Cassini Space Probe To Fall Into Saturn Friday Morning

Friday morning, around 5 am Pacific time, NASA will send the Cassini space probe falling into the planet Saturn -- until it is crushed by the pressure in the ringed planet's atmosphere. NASA is commanding Cassini to "commit suicide" before its propellant runs out and it can't be steered any more. Since Saturn has two moons which might harbor some sort of primitive life, we wanted to make sure we did not contaminate those worlds.

The planet Saturn is made mostly of gas and liquid (and its make-up is dominated by the two lightest elements in the universe, hydrogen and helium.) So you can't land ON Saturn, you can only fall INTO Saturn (like a giant ocean world.)

Cassini has been orbiting Saturn for 13 years, sending back amazing pictures and information on the planet, its complicated rings, and its 62 moons. It's made a slew of remarkable discoveries, including the presence of warm salt-water geysers on the relatively small moon called Enceladus, and lakes and rivers of liquid fuel oil on the giant moon Titan. It was launched 20 years ago (so it's had a long and fulfilling life for a spacecraft.)

Since April, it has been swooping in and out of the space between Saturn's cloudtops and its inner rings, an area we had never had the nerve to explore before. NASA estimates the spacecraft has traveled almost 5 billion miles in total and has sent back more than 450,000 picture (that's a Flickr file not even your most picture-taking relatives can compete with!)

In our image, you can see Saturn and its complex ring system, with a painting of the spacecraft above the planet's north pole, ready to make a dive.

Some of my favorite pictures in the introductory astronomy textbook I am the lead author on come from Cassini (which was the most complicated planetary explorer ever built.) On Friday morning, let's give it a thought as we wake up -- we'll miss you, Cassini!

You can see live coverage of the last days of the mission on NASA TV at: http://nasa.gov/live

You can access the image galleries and latest videos from the mission from this page (designed for the media, but which anyone can use): https://saturn.jpl.nasa.gov/mission/grand-finale/for-media/

By the way, you can access my free textbook at : http://openstax.org/details/astronomy 

Double Eclipse of the Sun; Eclipse Statistics

My favorite picture so far of the recent eclipse of the Sun is the one you see with this post. Photographer Simon Tang (who gave me permission to reproduce it here) took a sequence of photos from Huron, California, recording the International Space Station crossing the face of the Sun just as the Moon was eclipsing it.

Each of the images of the Space Station is less than 1/1000th of a second long, since the Station moved across the Sun in less than a second. The image is taken in H-alpha, a specific color of light emitted by hot hydrogen atoms in the Sun's lower atmosphere. You can see the Station close up in our second image.

NASA reports impressive statistics for the Aug. 21 eclipse: 90 million page views on NASA's two websites, 40 million views of the live broadcast, 3.6 billion users on social media, and the most popular Instagram image ever -- all of a celestial event with no politics, no national or religious affiliation. It was just nature, doing its thing, predictably, reliably, spectacularly.

In our own project, 2.1 million eclipse glasses were distributed to 7,100 libraries -- all to be given away free to the public. I was one of the astronomers leading the effort, and want to thank the Moore Foundation, Google, and NASA, for supporting the program to allow public libraries to help their patrons observe the eclipse safely. If only we could come together this well about other things!

Click on the images to see them bigger.