An Ode to Cassini

In early 2001, I was a fifth-grader and had been obsessed with our solar system’s planets my entire life. But, thanks in part to the Internet, I came to realize our solar system is more than just the row of planets on my placemat. It is a dynamic system with asteroids, comets, and moons, a lot of moons which look nothing like the one in our sky, each with its own story to tell. I spent countless hours reading about them — the fiery sulfur volcanoes on Io, the nitrogen plumes on Triton, the mysterious ocean of water underneath Europa’s icy crust.

But what was I to make of Saturn’s moons? The best pictures of Titan showed a hazy, orange orb and that was essentially all we knew about it. Enceladus was unusually bright — could that harbor an ocean underneath its ice like Europa? I wondered. Iapetus was oddly two-faced, but the data available was inconclusive as to the nature of the yin and the yang. And were the rest of the moons hiding secrets as well?

I learned that a spacecraft called Cassini was set to orbit Saturn for four years beginning in the summer of 2004. Moreover, a separate probe would detach from the main spacecraft and land on Titan! It was official: for the next three years, no other year in my mind mattered more. The countdown to 2004 had begun.

Cassini teased us with a few distant images of Saturn, but the mission truly started when it made its closest (and only) approach to the small moon Phoebe. The pictures showed, in detail for the first time, a battered, icy moon that likely originated in the Kuiper Belt. A few weeks later, Cassini entered orbit around Saturn, (still) the farthest planet any spacecraft from Earth has orbited. Data and pictures started trickling in at a faster pace. I was buckled up and ready to go for the next four years.

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Our First Step Out of the Solar System

Proxima Centauri
Astronomers today announced the discovery of a potentially habitable Earth-sized planet orbiting the star closest to the Sun, Proxima Centauri.

Proxima Centauri is 4.24 light-years away. To put that in perspective, the Milky Way galaxy (of which our solar system is a part) is about 100,000 light years across. If trekking the Milky Way from one end to another was equivalent to walking from New York City to California, Proxima Centauri would be within the first 200 yards. So on a cosmic scale, our nearest star is extremely close.

Not much is yet known about this new planet (formally called Proxima Centauri b). Its mass is believed to be between 1.27 and 3 times Earth’s mass, so it probably has a solid surface. Its orbit lies in the habitable zone, which means its surface is capable of supporting liquid water. The star it orbits is a red dwarf, a smaller and different kind of star than our Sun. Beyond these basic facts, many questions about this planet are still unanswered. Does it keep one side always facing its host star? Does it have any moons? Does it have an atmosphere? Does it have liquid water? Does it have life? What kind of life might evolve on such a planet?

These questions will not be answered quickly, but fortunately we will learn more about the planet in the coming years. The European Extremely Large Telescope, currently under construction and planned to be fully functional in 2024, will provide images 16 times sharper than the Hubble Space Telescope. This telescope will be able to resolve Proxima Centauri b and help study its properties. Moreover, now that astronomers all over the world know exactly where to look, further discoveries about the planet are likely to be made sooner.

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