen, water, etc).

We can listen passively for electromagnetic signals from other planets that might prove they have civilizations on them.

We can study meteorites that fall from space to Earth, and collect samples from comets and asteroids in our Solar System.

With our current understanding of physics, interstellar travel is difficult to foresee to happen soon; we will discuss the prospects and problems.

We will discuss all of the above in more detail in the course, including HOW we found all this out.