Welcome back to school! Here’s the first of this academic year’s space science updates, with information about Wednesday’s total lunar eclipse and tomorrow’s Cassini flyby of Titan.
Best wishes,
Jeff
1. TOTAL LUNAR ECLIPSE
Don’t miss this Wednesday night’s (Oct. 27) total eclipse of the Moon — it will be 2 1/2 years until the next total lunar eclipse. The eclipse will be visible throughout the United States, the rest of the Americas, and Europe. Totality will last more than an hour, starting at: 7:23pm Pacific time, 8:23 Mountain time, 9:23 Central time, 10:23 Eastern time, and so on. (For those of you in Europe, that makes the eclipse early Thursday morning.)
Questions you might want to ask your students in class:
- Wednesday night is not only the eclipse but it is also a full moon. Is this a coincidence or not? (Answer: not — a lunar eclipse can occur only when Earth’s shadow falls on the Moon, which means the Moon and Sun must be on directly opposite sides of the Earth, which is the condition for full moon. Thus, a lunar eclipse can happen only at full moon. Similarly, a solar eclipse can happen only at new moon.)
2. CASSINI AT TITAN
Be among the first people on your planet to find out what Titan looks like! Cassini will make its first close flyby of Titan tomorrow night (Oct. 26); more info and live webcast at http://saturn.jpl.nasa.gov. Why should you care about Titan? Here’s a few reasons:
- Although it is a "moon" because it orbits the planet Saturn, Titan is bigger than the planets Mercury and Pluto. In fact, it’s the 10th largest object in our solar system (after the Sun, the other 7 planets, and Jupiter’s moon Ganymede).
- Titan is the only moon in the solar system with a substantial atmosphere, and this atmosphere shares two interesting characteristics with Earth’s atmosphere: A similar atmospheric pressure (Titan’s surface pressure is only about 50% more than Earth’s) and a composition of mostly nitrogen (Earth’s atmosphere is 77% nitrogen and Titan’s is 90% nitrogen). Of course, there are also two important differences: (1) the rest of Earth’s atmosphere is mostly oxygen, while the rest of Titan’s atmosphere is argon, methane, ethane, and other hydrogen compounds; (2) Titan is extremely cold, with a surface temperature of nearly 300 degrees below zero (Fahrenheit).
- While the temperature is far too low for liquid water, there’s good reason to think that Titan may have lakes or oceans of liquid methane and ethane, and perhaps even methane/ethane rain or snow.
- And the possibility of these cold liquids raises at least some small potential for life: Although all life on Earth requires liquid water, it’s at least marginally possible that other liquids could support life. (Some sort of liquid is generally deemed necessary for life in order to transport chemicals from one place to another.) Don’t get overly hopeful: water has several chemical advantages over other liquids that make it seem far more suitable than other liquids as a molecule for life. Still, I won’t be completely blown away if we discover little cold-liquid critters on Titan.
Tomorrow’s flyby will take Cassini within about 750 miles of Titan’s surface, which means it will be only about 3 times as high above Titan as the Space Station is above Earth. In fact, Cassini will actually pass through Titan’s thin upper atmosphere. Instruments will study the atmosphere, while cameras will give us our best-ever views of Titan and radar will be used to map the surface. With luck, we’ll get a definitive answer to the question of lakes or oceans on Titan. Then, in January, a probe (called Huygens) will descend to Titan’s surface — that’s when you should be watching for the cold-liquid creatures staring into the probe’s cameras…
Questions you might want to ask your students in class:
- With its thick atmosphere, Titan is not much like our own Moon at all. So why do we call it a "moon"? (Answer:we define a "moon" as a body that orbits a planet, while a planet orbits the Sun. So Titan is a moon because it orbits Saturn.)
- Why is Titan so cold? (Answer: look at its distance from the Sun…)
- For those with some chemistry background: Why is water considered a better molecule for life than other liquids? (Answer: 3 advantages of water are: (1) liquid at higher temperature which means higher chemical reaction rates; (2) water is a polar molecule, which allows the formation of hydrogen bonds and affects how other molecules dissolve or don’t dissolve in water; (3) water expands when it freezes, so that ice floats and thereby can insulate liquid water lying under frozen ice.)
MAX UPDATE
Thanks to all of you who have sent your good wishes for our dog Max, star of my children’s book Max Goes to the Moon. Good news: his bone cancer is now in remission, following surgery to remove the tumor last May and treatment over the summer. Our local newspaper recently published an article about Max and me.